National Academies Press: OpenBook

Opportunities in Chemistry (1985)

Chapter: V. Chemistry and National well-Being

« Previous: IV. Dealing with Molecular Complexity
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 193
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 194
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 195
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 196
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 197
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 198
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 199
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 200
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 201
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 202
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 203
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 204
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 205
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 206
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 207
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 208
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 209
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 210
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 211
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 212
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 213
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 214
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 215
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 216
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 217
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 218
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 219
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 220
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 221
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 222
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 223
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 224
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 225
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 226
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 227
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 228
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 229
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 230
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 231
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 232
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 233
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 234
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 235
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 236
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 237
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 238
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 239
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 240
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 241
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 242
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 243
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 244
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 245
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 246
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 247
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 248
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 249
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 250
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 251
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 252
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 253
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 254
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 255
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 256
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 257
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 258
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 259
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 260
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 261
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 262
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 263
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 264
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 265
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 266
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 267
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 268
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 269
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 270
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 271
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 272
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 273
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 274
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 275
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 276
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 277
Suggested Citation:"V. Chemistry and National well-Being." National Research Council. 1985. Opportunities in Chemistry. Washington, DC: The National Academies Press. doi: 10.17226/606.
×
Page 278

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

CHAPTER V Chemistry and National Well-Being V-A. Better Environment Every society tries to provide itself with adequate food and shelter and a healthful environment. When these elemental needs are assured, attention turns to comfort and convenience. The extent to which all these wishes can be satisfied determines a society's "quality of life." However, choices are usually required because one or another of these needs or wishes is more easily satisfied at the expense of others. Today we find our desires for more abundant consumer goods, energy, and mobility in conflict with maintenance of a healthful envi- ronment. A major concern of our times is the protection of our environment in the face of increasing world population, increasing concentration of population (urbanization), and increasing standards of living. Environmental degradation with its accompanying threats to health and disruption of ecosystems is not a new phenomenon. Human disturbance of the environment has been noted from the earliest recorded history. The problem of sewage disposal began with the birth of cities. Long before the 20th century, London was plagued with air pollution from fires used for heating and cooking. An early example of an industrial hygiene problem was the reduced longevity of chimney sweeps attributed retrospectively to cancer arising from prolonged exposure to soot with its trace carcinogen content (polynuclear aromatic hydrocarbons). There is small consolation, though, in the fact that environmental pollution is not a new invention. The global population burgeons upward, while cities grow even faster. Per capita consumption and energy use continue to increase. Pollution problems are becoming increasingly obvious, and we are recognizing subtle interactions and secondary reverberations that went unnoticed before. A number of environmental disturbances have begun to manifest themselves on a global scale. Occasional industrial accidents, like those at Bhopal and Seveso, remind us that large-scale production of needed consumer products may require handling of large amounts of potentially dangerous precursor substances. 193

194 CHEMISTRY AND NATIONAL WELL-BEING On the positive side, the public awareness has been raised about the importance of maintaining environmental quality. In the United States, a large majority of citizens from across the political spectrum have indicated that they are prepared to pay more for "cleaner" products (e.g., lead-free gasoline) and to pay more taxes to improve their environment. These attitudes are spreading abroad, an essential aspect of containment of the problems more global in scope. Elective strategies for safeguarding our surroundings require adequate knowledge and understanding. We must be able to answer the following questions: What potentially undesirable substances are present in our air, water, soil, and food? Where did these substances come from? What options are there- alternative products and processes to alleviate known problems? What is the quantitative degree of hazard as a function of the extent of exposure to a given constituent? How shall we choose among and implement available options that over corrective action? Plainly, chemists play a central role in answering the first three crucial questions. To find out what is around us, we need analytical chemists to apply and develop ever more sensitive and selective analytical techniques. To track pollutants back to their origins, again we look to analytical chemists acting as sleuths, now usually in collaboration with meteorologists, oceanographers, voicanologists, climate dynamicists, biologists, and hydrologists. But finding origins can require detailed chemical understandings of reaction sequences and transformations that intervene between the source and the final noxious or toxic product. Then, developing options calls on the full range of the chemist's arsenal. If the worId's mortality rate from malaria is not to be reduced with DDT because of its environmental persistence, what substances can be synthesized that are as elective as DDT in saving lives and spontaneously degradable as well? If we must use lower grade energy sources to satisfy our society's energy needs, what catalysts and new processes can be developed to avoid exacerbating aIready-existing problems of acid rain and carcinogen release from coal-fired power plants? Thus our society must assure the health of its chemistry enterprise if it wants earlier warning of emerging environmental degradation, better understandings of the origins of that degradation, and access to a full array of economically feasible options from which to choose solutions. Other disciplines make their own particular contributions, but none plays a more central and essential role than chemistry. The fourth question, the quantitative degree of the hazard/exposure equation, is the province of the medical profession, toxicologists, and epidemiologists. These scientific disciplines face serious challenges now that society has recog-

V-A. BETTER ENVIRONMENT nized the inverse relationship between what is taken to be a tolerable risk and the cost to society in attaining it. The medical profession must refine its knowledge of risks associated with such substances as lead in the atmosphere, chloroform in drinking water, radiostrontium in milk, benzene in the work- place, and formaldehyde in the home. A qualitative statement that a certain class of substances might be carcinogenic will no longer suffice. We must be able to weigh risks and costs against benefits that would be lost if use of that class of substances were restricted. We must be able to compare these risks to those already present because of natural background levels. More importantly, society cannot afford to pay the exorbitant cost of eliminating all risk, because, as the requested degree of risk approaches zero, the cost escalates toward infinity. Finally, the choice among options and their implementation moves properly into the public arena. Chemists and scientists in the other relevant disciplines have a secondary, but important, informational responsibility here. Every political decision deserves the best and most objective scientific input available. There is nothing more frustrating to our citizens and our government than to befaced with decisions without the benefit of facts and a usefully predictive scientific knowledge base. Scientists, including chemists, must meet their responsibility to provide the public, the media, and the government with an objective picture expressed in language free of technical jargon to help establish the scientific setting for a given decision and the options that lie before us. Turning Detection into Protection All our environmental protection strategies should be founded on realistic hazard thresholds and on our ability to detect a particular offending substance well before its presence reaches that threshold. Chemists must continue to sharpen their analytical skills so that, even at minute concentrations well below the hazard threshold, a given substance can be monitored long before crisis-corrective action is dictated. When this is possible, we see that detection can be equated to protection. Unfortunately, the media, the public, and government agencies have too often equated detection with hazard as a result of the prevalent assumption that a substance that is demonstrably toxic at some particular concentration will be toxic at any concentration. There are innumerable examples to prove that this is not a generally applicable premise. Consider carbon monoxide (CO). This ubiquitous atmospheric constituent becomes dangerously toxic at concentra- tions exceeding 1000 parts per million and is considered to have adverse health effects for prolonged exposure to concentrations exceeding 10 parts per million. We do not, however, leap to the conclusion that CO must be completely removed from the atmosphere. This would be foolish (and impossible) because we live and thrive in a natural atmosphere that always contains easily detectable CO at about 1 part per million. Clearly, our task is to decide where we should place 195

196 CHEMISTRY AND NATIONAL WELL-BEING controls between the known toxicity threshold and the known safe range- as EPA has in fact attempted to do. In recent trends, the naive "zero-risk" approach is gradually being supplanted by a more sophisticated risk assessment/risk management rationale. In both the assessment and management phases, a major theme is the crucial importance of being able to analyze complex air, water, soil, and biological systems that may contain hundreds of natural chemical compounds. The roles that chemical analysis and monitoring play in protecting and managing our air and water resources are analogous to the role that intelligence-gathering plays in protect- ing and promoting the nation's public interest in the military, geopolitical, and economic realms. Conclusions regarding causes and erect, sources, movement, and fates of pollutants in crucial issues such as acid deposition, global climatic change, ozone layer destruction, and toxic waste disposal depend upon environ- mental measurements that must be made with sufficient selectivity and sensitivity. Enormously costly decisions about how to protect and enhance the quality of our air, water, and land resources are sometimes based on environ- mental "intelligence" that can be grossly inadequate and inaccurate. Crash projects to remedy crises caused by past indiscretions or ineffective strategies that were based on insufficient knowledge have been expensive. A small fraction of the money spent on such a corrective program, if invested in long-term fundamental environmental science and monitoring techniques, can significantly reduce the need for future expensive remedial programs. THERE ARE 22 DIFFERENT TETRACHLORODIOXINS Increased effectiveness of environmental measure- ments requires improved sur- veilIance tools. The challenge is to measure trace levels of a particular compound present in a complex mixture contain- ing many innocuous com- pounds. The principal objec- tives of research in envir- ct~o~ct Cl C1~0~ 2,3,6,9 C' Ct CO~O~Ct HOW MUCH IS IN THE TOXIC 2,3,7,8 FORM? AN ANALYTICAL CHALLENGE onmental analysis and moni- toring are improved sensitiv- ity, selectivity, separation, sampling, accuracy, speed, and data interpretation. For example, an active research area is connected with sepa- ration techniques to allow rapid and unequivocal analy- sis of complex mixtures of pollutants and pesticides found in toxic wastes, polluted streams and lakes, and biological samples. A success story in analytical selectivity is the development of analytical methods to allow separation and

V-A. BETTER ENVIRONMENT quantitative measurement of each of the 22 individual isomers of tetrachIo- rodioxin at the parts-per-trillion level. Research is needed on multi-stage separation and detection methods, such as tandem mass spectrometry. Additional research on developing techniques that exploit the separation powers of selective sorbents, liquid chromatography, supercritical fluid chromatography, field flow fractionation, and parametric pumping will be fruitful. Attention must be given to basic research that will produce selective detectors (based, e.g., on laser-induced fluorescence or on chemiluminescence) that can be used to simplify analysis and minimize inter- ferences that can accompany environmental sampling. Highly reactive species in the atmosphere cannot be sampled and transported to the laboratory for analysis. Such substances pose special challenges in measurement and will require research aimed at remote sensing techniques capable of measuring them in situ. Past successes include the measurement of formaldehyde and nitric acid in the atmosphere of Los Angeles, during severe smog attacks, by Fourier transform infrared spectroscopy in which absorbance due to these pollutants was measured in situ over a 1-kilometer path. With these experiments it was possible to perform a detailed characterization of the simultaneous concentrations of formaldehyde, formic acid, nitric acid, peroxyacetyl nitrate, and ozone in the ambient air at the part-per-billion level at which these substances are contributors to photochemical smog. Notice that 1 part per billion (1 part of a pollutant in 109 parts of air) is a minute concentration, but it is still sufficient to be significant in atmospheric reactions. Differential scanning laser devices based on radar-like technology ("lidar") have been used successfully to measure sulfur dioxide plume profiles downwind of coal-fired power plants at the part-per-million level. Tunable diode lasers are also capable of providing real-time in situ detection of pollutants from internal combustion engines and industrial processes. Several laser techniques, including linear methods (e.g., absorption, fluores- cence), nonlinear methods (e.g., coherent antistokes Raman spectroscopy, opti- cal heterodynes), and double resonance methods (e.g., laser magnetic reso- nance), need to be examined more extensively. Other spectroscopic methods, such as Fourier transform infrared and photoacoustic spectroscopy, are prom- ising and warrant further study. One goal of such research should be better measurements in the stratosphere and troposphere. Rapid, reliable, accurate, and less-expensive methods are needed for measuring concentrations of trace species, such as OH radicals, that play key roles in atmospheric chemistry. At the same time that research aimed at more sophisticated measurement technology is conducted, parallel efforts need to be devoted to simpler, less costly routine monitoring techniques. Research directed at fixing the chemical state of environmental constituents (speciation research) is gaining importance because we now recognize that transport mechanisms and toxicities vary markedly with chemical form. Chro- mium in the hexavalent oxidation state is toxic, while in the trivalent form it is 197

198 CHEMISTRY AND NATIONAL WELL-BEING much less so, and, for some living systems, it may be an essential trace element. Arsenic in some forms can move rapidly through aquifers, while other forms are rapidly adsorbed on rock or soil surfaces. Of the 22 distinct structural arrange- ments of tetrachIorodioxin, the most toxic is three orders of magnitude more toxic (to test animals) than the second most toxic. These examples illustrate the importance of analytical methods that allow identification of chemical form as well as quantity of potential pollutants. Electrochemistry, chromatography, and mass spectrometry are among the powerful tools for speciation studies. The complexity of environmental problems requires analysis of massive amounts of data. Research is needed to assist in the interpretation and wise use of the accumulated information. Developments in the field of artificial intelli- gence that use pattern recognition should provide valuable interpretive aid. Recent advances in microprocessors and small computers should be exploited to develop intelligent measuring devices and attention should be given to better handling, archiving, and dissemination of environmental data. Ozone in the Stratosphere The possibility of polluting the stratosphere to the point of partially depleting the protective ozone layer was first raised only about a dozen years ago. This seemingly improbable notion found much scientific support, and it is now one of the best examples of a potentially serious environmental problem of global extent. It is a problem, furthermore, that exemplifies chemistry's central role in its understanding, analysis, and solution. Why do we need to worry about stratospheric chemistry? Ozone in the stratosphere is the natural filter that absorbs and blocks the Sun's short wavelength ultraviolet radiation that is harmful to life. The air in the stratosphere a cloudless dry, cold region at altitudes between about 10 to 50 km mixes slowly in the vertical direction, but rapidly in the horizontal. Consequently, harmful pollutants, once introduced into the stratosphere, might remain there for periods as long as years, and, if so, they will rapidly be distributed around the earth across borders and oceans, making the problem truly global. A large reduction of our ozone shield would result in an increase of potentially dangerous ultraviolet radiation at the earth's surface. To understand how easily the ozone layer might be perturbed, it is useful to recognize that ozone is actually only a trace constituent of the stratosphere; at its maximum concentration ozone makes up only a few parts per million of the air molecules. If the diffuse ozone layer were concentrated into a thin shell of pure ozone gas surrounding the earth at atmospheric pressure, it would measure only about 3 millimeters (his inch) in thickness. Furthermore, ozone destruction mechanisms are based on chain reactions in which one pollutant molecule may destroy many thousands of ozone molecules before being trans- ported to the lower atmosphere, chemically transformed, and removed by rain. Chemistry's crucial role in understanding this problem has emerged through the identification and measurement of several ozone-destroying chain processes.

V-A. BETTER ENVIRONMENT Fifty years ago, the formation of an ozone layer in the midstratosphere was qualitatively described in terms of four chemical and photochemical reactions involving pure oxygen species (O. 02, and ON Today, we know that the rates of at least 150 chemical reactions must be considered in order to approach a quantitative model for simulating the present stratosphere and predicting changes resulting from the introduction of various pollutants. The chemistry begins with absorption of solar ultraviolet radiation by O2 molecules in the stratosphere. Chemical bond rupture occurs, and ozone, O3 and oxygen atoms, O. are produced. Then, if nitric oxide, NO, is somehow introduced into the stratosphere, an important chemical chain reaction takes place. UV down . \' STRATO SPHERED D to 18 OZONE ABSORBS UV LIGHT f~ -)N~O+hv~N + NO (33+ NO~N(~2 ~ O2 O ~ NO2 ~ NO ~ O2 NO2+ OH net °+O3 iO2+O2 50 km 280°E 0 7 tort HNO3 UV down ~ N2O ~ JO to 300 nm~ ~ TROPOSPHERE ~- ~ ~ ~~ KA1N 210 1E f I: : . : : 2 : : :! : : : _ ~ an _ _.-: .-:: __:: :-. - :~-:: =_—My_ - ~ ~ 7^ HA__ A. -c_ - ., _-. - .. : . e— -I -.~. -` ~ ~ V W ~ 1 ~ . : :~7~1 : :::::::: .:::::::: -'} I....:::: ' :-~_` _- ..~ .- .-. -' -.- ' ' c.' '-- - ' - ' ' - . ~ ..~ - ~ I ,.,.,., ,., ,. , , ., , , , c .. , ,, ,, . . _ .... 115~ _ ,d~ R;,~~1'~:'~''·'· ~~'"~"--— ¢~ 1O-15km ., 11~ ~ ~., The NO and NO2 reactions together furnish a true catalytic cycle in which NO and NO2 are the catalysts. Neither species is consumed, because each is regenerated in a complete cycle. Each cycle has the net effect of destroying one oxygen atom and one ozone molecule (collectively called "odd oxygen". This catalytic cycle is now believed to be the major mechanism of ozone destruction in the stratosphere. In the natural atmosphere, the oxides of nitrogen are provided by biogenic emissions at the Earth's surface by soil and sea bacteria of nitrous oxide, N2O. This relatively inert molecule slowly mixes into the stratosphere where it can absorb ultraviolet light and then react to form NO and NO2. Of course, oxides of nitrogen directly introduced to the stratosphere are expected to destroy ozone as well, and this was the basis of the first perceived threat to the ozone layer large fleets of supersonic aircraft flying in the _ stratosphere and depositing oxides of nitrogen via their engine exhausts. Nuclear explosions also produce copious quantities of oxides of nitrogen, which are carried into the stratosphere by the buoyancy of the hot fireballs. A significant depletion of the ozone layer in the event of a major nuclear war was 199

200 CHEMISTRY AND NATIONAL WELL-BEING forecast in a 1975 study by the National Academy of Sciences, although this environmental erect of nuclear war may pale in comparison with the recently suggested potential of a "nuclear winter." Both effects underscore the delicacy of the atmosphere and its sensitivity to chemical transformations. Then, in 1974, just as the possible impact of stratospheric planes was reaching the analysis stage, concern was raised about other man-made atmospheric pollutants. Halocarbons, such as CFCI3 and CF2CI2 (chIorofluoromethanes, or CFMs), had become popular as spray-can propellants and refrigerant fluids, mainly because of their chemical inertness. The absence of reactivity meant absence of toxicity or other harmful effects on terrestrial life. Ironically, this meant that there was no place for the CFMs to go but up up into the stratosphere where ultraviolet photolysis could occur. Chemists then recognized that if this occurred, the resultant chlorine species, CT and ClO, could enter into their own catalytic cycle, destroying ozone in a manner exactly analogous to the destruction caused by the oxides of nitrogen. , . STR A TO split Fit UV down to 180nm rCF2CD2 + he ) C9 + CF2CD OZONE |F O3 ~ c/ ~ L9U · oz ABSORBS ~ 0 ~ coo ~ c, ~ O2 LIGHT l net ° ~ O3 ~ O2+ O2 ~ UV down ~ CF2C02 relet HC0 TROPO SPHERE I_ ~ - - - Ad. - - ~ . - -. _ 50 Em 280° ~ \0.7 tort CD ~ CHID 10-15km RAIN 210°Z ~ . . . . . . . ~ . . ^ : . . . . arc ~ ~~ ~ ~~ ~~. ~ 70torr A is. ~ . ..... . ~ ~ ~ , ^,~ ~-------·-----~-·~-~~-;- - --.--. - ·-~ Once this possibility had been recognized, analysis of the whole stratospheric ozone chemistry began in earnest. An international committee of scientific experts assembled by the National Academy of Sciences examined in detail the state of our knowledge of every aspect of the problem. It became clear that the additional chemistry introduced to the stratosphere added not just these 2 catalytic chemical reactions to the roster, but a total of about 40 new reactions involving such species as CI, ClO, HCI, HOCI, ClONO2, the halocarbons, and several others. Most of these reactions had never before been studied in the laboratory. I,aboratory kineticists and photochemists responded to the challenge by .

V-A. BETTER ENVIRONMENT providing reliable rate con- stants and absorbances for the proposed processes using the growing arsenal of mod- ern experimental methods. Recent progress in the exper- imental accomplishments of this field has been remark- able. It has become possible, a/ CH4 ~ O3 \ HOCl /\ To HCl _ Cl OH `` ClO O1 NO / for example, to generate he \ / NO2 nearly any desired reactive REACTIONS KEY TO \ molecular species in the labo- STRATOSPHERIC \ ~ ratory in a variety of ways, to PROTECTION ClONO2 bring them together with other reactive species, and to measure their rates of reaction under known, controlled conditions. Such direct measurements of these extremely rapid reactions were only a distant goal a decade ago, but they are now a reality. Finally, field measurements of minor atmospheric species have been revolu- tionized by some of the recent advances in analytical chemistry. Methods originally developed for ultra-sensitive detection of extremely reactive species in laboratory studies have been modified and adapted to measure such constit- uents as O. OH, Cl, ClO and others at parts-per-trillion concentrations in the natural stratosphere. This has been accomplished recently in experiments in which a helium-filled balloon carries an elaborate instrument package to the top of the stratosphere where the package is dropped while suspended by a parachute. As the instrument traverses the stratosphere, it measures concen- trations of several important trace chemical species and telemeters the infor- mation to a ground station. Very recently, the first successful reel-down experiment was performed in which the instrument package was lowered 10 to 15 km from a stationary balloon platform and reeled back up again like a giant yo-yo. This method results in a huge increase in the amount of data that can be obtained in a single balloon flight. It will also allow for the first time a study of the time evolution and variability of the stratosphere. Much has been accomplished in the past 10 years. Many of the needed 100 to 150 photochemical and rate processes have been measured in the laboratory, and many of the trace species measured in the atmosphere. Yet, research remains to be done. For example, two of the important chemical species containing chlorine, HOCl and ClONO2, have yet to be measured anywhere in the stratosphere. Refinements in the reaction rates for many of the important processes are still required, and exact product distributions for many of the reactions are still lacking. Nevertheless, the original NAS study, the research 20}

202 Natural Sources Marsh— I ndustry—Transportation Ocean Man-made Sources CHEMISTRY AND NATIONAL WELL-BEING programs it spawned, and the subsequent follow-up studies provided a firm and timely basis for legislative decisions about regulation of CFM use. Industrial chemists produced alternative, more readily degradable substances to replace the CFMs in some applications. Monitoring programs are in place so that trends in the stratospheric composition can be watched. The stratospheric ozone issue provides a showcase example of how science can examine, clarify, and point to solutions for a potential environmental disturbance. Premature initiation of regulation was avoided because the problem was recognized early enough to permit deliberate, objective analysis and focused research to narrow the uncertainty ranges. From first recognition on, chemists played a lead role. Reducing Acid Rain Acid rain is one of the more obvious and pressing results of degradation of air quality. Acidic substances and their precursors are formed when fossil fuels are burned to generate power and provide transportation. These substances are principally acids derived from oxides of sulfur and nitrogen. There are some natural sources of these compounds such as lightning, voIcanos, burning biomass, and microbial activity, but, except for rare volcanic eruptions, these are relatively small compared with emissions from power plants, smelters, and vehicles in industrial regions. The effects of acidic rainfall are most evident and highly publicized in Europe and the northeastern United States, but areas at risk include Canada and Prevailing Winds ~ ,.. i' Airy': .' . it, '\ W >'W\ W" , ~ ~ ,' ',, Photochemistry _,~T: ~c~ ~3~ ~ Aquatic Ecosystem ACID RAIN—SOURCES HERE, IMPACT THERE

V-A. BETTER ENVIRONMENT perhaps the California Sierras, the Rocky Mountains, and China. In some places precipitation as acidic as vinegar has occasionally been observed. The extent of the erects of acid rain is the subject of continuing controversy. Damage to aquatic life in lakes and streams was the original focus of attention. More recently, damage to buildings, bridges, and equipment has been recognized as another costly consequence of acid rain. The effect of polluted air on human health is the most difficult to quantify. Greatest damage is done to lakes that are poorly buffered. When naturally alkaline buffers are present, the acidic compounds in acid rain, largely sulfuric acid, nitric acid, and smaller amounts of organic acids, are neutralized, at least until this alkalinity is consumed. However, lakes lying on granitic (acidic) strata are susceptible to immediate damage because acids in precipitation can dissolve metal ions, such as aluminum and manganese, causing reduction in biological productivity and, in some lakes, the decline or elimination of fish populations. Damage to plants from pollution ranges from adverse effects on foliage to destruction of fine root systems. In a region such as the northeastern United States the principal candidates for pollutant reduction are the power plants burning coal with high- sulfur content. Chemical scrubbers that prevent the emission of the pollutants offer one of the possible remedies. Catalysts that reduce oxides of nitrogen emissions from both stationary and mobile sources offer yet another example of the role that chemistry can play in improving air quality. The various strategies for reducing acid rain involve possible investments of billions of dollars annually. With the stakes so high, it is imperative that the atmospheric processes determining the transport, chemical transformation, and fate of pollutants be well understood. Acid deposition consists of both "wet" precipitation (as in rain and snow) and dry deposition (in which aero- sols or gaseous acidic com- pounds are deposited on sur- faces such as soil particles, plant leaves, etc.~. What is finally deposited has usually been injected into the atmo- sphere in a quite different chemical form. For example, sulfur in coal is oxidized to sulfur dioxide, the gaseous form in which it is emitted from smokestacks. As it moves through the atmo- lARGE UNCERTAINTIES REMAIN IN THE GLOBAL NOx BUDGET sphere, it is slowly oxidized and reacts with water to form sulfuric acid the form in which it may be deposited hundreds of miles downwind. The pathways by which oxides of nitrogen are formed, undergo chemical 203 TROPOPAUSE -o 5 Z o , _ V) 0 1 ~14 28 En as ~ ~ :, ~ 4-24 ,~ - 1 ° NH3 + OK] ~ NOx 1 1- 10 L I GHTN I NG (PRECIPITATION: ~ —W~ MICROBIAL I ACTIVITY DRY DEPOSITION 12-42 IN SOILS I j ~ 1 4 - 1 6 12-22 TERRE STR 1 A L < 1

204 CHEMISTRY AND NATIONAL WELL-BEING transformation, and are eventually removed from the atmosphere are also very complex. Nitrogen and oxygen, when heated at high temperatures in power plants, home furnaces, and vehicle engines, form nitric oxide, NO, which reacts with oxidants to form nitrogen dioxide, NO2, and eventually nitric acid, HNO3. Quantitative estimates of the global budget for the oxides of nitrogen still contain unacceptably wide uncertainty ranges. It can readily be seen that without a thorough knowledge of the biogeochemi- cal cycles for the various chemical forms of nitrogen, sulfur, and carbon, and of the global compartments from which these species arise and are partitioned into, it will be difficult to select air pollution control strategies with confidence. Atmospheric and environmental chemistry are central to a clearer and more healthful environment. Development of reliable methods of measurement of trace species in air, kinetics of important atmospheric reactions, and the discovery of new, more effective, chemical processes for reducing pollutant emission are goals that should receive a national commitment for the coming decade. To minimize acid rain in a cost-effective manner, we must develop a better understanding of the chemistry of the oxides of nitrogen and sulfur as well as hydrogen peroxide, ozone, formaldehyde, and other species In crouch ctropiets anci in the vapor state. The detailed pathways for oxidation of precursors to products are not yet established. Problems are sometimes encountered in extrapolating from laboratory experiments and computer-based models to actual field condi- tions. Frequently, the rate laws and equilibrium constants established under ideal laboratory conditions become difficult to apply to the more complex mixtures and conditions present in the atmosphere. The role of aqueous phase photochemistry in chemical transformations within clouds is not known. Atmo- spheric chemistry that occurs in daylight drives reactions to favor products different from those formed at night, so more research is needed at field stations around the clock, as well as in the laboratory. The roles of reactive species, such as the radicals OH, OOH, and NO3, in oxidation reactions leading to scavenging of pollutants from the atmosphere need to be better understood in the heterogeneous atmosphere. While systems are easier to study in the gas phase, much important chemistry probably occurs at the liquid droplet-gas phase interfaces, or within the droplets. Most earlier work has focussed on the inorganic constituents of acid precipitation, but certain organic species may potentiate or inhibit reactions. For example, organic compounds in surface organic microlayers covering water droplets may alter mass transport of reactants or act as either catalysts or inhibitors. Guarding Against Climate Change: The Greenhouse Effect In the quest for food, goods, heat for homes, and energy for our industrial society, we have increased the concentrations of many trace gases in the

V-A. BETTER ENVIRONMENT atmosphere. Some of them absorb and retain solar energy and may eventually cause inadvertent climate change with catastrophic consequences. If the release of these gases to the atmosphere from man's activities causes significant global warming, results might be flooding due to melting polar ice, loss of productive farmland to desert, and, ultimately, famine. The most publicized of these solar energy traps is carbon dioxide, but the combined effect of increases in nitrous . . . ~ ~ ~ ~ ~ ~ 1 ~ 1 _ ~ _ ~ ~ 1_ ___ ~~ : ~ ~ oxide, methane, and otner gases COU1Ct equal gnat of caroun u~ux~u~. Approaches used to reduce emission of other pollutants are not appropriate in the case of carbon dioxide, because it is generated in enormous quantities from the burning of fossil fuels and biomass. Here the biogeochemical cycling of carbon assumes great importance. What impact will the "slash and burn" clearing of forests and jungles in the third world countries have? Will increases in biological productivity due to small rises in global temperature result in enhanced photosynthetic removal of carbon dioxide from the atmosphere? What role does methane, which is biogenically produced by termites and other species, play? Are atmospheric particulates coming from human activities likely to block sunlight and offset the effects of increases in carbon dioxide, methane, and .. .. ~ ~ nitrous ox~cte~t Large lenses of stratified soot and other aerosols have been observed in Arctic regions. The origin, composition, radiative properties, fates, and effects of these aerosols constituting "Arctic Haze" all need to be clarified. The behavior of soot in the atmosphere takes on even greater significance in light of the uncertainties about the possible atmospheric effects of nuclear warfare. It was not until 1982 that the hypothesis of global cooling from soot generated by nuclear war was advanced. This concept has since been termed "nuclear winter" because even limited nuclear wars have been predicted to cause the generation and injection into the atmosphere of so much soot that crops would freeze in summertime. Great uncertainties exist concerning the residence time of aerosols in the atmosphere and the effects of soot on radiation balance. Unlike local pollutants, the global pollutants are vexing because they require action on a global scale, and the citizens of different countries view their priorities differently. What is needed by all is a solid science base, upon which difficult decisions can be based. Whether individual countries have emphasized fossil fuel versus nuclear fuel in the past has been based primarily on economic factors such as whether that nation had abundant coal reserves. As global threats like carbon dioxide build-up (exacerbated by coal burning) become more clearly defined, we may be forced to re-evaluate the costs and benefits of nuclear power. It takes years to develop sufficient knowledge to allow a wise choice. We must accumulate that knowledge so that we can choose with confi- dence . . . weighing wisely the real threat posed by carbon dioxide build-up, with possible mitigation strategies, against a clearer picture of the options before us, including the environmental and waste disposal problems of nuclear energy generation. 205

206 CHEMISTRY AND NATIONAL WELL-BEING Cleaner Water and Safe Disposal of Wastes Our surface and subsurface waters are precious resources. Most of us take it for granted that when we want a drink of water, or to go swimming or fishing, our streams, lakes, and aquifers will be safe to use. Our progress in protecting water bodies from contamination has not generally been as successful as our efforts in cleaning up pollution in the air. Nonetheless, some important progress has been made. Lake Erie, once thought doomed to die biologically from eutrification induced by phosphates and other nutrients, is making a comeback. Improved water treatment, coupled with more rigorous attention to hazardous waste treatment and disposal, holds the key to future advances. To recognize and control the sources of pollution, we must understand the intricacies of pollutant movement and conversion. Nearly half of the citizens of the United States depend upon wells for their drinking water. A recent NAS assessment of groundwater contamination estimated that about 1 percent of the aquifers in the continental United States may be contaminated to some extent. Evidence of subsurface migration of pollutants makes it increasingly important to protect, with the best science and technology available, the aquifers feeding those wells. A number of disposal practices and waste repositories involving burial in the ground have been used for many years with only minimal groundwater contamination. Procedures have been predicated on the assumptions that the waste material was unlikely to migrate and that, over time, the compounds would be oxidized, hydrolyzed, or microbially decomposed to harmless products. Now, however, some instances of serious groundwater contamination have appeared. Some compounds have proven to be more stabile and mobile than expected, while some of them are bacterially converted into more toxic and mobile forms. In retrospect, it is clear that the scientific knowledge base for the earlier decisions was inadequate. Proposals currently under consideration for recovering seriously contami- nated aquifers are soberingly expensive. For example, estimated costs for "containment" efforts at the Rocky Mountain Arsenal near Denver, Colorado, are about $100M and for "total decontamination" up to $1B. Such enormous prospective clean-up costs require thoughtful weighing of the cost/benefit trade-offs to society in deciding what to do. More relevant here is the inescap- able conclusion that it is only prudent to invest the much smaller amounts of public funds into research that will better define clean-up options and lessen the chances of recurrence. If the subsurface is to be used as a repository for our wastes, we must have much more thorough understandings of the physical/chemical/biological system it presents. We must be able to predict the movement and fate of waste compounds with greater confidence than is now possible. Laboratory and field studies must examine migration of compounds and ions through subsurface strata, and we must develop new analytical techniques for detecting and

V-A. BETTER ENVIRONMENT Well Deep-Well ma:_ Disposal Injection Spills and Buried Leaks Wastes 207 IT GOES IN HERE—BUT IT COMES OUT THERE following the movement of polluted subsurface plumes (e.g., by measuring subsurface soil gases). Groun(lwater quality can also be improved by developing better methods for treating wastewaters, including industrial wastewaters containing especially stable contaminants. Conventional wastewater treatment depends upon combi- nations of chemical and biological processes. While this is elective for some types of wastes, research is needed on advanced techniques, such as ozonization, "wet air oxidation" (high temperature and pressure aqueous oxidation), plasma and high temperature incineration, and absorbents and resins for pollutant removal (including hybrid systems involving biological degradation). Innovative methods for recapture and recycle of valuable substances, such as metals that would otherwise contribute to water pollution, are also needed. Solvent extraction, ion exchange, reverse osmosis, and other chemical separa- tion processes deserve study. Mines pose special problems. Acid mine drainage and mobilization of radioactive mine tailings are subjects of continuing studies that should reduce adverse erects. Agriculture has depended increasingly on pesticides to control disease and insects and to Tower the cost of food production. An undesired result has been inadvertent contamination of water supplies in some areas. Assessment of the fate of pesticides and development of acceptable alternatives are important research objectives. It seems clear that chemists, geologists, and environmental engineers will Well

208 CHEMISTRY AND NATIONAL WELL-BEING need to address many of these problems in water and waste treatment at increasing levels of activity to safeguard our water resources. Radioactive Waste Management At present, it is thought that the best place to store radioactive waste is underground. This means that an understanding of the fundamental geochemistry is required. We must be able to make reliable predictions concerning possible radionuclide migration through the media surrounding the repository. However, mathematical modeling of the transport process to calcu- late the capability of a given site to contain stored radionuclides requires knowledge in several key areas. These begin with the response of the geochemi- cal system (groundwater chemistry and mineralogy, for example) to the repos- itory environment (radiation and temperature effects). Next we must learn about the manner in which radionucTides are transported under repository and natural conditions (e.g., complexation by organic and inorganic ligands, and transport by colloids and particulates). Then, mechanisms for radionuclide retardation must be better understood. Among these are solubility behaviors of both fission products and transuranic elements (the physical chemistry of multivalent elements in near-neutral solution), sorption mechanisms, and the effects of long-term nonequilibrium water-rock interactions. Then, we must face the challenge of validating predictions for 105 years or so into the future, perhaps by comparison with observations from the geologic record, including those connected with the Oklo natural reactor sites. Finally, we should be looking into ways to cope with radioactive wastes other than underground storage in perpetuity. Perhaps fully recoverable, monitorable, temporary stor- age (either surface or underground) would give more well-defined risk control and, at the same time, be more practical. Again, a variety of chemical problems needing research arise here the optimum chemical form of the stored radio- active elements, cladding, corrosion but none seems to rule out this option in advance.

V-B. CONTINUED ECONOMIC COMPETITIVENESS V-B. Continued Economic Competitiveness introduction The chemical industry is difficult to describe briefly. It encompasses inorganic and organic chemicals employed in industry, plastics, drugs and other biomed- ical products, rubber, fertilizers and pesticides, paints, soaps, cosmetics, adhe- sives, inks, explosives, and on and on. The value of U.S. chemical sales in recent years has been in the neighborhood of $175-1SOB annually, with a favorable balance of exports over imports of about $10-12B. Employment in U.S. chemical and allied product industries is more than a million, including more than 150,000 professional scientists and engineers. The numbers are as imprecise as the definitions of fields, but they are large and the effect on the economy is important. However, the narrow context of the foregoing numbers does not adequately indicate the pervasive presence and impact of chemistry in our society. Chemical products are in many cases supplied to other industries to be processed and resold with value added. Beyond this aspect, chemistry extends beyond the range of chemical products and materials. Chemical processes are abundant and growing in modern manufacturing sequences. Mechanical oper- ations, such as cutting, bending, drilling, and riveting, are being replaced by processes such as etching, plating, polymerization, cross-linking, and sintering. For example, electronic microcircuits are produced through a sequence of perhaps a hundred chemical process steps. Finally, chemistry is the science on which our ability to understand and manipulate living systems is based. Heredity is now understood in terms of the chemical structure of genetic material. Disease and treatment are chemical processes. Every medicine that a doctor prescribes is a chemical compound whose effectiveness depends upon the chemical reactions it stimulates or controls. The business climate of the chemical industry is complex and changing. The U.S. situation is particularly difficult owing to the confluence of many diverse factors that are unique or more advanced than in other countries. Antitrust law and enforcement in the United States strongly discourages cooperative actions on the part of U.S. corporations. This results in competition between individual U.S. companies and consortia of foreign corporations and governments. Govern- mental policies in regard to industries based on science are frequently more favorable abroad than in the United States. No easy solution is in sight. International competition in the petrochemical arena is becoming severe as nations controlling cheap and abundant feedstocks establish their own manu- facturing complexes to refine crude of] and produce polymers and other products higher on the value scale. It is probably too early to measure the impact of this movement, but large-volume producers in developed nations are wary. It seems probable that the threat will be concentrated in commodities (e.g., ethylene glycol, polyethylene) with the largest established markets. It remains to be seen 209

210 CHEMISTRY AND NATIONAL WELL-BEING in which markets producers in less developed countries can effectively compete, lacking, as yet, a strong base in marketing and research. The chemical industry is also confronted with an active and growing public concern for health and safety as these relate to exposure to chemicals. The movement is most advanced in the United States where diverse responses range from sensible prudence to unreasoning panic. It manifests itself economically in increasing costs for environmental maintenance and worker safety, for proving safety and effectiveness of new products, and for protection against product liability. The soundness of individual concerns aside, it can be seen that the cost to the competitiveness of the U.S. chemical industry has been enormous, the more so in view of the fact that comparable industries abroad have not yet felt the full impact of these pressures of public concern. Thus it is not surprising that the profitability of chemical companies in the United States has become a cause for national concern. The uniquely advanced standard of living in the United States owes a great deal to innovations and productivity of the nation's chemical businesses. Preservation of this quality of life requires that the United States remain a strong and leading competitor in chemistry and other technologies. A key issue responsible for past success has been the strength of U.S. university research and the effective employment of its productivity. Vigorous support of this academic research community is a critical first requirement for maintaining the competitive position of the U.S. chemical industry. Past Successes and Recent Trends The history of chemistry over the last century is filled with examples of research advances that led to new products and concepts. A hundred years ago, dyestuff chemistry was active. The petrochemical industry Iotas small in 1940, but it is immense today, and polymer innovations run in parallel. New pharmaceutical products have grown vigorously on the basis of highly sophis- ticated synthetic chemistry. Recent studies, however, have led to the conclusion that the pace of innovation in commodity and industrial chemicals is diminish- ing, and the power of these parts of the industry to sustain their growth is in question. Classification and analysis of innovations indicate that chemical product and process advances have fallen off alarmingly over the past 10 years. The trend permits some observers to portray chemistry as a mature field that has exhausted its opportunities to replace natural materials with superior synthetic materials. These are sobering thoughts both for the industry and, more seriously, for the nation itself. Another analysis is possible, however. The time scale of the recently per- ceived decline is short, and projections are risky. The only prediction that is easily made is that changes are inevitable. New products are sure to enter the marketplace. Will a significant fraction of them be ours? New processes are certain to be needed as people worldwide move to new feedstocks and new

V-B. CONTINUED ECONOMIC COMPETITIVENESS energy sources. In this country, we are learning to accommodate to pressures for increased attention to health and environmental impacts pressures that are just beginning to be felt by foreign competitors. This is not a time to assume that we should be resigned to paying royalties abroad and to surrendering our - positive balance of trade in chemicals. Innovations take years to develop, and we should be looking to our future in a time when the field of chemistry is changing and international competition is keen. Our future lies in the health of our research effort in chemistry. It must be maintained and strengthened. Energy and Feedstocks Energy and chemical feedstocks are intrinsically tied together through their overwhelming dependence on petroleum. Energy uses account for most of the consumption of organic materials. Burning of petroleum goes on at an ever-increasing pace, and the future crisis of supply is directly related to this fact. Throughout much of the worlds neonIe have come to take petroleum-derived heat and transportation for granted. Thus the inevitable depletion of the earth's petroleum resources will strongly affect the style and standard of living of people everywhere. The effects of depletion should become evident within two decades and become severe within four decades. Hubbert estimated in 1970 that 80 percent of the worId's ultimate production of of] and gas will be consumed between 1965 and 2025. The estimate seems to be receiving confirmation in current discovery and consumption rates, but its alarming implications are clearly not grasped by the public. Petrochemical uses of petroleum account for only a few percent of the total— 3 to 5 percent by most estimates. Thus the chemical industry is not the cause of the approaching era of depletion, but the effects will be felt within the industry as feedstocks and processes change. The effects on feedstocks will probably be less dramatic than the reductions in energy uses. Petrochemical uses are characterized by higher value added, and they can withstand the coming price increases brought on by depletion better than uses involving combustion. Further, processes are already known for the conversion of coal to suitable forms for use as feedstocks, and coal deposits are more abundant. Therefore, it is expected that the repercussions of petroleum depletion in chemical feedstocks will be much less important than in energy production. 211 - :~ 0 a Zen 0 4:, :D c 0 ~ A: 0 ~ _ OO:o 2050 2100 _= / 1965 - 2025 is_ 1 1 9 30 ~ 9 5C 2000 20 50 2 1 00 YEAR An Estimate: Worldwide Production of Gas and Oil Renewing Our Industries International competition is a general problem for U.S. industry and is generally recognized as such. Steel, automobiles, communications, textiles, and machine tools are examples of industries that have had significant problems. It

212 CHEMISTRY AND NATIONAL WELL-BEING is instructive to consider the response to these pressures in the specific case of automobiles to illustrate the central role of chemistry in maintaining and improving the U.S. position. The U.S. automobile industry evolved into a gigantic business during the first half of this century. In the l950s and 1960s American products took on a character that enjoyed excellent success. The vehicles were large, heavy, and powerful. Fuel was abundant and inexpensive, so, with little incentive to conserve, fuel economy was not an important consideration. The cars were built for the American market and few were exported. Similarly, few foreign-buiTt cars made their way to North America. By the mid-1960s, however, Volkswagon had become a significant supplier to the U.S. market with sales of more than half a million small economy cars per year. During the 1970s the market was further invaded by cars of Japanese manufacture. Pursuing an aggressive policy of collecting design, technology, engineering, and assembly information, much of it from the United States, the Japanese developed the most automated and efficient car building facilities in the world. These facilities, and a commitment to quality, produced the worId's most fuel-efficient and least expensive cars. At the same time, legislation was passed in the United States that specified mandatory fuel economy objectives and placed strict limits on air pollution from automobile emissions. The American car was required to change dramatically, and the investment required by the manufacturers was high, approximately $80B. The objectives are being achieved through a variety of developments, every one involving chemistry: new and lighter materials, better combustion control and engine efficiency, catalytic exhaust treatment, reduced corrosion. smaller size, transmission improvements, etc. Polymers, aluminum, and high-strength alloy steels are employed for weight reduction. New chemicals for of] additives and improved rubber formulations for underhood tube and hose applications are solving problems of engine compartment temperature brought on by aerodynamic designs featuring sIop- · . . in. · . ~ ~ . ~ .. .. · . · · . .. . .. lng floods. l he ricing comfort ot the smaller cars IS being Improved through the use of vibration damping butyl rubber. Tire tread compounds are being reformulated to reduce rolling resistance. New, high-solid, solvent-based paints are being developed to reduce air pollution. Chemically based rust proofing _ systems are being introduced to prolong life. Contemporary U.S. cars contain more than 500 pounds of plastics, rubbers, fluids, coatings, sealants, and lubricants, all products of the chemical industry. Further inroads of plastic materials can be expected as research leads to the process innovations that are needed. Reaction injection molding is a recently introduced process for making large parts like fenders and hoods. High- performance composites, i.e., stiff fibers in a polymer matrix, have already appeared as drive shafts and leaf springs. Some advanced models have frames and bodies made of composites. Long cycle times caused by slow cure of the matrix resins is an economic limitation that is receiving research attention. In

V-B. CONTINUED ECONOMIC COMPETITIVENESS this connection, it should be noted that new designs for light aircraft (i.e., general aviation) have airframes that are almost entirely composites. For automobiles, the use of composites may lead to new design-fabrication methods that will greatly reduce the number of parts to be assembled. Chemistry lies at the root of all of these advances. Clearly the problems faced by the American automobile industry are complex mixtures of historical preferences, social pressure, legislation, and vigorous outside competition. Chemistry is an essential technology in any successful response to these pressures. New Horizons The chemical industry is changing, and chemical science is becoming impor- tantly interwined with other areas of science and technology. To an increasing degree chemists must be adept at dealing with subjects and practitioners of allied technologies. Chemistry is critical in providing materials and processes for American industries, meeting their needs across the spectrum from mature industries (new electrode materials for aluminum production, Tow-cost sweet- eners for the food industry, etc.) to rapidly growing, high-technology areas (high-performance composites for aircraft, improved ceramics for electroncs and engines, protein pharmaceuticals, etc.~. Each of these areas requires develop- ment of chemical products that respond to markets outside of chemistry, as in the representative examples given below. Biotechnology Biotechnology is not new. The ancients knew how to bake and brew thousand of years ago. The processes of fermentation, separation, and purification have Tong been familiar. Until recent years the field might have been labeled applied microbiology. As the molecular structure and basic chemistry of genetic material became known, a new era of biotechnology opened up. It led to gene- splicing procedures that enabled biochemists to cause bacteria to produce complex molecules that exhibit important biological activity. Enzymes have been found that will break chemical bonds in DNA chains at specific points and allow foreign DNA to be inserted with new chemical bonds. The altered DNA then produces proteins according to its revised code. The protein products can be hormones, antibodies, or other complex chemical compounds with specific properties and functions. Interferon, produced by hnn.teria with a human gene ~ 1 1 ~ ~ _1 _ spliced in place, Is expected to be valuable In treating a variety of creases. Human insulin is already being marketed. Activity is intense, and commercial enterprises are emerging rapidly. The area of biotechnology is an exciting and exuberant realm for scientists, engineers, and investors. Although some of the expectations appear to be extravagant, there can be no doubt that this is an area that will see many important economic developments in the coming decades. The United States is at present the world leader, with basic chemical and molecular biological 213

214 CHEMISTRY AND NATIONAL WELL-BEING research feeding an elective commercial community. Europe, with strong, relevant research, and Japan, with a leading position in fermentation processes, can be expected to challenge the U.S. position. The advances that will determine the future of the field will accrue through the practice of pure chemistry at its most sophisticated reach. Increasingly, progress depends upon a deep under- standing of biology at the molecular level. Basic research on the molecular structure and chemistry of biological molecules will be a crucial ingredient as we try to maintain our current leadership position in biotechnology. High-Technology Ceramics Ceramics are materials with high temperature stability and hardness; they tend to be brittle, and they are difficult to shape. Ceramics are now of major commercial interest for components of electrical devices, engines, tools, and a wide range of other applications in which hardness, stiffness, and stability at high temperatures are essential. Major advances in their use can be anticipated because of new chemical compositions and novel fabrication techniques. For many, many centuries, ceramic pieces have been made from a slurry or paste of a finely ground natural mineral. The slurry is formed or cast in the desired shape and then "fired," i.e., heated to a temperature high enough to burn away the added slurry components and to melt and join the mineral particles where they touch. The strength of the final object is critically limited by small imperfections. . - A number of new chemical techniques are now being developed to synthesize ceramic precursors and to produce final products more free of defects. These techniques depend upon control of reaction kinetics and tailoring of molecular properties. Thus controlled hydrolysis of organometallic compounds is used to generate highly uniform ceramic particles ("sol-ge] technology". Organometal- lic polymers can be spun into fibers and pyrolyzed to produce important materials like silicon carbide. Reaction of volatile chemical precursors at high temperature in the vapor phase, followed by controlled deposition of the reaction products, can give highly uniform temperature-resistant coatings to preshaped objects. Addition of suitable impurities ("doping agents") can change properties dramatically. For example, alumina ceramics can be significantly toughened by addition of zirconia. The production of ceramics has a major economic role that will surely grow as new materials are discovered and developed. Chemical advances will be essential to this growth by providing new precursors and more controlled production techniques. The potentialities have been recognized abroad, where major research programs on ceramics have been launched (particularly in ~Japan). To remain competitive, U.S. research efforts must be strengthened. Advanced Composites and Engineering Plastics The discovery of ultrahigh-strength fibers based upon graphite embedded in a matrix of organic polymer has led to development of a new class of materials

V-B. CONTINUED ECONOMIC COMPETITIVENESS now referred to as "advanced composites." A fiber, such as a graphitic carbon chain, a mineral fiber, or an extended hydrocarbon polymer, is suspended in a conventional high-polymer matrix, such as epoxy. The resulting composite can exhibit tensile strength comparable to that of structural steel but at a much lower density. Because of this high strength-to-weight ratio, such composites are finding abundant applications in the aerospace industry. Significant weight reductions are achieved in commercial and military aircraft that use airframes and other aircraft components made of composites. Other applications include space hardware, sporting goods, automotive components (e.g., drive shafts and leaf springs), and boat hulls. There has also been a rapid development in tailoring polymer mixtures to obtain particular properties or behavior. Success with these polymer "alloys" or "blends" has required a high degree of chemical understanding of the molecular interactions at phase boundaries between two polymers that are not mutually soluble. An example is the commercial polymer blend called Zytel Y.T.~, a thermoplastic nylon toughened with a hydrocarbon elastomer. The development of this high-performance plastic was based upon extensive studies of interac- tions at interfaces between different polymers. Plastics are also being developed for high temperature applications, such as engine blocks for automobiles. A prototype "plastic engine" based on reinforced polyamide and polyimide resins has been demonstrated in a competitive racing car. An engine-weight reduction of 200 pounds can be achieved, with obvious benefit to fuel economy. These technologies are moving forward rapidly around the world. Carbon fiber production is currently dominated by Japan, while the United States leads in high-strength polymeric fibers. Research will figure importantly in the evolution of such readerships. New rapid-curing matrix materials are needed. The nature of the bonding region between the fiber and its composite matrix environment is an important factor in structural performance but poorly understood chemically. These and other fundamental questions remain to be investigated. Other countries have initiated strong programs to address these questions: Japan has identified composite materials as a thrust area; Germany has established a new Max Planck Institute in this field; other countries are actively pursuing the opportunities. While U.S. industrial laboratories have recorded some gratifying commercial successes, our basic research activity must be more strongly encouraged and stimulated to ensure continued U.S. compet- itiveness on the world scene. Photo imaging The purpose of photography is to produce an accurate and lasting record of the image of an object or a scene. With a history of 150 years, the silver halide process has evolved from complex procedures conducted by specialists with a working knowledge of photochemistry into a pastime through which untrained individuals can produce likenesses of outstanding clarity and accuracy. The .., 2~15

216 CHEMISTRY AND NATIONAL WELL-BEING individual presides over remarkable feats of optics and chemistry to produce these pictures on the spot, usually without having the faintest appreciation of what goes on in the camera or on the film. The result brings pleasure and useful pictorial images to people throughout the world. The chemistry of the photographic process can be usefully divided into the inorganic photochemistry of the silver halide and the organic chemistry of sensitization, development, and dye formation. When radiation strikes a microcrystal of a silver halide, a latent image is formed that is believed to consist of a few atoms of metallic silver. The metallic silver functions as a catalyst for the reduction of the entire grain under the chemical action of a reducing agent, the developer. The silver halide grains in a photographic film are typically of the order of a micrometer in size, and control of the size and shape of the particles is important. Although silver halides are sensitive only to light at the blue end of the spectrum, the grains can be activated at longer wavelengths with sensitizing dyes absorbed on the crystal surface. These molecules are coated onto the silver halide surface in layers less than one- thousandth-of-a-millimeter thick. Color is achieved when the oxidized form of the developer reacts with a color coupler to give a dye of the required hue. By combining the 3 color primaries, 11 colors can be achieved. Conventional color photography involves several carefully controlled chemical processes, including development, bleaching, fixing, and washing. In color instant photography these steps must be combined in a single planar unit, which can be processed in the light without temperature control. A typical instant film contains over a dozen separate layers with thicknesses of the order of 1 micrometer each. Physical chemical factors, such as solubility and diffusion, are critical as are the chemical reactions occurring in the various layers during processing. The sophistication of the chemistry of instant color photography is difficult to comprehend and presents a striking contrast with the simplicity of operations required of the user. In this important area of our economy, new technological achievements continue to appear, ranging from amateur photography to such demanding and esoteric uses as photoresists for semiconductor production (see below) and infrared mapping of the earth's resources from satellites. Competition from abroad is strong, particularly in the mass market area. The United States has been the world leader in photographic technology for many years in an industry where the connection with our traditional research strength in photochemistry is clear. We must keep it so. Microlectronic Devices The microelectronics revolution has already had an enormous impact on the industrialized world, and it is clear that there is a great deal more to come. The best known device is the microprocessor, a remarkably intricate and function- ally integrated electrical circuit built on a tiny silicon "chip." Some micropro-

V-B. CONTINUED ECONOMIC COMPETITIVENESS cessors and the latest high-capacity computer memory chips contain hundreds of thousands of individual transistors or other solid state components squeezed onto a piece of silicon about one-quarter-of-an-inch square. These "chips" are currently made from highly purified, elemental silicon containing impurities deliberately implanted in specific locales to form individ- ual devices with desired electronic functions: amplification, rectification, switching, storage of on-o~Iogic information, etc. These minute devices are then interconnected by metal "wires" on a microscopic scale. All this is clearly inorganic chemistry; there is no organic material present finally other than an organic polymer coating for protection against deterioration. However, an important point not generally realized is that the fabrication of these exquis- itely complex devices depends critically on thin (less than 1 micron thick) organic films of radiation sensitive polymers whose technology involves organic chemistry, photochemistry, and polymer chemistry. The purpose of the films is to permit selective doping in the pattern of a desired electrical circuit. Because steps in the process involve high temperature, a thin layer of silicon dioxide is used as the masking layer that determines whether or not the underlying silicon is acceptable for doping. Organic mate- rials called photoresists are used to form the primary pattern that is transferred into the silicon dioxide layer. In photolithography, chem- ical changes in the photore- sist material are initiated by exposure to light. In these changes, covalent chemical bonds are ruptured (or formed) through light-sen- sitive functional groups at- tached to the polymer struc- Ez1 ILLUMINATED AREAS NEGATIVE RESIST O RENDERED I NSOLUBLE - - sure. The chemical bond changes result in a local in- crease (or decrease) of the photoresist solubility in a suitable solvent. Thus after exposure through a mask, an image of the mask can be de- veloped merely by washing in the solvent. What is not gen- erally appreciated is that this solubility is achieved through carefully designed polymer photochemistry. Existing organic photore- 217 LIGHT MASK ~~/ ~ — — ~ ,PHOTORESIST t::::::::1 1:::::::::! 1:::::::~~ ,,,,,, —SILICON DIOXIDE t __ SILICON ~ ( rid ETCHED FILM PATTERNS RESIST REMOVED ,~ POSITIVE RESIST: 13RENDERED SOLUBLE . ~ ~ 1 K EY STEPS I N THE FABRICATION OF SILICON INTEGRATED CIRCUITS USING PHOTORESISTS

218 CHEMISTRY AND NATIONAL WELL-BEING sists could achieve the spatial resolution that wasconsidered adequate up to the early 1970s when individual integrated circuit feature sizes were in the range of 3 to 10 microns. However, the inexorable desire for continued increase in device density has demanded ever smaller features. A decade ago it became apparent that new photoresists would be needed because existing materials were not capable of defining the feature sizes (1 to 2 microns) soon to be required. The development of these materials has been made possible by research advances in polymer chemistry, photochemistry, and radiation chem- istry. Because these feature sizes are close to the wavelength of light used for conventional optical imaging (.4 microns), diffraction effects caused by the features on the mask (a mask is analogous to a photographic negative) become important. These ejects can be reduced by using shorter wavelength radiation. There has been extensive development of resist materials that are chemically sensitive to exposure with electron beams, X-rays, and short-wavelength ultraviolet light instead of the near ultraviolet light now used. Masks are made by chemically etching thin chromium films deposited on glass, using a resist that is patterned by exposure to a computer-controlled electron beam. The development of the organic resist material used for defining the metal pattern rests on relatively recent research in both polymer chemistry and radiation chemistry. Many new types of chemical reactions are involved, and the advances in integrated circuit complexity could not have occurred if these new materials had not been available. Virtually none of them existed in 1970. Examples of new electron-beam resists are the copolymers of various alkenes and sulfur dioxide whose synthesis and radiation sensitivity were discovered in fundamental studies over the last two decades. Because optical technology is both well established and the simplest type to implement, it is receiving strong support. New high-resolution photosensitive organic materials are under development in the United States, Japan, and Europe. Researchers have taken advantage of such diverse photochemistry as that of ortho-nitrobenzy] and other photochemically removable protective groups that were designed for protein and natural product synthesis. There has also been some success in using theoretical organic chemistry in the design of materials with specific optical absorption band changes. A current trend in semiconductor fabrication is to use reactive gas plasmas instead of liquid solutions to etch the substrate under the photoresist mask. Most organic materials are not sufficiently resistant to these vigorous condi- tions, and it has taken much research to provide a few useful materials. It is difficult to design materials having the necessary combination of physical and chemical properties. Their development will draw on continued research ad- vances in polymer chemistry and photochemistry, including laser-induced chemistry. Progress in the relevant areas of chemistry will be one of the important factors if we are to retain competitive advantage in this rapidly moving and economically critical technology.

V-B. CONTINUED ECONOMIC COMPETITIVENESS Analytical Instrumentation The greatly increased demand for analyses in important applications, such as industrial processes, the environment, and health, has pushed worldwide sales of analytical instruments from $300M to $3B per year in the last decade. U.S. manufacturers have dominated this market, with a currently favorable trade balance of nearly $1B. Instrument obsolesence times are commonly 6 years or fewer, placing great emphasis on innovative research and new applications. While innovations are coming from physics, electronics, computer sciences, and biology, chemistry remains central to continued leadership in this area. To cite two examples, U.S. chemists have been at the forefront of exciting new developments using lasers and computers. As described elsewhere in this report, laser excitation can provide specific, sensitive data on elements and molecules and their environments, with the variety of new methods increasing on an almost daily basis. Dedicated computers are taking over more and more of the task of operating complex instruments, handling their high data rates, and even producing final reports. Like the increasing pervasiveness of the computer in modern society, the development of analytical instruments of improved accuracy, speed, and speci- ficity at lower prices will certainly lead to new applications, such as those in automated industries, preventative medicine, and environmental warning systems, as well as greatly improved research efficiency. Retaining and increas- ing U.S. leadership in analytical instrumentation should thus bring benefits far beyond an attractive balance of trade. MoZecular-Scale Computers Miniaturization of electrical devices has been one of the most significant factors in the rapid advances that have made modern computers possible. Circuit elements in present silicon chips have dimensions near 1 micrometer, i.e., in the range of 10,000 5. However, it may be that fabrication of microscopic devices based upon silicon and other semiconductor methods is beginning to push against natural barriers that will limit continued movement toward increasingly compact devices. Thereafter, breakthroughs will be needed. Where will we turn when existing technologies are blocked by intrinsic natural limits? Irresistibly, we must contemplate molecular circuit elements that wit] permit us to move well inside the 10,000 ~ limit. We are led to picture computer devices on the molecular scale. As is normal, adventurous concepts generate exciting, often emotional con- troversy. Advocates tend to be glowingly enthusiastic, in both expectations and claims. At the other extreme, there can be outright disdain from those dedicated to currently successful and still advancing technologies that would be made obsolete by the new directions. However, the arguments of even the most sophisticated detractors are disarmed (contradicted?) by the fact that this intelligent opposition is being generated in a working computer using exactly 219

220 CHEMISTRY AND NATIONAL WELL-BEING ~ 1 the structure under challenge, the human brain! In an age of machine synthesis of DNA segments and laboratory design of artificial enzymes, it would be excessively timid to say that we can neither learn nor mimic the elegant circuits that each of us depends upon to read and consider these printed words. In a three-dimensional architecture, use of molecular circuit elements with 100 ~ spacing would provide packing a million times more dense than any now achievable. The materials under discussion range from entirely synthetic electrically conducting polymers to natural proteins. Molecular switches, the basic memory elements of the proposed computer, might be based upon double bond movement in polyacetylene, photochromism, or molecular orientation in solids. Ideas about connecting the molecular elements to external devices are still vague. There are those who dismiss as far-fetched the idea of man-made molecular scale computers. Only a few decades ago, however, these same individuals might have classified as science fiction a proposal that someday there would be a man on the Moon, that fertility could be controlled by taking a pill, or that we could learn the structure of DNA. But since we know that molecular computers are routine accessories in all animals from ants to zebras, it would be prudent to change the question from whether there will be man-made counterparts to questions concerning when they will come into existence and who will be leading in their development. The when question will be answered on the basis of fundamental research in chemistry; the who question will depend on which countries commit the required resources and creativity to the search. The United States will want to be in the forefront, and we must be sufficiently bold to support the fundamental research programs that will move us toward this goal. Conclusion The field of chemistry in the United States has great industrial and economic importance. The consistent and significant positive balance of payments, even in the era of an over-strong dollar, is an indication of intrinsic strength. The continuing flow of innovations that benefit society is encouraging. U.S. univer- sities are the best in the world, and year by year they draw students from throughout the world for graduate study. In each of these aspects, the United States leads the world. Even so, there are abundant challenges to the chemical strength of the United States from Europe, from Japan, and from some of the less-developed countries. The United States must work hard and creatively to maintain its leadership in view of unfavorable antitrust regulation, environmental restrictions, health and safety requirements, wage rates, and currency leverage, all of which make the competitive position of U.S. chemical products difficult to retain. Answers lie in objective justification of any restraints imposed by legislation, with balanced concern for the important social values represented in current regu- lations. And we must continue to stimulate the academic and industrial

V-B. CONTINUED ECONOMIC COMPETITIVENESS research that maintains the knowledge base from which we derive our compet- itive edge. To this end, efforts must be made to attract an adequate share of the finest young minds to the field of chemistry. Support for university research in chemistry must be enhanced to produce the best-equipped laboratories in the world and retain the most gifted faculties. Only a sustained and vigorous approach will be effective in maintaining our position in the essential field of chemistry, so necessary to any high-technology society. 221

222 CHEMISTRY AND NATIONAL WELL-BEING V-C. Increased National Security The nation's security depends upon its people being well and healthy, having an adequate food supply, and living in a safe environment. It depends upon there being an ample, assured supply of appropriate energy sources for trans- portation, production, and communication. Still another requirement is an adequate domestic store of critical materials, as well as alternative materials for the most important applications and for those materials whose supply is most vulnerable to interruption or termination. Maintaining national security requires not only that health, food, environment, energy, and materials be adequate today, but also that we can ensure that they will still be adequate for future generations and changed geo-political circumstances. This requires, and indeed is critically dependent upon, basic chemical research. Other sections of this report document the ways in which meeting these basic needs will depend upon advances in chemical research. The nation's security also depends upon having a strong, healthy economy that leads to full employment, a desirable standard of living, domestic well-be- ing, and productive flexibility. Here also, as illustrated in the preceding section of this report, it is clear that the contribution of chemical research to industrial productivity has a large influence on national employment and upon the nation's position in international trade. A stable, secure economy is one that can compete internationally and whose strength is not critically dependent upon events outside the nation's control. Finally and ultimately, national security depends upon the ability of the nation to defend itself and to deter and prevent armed conflict. In these areas, chemistry, "the central science," again plays a critical part. Strategic and Critical Materials As noted in Section IlI-C, a "material" is a chemical substance out of which useful things are made including things like armor plate, jet engine turbine blades, spacecraft heat shields, air frames, submarine hulls, flakjackets, and infrared detectors. When an application has crucial importance to our national defense, the requisite material is called a strategic material. When an applica- tion has crucial importance to our industrial strength, the requisite material is called a critical material. An important element of our national security is connected with identifying those strategic and critical materials whose avail- ability might be limited or cut off by political developments abroad. Fundamen- tal research areas that lead to new and alternative materials add to our options in the event of such cut-off they furnish appropriate places for defense investment. By the Dante token, the possibilities for new defensive systems and weapons depend to a great extent on the invention and development of new materials with which to make them. Advanced weapons need materials that are lighter, stronger, tougher, and cheaper than presently available. The pursuit of new

V-C. INCREASED NATIONAL SECURITY materials and the study of chemistry are inextricably linked through the need to understand material behavior at the molecular level and the need to synthesize new chemical compounds. Efficient processing of new materials requires development of on-line chemical analytical techniques. New ways of controlling surface, solid state, and polymer chemistry will play a lead role in developing materials of superior hardness, shatter resistance, weight, flow properties, corrosion protection, and wear resistance, for use in non-nuclear and nuclear defense systems and weapons. These materials may be alloys, polymers, ceramics, or fiber-reinforced composites. Fundamental ad- vances in understanding the structure, bonding, and chemical reactivity at surfaces should also result in the development of improved coatings for antiradar, reduced drag, and resistance to intense laser radiation. There are four areas of chemistry that will make particularly significant contributions in the development of new materials and of new pathways to existing materials. Surface Chemistry Innovative applications of surface chemistry and integration with mutually supportive advances in other aspects of surface science are needed for corrosion protection, coating adhesion, welding and joining, hardness, and wear resist- ance all of which contribute to and determine the electiveness, cost, and useful life of weapons systems. Inhibiting corrosion alone is a major expense of military hardware. Enhanced understanding of interracial chemistry will also facilitate better coatings, such as antiradar (stealth) coatings for aircraft, missiles, satellites, reentry vehicles, and ships; antisonar coatings for ships and submarines; reduced-drag coatings for attack submarines; enhanced reflectivity coatings for high-power-laser mirrors, and many others. The development of high-performance, fiber-reinforced composites of metals, ceramics, or polymers depends on a better understanding of the surface chemistry at the fiber/matrix interface. Synthesis and Properties of New Solid State Materials An important part of future defense strategy is superior electronic warfare, consisting of command, control, communications, intelligence, and electronic countermeasures. Advances in this area depend upon development of new nonlinear optic, electro-optic, and electronic materials. For example, we need ultrafast electronics that are intrinsically resistant to damage by X-rays, gamma rays, neutrons, and particle beams. We also need high-power-laser frequency multipliers, infrared and ultraviolet electro-optic materials, and nonlinear optical absorbers to protect against laser beams. Advances in these areas will come through research into the optical, electronic, and crystal structure of new chemical compounds. Such research permits us to design substances with desired macroscopic properties, and it provides the synthetic techniques needed to make those substances. 223

224 CHEMISTRY AND NATIONAL WELL-BEING Modern weapons and weapon concepts depend increasingly upon the use of polymers and polymer composites as materials to meet stringent physical requirements of weight, density, and strength. Development of these new polymers is the task of the polymer chemist working with other polymer scientists. As described in Section ITI-C, new polymers have potential for applications ranging from structural materials that compete with steed to novel electronic materials that may be our future semiconductors. Long-term storage of nuclear weapons adds to the demands for new materials. Crucial to stockpile lifetime and reliability are the questions of how, why, and when materials age and deteriorate, including underexposure to radioactivity. Because composite materials are of increasing importance, this knowledge must include basic understanding of the chemistry at the component interfaces within a composite and how that chemistry is affected by prolonged degradation in hostile environments. Catalysts The development of more specific, faster, more uniform catalysts will radi- cally change the cost and availability of advanced chemicals and materials. For example, the study of catalysts has led to new techniques of polymer synthesis that have allowed new polymers to be developed and made advanced polymer alloys available for modern weapons. In addition to offering the possibility of new and better materials, highly specific catalysts can also reduce the cost of militarily important chemicals and thus make them available for practical use (see Sections VII-A, IlI-B, and V-D). Separations Chemistry OPTIMUM .8 .6 Cat: o ~ 1.4 - 1 2 1.0 1 - \ INdl/ ~ /IPrl \~ ~ UNDER SELECTIVE \ / RADIATIVE EXCITATION \ ,,,,1,,,,1,,,,1,,,,1,, 1.5 2.0 2.5 3.0 HCQ CONCENTRATION AT ALL HCQ CONCENTRATIONS SELECTIVE EXCITATION FAVORS NEODYMIUM Separations chemistry is the application of chemical principles, properties, and techniques to the separation of specific elements and com- pounds from extraneous ma- terials (including mineral ores) and from each other. It has applications in such di- verse areas as the nuclear fuel cycle, analytical chemis- try, and biochemistry. It cap- italizes on the differences in such properties as solubility, volatility, adsorbability, ex- tractability, stereochemistry, and ion properties of elements and molecules. As an exam-

V-C. INCREASED NATIONAL SECURITY TABLE V-1 Essential Defense Uses of Some Materials Materiala System Carbon Be Fiber Co Mn X X X X X X X X X X X X X Pt Quartz Ti Satellites Aircraft Engines Helicopters Missiles Tanks Artillery Ammunition Ships Submarines X Mines Electronics X Support industries a Be Beryllium Or Chromium Co—Cobalt Ge Germanium X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Mn Manganese Pt- Platinum Ta Tantalum Ti Titanium pie, the rare earth elements neodymium (Nd) and praeseodymium (Pr), impor- tant in laser manufacture, must be separated from the mineral monazite. A difficult part of this extraction is the separation from chemically similar cerium. Photochemical studies show that this separation can be enhanced manyfold by selective excitation that exploits the different chemistries of the elements under excitation with light. Many vital materials result from application of separations chemistry. They range from biochemicals separated from living organisms to the chromium needed to produce the stainless steels used in defense, medical, and industrial products. They include catalysts, pigments for protective coatings, fertilizers, and materials used to produce energy and to facilitate communication and transportation. The availability of critical and strate- gic materials to U.S. industry and the military is dependent in many instances on the development of practical, econom- ical chemical separations methods. Table V-1 illustrates the essential defense uses of some materials, all but two of which are imported. Table V-2 adds quantita- tive data on U.S. dependence on imports for some critical metals and minerals. Future availability of such elements as chromium, the platinum group elements, and others may depend critically upon developing chemical separations pro- 225 TABLE V-2 U.s. Import Dependence, Selected Elements (Imports as Percent of Apparent Consumption) 1950 1980 Manganese Aluminum (bauxite) Cobalt Chromium Platinum Nickel Zinc Tungsten Iron (ore) Copper Lead 77 71 92 100 91 99 37 80 35 59 97 94 93 91 87 73 58 54 22 14 <10

226 CHEMISTRY AND NATIONAL WELL-BEING cesses for chemical mining or for their extraction from low-grade but indigenous ores or geothermal brines. In those cases where substitutes based upon more abundant elements can be found for the critical materials, chemical separations processes will be needed for increased economical recovery of many of the substitutes. Historically, high-technology defense materials that have come from defense research of the types described above have quickly moved into the private sector to yield additional positive economic and social benefits. Surveillance and Intelligence Many important applications of chemical procedures relate to the prevention or early warning of armed conflict. Examples include sensor development to identify rocket plumes or high-explosive phenomena; the use of neutron and gamma emission data, instrumentation, and techniques for safeguard surveil- lance to ensure the nonproliferation and control of nuclear materials; the analysis of radioactive debris from nuclear events; and the development of methods for identification of specific trace chemicals resulting from various potentially military-related chemical processes. These technologies clearly have implications in surveillance and treaty verification, and the resulting analytical and modeling efforts greatly affect our defensive posture in the prevention of armed conflict. Past efforts in these areas have brought about substantial advances in defense capabilities, as well as an appreciation for the capabilities of other nations. For example, much of what we now know about advanced foreign nuclear weapons technology comes from gas and particle analysis, remote from the scene of use, coupled with appropriate modeling. More detailed knowledge of actinide and fission product behavior than we currently have is required if we are to be ready for probable future developments. Many of the techniques developed for nuclear surveillance (and for defense against chemical and biological warfare) are also used to detect and counter potential terrorist activities. However, the remote detection of explosives remains a difficult problem and is the subject of current and future research into the development of appropriate noninvasive trace chemical analyses. Case History: Theoretical Chemistry and Rocket Surveillance Of concern to all Americans is defense against intercontinental ballistic missile attack. Early warning and activation of a defense system is crucial. Much of the current defense approach is based upon detection of a missile plume's characteristic emission of light, termed its signature. The signature identifies the origin of the rocket and provides a mechanism for an antimissile device to key onto the intruding missile and destroy it. The radiation from the rocket plume is responsible for the plume signature. This radiation is characteristic of the fuel components used to propel the rocket and is partially caused by collisions among molecules produced in fuel combus-

V-C. INCREASED NATIONAL SECURITY tion and the components of the upper atmosphere. Such collisions cause plume molecules, such as H2O and CO2, to be excited into higher-lying energy states, which subsequently emit radiation. One must know the details of this radiation to design detection devices, and the details require a knowledge of the probabilities that collisions among plume and atmospheric compounds will cause excitation. In this example, the requisite information was not available from experiment. As an alternative, ab initio quantum chemistry and molecular dynamics methods were used to obtain the required information. Potential energy surfaces that govern the collision of 0~3P) atoms, the principal component of the upper atmosphere, with H2O and CO2 molecules were calculated using highly accurate, many-body methods. Employing these surfaces, quasi-cIassical dynamics methods were used to obtain the excitation probabilities. The results served as an essential input to the detector design. Similar theoretical approaches have been used to calculate the radiation signature resulting from nuclear explosives. Nuclear Power and Nuclear Weapons Since their participation in the discoveries of nuclear fission and of the first transuranium elements, nuclear chemists have played indispensable roles in the nuclear energy program in this country. This has been equally true in both the military and civilian applications of nuclear energy. The technological requirements of these programs are often so closely related to fundamental research that it becomes difficult to separate the two. A prime example of close relationship between applied and basic research is found in the chemistry of the transuranium elements. The chemical properties of these elements were first established by following their radiations when the elements were available only in unweighably small quantities. A cadre of skilled chemists were able to apply their fundamental knowledge of chemistry to synthesize and separate the new element plutonium. They were also able to extend our knowledge and synthesize a whole new region of the Periodic Table that of the transuranium nuclides. The methods devised for the original, large-scale processes to separate plutonium from irradiated uranium fuel, based on the knowledge of actinide and fission product chemistry at that time, are still in use. A present concern in the United States should be to maintain and extend our knowledge of fundamental actinide and radiochemistry; many experts are nearing retirement, and replacements are not being generated at the universi- ties because of the interdisciplinary nature of the field, the expense of adequate training, and, in part, public attitudes toward uses of nuclear energy. Yet, a new generation of such experts will surely be needed, no matter what future course is followed regarding manufacture or disposal of nuclear weaponry or use of nuclear power. We must still be able to deal effectively with the radioactive materials and wastes already in existence. 227

228 CHEMISTRY AND NATIONAL WELL-BEING Nuclear Reactors Nuclear reactors play a part in national defense in the production of electrical power, in the production of plutonium and tritium, and in propulsion, especially of submarines. The design and operation of nuclear reactors are primarily the province of reactor physicists and engineers, but scores of problems encountered in reactor construction and operation call for the skills of the nuclear chemist. Monitoring the purity of materials needed for construction depends upon chemical analytical techniques. Detailed understanding of the neutron economy in a reactor requires nuclear chemists to establish rates of plutonium produc- tion and destruction, efficiency of use of the fissionable material, and breeding capabilities. In the design of new types of reactors, extensive studies of the nuclear reaction and disintegration probabilities of individual isotopes of the heavy elements are often crucial. These studies are carried out usually to obtain fundamental data on the stability and reactivity of nuclei. Tritium Production Tritium is also required for nuclear weapons, not only for development of new weapons, but for maintenance of existing weapons. Because of its relatively short half-life of only 12 years, it cannot be stockpiled and must be continually produced in fission reactors via the reaction of thermal neutrons with lithium-6. New production, extraction, and purification technologies at existing facilities as well as the design of new reactors that would combine tritium production with power production can be envisioned. Fundamental chemistry to develop new target materials and a study of tritium retention and binding as well as studies of tritium diffusion mechanisms are needed. Improved and more economical methods for separation of tritium from other hydrogen isotopes are possible. Actinide Chemistry Development of nuclear reactors, power sources, and weapons requires the production and chemical separation, not only of the fissionable materials, plutonium and uranium, but of a number of other unusual elements as well. A knowledge of their chemistry and their complex metallurgy is essential. The actinide elements (including uranium) constitute a frontier region of the Periodic Table. Their properties can neither be interpolated nor simply extrap- orated from those of the lighter elements. It is possible to develop new, more efficient methods for separation of these elements (as well as plutonium) from irradiated fuel. For example, new methods (photochemical, pyrochemical, electrochemical) for adjusting oxidation states that do not require addition of large volumes of solution or additives requiring costly waste disposal would result in large savings and less impact on the environment. More efficient and economical methods of isotope separation are also possible, including methods based upon laser processing or chemical exchange.

V-C. INCREASED NATIONAL SECURITY Laser Isotope Separation The application of lasers to isotope separation must be counted an important national security development because of its potential applicability to purifica- tion of fissionable isotopes. Multiphoton excitation has been discussed in Section IlI-D with reference to the possible separation of fissionable isotopes through selective laser excitation. A number of tuned-laser excitation schemes have been tried, and chemists were usually involved. The multiple photon excitation of SF6 (or its structural analogue, UFO) with a tuned infrared laser is most clearly a chemical process. First, the excitation ruptures a chemical bond to produce two reactive fragments, SF5 (or UF5) and F atom, which must then be chemically trapped to retain the isotopic specificity. Clearly, research on any such scheme that shows promise must be pursued. Any such process, if successful in decreasing costs, would increase access to fissionable materials, both here and abroad, plainly a matter that affects our national security. Radiochemical Detection A continuing problem in the development of nuclear weapons is the assess- ment of the performance of new designs. Nuclear and radiochemistry have provided the basis for sophisticated and detailed analysis of the performance of nuclear devices. Ultrasensitive and selective analyses have been devised, including high-sensitivity mass spec- trometry, such as resonance ionization and ac- celerator-based mass spectrometry, isotope separation, sensitive radiation measurement in- strumentation, and radiochemical separations for nearly every element in the Periodic Table. As a particular example, nuclear bomb testing dis- perses in the atmosphere large amounts of fission products whose presence reveals both the event and the type of nuclear testing. Many of these fission product elements already exist in the en- vironment from natural sources; their presence can interfere with detection of the more telltale elements present only because of a fission event. Lutecium is an example of the latter, but its detection can be obscured by the much larger natural background levels of chemically similar ytterbium. A solution is provided by tuned laser excitation in a mass spectrometer. At the reso- nant laser frequencies at which lutecium can be photoexcited to ionization, the ytterbium back- 229 THERMAL Ytterbium Background Yb J he in T I Yb~ r 1 j ~ 1 1 ~ . L ASER Lu Lu Luteclum (from a nuclear esp10sion ) 1: 1 1 1 1 1 SELECTIVE LASER EXC I TAT I ON IN MASS SPECTROMETRT 1 ~ 176 174 172 170 MASS (amu) MON ITORING NU CLEAR TESTING WITH SELECTIVE MASS SPECTROMETRY

230 CHEMISTRY AND NATIONAL WELL-BEING ground can be completely suppressed so that minute levels of Jutecium and its isotopic distribution can be measured. In addition to analyzing for the fissile materials and fission products from a nuclear device, sensitive analyses are performed for the nuclear reaction products of specific elements added as so-called "radiochemical detectors." To interpret the results of these analyses, relevant nuclear data such as neutron cross sections, fission yields, and neutron emission for various fissioning systems must be measured. In this way, thermonuclear as well as fission yields and efficiency can be measured, and neutron fluxes and energies can be determined. Processing and Reprocessing The recent emergence of plutonium pyrochemical processes (electrolytic or chemical processes that use oxidation-reduction reactions to eject chemical separations at elevated temperatures) has resulted in a dramatic increase in the ability to produce high-purity plutonium metal from scrap residues. These processes resulted from basic chemical studies during the sixties. Currently, ton amounts of metal are produced by pyrochemical processes each year, but many tons still remain tied up in scrap residues. Advanced pyrochemical methods promise more efficient recovery based on recent research progress in molten salt-molten metal chemistry. For example, present plutonium pyrochemical operations are limited to plutonium-rich metal systems with melting points less than 800°C; processes are needed for uranium-plutonium systems with melting points of about 1000°C. Basic chemical studies are required to identify materials and equipment for high temperature operation and to identify low-melting multicomponent metal systems that could be used as solvents for high-melting scrap. Pyrochemical processes have the advantage of generating few new waste streams. Most of the waste streams that are produced are discarded to retriev- able storage. The high cost of disposal and storage, however, suggests that much of this waste should be purified and recycled rather than discarded. For example, waste CaCI2-CaO salts generated during the reduction of PuO2 to metal could be reused by conversion of CaO to CaCI2. Currently, the only nuclear reprocessing being done in the United States is related to national defense. Increasing the efficiency of this operation will increase the recovery of materials needed for the nuclear weapons program and also reduce the waste disposal problem. Of course, it remains a national responsibility to provide for the safe storage and isolation of radioactive waste generated by our nuclear weapons program. High-Speed Chemistry: Explosives and Fuels The design and production of improved fuels and explosives for propulsion and munitions continues to be of central importance to our national security. This area will be moved ahead rapidly on the basis of the rich opportunities

V-C. INCREASED NATIONAL SECURITY before us in reaction dynamics, molecular dynamics, theoretical chemistry, and solid state chemistry. Even though the chemistry of explosives has been studied for hundreds of years, the underlying principles that would lead to predictive models for synthesis of better explosives are only now on the threshold of being understood. There are two areas where considerable progress is expected in the coming years. Detonation Chemistry Conventional condensed-phase explosives yield detonation waves with veloc- ities in the order of 9 Parsec, densities greater than 2 g/cm3, temperatures of several thousand degrees, pressures of the order of 500 Kbar, and a chemical reaction zone where the energy necessary to sustain the detonation is released in less than 10 nsec. The study of chemical reactions under any one of these experimental conditions is difficult, and their combination pushes the limits of chemical science. Recently, several nonlinear laser diagnostic techniques have been demon- strated that allow spectroscopic examination of shock-compressed materials. For example, using a laser method called "backward stimulated Raman scat- tering" in shock-compressed benzene, molecular vibrational frequency shifts have been measured as a function of pressure. Such data permit determination of pressure and temperature-induced changes in the intermolecular potentials. Other recently developed laser-based methods, such as "reflected broadband coherent anti-Stokes scattering," have allowed simultaneous spectroscopic monitoring of several constituents in shockcompressed systems. Finally, subpicosecond (i.e., less than one-trillionth of a second) laser diagnostics are being developed to determine the important energy transfer pathways at the molecular level in detonating systems. Synthesis of New, Tailored Explosives Recently, there has been considerable advance in our ability to predict the densities of organic compounds. Since density is an important factor in the energy of an explosive, this advance has stimulated and guided synthetic efforts toward new explosive molecules. Extension of these density prediction tech- niques to the prediction of crystal structures may provide a route toward the estimation of other important physical properties of proposed explosives and aid the search for high-pressure synthetic methods to produce unusually dense structures. These fundamental studies may also lead to an understanding and mitigation of the events that lead to the accidental initiation of explosions and to techniques for formulating energetic explosives research that have improved both mechanical and safety properties. Other basic questions in explosives research involve understanding and improving the relatively poor efficiency (10 231

232 NO NO2 l2 1 < 1 ~ N—~—N/ 1 1 NO2 NO2 BICYCLO-HM X o O2N~ J|_ / O2 N ~ O2N —It NO2 N\2 ~ N ~ ANON O2N _ N NO2 10-hIEM8ERED RING HEX HOMOLOG O2N NO2 / \ KN No O2N—N >~( N—NO2 ON NJ \ / O2N NO2 DIKETO-HMX Dl-RD X X = NO2 \N— No x N_N N. N N HEXA-HIVIX H2N N NH2 XoX O2N NO 2 ANPZ HETEROCYCLIC RING COMPOUNDS: POSSIBLE NEW EXPLOSIVES ? CHEMISTRY AND NATIONAL WELL-BEING to 20 percent) with which an explosive material's chemical energy is transformed into ex- plosive (translational) en- ergy. Somewhat analogous to the studies of detonation and ex- plosion initiation are studies of the basic mechanisms of chemical reaction that occur in the combustion of solid and liquid fuels and propellants. Use of modern spectroscopic diagnostic techniques to un- ravel rapid, complex chemis- try at the molecular level is considerably more advanced and pervasive in the study of propellants than it is in the study of explosives. The underlying theme is that fundamental understanding will lead to improved efficiency saving weight, energy, and money and, perhaps, to new "exotic" fuels. Areas of particular current interest are: Chemical Kinetics of Combustion The larger fraction of our propulsion and transportation system depends upon combustion processes (vehicles, ships, planes, rockets, etc). As presented in Section ITI-B and expanded in IlI-D, this is a time of special opportunity for understanding the basic chemical steps involved in combustion initiation, flame extinction, flammability limits, energy pathways among molecular degrees of freedom, and combustion instabilities. Plainly such understandings will strengthen our weapons and defense systems. They will help us inhibit or prevent unwanted combustion events fires and accidental explosions and enable us to increase the rate of heat release and the combustion intensity in practical systems. Even when fuels or combustibles are not gaseous, gaseous reaction rates may control the chemical behavior. Illustrations include the extinction of burning fuel droplets and the production of soot in burning oil sprays. Both national security and nonmilitary applications of combustion processes warrant full exploitation of this active research frontier. Containment or Treatment of Hot Combustion Products This field requires knowledge of fluid flows and advanced cooling techniques, catalytic and corrosive reactions on hot surfaces, and participate formation and

V-C. INCREASED NATIONAL SECURITY deposition from hot gases. It also prescribes improved high temperature materials (metals, ceramics, Tubricants). Enhanced Diagnostic Techniques Combustion systems, with their multiphase nature and rapidly fluctuating variables, have long represented a formidable challenge to experimental diag- nosis. Now many advanced laser spectroscopic techniques are yielding valuable chemical information on gaseous constituents and their temporal and energy behavior. As an example, it is now possible to map the temperature within a flame by recording the vibrational excitation of a combustion product across a two-dimensional slice through the flame. Thus, two tuned lasers can simulta- neously excite fluorescence of OH molecules, one laser probing the vibrationally "cold" OH molecules (v = 0), the other laser probing the vibrationally "hot" OH molecules (v = 11. The relative populations of the two states furnishes a local thermometer at the site of fluorescence. With linear array detectors, vidicons, digitizers, and computer-controlled representations, an accurate, two- dimensional temperature map within the flame can now be recorded. As such powerful techniques are extended and become more widely available, the accurate characterization of flame temperature and concentration profiles will permit fundamental refinement of kinetic models. These will help us understand and control flame propagation velocity, ignition delay, ignition energy, quenching distance, flammability limits, and stability limits. Perhaps we will also learn more about detonation velocity and the response of energetic chemicals to combustion suppressants. The latter are of importance with respect to fire hazards. ~ ~ - ~ Modeling of Turbulent Combustion Systems Mathematical models that appropriately simulate turbulent systems must be developed to aid designers of combustion systems; key experimental parameters have to be identified to test the theories. The flow in nearly all practical combustion devices, especially efficient pulsed combustors, is turbulent. There- fore, it is of key importance to consider the effect of the turbulence on the chemistry of flames, as well as the interaction of these features with the multiphase character of most practical combustors. In many instances, the chemical reaction rates are sufficiently fast relative to the turbulence time frame that reactions are effectively over as soon as the reactants contact each other on a molecular scale. In other instances, chemical reactions may lag significantly behind the turbulent fluid-mixing time scales. In most hot, chemically reacting systems, a mix of rates prevails. The chemical kinetics and turbulent fluid-mixing rates are intertwined in a complex fashion, offering a challenge to both theory and experiment. Such research has obvious relevance to propulsion systems and hence to defense goals. It is likely, as well, that advances here would have valuable 233

234 CHEMISTRY AND NATIONAL WELL-BEING applicability to problems faced by the chemical industries in their attempts to find reliable methods for destruction of hazardous wastes by combustion process. Chemical and Biological Defense Chemistry plays a critical role in developing defenses against non-nuclear weapons and in strengthening our non-nuclear deference. For those who see potential retaliation as an effective deferent, there is concern that the United States, having unilaterally stopped the research, development, and production of chemical and biological stockpiles from 1969 to 1983, is vulnerable to attack by forces with superior offensive and defensive chemical and biological weapons. Surely we cannot assume that a potential enemy of the United States would also refrain from developing such weapons and categorically refuse to use them. Hence, we must keep aware of the state-of-the-art and be ready with adequate sensing and monitoring methods. We must have in place a sound defensive capability that includes the ability to detect such agents, to sound alarm, and to take protective countermeasures. Acquisition of these abilities and the devel- opment of optimum strategies for destroying and counteracting the effects of chemical and biological agents will require the development of novel analytical and spectroscopic methods, a definition of the basis of action at the molecular level, and identification of populations at risk because of the intrinsic and environmentally induced variability of response. Chemical and Biological Agent Detection The rapid detection and unequivocal identification of chemical and biological agents is a key ingredient in defending against agent attack. As a consequence there is major emphasis on the development and deployment of ultrasensitive and highly specific (i.e., low false alarm rate) methods for agent detection. While the molecular species of interest differ greatly, the desired end plainly has much in common with environmental monitoring. For example, the techniques under study for remote sensing of atmospheric pollutants are clearly applicable (e.~.. ~ ., . . . ~ . . ~ . ~ ~ .. . lOng-patn In S1tU r ouster transform infrared metnous and laser-based "lidar": see Section V-A). More generally, advances in analytical chemistry and bio- chemistry will play a pivotal role in meeting this objective, with several notable techniques already demonstrated and currently under further development. One such example is tandem mass spectrometry (MS/MS), a technique whose unusual specificity, sensitivity, and response speed make it promising n~ ~ universal detector for vaporized chemical agents. In operation, the atmospheric sample flows continuously through an electrical discharge, and the ions pro- duced are drawn through a differentially pumped orifice into the first mass spectrometer, where ion masses corresponding to the targeted compounds are selected. Each of the mass species is then fragmented separately to produce a characteristic mass spectrum (usually dozens of peaks) measured in the second mass spectrometer. To produce a false alarm, a stray substance must not only

V-C. INCREASED NATIONAL SECURITY yield the same primary mass, but its secondary products must have the same masses and abundances. Subpicogram sensitivities and subsecond response times have been demonstrated when only a few targeted compounds are sought. For more comprehensive sets of possible agents, the Fourier transform MS/MS is promising in that it simultaneously separates all masses (rather than scanning masses sequentially) and can measure the resulting secondary spectra simultaneously at high resolution. Instrument size and simplicity is a challeng- ing problem. However, the critical analytical information relevant to the absence of life on Mars provided by a double-focusing mass spectrometer weighing only 12 pounds (aboard the 1972 Mars Viking Lander) shows what can be accomplished. Furthermore, laboratory detection limits for continuous mon- itoring of deliberately added contaminants have been demonstrated in the parts-per-trillion range (bromine, 70 ppt; pyridine, 2 ppt; aflatoxin, 10 ppt; and tetrachIorobenzodioxin, 1o-~2 grams). A second example is "metastable atom-induced fluorescence," a technique that has significant potential as a detector for chemical agents. In this approach, highly energetic inert gas at- oms (e.g., helium, argon) pro- duced by a low-voltage elec- trical discharge are mixed with a trace impurity. The metastable atoms are suffi- ciently energetic to cause de- composition of the trace mol- ecules into excited fragments characteristic of the impurity. Each excited fragment emits a unique optical spectrum that makes possible its iden- tification. Thus, the atom- induced spectra of various chemical agents (nerve, mus- tard, blood) provide much less ambiguous identifications be- cause of the unique groupings of fragments. Furthermore, such spectra are capable of extremely sensitive detection. At this writing, 50 parts per trillion of the mustard simu- lant 2-chioroethylethylsulfide (2-CEES) in air has been de- t.~?~.ted. DETECTION of CHEMICAL AGENTS o I! S(CH2CH2CI)2 (CH3)2CHO—P—F MUSTARD AGENT CH3 NERVE aGENT HCN BLOOD AGENT if, \\ ~ - + 300 VOLTS of= ~~ r He* ~ ~ ~ HELIUM . ;. * .- AGENT ...` ., .. ~ ..... CS* (257 nm) MUSTARD aGENT . . AG ~ ~ ENT3 ..:... . . . ..... i, PO* (325 nm) NERVE AGENT ~ _- ~ ALARM./ \\\\\' tll///y CN* (388 nm) BLOOD AGENT _~ _ _ _ Circular intensity differential scattering (CIDS) is a potentially powerful 235

236 CHEMISTRY AND NATIONAL WELL-BEING BA CTER I A GC 4 9 - 5 I PER CEN T l Em / \ ~ 1 1 - ~ I'll o - V. FLUVIALIS l l ~ M. MORGANII (J ——E. cold K 1 2 technique for detecting bio- logical agents. In CIDS the differential scattering of left and right circularly polarized light is observed. It is very sensitive to differences in long-range order among bio- logical macromolecules, such as the DNA or RNA in a virus or bacterium. This probe has been used to distinguish among a wide variety of microorganisms. For exam- ple, it is capable of clear dis- crimination among bacteria CIRCULAR POLARIZED LIGHT SCATTERI NG DIFFERENTIATES SIMILAR BACTERIAL AGENTS haVlNg a slmllar guanlne- cytosine nuclei acid base con- tent. Such discrimination is, of course, a necessary first step toward protection and defense. Currently, an aerosol CIDS flow cytometer for detecting bacterial aerosols as 1 . , 1 30 60 90 120 150 180 SCATTERING ANGLE (degrees) A a first line of defense against biological agent attack is being evaluated. Protection Novel ways are being developed to promote the induction of protective responses in humans (e.g., through the synthesis of specific immunoglobulins and other proteins) that will greatly reduce the toxicity stemming from exposure to chemical warfare agents. Studies to date have focused on ways of enhancing protective response in cells that reduce cell killing associated with exposure to alkylating agents by factors in excess of 100-fold. Major effort has been directed toward devising means for increasing the magnitude of the protective response to poisons and toward investigating the underlying mech- an~sms. Similarly, contamination of equipment as a result of chemical or biological attack could render it harmful to the user. Methods must be developed that allow for safe, nondestructive decontamination. They could take the form of novel protective coating materials or noncorrosive/nontoxic decontaminating fluids. Complementary chemical systems using both of these approaches may be required. Furthermore, periodically, stores of obsolete munitions containing chemical agents must be destroyed. Methods currently available are prohibi- tively costly and hazardous. The development of efficient, environmentally acceptable processes would be a major contribution to national security and,

V-C. INCREASED NATIONAL SECURITY again, it would probably help us deal with potentially hazardous industrial wastes. New Frontiers in Defense New directions in defense include increasing research emphasis on sophisti- cated detection, reliable defensive weapons that counter other weapons, and high-technology weaponry, including chemical lasers. In these developments, chemistry plays a vital part, as exemplified by spectroscopic-based detection schemes, lightweight polymer-based materials, stealth coatings, and laser- resistant coatings. The growing emphasis on the importance of space to national strategic defense requires development of new materials that can perform reliably in a vacuum environment. Emphasis on space may also lead to the reality of people living and working away from the planet earth. The first step will be the establishment of space stations in earth orbit. The greatest barrier to the establishment of man's continued presence in space is the cost and difficulty of transporting construction materials from the earth's surface to orbit. In the long term, we must see if these materials could be made from lunar resources. Space or lunar materials processing will require vision and creativity across all scientific and engineering disciplines. Chemists will play a major role as we develop maintainable lunar habitat atmospheres, invent novel processes for producing construction and propellant materials from lunar resources, and develop novel Junar-based electrical power generation processes. Conclusion The ingredients that make for a healthy and satisfied populace, in both the nation and the world, are the key factors underlying national security. Chem- istry plays a major role here in areas ranging from agriculture, health, and environment to a dynamic, productive economy. In addition, however, the nation needs the ability to defend itself and to prevent and deter armed conflict. In these areas also, chemistry plays a vital role, touching all aspects of defense from propulsion, weapons materials, and classical munitions to the most advanced strategic concepts. 237

:::: hi: ::::::: ~ ::~ ::::::: :~:: ::::::::: ::::: :::::::::: : :::::::::::: ::~:::: ~::~::::: ~~:~is~a~:central~:~scl~en£e~ ~:~ ::: :~ :: ~~ ~~ i: :: :: ~ ~ : 1 : ~ ~ : : ~ ~ l: :: ::. ~ ~ : : ~ ~~ ':~' ]~ J responds~:~to~socleta: .::ne:e~c A. ::: : : : ~ : ~~ ~~ ~ ~~ ~ ~~ ~ ~~ Its critical in~T\~an\~atter~t~to~.~ ~~ ~ ~ :~ ~~ : ~ ~ : :~ ~ ~ ~ : : ~ : ~ : ~ : : : ~ I::, ~ :: : : :: a: 7:~:: ::~ :::: : ::: ~ ~ : ~ : :: . ::: ~ ~ ~ ~ :~ ~ : ~ ~ ~~:~:~ ~~:~ :::: ::~:~mon::l~ro~r~:anGfi::p~ro~tect~our:~en~v~z~ro:n:me~nt~::: ::::: :: : ~ Age: ~~:~:~ :: :

Libraries into Space Unbelievable though it sounds, we may have to place Whole libraries in a space- like environment over the next decade! This strange proposal is not made because . . our or siting astronauts need more reading material, but because if we don't do that or somet sing similar, most of our books won't be around very long for the rest of us to ~read. An alarming and little known problem faces mankind today—the vast majority of books, those printed since the 1~850s, are relentlessly yellowing and ':,. t ~ :~., . .~ ~ -, . . ~ ~ .^ . ~ crumDllng o c us ;. ne 1Inrary at one umversr By ot ,a 1torma at tier Be ey a One ~ ~: ~ ~ stand Into lose I )u,: ~ J ~ Jooks~ anc .: period .ica. .s per year to decomposition. This is not ~ . . . Because ot air po utlon; t Be source ot the destruction lies in the very paper on which the books are~printe~d. Now, some clever chemists have discovered that, surprisingly, a trip into fan environment similar to space provides at least one solution to this · vexing pro b em. ~ ~ ~ rapermaK~ng processes used since tne 1850s ;un~versally employ an alumros~n sizing to keep ink from "feathering" or spreading on the paper. Slowly, this paper- maker's~alum—aluminum sulfate combines with moisture in the pages~and in the air to form sulfuric acid. This aggressive substance, in turn, facilitates attack on the cellulose fibers in the paper,~breaking them into smaller and smaller *agments and, ultimately, to dust. Between 75 and 95 percent of the deterioration in "modern'' paper is caused by such acid attack. In recent years, chem~sts~have developed a number of acid-neutralizing processes for books. One of these, developed in the Library of Confess research laboratory, suggests that the chemical diethyl zinc may be ideal for the job. Diethyl zinc is a gas, so Its molecules can easily permeate even a closed book. Once inside, the substance deacidifies each book and then looks ahead to the fixture by leaving an ::: alkaline residue of zinc oxy-caribonate. This residue, uniformly distributed through- :: : out the~paper fibers, protects the book from any future acid attack. Ironically,; this li~-s~ing agent, ~ diethyl zinc, bursts into flame on contact with · : ~ : : ~ ~ ~ ~ · ~ i : ~ ~ , T T ~ ~ · ~ · ~ ~ air ant ~ exp or es wnen 1l touches water. now Does a chemist worn with a compound that cannot be exposed to air or water? In a deep space environment, of course. A suitable location was found at NASA's Goddard Flight Center, where 5,000 books from the Library of Congress took a simulated flight, not on a rocket . , ~ , ~ ~ · . · ~ . Into space, out In a laboratory space-slmulatmg vacuum cnamner. lo. , .. . . .. . ~ . . . . . . ~ ~ ~ 1rst2 tne ~QOKS were thoroughly orled by warming Aver vacuum for about 3 days. Then, with all oxygen removed from the cham- ber, gaseous diethyl zinc was introduced and allowed to diffuse into the books. As the neutralizing reaction proceeds, harm- less ethane gas is produced and pumped away. Then the pro- tective zinc oxy-carbonate is formed. The results have been ex- . . ~ · · . . . · ~ . . - . . ~ treme~ly promlsmg, and, as ~tne technology Is pertecteal, llorarles across the nation will be looking to install huge deacidific~ation facilities. These countermeasures. coupled with the~new "alkaline / \ I ~ \ :' \ \ I:_ en ~ , ~ reserve', papers now used in modern printing, promise that the pro- MY cious heritage of the world's libraries, including the enormous Library of Congress, will be preserved for future generations to enjoy, and profit from, just as we do today. 239

240 CHEMISTRY AND NATIONAL WELL-BEING V-D. Intellectual Frontiers This chapter has shown how chemistry offers societal benefit connected with better environment, sustained economic competitiveness, and increased na- tional security. These benefits draw upon the entire spectrum of chemistry, and they flow from research discoveries across the whole range. Nevertheless, some intellectual frontiers are specially well placed here. For example, the surface sciences, with their implications for new heterogeneous catalysts furnish a wellspring of critical importance in international competitiveness. Condensed phase chemistry and new separations techniques also can be expected to contribute fruitful new dimensions to our competitiveness in foreign markets. Next, the new frontiers in analytical chemistry support and contribute to advances in all other areas of chemistry. Analytical chemistry is the corner- stone upon which our monitoring and management of the environment is built. Finally, nuclear chemistry was nurtured in the World War IT Manhattan Project and its health continues to be of prime importance, since world peace depends upon a balance of nuclear arms. In each of these subjects, there are opening frontiers and rewarding intellec- tual opportunities to be pursued. Chemistry at Solid Surfaces The surfaces of metals and ionic solids are intrinsically chemically reactive. The reason is clear: the bulk crystal takes a structure that provides for each interior atom optimum chemical bonding to neighboring atoms around it in all three dimensions. At the surface, however, the atoms have unsatisfied bonding capacity because the neighboring atoms are missing in one direction. Hence, this is a region of special chemical behavior, one of unusual interest to chemists. The importance of this special behavior simply cannot be exaggerated. Corro- sion occurs, of course, at iron surfaces, with obvious deleterious effect on many structures of great utility, from the lofty Eiffel Tower to the lowly nail. It has been estimated that corrosion costs the U.S. economy billions of dollars annually. At aluminum surfaces, there is rapid reaction on exposure to air that forms a protective and quite inert oxide coating. Hence we can safely have the convenience of aluminum foil in the kitchen, despite the fact that aluminum is flammable. But by far the greatest importance of surface chemistry is that it confers upon some surfaces extremely effective catalytic activity. This capacity of a solid surface to speed up chemical reactions by many orders of magnitude without being consumed is called heterogeneous catalysis. Its significance has been extolled in Sections IlI-A and IlI-B as the basis for commercial processes of immense economic value. It is one of the most important and active frontiers of chemistry. Heterogeneous catalysis is not new. What is new is the array of powerful instruments developed over the last 15 years that provide, at last, experimental access to the chemistry on a surface while that chemistry is taking place.

V-D. INTELLECTUAL FRONTIERS Without such techniques, catalysis has remained over many decades largely an empirical art. Now we have instruments with which to characterize precisely the nature of the catalyst surface and to study molecules while they are reacting there. Now we are accumulating the store of quantitative data needed for catalysis to become a science. Already, catalyst design and fabrication has become a high-technology industry. The intellectual challenge to understand the chemical behavior of surface-adsorbed monolayers has propelled surface science into the mainstream of fundamental research in departments of chem- istry and chemical engineering. This research will have impact on many important technologies. The instrumentation of the surface sciences will be described in Section V-E. Some research highlights and productive frontiers are described below. The Structure of Solic! Surfaces Metallic crystals can exhibit a variety of surfaces depending upon the angle of the surface relative to the natural crystal axes. The most stable surfaces tend to be flat and close-packed with each surface atom sur- rounded by a large number of nearest neighbors. Other sur- faces may be formed, how- ever, that are stepped, with terraces several atoms wide and separated by steps of monatomic height. Atoms at these ledges are even more exposed, hence more reactive than surface atoms embedded in the smooth terraces. Fur- ther, there may be kinks in the steps, or the surface may be "rough" with atomic-size openings between surface at- oms with, again, special reac- tivity. Such chemically im- portant surface irregularities can now be identified by low- FLAT ( ~ ,0,0) TERRACED ( 7,7.5) FLAT ( I, I, I ) K1NKED( I 0.8.7) CHEMISTRY ON A PLATINUM SURFACE DEPENDS ON THE SURFACE EXPOSED energy electron diffraction (LEED). How important this can be is illustrated in the catalytic production of ammonia from nitrogen and hydrogen on single crystals of an iron catalyst. The effectiveness of a catalyst depends upon how rapidly each surface site can adsorb reactants, encourage them to rearrange chemically, and then release the products so that the site can begin the process again. The iron crystal face designated (1,1,1) is about 430 times more active than the closest-packed (1,1,0) 241

242 CH; CH2 CH3 H3C CH2 CH2 CHEMISTRY AND NATIONAL WELL-BEING crystal face and 13 times more active than the simpler (1,0,0) face. It is now believed that the rate-limiting step is the rupture of the strong nitrogen- nitrogen bond of N2 (225 kcal/mole) and that this occurs with an activation energy near 3 kcal/mole on the (1,0,0) face but with nearly zero activation energy on the specially active (1,1,1) surface. A second, equally important, example is the use of a platinum catalyst to restructure alkane hydrocarbons to forms with better combustion properties (e.g., octane number, volatility). Now, it is possible to discern which catalyst ~ surfaces optimize the desired AROMAT1 ZAT I ON ) (1,1,1), (755) CTCLIZATION PLATINUM CATA LT ST H2 CH Hi' MACH + 4 H HO; CH Cow ~ H2 \CH—CH3 + H2 H2C'/ ( 1,O,O) CHz 1 SOMERIZATION > ( 1,0,0) H7DROGENOLTSI S ZINEED (10,S,7) tH3 H3C C; CH 3 C H2 H3C /C~ H' C H3 C H2 . products. Thus n-hexane, an extended-chain structure with low-octane number, can be converted to forms with higher-octane numbers, such as benzene and branched or cyclic alkanes, using a plati- num catalyst in the presence of hydrogen. We now know that benzene is favored on the flat ( 1,1,1 ) surface or on stepped surfaces with ter- races of (1,1,1) orientation, like (7,5,61. In contrast, for- mation of branched or cyclic alkanes is favored on the flat, (1,0,0) surface or stepped sur- faces with (1,0,0) terraces. Kinked surfaces, like (10,S,7), tend to produce less desirable products like propane and ethane. Knowing this, He can seek a reagent that will permanently bind to and block ("poison") these active "kink" sites to eliminate their less desirable products. Because of their influence on catalytic action, surface structures are attract- ing much research interest. Small particles tend to display many different surfaces, depending on method of preparation. As the metallic particle grows, it becomes more like the bulk material and tends to disfavor surfaces with terraces and kinks. Atoms in the surface layer may take an equilibrium spacing from the second layer several percent closer than is found for interior layer spacing. Even more drastic, because of the incomplete bonding of surface atoms, they may seek equilibrium positions different from the packing in the bulk material in order to optimize their bonding. Such "surface reconstruction" has been found for platinum, gold, silicon, and germanium. Another important question that can now be experimentally explored is the surface composition. Even the purest samples will have some impurities, and these may noticeably affect some properties of metals and semiconductors. Relevant to surface chemistry is the question of the extent to which a given DIFFERENT SURFACES FAVOR DIFFERENT PRODUCTS

V-D. INTELLECTUAL FRONTIERS impurity preferentially concentrates at the surface. Indeed, this may be the rule rather than the exception. The difference in bonding between host and impurity atoms explains why the bulk material tends to reject the impurity. The same difference may cause the impurity to be a welcome addition to the surface, where host atoms alone cannot satisfy their bonding capability. There are cases in which impurities at the parts-per-million level are so concentrated at the surface that they can cover it completely. Of course, this issue is always present in binary or multicomponent alloy systems. There is excess silver at the surfaces of silver-gold alloys, copper at copper-nicke] alloy surfaces, and gold at gold-tin alloy surfaces. Some metals that are not miscible in bulk are found to be completely miscible (mutually soluble) on a surface. Thermodynamic models are being developed to predict the surface composition to be expected for a given bulk composition. Experimental data and understandings are especially needed at this time when a variety of binary and ternary substances are under study because of their interfacial electrical properties. In summary, determination of the atomic structure of surfaces and surface composition is basic to understanding the wide variety of surface properties now finding important practical applications. They are the starting point for advanc- ing corrosion science, heterogeneous catalysis, lubrication and adhesion, as well as for producing new surfaces and interfaces with novel electronic properties. Adsorbec! Molecules: Chemical Bonding at the Surface For many decades, the adherence of a substance to a surface was measured by the ease of its removal on warming. Some substances are easily removed at temperatures near or below room temperature. Such a situation is traditionally categorized as "physisorption": the adsorbed substance retains its molecular integrity and is bound to the surface only by weak forces, such as van der Waals or hydrogen bonding interactions. Other substances are more tightly held by the surface and can be removed only by heating to much higher temperatures- perhaps 200 to 600°C. Here, covalent bonding to the surface is involved, and the molecular structure of the adsorbate can be expected to differ from what it was before adsorption. This situation is called "chemisorption," and it is usually if not always involved at some stage in any heterogeneous catalysis. Hence, understanding of the molecular structure and chemical properties of chemisorbed molecules lies at the heart of heterogeneous catalysis. Among small molecules, carbon monoxide on metal surfaces has historically been given most attention, in part because of especially favorable spectroscopic properties that facilitated detection of the small number of molecules on the surface. This history turns out to be fortunate, for one of today's pressing problems is the conversion of coal to useful hydrocarbon feedstocks, and many catalytic schemes use carbon monoxide as an intermediate via "syn gas," a mixture of CO and H2 derived from coal (see Section IlI-A and Table TIT-4 in Section IlI-B). 243

244 ETHYLENE ON | | \ RHODIUM tl,l.l ~ ~ I CATALYST - ),1` , 1 137 C 1000 2000 3000 cm ' VIBRATIONAL FREQUENCY MOLECULAR FINGERPRINTS REVEAL THE REACTION PRODUCTS ON SURFACES ~ CCH CCH2 ~ CCH3 ~h _ am; j~~CH3 ~ ~ _ I F C CHEMISTRY AND NATIONAL WELL-BEING A second key example is that of adsorption of ethylene on catalytic metal surfaces. It has been known, from its thermal behavior, that ethylene chemisorbs on platinum and rhodium catalysts. Now, we can add information about the structures that are formed on the surface through direct observation of the vibrational frequencies of the adsorbed species. While direct observation of these frequencies through infrared absorption spectroscopy is sometimes possible, the advent of electron energy loss spectroscopy (EELS) has greatly accelerated such studies. The characteris- tic molecular frequencies are imprinted on the energy distribution of electrons bounced off the metal surface, and they provide a fingerprint that is readily interpreted by a chemist experienced in relating infrared spectra to molecular structures. For ethylene on rhodium, the EELS spectrum plainly shows that, after adsorption, the ethylene molecule has been structurally altered even at room temperature. Then, on warming 50°C or so, the spec- trum begins to change still more. By the time the temper- ature has changed by 100°C, the spectrum shows that reac- tions have taken place, and the hydrocarbons now present on the surface have new structures. These EELS spec- tra reveal, then, which of the possible surface structures, C2H3, C2H2, C2H, CH3, CH2, and CH are present at a given temperature and, hence, the sequence of their formation as the temperature is raised. Such intimate knowledge of the chemical events taking place on the catalyst surface furnishes the basis for a detailed understanding of the catalytic dehydrogenation and hydrogenation of ethylene. ETHYLENE ON RHODIUM ~ -I ~ ~ I_, ~~ ~;~ WHICH STRUCTURES ARE PRESENT? - ~ Co-Adsorption on Surfaces The realm of chemistry on surfaces takes on new dimension when two substances are adsorbed on the same surface. Then attention shifts from the interaction of the adsorbate with the surface to the interaction of two different species when they share the special environment provided by the surface.

V-D. INTELLECTUAL FRONTIERS The first way in which this interaction can occur is when one adsorbate changes the special environment seen by the second adsorbate. An example has already been mentioned in which one adsorbate attaches so strongly to partic- ular sites that another adsorbate is denied access to them. For example, a clean molybdenum metal surface will decompose the sulfur-containing molecule, thiophene, C4H~S. However, if elemental sulfur is co-adsorbed, it chemisorbs quite strongly at the active sites needed for thiophene decomposition. Thus sulfur "poisons" the catalyst for this particular reaction. As a second example, carbon monoxide is physisorbed on rhodium, as shown both by its ease of removal on warming and its vibrational frequency on the surface, which is close to that of gaseous carbon monoxide. If, however, the rhodium is 50 percent covered by co-adsorbed potassium, CO becomes chemisorbed. The EELS spectrum shows a CO vibrational frequency appropri- ate to a bridged structure with a double-bond carbon-oxygen frequency. Under these conditions, hydrogenation of CO is facilitated with the desirable outcome that higher molecular weight alkanes and alkenes are obtained. Explanations are based upon the ease of ionization of potassium and the effect of such electron-release in the presence of the metal surface. Still to be mentioned is the direct reaction between the two adsorbates. In the future, this will be seen as the most prolific source of the new chemistry that can take place in this special reaction domain. An obvious example has been cited- the hydrogenation of ethylene. When hydrogen adsorbs on platinum or rhodium, the H2 molecule is split and the two atoms are separately bonded to metal atoms. Now, when ethylene is co-adsorbed, it does not encounter H2 at all. Instead, it finds individual hydrogen atoms attached to the surface. Plainly, if co-adsorbed hydrogen and ethylene react, they will follow a reaction path characteristic of the species on the surface and governed by activation energies unrelated to those associated with a gas phase encounter between H2 and C2H4. Energy Transfer During Gas-Surface Collisions Currently the energy transfer between molecules impinging on the surface of a solid is under active investigation. The purpose is to learn how translational and internal energies of incident molecules are exchanged with the character- istic vibrations of the crystalline surface. Such data should be relevant to residence time and energy content of molecules as they adsorb and desorb. Molecular beams are used, and the results to date have contained surprises. Energy transfer to the surface is less facile than expected, and it can be surface structure-sensitive. Rotational and vibrational energy contents are separately influenced by the surface temperature but not in simple ways. More experimen- tal data and theoretical treatments are needed so that we can accurately describe surface dynamic phenomena. 245

246 CHEMISTRY AND NATIONAL WELL-BEING Surface Electrical Properties A nonconducting material invariably displays an electrical space-charge at an interface with vacuum or other media. These space-charges find important applications in the colloid sciences, semiconductor surface devices, and in modern printing and copying technologies. Surface ionization, field ionization, and photoelectron emission are electrical characteristics of surfaces that are coming under scrutiny and finding a variety of applications. Novel Spectroscopic Technologies Many of the most modern techniques of surface science require that the measurement be carried out in ultrahigh vacuum (i.e., below 10-9 torr). This is a considerable limitation because every practical application of surface behav- ior occurs in the presence of gas, liquid, or another solid at the interface (including, of course, all catalysis). Desperately needed are comparably sensi- tive experimental techniques that permit study of chemical behavior at the interface between a solid surface and a second medium at significant density. Attenuated total reflectance {R and grazing-incidence infrared spectroscopy have been in use for some time, and the new Fourier transform difference techniques are significantly improving our ability to detect the tiny infrared absorbances offered by less than monolayer coverages. Tunable infrared lasers offer further improvement that has not yet been exploited. New discoveries and developments can be anticipated to join the two already mentioned in Section IlI-A surface-enhanced Raman and surface-enhanced second harmonic gener- ation. Up to million-fold enhancements of Raman intensities for surface- adsorbed molecules have been demonstrated for particular adsorbants on particular surfaces. It is already clear that surface preparation is an important factor, and there is not yet sufficient clarity in the theoretical explanations under consideration to specify the range of applicability to be expected. Perhaps more general applicability will be provided by second-harmonic generation, using laser sources, since the eject depends upon the intrinsic dielectric ~ ~ -A . . ~ . . . asymmetry provided by a phase boundary. In principle, small surface asymme- tries can be dealt with by using higher laser power the nonlinear behavior can be proportional to the cube of the power. Furthermore, pulsed lasers can be used, which suggests the possibility of temporal studies on the nanosecond to picosecond time scale. We have only begun to explore the range of potentialities that has been opened by the new instrumental techniques for studying chemistry at inter- faces. Vapor and plasma depositions are providing opportunities for thin-fiIm depositions that affect a variety of surface behaviors. Epitaxial influences are being exploited. Energetic ion implantation permits controlled injection of desired impurities near or on the surface of a metal or semiconductor. Rapid energy-deposition from lasers permits melting and rapid cooling of surface regions that can freeze into glassy form or with a high temperature composition

V-D. INTELLECTUAL FRONTIERS and structure. Conducting polymer films may alter or reroute electrochemical phenomena that exhibit luminescence or function as molecular switches or molecular logic devices. Many biological processes, too, take place at solid-liquid interfaces; surface science research may provide molecular-level scrutiny of such processes as they may be taking place in vivo, conceivably in the cell, in the brain, in bone, etc. Applications have already appeared and more can be expected in better control of abrasion, corrosion, and high temperature performance, as well as in design and fabrication of new semiconductors and other electrical devices. Most important, however, will undoubtedly be the full exploitation of surfaces as a new reaction domain, as we develop our fundamental understandings of heterogeneous catalysis. Condensed Phase Studies The study of condensed phases illustrates in an especially clear way the central position of chemistry, both as an intellectual discipline and as an applied field. The great challenges facing solid state science, earth science, biochemis- try, and biophysics all involve the ability to understand and manipulate the properties of condensed phases. These properties result directly from the interatomic and intermolecular forces between chemical entities present in these phases. In addition, almost all useful materials and the majority of practical processes involve one or more condensed phases. Optical and Electronic Properties of Solids Over the past 15 to 20 years, high pressure has proved to be a powerful too] in the study of electronic phenomena in solids. Basically, increased compression increases overlap among adjacent electronic orbitals. Since different types of orbitals have different spatial characteristics, they are perturbed to different degrees. This "pressure tuning" is the element that makes pressure effects a powerful too] for characterizing electronic states and excitations, testing theo- ries, and uncovering electronic transitions to new ground states with different physical and chemical properties. Conceptual areas to which pressure effects are adding important new insights include ligand field theory, van VIeck's theory of high-spin to low-spin transi- tions, and Mulliken's theory of electron donor-acceptor complexes. Pressure effects are also extending the Forster-Dexter theory of energy transfer in phosphors and theories of the efficiency of a variety of laser materials, including Il-V! and IlI-V compounds that exhibit the zincblende structure, and rare earth oxides and chelates. Many instances of electronic transitions that show pronounced and meaning- ful response to high pressure have been found. For example, the insulator- conductor transitions for 9 elements and 40-60 compounds (the first organic superconductor exhibited superconductivity between 6 and 18 kilobars). Other cases are paramagnetic-diamagnetic transitions in ferrous compounds, a fer- 247

248 CHEMISTRY AND NATIONAL WELL-BEING romagnetic-diamagnetic transition in iron, photochromic-thermochromic tran- sitions in aniTs, spiropyrans, and bianthrones, and electron transfer transitions in 20-30 ethylene diamine complexes with resultant chemical reactivity of a new type. I,iquids Many of the fundamental processes of nature and industry take place in the liquid state. The rate of transport of molecules in solution can limit the speed with which a synthetic chemical reaction can occur, a nerve can fire, a battery can generate current, and chemicals can be purified and isolated by separation. A properly chosen liquid solvent can accelerate a chemical reaction by a million- fold or slow it down by a comparable factor. Molecules in liquids can be highly efficient agents for storing or transferring energy. The structure of liquid water influences the course and nature of biochemical processes essential to life. In recent years there has been significant progress towards a better understanding of the liquid state based both on theoretical and experimental work. These advances have been fueled by developments in three areas: experimental techniques, large-scare computer simulation, and new theoretical tools. The enormous progress in the field of liquids can be traced in no small measure to the constant interplay among these areas. The structure and dynamics of a wide range of fluids, from liquid hydrogen to molten silicates, can be investigated by a number of spectroscopic techniques, such as X-ray and neutron diffraction, nuclear magnetic resonance, laser Raman, and Rayleigh scattering. In the context of experimental studies, it is important to note that pressure as an experimental variable provides much information about molecular motions and interactions in liquids. However, constant pressure, constant volume, and constant temperature experiments are all needed to test, rigorously, theoretical models of liquids and establish a firm experimental basis for the development of new models. Among the newer experimental approaches, relaxation techniques are particularly powerful. The techniques of nonlinear laser spectroscopy provide new information on the picosecond time scale (load see) about the freedom of movement of a solute molecule in its solvent cage. Now we can watch fundamental chemical events as they take place: how two iodine atoms combine in a liquid to produce an iodine molecule, how a stilbene molecule interconverts between different conforma- tions, how electrons released in liquid water become "trapped," or "solvated," and how energy deposited in a solute molecule like nitrogen or benzene is transferred to its solvent environment. Quite a different opportunity area is connected with liquid-solid phase transitions in small clusters. We have a variety of new experimental methods for producing and studying small clusters as well as the theoretical tools with which to interpret the results. We can Took ahead to an understanding of how bulk phase transition properties emerge as cluster size increases. Another major stimulus to progress in studies of liquids is in computational

V-D. INTELLECTUAL FRONTIERS technology: the impressive calculational power of high-speed computers has been brought to bear on liquid-state structure and dynamics. In the Monte CarIo computer technique, hundreds of thousands of configurations of the molecules are sampled by probability methods. The output is two-fold. First, thermody- namic data is generated for fundamental studies, for comparison with experi- ments, and for predictions under conditions difficult to obtain experimentally. Second, detailed descriptions of the structure are provided in many cases at a molecular level beyond that experimentally accessible at this time. An example is the simulation of ionic solution structure near an electrified surface, as in an electrochemical cell. Quite a different computer-based technique has been labeled "molecular dynamics" (MD). The positions and orientations of hundreds of molecules can be simulated and tracked in their time evolution under thermal agitation to provide a detailed picture of both liquid-state structure and dynamics. The MD methodology has now been applied to quite an array of fundamental problems of the liquid state. Favorite and important objectives of such simulations are to mode] the properties of water and of proteins as they exist in water. Beyond these, even a limited listing of applications conveys the scope of the method: molecular motion and energy transfer, chemical reactions, liquid-solid and liquid-gas interfaces, phase transitions, ionic solutions, molten salts, and glasses. The remaining source of advance in liquid-state science has been the development of new theoretical approaches and methods. In the area of structural and equilibrium properties, powerful new perturbation theories based on the key features of intermolecular forces have been proposed and focused on liquids of considerable complexity, e.g., a new theory for the hydrophobic eject, which plays an influential role in the stability of biologically important macromolecules in water. Both theory and computer simulation add more depth to our understanding of this crucial factor in the organization and function of biological systems. In the area of liquid-state dynamics transport, energy transfer, and reac- tion the introduction and development of the time correlation function method has had a profound impact on theory. The theorist has new analytical methods with which to attack the calculation of transport, energy relaxation, and chemical rate properties. For example, coherent, pulsed laser excitation of a solute molecule provides evidence about molecular reorientation times in the liquid state, but time correlation functions are needed to interpret such data. Until recently, most experimental work has focused on investigation of single-molecule properties, such as reorientation and vibrational dephasing, which reflect only indirectly the influence of the intermolecular interactions. However, by studying spectra induced by such molecular interactions, one can obtain direct information about the interactions. There should be increased emphasis on studies of density effects on collision-induced scattering. Other areas that show special promise for future work are chemical reaction dynamics 249

250 CHEMISTRY AND NATIONAL WELL-BEING in liquids, phase transitions involving liquids, solids, and mesophases, such as liquid crystals, and interfacial phenomena involving liquids. Chemical synthesis in liquids under high pressure deserves special mention. Chemical reaction as it takes place under high pressure (e.g., at thousands of atmospheres pressure) gives unique insight into reaction mechanisms and, as pointed out by example in Section IlI-D, control over product distribution. High- pressure studies reveal the volume profile of a reaction including during its passage through the rate-limiting transition state and in this way a new type of information is gained about reaction pathways. Thus we can learn about the concertedness of a multiple-bond reorganization, salvation reorganization dur- ing reaction, and location of the transition state along the reaction coordinate. Additionally, the PV work term becomes comparable to the energy and entropy barriers for reaction. Thus the role of pressures in excess of 10 kilobars is a valuable new dimension of organic synthesis in solutions, a dimension, as yet, little explored. Critical Phenomena For any fluid, there is a range of temperature and pressure within which the liquid and gaseous states cannot be differentiated. Fluid behavior under these "critical conditions" can differ markedly from normal behavior and give rise to new phenomena. The past 20 years have seen a revolution in our understanding of such critical phenomena. Undoubtedly the most important single theoretical advance in our understanding in the last 15 years has been the development of the renormalization group approach. The theory is couched in relatively new- conceptual terms (noncIassical critical exponents, scaling, and universality cIasses). It shows computational promise for quantitative expression of the functional form and exponents in our description of fluid properties and their dependence upon the molecular parameters and the experimental variables (the scaling equation of state). The theory has predictive capability that recently received striking verification by experiment. The discovery of tricritical points, at which three phases become simulta- neously identical, and the theoretical and experimental elucidation of the properties at these points has been another significant development of the last decade. Surfaces and interfaces of near-critical fluids and fluid mixtures can themselves exhibit transitions and critical phenomena. The surface tension and interfacial profile between near-critical coexisting phases exhibit unusual (noncIassical) critical behavior that has been treated theoretically and mea- sured experimentally. The discovery that a polymer unit isolated in a good solvent is itself a near-critical object and that statistical models already developed to treat other phenomena (e.g., magnetism) are applicable to dilute polymer solutions has enriched the study of both critical phenomena and polymers. An example is provided by the polymerization transition in pure liquid sulfur at 160°C, which is related to critical phenomena in ferromagnets. The past 15 years have seen the intoduction of the critical point and critical

V-D. INTELLECTUAL FRONTIERS phenomena into practical and engineering applications. The use of critical point drying is now a standard sample preparation method in electron microscopy. "Super-critical" extraction is now used in research applications in liquid chromatography and commercially in the preparation of a wide variety of products. The latter include extraction of perfume essences and the removal of caffeine from some instant coffees. The dramatic changes in solvent power with very small changes in pressure or temperature near the critical point make it seem likely that increasing use will be made of near-critical fluids for other practical applications. Chemistry of the Earth and Extraterrestrial Materials Geochemical phenomena involve complex mixtures, frequently with a num- ber of phases as well as very high pressures and temperatures. Recent advances in high-pressure technology have made possible studies that duplicate condi- tions well into the Earth's core. In recent years many Earth scientists have studied the "geochemical cycles" of elements that is, the changing chemical and physical environment of a given element during such Earth processes as crystallization, dissolution, metamorphism, and weathering. These processes may lead to concentration (e.g., ore deposits) or dispersion of an element. The geochemical cycle of carbon has provided a focus for the reawakened field of organic geochemistry. Research on the stability, conformation, and decomposi- tion reactions of fossil organic molecules has led to greater understanding of the genesis and constituents of coal, oil, and other organic deposits. Such knowledge has obvious value that extends from guiding our exploration for new fossil fuel deposits to helping us decide how to use the ones we have. Radioactive isotope geochemistry first received widespread notice and appli- cation as a dating technique. Now there are many new applications, including some that involve stable isotopes in studies of fluid flow and reaction kinetics relevant to geochemical processes. Furthermore, the Earth's unique isotopic signature imposes severe constraints on theories of the origin and chemical evolution of the Earth. Meteorites are of considerable chemical interest because they include the oldest solar system materials available for research, and they sample a wide range of parent bodies some primitive, some highly evolved. Meterorites carry decipherable records of certain solar and galactic ejects and yield data other- wise unobtainable about the genesis, evolution, and composition of the Earth and other planets, satellites, asteroids, and the Sun. Isotopic anomalies in many metals and gaseous elements and compositional data particularly trace ele- ments- have shed light on all stages of meterorite parent body (asteroidal) formation, evolution, and destruction. Organic compounds found in some meteorites might provide clues to those compounds that were precursors to life, to interstellar molecules, and to cometary material. 251

252 CHEMISTRY AND NATIONAL WELL-BEING Analytical Chemistry Characterization and measurement of atomic and molecular species quali- tative and quantitative analytical chemistry uniquely contribute to and benefit from the current rapid progress in science. Basic discoveries in physics, chemistry, and biology are providing the bases for new analytical methods and computerized instrumentation. In reciprocation, these new capabilities are central to research progress in chemistry, other sciences, and medicine, as well as to applications in environmental monitoring, industrial control, health, geology, agriculture, defense, and law enforcement (for the Hitler diaries, the disagreements of historians and handwriting experts were settled quickly through chemical analysis). Further, the 10-fold growth of the analytical instrumentation industry to $3B sales worldwide has been led by the United States with its nearly $1B positive balance of trade in this area. A key factor in this growth has been the incorporation of computers into analytical instrumentation. The benefit is well-deserved because the advances in solid state technology critical for modern computers have been dependent on analytical advances, such as new capabilities to analyze trace impurities in silicon. Now microprobe analyzers using computer imaging techniques are answering questions critical to making microcircuitry even smaller, producing computers that are faster, more reliable, and cheaper. Closing such loops challenges the best basic chemistry, and it also generates unusual intellectual opportunities at the frontiers of science. A few examples illustrate the broad range of the challenges. Analytical Separations Analysis of many complex mixtures is possible only after fractionation into components. Then, a variety of identification and quantitative measurement schemes become effective that would be ambiguous or impossible if applied to the unseparated mixture. Hence, devising new separations for use in an analytical context is an active field of research. There is no single technique more effective and generally applicable than the chromatographic method. The basic principle depends upon the fact that each molecular species, whether gaseous or in solution, has its own characteristic strength of attachment to and ease of detachment from any surface it encoun- ters. The differences in these attachment strengths can furnish a basis for separation. The differences can depend upon heat of adsorption, volatability, solvation, molecular shape (including stereogeometry), charge and charge distribution, and even functional chemistry. Great ingenuity has made it possible to use the whole range of molecular properties for analytical separa- tions that can require only tiny amounts of material. The different instrumental methods of chromatography will be discussed in Section V-E. For our discussion here, a few examples will illustrate the potential. Liquid chromatography, in which a solution of the mixture of interest

V-D. INTELLECTUAL FRONTIERS passes through a column loaded with a suitable particulate material, can separate and reveal the presence of as little as 1o-~2 grams of a substance in a mixture. For gaseous samples, the technique can discriminate literally thou- sands of components in mixtures such as those from flavors, insect communi- cation chemicals, and petroleum samples. It is even possible to separate compounds that differ only in isotopic composition (e.g., deuterium for hydro- gen). Two-dimensional chromatography can give additional specificity, resolution, and sensitivity when coupled with techniques such as iso- electric focusing. For exam- ple, 2-D electrophoresis can resolve 2000 blood proteins by separating a mixture spot linearly under one set of con- ditions, and then using an- other set of conditions to sep- arate further the initial line of spots at right angles. Spot locations and amounts can be measured quantitatively with computerized scanning based on NASA programs developed for satellite pictures. PROTEIN GEL PATTERN HU MAN MYA LOMA SER U M 5uQ Optical Spectroscopy The intellectual opportunities in this field, which introduce a host of valuable analytical techniques, can be illustrated by two notable achievements of the last decade: the incorporation of computers as an integral part of most instrumen- tation and the detection of single atoms and molecules. "Smart" commercial instruments now have microcomputers preprogrammed to carry out a wide variety of experimental procedures and sophisticated data analyses. The more powerful computers of the future will digest the huge volumes of data from spectroscopic methods (especially Fourier transform and two-dimensional meth- ods) much more efficiently. This will further improve resolution, detection limits, interpretation, spectral file searching, and presentation of the results with 3-D color graphics in "real-time" to permit direct human interaction with the experiment. Intense laser sources of electromagnetic radiation are revolutionizing analyt- ical optical spectroscopy. An obvious benefit is increased sensitivity. In special cases, resonance-enhanced multiphoton ionization has achieved the ultimate sensitivity~etection of a single atom (cesium) or molecule (naphthalene) and achievements in laser-induced fluorescence are approaching this limit. Laser remote sensing, such as for atmospheric pollutants, is effective at distances of 253

254 CHEMISTRY AND NATIONAL WELL-BEING ., nit_ CCI4 CFC13 600 650 700 750 , CO CF2 C12 L ~ ~~3,CO2_ it. -no 950 1000 1050 1 100 ~ (cm~l) N2O . 1150 1200 1250 1300 FOURIER TRANSFORM INFRARED N IGHT SKY SPECTRUM over 1 mile; fluorescence ex- citation and pulsed laser Ra- man with time-resolved rang- ing are particularly prom- · ~ slng. To use the wavelength se- lectivity of the laser to give specificity for mixture analy- sis often requires the develop- ment of new strategies be- cause many atomic and molecular transitions are much broader than the laser line width. For example, dra- matic line narrowing results from cooling through super- son~c expansion for gases or with liquid helium for mole- cules embedded in a cryogenic solid (matrix isolation). These complementary techniques minimize interference by rotational and vibrational transitions and substan- tially improve detection sensitivity and diagnostic capability. The spectroscopic potentialities of synchrotron sources have barely been tapped, and free-electron lasers as light sources are on the horizon. Synchrotron light sources designed to bridge the gap between laser ultraviolet sources through the vacuum ultraviolet to the soft X-ray region will undoubtedly open up a variety of unique analytical applications. Free electron lasers, too, show great promise for extremely high brightness at whatever design wavelength is selected, beginning at the microwave range, extending through the far- and mid-infrared, and reaching to the ultraviolet. For example, analytical applica- tions in chemistry would surely result if these design specifications were to be directed toward developing an intense, continuously tunable, short-duration pulse (10 picoseconds) mid-infrared light source. Mass Spectrometry Because this method involves separation of gaseous charged species according to their mass, its intellectual frontiers embrace ionic structure, thermochemis- try, and gas phase reactivity, and they provide important insights into solution reactions and theoretical chemistry. On the other hand, the methodology offers unusual analytical advantages of sensitivity (detection of single ions), speci- ficity (peaks at 102 to 106 possible mass values) and speed (10-2 see response) attributes making for a nearly ideal marriage to the dedicated computer. In the celebrated Viking Mars Probe, mass spectrometry was the basis for both the

V-D. INTELLECTUAL FRONTIERS upper atmosphere analysis and the search for organic material in the planetary soil. Such sensitive soil sniffing to detect hydrocarbons might become a fast method for oil exploration. A special tandem-accelerator/ MS can detect three atoms of i4C in 10~6 atoms of i2C, which corresponds to a radio- carbon age of 70,000 years. The broad applications of mass spectrometry include the analysis of elements, iso- topes, and molecules for the semiconductor, metallurgi- cal, nuclear, chemical, petro- leum, and pharmaceutical in- dustries. Large Molecules Vital to Biomedicine and Inclustry 2876 2744 Ace;; 2524 3053 ~111~ t22q 2000 2500 3000 MASS IN A M.U. MASS SPECTRUM BY LASER DESORPTION I o~8 GRAMS POLYETHYLENE GLYCO L A recently developed series of related techniques uses ion, neutral, and photon bombardment (see Table V-3) to desorb ions from solid samples. These techniques dramatically increase the molecular weight range of mass spectrometry. Plasma Resorption with 252Cf has given molecular ions of molecular weight 23,000 from the polypeptide trypsin, while FAB has provided extensive structure information on a glyco- protein of molecular weight above 15,000. Laser and field desorption have produced molecular ion mass spectra displaying the oligomer distribution of TABLE V-3 Desorption Ionization Techniques for Analysis of High-Molecular- Weight Substances Field Desorption (FD). Samples placed on a fine, carbon-coated wire are subjected to heat and high electric fields. Commercially available, somewhat erratic, but has been productively employed. Plasma Desorption (PD). Samples placed on thin foil are bombarded with high energy fission fragments from radioactive californium (25 Cf) or ions from an accelerator. Not commercially available. Secondary Ion Mass Spectrometry (SIMS). Solid samples are bombarded with kilovolt electrons. Low electron fluxes are used for molecular SIMS; high fluxes for inorganic analysis and depth profiling. Commercially available. Electrokydrodynamic Ionization (EHMS). Samples are dissolved in a glycerol-electrolyte solvent. Desorption from solution occurs under high electric fields and without heating. Almost no molecular fragmentation! Not commercially available. Laser Desorption (LD). Both reflection and transmission experiments and various sample preparations can be used. Tendency toward thermal degradation. Commercially available with time-of-flight mass analysis. Thermal Desorption (TD). Sample is placed on probe tip which is heated to desorb ions (no ionization filament is used). Useful for inorganic analysis; recently applied to organic salts. Fast Atom Bombardment (FAB). Samples in solution (usually glycerol) are bombarded with kilovolt- energy atoms. Fluxes higher than in SIMS. Wide applicability to biological samples, including pharmaceuticals. Commerically available. 255

256 CHEMISTRY AND NATIONAL WELL-BEING polymers. Separation of such complex mixtures is far beyond the capability of other methods. In "tandem" mass spectrometry, one mass spectrometer (MS-~) feeds ions of a selected mass into a collisional zone that induces fragmentation into a new set of fragment ions for analysis in a second mass spectrometer (MS-~. This technique, abbreviated MS/MS, offers a particularly promising frontier for anayIsis of mixtures of large molecules. "Soft" ionization that avoids extensive fragmentation is used first to produce a mixture of molecular ions. From this mixture, one mass is selected by MS-T, and it is more vigorously fragmented to produce an MS-~l spectrum that characterizes the structure of the correspond- ing component. High speed and molecular specificity are important features of MS/MS. It is a powerful tool for analysis of groups of compounds sharing common structural features. It is particularly effective in removing background signal due to the contaminant species usually present in biological samples. It is now possible to sequence peptides with up to 20 amino acids and, in some instances, with sample sizes as small as a few micrograms. Instrumentation Developments in many fields have led to improved MS hardware. The quadrupole mass filter, which is unusually simple and computer-controlIable, has revolutionized routine GC/MS analyses and is similarly promising for LC/MS and MS/MS. Inhomogeneous high field magnets developed for high energy accelerators have given a 10-fold increase in mass range for double- focusing instruments to take full advantage of the new methods to ionize high MW compounds. Time-of-flight instruments with their unlimited mass range give accurate molecular weights with 252Cf plasma Resorption using subnanosecond timing circuits. The Fourier transform mass spectrometer, based on ion cyclotron resonance and equipped with a superconducting magnet, can give unusual resolution (>106 at m/z = 100), nondestructive and simulta- neous measurement of all ions, and the ability to do time-separated mass analyses. Combined ("Hyphenated") Techniques There is a growing appreciation for the synergistic benefits of using- these computerized instruments in combination, such as the mass spectrometer coupled to a chromatograph (gas or liquid, GC/MS or LC/MS) or to another mass spectrometer (MS/MS), or these coupled with the Fourier transform infrared spectrometer (GC/IR, GC/IR/MS). High-resolution (1/104) MS gives 1 part-per- trillion (1/10~2) analyses for the many forms of dioxin (TCDD) to see if they are present in human milk and the adipose tissue of Vietnam war veterans (see Figure, Section V-A). GC/MS is necessary for the specific detection of 2,3,7,8- TCDD, the most toxic dioxin isomer. GC/MS is used routinely for detecting halocarbons in drinking water, polychIorobiphenyIs (PCB), viny] chloride, nitrosamines, and for most of the EPA list of other "priority pollutants." MS/MS

V-D. INTELLECTUAL FRONTIERS with atmospheric pressure ionization can monitor many of these contaminants continuously at the parts-per-billion level, even from a mobile van or helicopter. The high specificity as well as sensitivity of these methods make them especially promising for nerve gases, "yellow rain," and natural toxins in foodstuffs (10-~i g vomitoxin in wheat) and plants ("Ioco weedy. Metabolites found by GC/MS have led to the identification of more than 50 inborn errors of metabolism in newborn infants; early identification is usually critical in preventing severe mental retardation or.death. One of the most exciting intellectual frontiers is the possibility that routine profiling of human body fluids may detect incipient disease states; here the molecular complexity will challenge even the combined information provided by chromatographic reten- tion times coupled with infrared and mass spectral data. Surface Analysis Most modern techniques for the characterization of surfaces have been developed since 1970. These techniques provide complementary information, so that sophisticated research requires multitechnique instrumentation that is, therefore, expensive. Understanding surface chemistry demands unusual infor- mation, such as the composition of the first atomic layer of the surface and of the molecular species on the surface. The surface layer can be sampled with secondary ion mass spectrometry (SIMS). Because this method strips away the surface during the measurement, continued bombardment then samples under- lying layers for depth profiling. Even horizontal spatial information can be obtained at 400 ~ resolution. Characterizing surface molecular species, which is basic to understanding heterogeneous catalysis, brings additional intellectual challenges. Desorption mass spectrometry can now identify species with molecular weights of several thousand, but the eject of desorption on structure needs further study. Tech- niques providing detailed information on molecule-surface interactions, such as low-energy electron loss spectroscopy and surface-enhanced Raman, give prom- ise of directly visualizing the dynamics of surface chemistry. Here, special challenges abound: sensitivity requirements are staggering (a 1-mm2 mono- layer of benzene weighs less than 10-9 g), and atmospheric pressure reactions require special interfaces to use high-vacuum (10-~2 atm) surface spectroscopic techniques. ElectroanaZytical Chemistry Electrochemistry is also an interfacial science, and it presents basic chal- lenges to the understanding and control of the properties of surfaces and the processes that occur there. Improved ion selective electrodes demand a deeper understanding of molecular-scale electrochemistry. To obtain picomole sensi- tivity (10-~2 moles) and specificity of stripping using pulse voltammetric techniques, we depend heavily on solid state circuitry and microprocessors. Improved sensitivity and miniaturization (electrode area a few square microns) 257

258 CHEMISTRY AND NATIONAL WELL-BEING have made possible continuous analysis in living single cells. Other successful applications in difficult environments include flowing rivers, liquid chromato- graphic detectors, nonaqueous chemical process streams, molten salts, and nuclear reactor core fluids. Another vital frontier is the direct application of surface science techniques (LEED, Auger, ESCA, and Raman) to the study of electrode surfaces. Funda- mental advances in electrochemistry will not only yield important improve- ments in this nondestructive, inexpensive analytical tool, but also in such commercial devices as batteries and fuel cells. Computers in Analytical Chemistry There has been repeated reference to the opportunities for analytical instru- mentation opened by the recent growth in both the speed and availability of digital computers. Dedicated microprocessors or minicomputers that increase the cost of an instrument by less than 50 percent can increase its capabilities many fold. Whole body scanners based upon three-dimensional nuclear mag- netic resonance techniques would not be practical without fast Fourier trans- form and data interpretation capabilities. FT/NMR, FT/infrared, and FT/mass spectrometry have led to similar dramatic improvements in the specific detec- tion of complex molecules (NMR, 10-8 g; {R. 10-~° g; MS, 1o-~3 g). Computer- aided pattern recognition should be applicable when data from several tech- niques can be obtained. Computer data reduction and interpretation have greatly increased the efficiency of trained scientists. With this revolution has come an increasing awareness of the need for better training to ensure "computer literacy" among scientists, especially analytical chemists. The in- creasing complexity of science and the explosive growth in the data acquisition rate of instruments will continue to challenge improved computer capabilities for many years. The current impressive progress in analytical instrumentation and method- ology has drawn heavily on fields such as lasers, electronics, computers, chromatography, mass spectrometry, and the surface sciences, in each of which the United States is a world leader. Combining relevant discoveries in these fields with those of chemistry to find better analytical solutions to old and new scientific problems is a current intellectual challenge. The resulting analytical capabilities should be a key element in future progress in these scientific fields and their commercial outlets, as well as in the manufacture of analytical instrumentation. Separations Sciences Separations chemistry has already been discussed in Section V-C and again in this section under Analytical Chemistry. Thus, while it is a well-defined body of chemical science, it also cuts across several more or less classical or conventional areas of chemistry. It is well defined in that it is concerned with the application of chemical principles, properties, and techniques to the sepa-

V-D. INTELLECTUAL FRONTIERS ration of specific elements and groups of elements from extraneous materials and from each other. It is a cross-cut field in that it has applications in diverse areas as enumerated in Section V-C. Quite a number of applications ot separations chemistry have been mentioned in earlier sections, ranging from biochemicals separated from living organisms to processes that furnish continuous supplies of critical and strategic materials. Research advances in separations will have industrial applications of substan- tial economic and strategic importance. The example of critical metals men- tioned in Section V-C (see Table V-2) provides a case in point. Almost 90 percent of our use of the critical metal platinum, in great demand as a catalyst, is met by imports; mining of the major platinum source in the United States (in Stillwater, Montana) has not yet begun. A second, undoubtedly more important example, concerns our access to uranium. Chemical separations, and their implementation in chemical engineering processes, are vitally important in developing the nuclear fuel cycle. About 13 percent of the nation's electrical energy is derived from nuclear energy. A much larger percentage is provided to the industrialized Northeast. Uhemlcat separations are used at the uranium mill where the very low-grade uranium ores (typically .1 to .3 percent U3OS) are treated in highly selective chemical processes to produce a concentrate of greater than 80 percent U3O~. Subsequent chemical separations, based on solvent extraction or formation of a volatile fluoride, produce a uranium product pure enough for use in nuclear reactor fuel manufacture. After removal from the reactor, the highly radioactive fuel is subjected to a selective, remotely operable chemical process that separates uranium and plutonium from the fission products to high levels of purity, in a safe reliable manner and on a large scale. Chemical separations processes have also been devised to separate useful fission products from the fission product waste stream. Research in the separations sciences must have wide scope. It focuses strongly on investigation of the properties of the liquid state at its most fundamental level, including solvent-cage reorientation, solvent-solute interactions, and chemical behaviors of fluids under extreme pressures and temperatures. Sepa- rations are typically much less efficient, thermodynamically, than other steps in chemical processing. With new insights, we may learn how to carry out separations more efficiently and how to optimize the rate of the process in view of its intrinsic thermodynamic implications. The chemical engineering commu- nity will furnish important contributions; practical applications can be antici- pated. Nuclear Chemistry Since the days of the Curies, chemists have played a key role in the fundamental exploration of radioactivity and nuclear properties, as well as in nuclear applications to other fields. Most of the advances in our understanding of the atomic nucleus have depended strongly on the complementary skills and ~ v approaches of physicists and chemists. Furthermore, the applications of nuclear 259

260 CHEMISTRY AND NATIONAL WELL-BEING techniques and nuclear phenomena to such diverse fields as biology, astronomy, geology, archaeology, and medicine as well as various areas of chemistry have often been and continue to be pioneered by people educated as nuclear chemists. Thus the impact of nuclear chemistry is broadly interdisciplinary. Studies of Nuclei and Their Properties With over 2600 different nuclear species now known and new ones being discovered every month, there is a vast range of nuclei to explore, and they exhibit a wide spectrum of properties. Some nuclear states are well described in terms of the motion of a few nucleons in an average potential and single-particle or shell-model states, while others involve collective motions such as rotations and vibrations. Nuclear spectroscopy, the systematic study of excited states of nuclei, has greatly advanced since the 1960s and has led to greatly improved models; nuclear chemists have made significant contributions to this field, especially in regions of deformed nuclei, such as the actinides and lanthanides, where rotational, vibrational, and intrinsic single-particle states have been used extensively in testing nuclear models. New phenomena, such as changes of nuclear shape with increasing nuclear spin, have been discovered. Particularly interesting advances have been made in extending our knowI- edge of nuclear and chemical species at the upper end of the Periodic Table. In the last 15 years, elements 104 to 109 have been synthesized and positively identified, often by ingenious new techniques necessitated by the fact that the half-lives of these species are very short, down to milliseconds. In addition to these new-element discoveries, many new isotopes of other transuranium elements have been found, and the study of their nuclear properties has played a vital role in advancing our understanding of alpha decay, nuclear fission, and the factors that govern nuclear stability. Fission research in particular has borne rich fruit: totally unexpected changes in fission properties (mass and kinetic-energy distributions of fragments) with changes of only one nucleon in the region of fermium indicate a dominant effect of the doubly closed shell configuration of i32Sn (50 protons, 82 neutrons) among fission fragments. Thee study of spontaneously fissioning isomers among the heaviest elements has led to the important realization that the potential energy surfaces of nuclei in this region have two minima, and this, in turn, opened the way to a new and powerful approach to calculating such surfaces the so-called shell correction method. Along with the advances in understanding nuclear properties goes new insight into the chemistry of the elements at the upper end of the Periodic Table. The prediction that the actinide series ends with lawrencium (element 103) has been confirmed by experiments that have shown element 104 to have the properties expected of a group TVb element. This confirmation has put predic- tions of the chemical properties of higher-, elements on a firmer footing. Further exploration of the limits of nuclear stability is clearly in order, both at the upper end of the table of nuclides and on the neutron-rich and neutron-

V-D. INTELLECTUAL FRONTIERS poor sides of the valley of stability. Newly discovered reaction mechanisms, such as multinucleon transfer reactions at near-Coulomb-barrier energies, promise to give access to more neutron-rich and therefore much longer-lived (minutes to hours) isotopes of elements with Z > 100 than have been available. This should open the way to more detailed investigations of the chemistry of these interesting elements at the upper end of the actinide series and beyond, where relativistic ejects on the atomic electrons should play an increasingly prominent role. The quest for "superheavy" elements, i.e., nuclear species in or near the predicted "island of stability" around atomic number 114 and neutron number 182, has so far not been successful. However, new attempts in this direction are in preparation because it has recently become clear that the conditions used in past experiments were probably not at all optimal. Nuclear Reactions In the realm of nuclear reactions, the last decade has brought to light a new mechanism in heavy-ion induced reactions termed deeply inelastic collisions; this process is characterized by the damping of large amounts of collective nuclear energy through interactions with nucleonic modes of excitation. Studies of such damped collisions give information on the cooperative phenomena and relaxation processes occurring within a small quantal system initially far from equilibrium. Other major advances that have resulted from nuclear reaction studies have been extensions of the nuclide chart to extremely neutron-rich and neutron-poor nuclides. SpalIation reactions with high energy protons, transfer reactions with heavy ions, and multiple neutron capture reactions in high neutron fluxes are among the approaches used in this quest to reach or approach the limits of nuclear stability. Much improved nuclear systematics, new insights into nu- clear reaction mechanisms, and even the discovery of new modes of radioactive decay (proton emission and 2-neutron emission) have resulted. The studies are also of relevance to astrophysics, especially for understanding and calculating nucleosynthesis by rapid successive neutron captures, a process believed to be responsible for element building to the highest Z's in stellar environments of extremely high neutron fluxes, such as those that may exist in certain types of supernovae. Another current challenge in nuclear reaction research is the attempt to produce nuclear matter under extreme conditions of density and temperature that encroach those thought to have existed in the earliest stares of the . . ~ expanding universe. Such conditions can presumably be produced in head-on collisions of heavy ion beams accelerated to relativistic energies, and accelera- tors capable of producing the requisite beams will soon become available. Space Exploration The breadth of applicability of nuclear techniques is demonstrated in the exploration of the Moon and our companion planets during the past two decades. 261

262 CHEMISTRY AND NATIONAL WELL-BEING For example, the unmanned Surveyor missions to the Moon provided the first chemical analyses of the moon, employing a newly developed analytical tech- nique that used the synthetic transuranium isotope 242Cm. The analyses identified and determined the amounts of more than 90 percent of the atoms at three locations on the lunar surface. These analyses, verified later by work on returned samples, provided answers to fundamental questions about the com- position and geochemical history of the Moon. Nuclear techniques also played an important role in the chemical analyses performed by Soviet unmanned missions to the Moon and in experiments designed to seek life on the surface of Mars by the U.S. Viking missions. Similarly, activation and isotopic analyses were prominent in the analyses of returned lunar samples of the concurrent intensive studies of meteorites, making possible elucidation of the temporal history of the Moon and meteorites. Isotopic Anomalies Ever since the discovery of the isotopic composition of the chemical elements, it has been assumed that this isotopic composition is essentially constant in all samples, an assumption that provides the basis for assigning atomic weights. The only exceptions involved elements with Tong-lived radioactive isotopes. However, since 1945, human operations have affected the atomic weights of several elements (e.g., Li, B. U) under some circumstances. More fundamen- tally, it has been discovered that the solar system is not composed of an isotopically homogeneous mixture of chemical elements. Even for an element as abundant as oxygen, variations of the isotopic abundance have been noted for different parts of the solar system. Such isotopic variations have now been established for several chemical elements, and they provide clues to the nucleosynthetic processes that gave rise to the chemical elements, as well as to the conditions that prevailed at the birth of the solar system. A startingly large isotopic anomaly was discovered in the uranium of uraninite ore samples from the OkTo mine in Gabon (West Africa) in 1972. Anomalously Tow isotopic abundances of uranium-235 in these ores led to the astonishing conclusion that, 1.S billion years before the first manmade nuclear reactor, nature had accidentally assembled a uranium fission reactor in Africa! This reactor was made possible by the higher 235U concentration (~3 percent instead of the present-day .7 percent) at the time. Massspectrometric analyses of various elements in the Oklo ore not only proved that isotopic compositions labeled them unmistakably as fission products, but also made it possible to deduce such characteristics of the reactor as total neutron fluence (~.5 x 102i neutrons cm-2), power level (~20 kW), and duration of the self-sustaining chain reaction (~106 years). An important practical result of the Oklo studies is the fact that most fission products as well as the transuranium elements produced in the reactor did not migrate very far in 1.S billion years. This has clear implications for the possibility of Tong-term confinement of radioactive waste products in geologic formations. An interesting scientific fringe benefit of the

V-D. INTELLECTUAL FRONTIERS Oklo event is that, from detailed analyses of the isotopic composition of the residual fission products, it has been possible to set upper limits, orders of magnitude lower than by any previous method, on the variation with time of some fundamental constants, such as the fine structure constant and the coupling constants for strong and weak interactions. This is significant because such variations are the consequence of certain cosmological theories, and the limits set by the Oklo data help to narrow the choice of acceptable cosmological models. Solar Neutrino Experiments For nearly 40 years it has been almost universally accepted that the Sun's energy, on which life on Earth depends, is produced by a series of thermonuclear reactions deep in the solar interior. It is also generally agreed that the only radiations produced in these reactions that can penetrate through the sun and reach us are neutrinos, so that the only experiment to date that can be considered a probe of the postulated reaction sequence is an attempted radiochemical measurement of the neutrino flux from the Sun. Neutrino capture by 37C1 to form radioactive 37Ar has been monitored since 1968 in 650 tons of perchloroethylene in a deep mine in South Dakota. This painstaking experiment—only a few neutrinos are captured per month—indicates a solar neutrino flux about one-fourth of the theoretically predicted value, which casts doubts on the completeness of our understanding of how the sun and other stars generate their energy. This discrepancy between theory and experiment has led to much re-examination of the astrophysical models and of the nuclear data underlying the flux prediction, but no satisfactory resolution has been found. To determine whether the source of the discrepancy is to be sought in the astrophysical models or in fundamental properties of the neutrino, another radiochemical neutrino detection experiment is being prepared. It uses 71Ga as the detector because its response is much less model-dependent than that of 37C1. Nuclear Chemistry in Med icine Nearly 20 million nuclear medicine procedures are performed annually in the United States. Advances in nuclear medicine depend crucially on research in nuclear and radiochemistry. For example, great progress in our knowledge of the chemistry of technetium in the past decade will clearly lead to much more effective applications of 99mTc, the most widely used radionuclide, because the physical and chemical properties of technetium compounds can be related to their in vivo activity in pathological states. Another important example is the development of ingenious, rapid online methods for labeling a variety of compounds with cyclotron-produced short- lived positron emitters, such as 1lC(20m) and 1sF(110m), with very high specific activities. Such compounds, e.g., 18F-2-deoxy-2-fluoro-D-glucose and 1-llC- palmitic acid in conjunction with positron emission tomography (PET), are 263

264 CHEMISTRY AlY7D NATIONAL WELL-BEING finding important new research and clinical applications in neurology and cardiology. Future progress in nuclear medicine will clearly require close collaboration among scientists in various disciplines, including radiochemists and nuclear chemists. One of the challenges is the radionucTide labeling of monoclonal antibodies which, if successful, would open up a whole new area of imaging and therapy. Stable isotopes, in conjunction with NMR spectroscopy, also have important applications in medicine. With i3C and t5N tracers, NMR spectroscopy of humans will make possible new insights into the molecular nature of diseases, provide a noninvasive method for their early detection and for the clinical management of patients, and make possible in vivo studies of metabolic processes. This has led to one of the most exciting developments of the last few years- large-object imaging. The presence and chemical form of key elements can be mapped in entire human organs in living patients. These powerful, noninvasive techniques were literally undreamt of 15 years ago. They have arisen in response to demands for the ability to study via NMR ever larger biomolecules as well as biological systems in vivo.

V-E. INSTRUMENTATION V-E. :Instrumentation As in earlier chapters, sophisticated instrumentation has figured prominently in our discussions of environmental monitoring, international competitiveness, and national security. The techniques of the surface sciences are of dominant importance to the advances being made in catalysis, upon which so many industries depend. Chromatography joins mass spectrometry (Section IV-E) and laser spectroscopy (Section IlI-E) as a ubiquitous tool in analytical chemistry. Infrared spectroscopy typifies the several optical spectroscopic methods that are finding effective use in environmental monitoring as well as in research applications. Surface Science Instrumentation Surface science is one of the most rapidly growing areas of the physical sciences at this time. The development of an array of powerful instruments that can reveal the atomic structure and chemical composition of surfaces has been largely responsible for the rapid rise. The field has been stimulated, as well, by a wide range of important applications. For example, surface and thin film electrical properties, with relevance to miniaturization of semiconductor de- vices, have attracted the interest of many physicists. Both physicists and chemists are investigating surface etching and epitaxial growth, with the same application in mind. But surely the prospect of understanding catalysis on a fundamental level is one of the most exciting and significant frontiers opened by these new instruments. This is, of course, a realm for chemists. No doubt the historical pattern of NMR will be repeated physicists have perfected a remark- able set of instruments with which chemists will open the cornucopia of catalysis. Instruments for the Study of Surfaces The various techniques of surface science probe the surface with particles or photons. Among the particles that have proven useful are electrons, ions, neutral atoms, neutrons, and electronically excited atoms (metastables). Photon probes extend from the X-ray region to the infrared. When particles are used, either as incident projectiles or as secondary indicators of high energy photon- induced processes (e.g., electron-ejection following X-ray absorption), ultrahigh vacuum environments are essential (10-9 to 10-~° torr). In contrast, photon probes can be effective when the surface is in contact with a gas at high pressure or a liquid, the conditions under which surface catalysis can occur. A second aspect of categorization is the type of information provided. A key question about chemistry as it takes place on a surface is the molecular structure of the molecules that have become attached to the surface. Is each molecule essentially intact (physisorbed) with its structure and bonding little changed? If so, the surface may be serving only as a site for reaction, immobilizing the reactant as it awaits its fate. Or does the molecule react with 265

266 CHEMISTRY AND NATIONAL WELL-BEING the surface, so that it is attached more strongly (chemisorbed)? If so, it has acquired a new molecular identity, undoubtedly with changed chemical behav- ior. Second, we would like to know the structure and composition of the surface, for in chemisorption, the surface is itself a reactant. Finally, it is useful to understand the bonding of the solid itself in this zone of discontinuity, where one bulk phase ends and another begins. Table V-4 lists more than 15 types of the surface science measurements that TABLE V-4 Surface Science Instrumentation Relevant to Chemistry on Surfaces Surface Analysis Method Acronym Electron energy loss EELS spectroscopy Infrared spec- IRS troscopy Raman Thermal Resorption Extended X-ray ab- sorption fine structure Molecular beam scattering TDS EXAFS Auger AES, spectroscopy Auger Secondary ion mass SIMS spectroscopy Ion sputtering X-ray and UV pho- XPS, UPS, toelectron spec- ESCA troscopy Ion scattering ISS Low energy electron LEED diffraction Scanning electron SEM microscope Laser microprobe mass spectrome- try Laser-induced sec- ond harmonic generation Bombard or Irradiate with: Electrons, 1-10 eV Infrared light Heat X-rays Physical Basis Vibrational excitation of surface molecules by inelastic reflection Vibrational excitation by absorption Visible light Raman scattering, reso- nant, surface - enhanced Thermally induced de- sorption, decomposi- tion of adsorbates Interference effects in photoemitted electron Molecules of known energy Electrons, 2-3 keV X-rays Ions, 1-20 keV Inelastic reflection off surface Electron emission from excited surface atoms Ion beam-induced ejec- tion of surface atoms as ions Inert gas ions Surface atom ejection by ion bombardment Electron emission from inner shells X-rays, (synchrotron) UV light (21 eV) Inert gas ions Electrons, 10- 300 eV Electrons Visible, UV light Visible, UV light Information Obtained Molecular identity, orienta- tion and surface bonding of adsorbed molecules (Same as above) Vibrational spectrum ad- sorbed molecules Desorption energetics, surface chemistry of adsorbates Atomic structure of surfaces, adsorbates, nearest neigh- bor distances Energy transfer to surface Surface composition Surface composition Elastic scattering Elastic back scattering, diffraction Electron scattering Focused light-induced molecular Resorption High-photon field non- linear effects Surface composition, depth profiling Surface composition near sur- face (100 A) oxidation states Atomic structure and compo- sition of surface Atomic surface structure Surface topology 200-micron surface composi- tional mapping Detection of molecules at a solid-solution interface

V-E. INSTRUMENTATION are now in use. Some of the listings embrace two or more techniques and, even so, the table is not all-inclusive. The first six are the methods most responsive to the first set of questions posed above. The other instruments mainly provide information about the surface itself, its structure, composition, and bonding in the first few layers. Plainly, coupling two or more complementary methods can greatly enhance the significance of any single measurement used alone. Among the electron probes, Tow energy electron diffraction (LEED) reveals the atomic structure of clean, ordered surfaces and ordered structures of monolayers of adsorbed atoms and molecules. Its role in determining bond distances and bond angles is the same in surface chemistry as the role played by X-ray diffraction in the structural chemistry of solids. Electron energy Toss spectroscopy (EELS) detects the vibrational modes of surface atoms and mole- cules with an energy resolution of about 40 cam. Scanning electron microscopy (SEM) yields surface topology with about a 300 ~ spatial resolution. Auger electron spectroscopy determines the surface composition with a sensitivity of about 1 percent of a monolayer for most elements (10~3 atoms/cm21. X-ray photoelectron spectroscopy (X-Ray PES) also determines the composition of surfaces and of the near-surface region (~ 100 it), as well as the oxidation states of the surface. Photoelectron diffraction uses the diffraction of photoelectrons for surface structure analysis as they exit from the solid into vacuum. Ultraviolet photoelectron spectroscopy (UVPS) uses He ~ radiation (21.2 eV) or synchrotron radiation to eject electrons from the valence shell of atoms or molecules or from the valence bands of solids at the surface. In this way, the surface electronic structure is explored. Ton scattering from surfaces has been used for surface composition analysis with great sensitivity, 109 atoms/cm2. In secondary ion mass spectroscopy (SIMS), neutral and ionized atoms and molecular fragments are ejected by bombardment with high energy (1-20 Key) inert gas ions. Ton scattering spectroscopy determines the surface composition by the energy change of inert gas ions upon surface scattering. Ion sputtering or ion etching removes atoms from surfaces layer by layer. The combined use of ion sputtering and electron spectroscopy yields a depth profile analysis of the chemical composition in the ~ . near-sur~ace region. Diffraction techniques with helium and other atoms are used to determine surface structure and roughness. Energy transfer during molecular beam- surface scattering yields information about the dynamics of elementary surface reaction steps of adsorption, surface diffusion, surface reactions, and Resorption. It also provides information about the nature of the attractive potential between the molecule that approaches the surface and the surface atoms. Grazing angle X-ray diffraction provides still another method for learning the atomic structure of surfaces and interfaces. Extended X-ray absorption fine structure measurements (EXAFS) can be used to determine nearest neighbor population and interatomic distances for small dispersed particles and surfaces. The availability of high-intensity laser sources is now awakening the develop- ment of a new set of surface sensitive techniques. Surface infrared spectroscopy, . 267

268 TABLE V-5 ~ ~ ~ . CHEMISTRY AND NATIONAL WELL-BEING laser Raman spectroscopy, second harmonic generation surface spectroscopy, and laser ellipsometry all provide information about the surface chemical bonds of adsorbed atoms and molecules. Solid state nuclear magnetic resonance is specially well suited for determination of the structure of high surface area solids like the molecular sieve materials. Instrument Developments Needed There are many, well-perfected techniques for the study of surfaces under well-controlled conditions. Developments of the next few years will focus more attention on techniques that clarify the molecular structure and behavior of the adsorbate. EELS is such a technique. While great effort and design skill has been invested in achieving the EELS resolution now available, about 40 cm-i, it is only marginally able to provide the structural information desired. A 10-fold improvement is needed, to a spectral resolution of 5 cm-i or better; such a gain would enormously increase the value of this technique. Research systems have been built with capacity to move a sample from an ultrahigh vacuum environment into contact with a gas and then to return to the vacuum situation. This is an important capability and should be made available commercially. Surface samples should be readily held at cryogenic tempera- tures down to 4 K. Laser techniques, too, offer special promise for chemistry- oriented surface studies. Then, to open the door to kinetics of reactions as they take place on surfaces, techniques must be developed for pulsed excitation and subsequent temporal analysis on a short time scale. Costs Table V-5 lists some of the most important instruments from Table V-4 and approximate current costs. It is important to realize that rarely can an investigator ef- fectively address a problem of surface chemistry with only one of these techniques. In- stead, an effective laboratory will need the synergism and flexibility provided by having access to three or four comple- mentary techniques. For ex- ample, the first five entries in Table V-5 are mutually sup- portive. Thus, the research group of a single investigator will require a capital investment exceeding $500K and, of course, a substantial on-going support to ensure cost-e~ective maintenance and operation of these systems. The instruments listed in Table V-4 permit us now to inaugurate a new era Approximate Current (1985) Costs ($) for Surface Science Instruments Electron energy loss spectrometer Low energy electron diffraction Auger electron spectrometer Tunable laser sources and detectors Thermal Resorption mass spectrometry X-ray photoelectron spectrometer TDS XPS _ A A Ion-scattering spectrometer ISS Secondary ion mass spectrometer (static mode) SIMS Secondary ion mass spectrometer (dynamic mode) SIMS Rutherford back-scattering system Laser microprobe mass spectrometer Raman microprobe X-ray absorption fine structure attachment to synchrotron EELS 200-225K LEED 150-175K AES 150-250K 100-150K 150-200K 150-200K 150-175K 170-200K 650-700K 500-600K 300-325K 150-170K 400-500K EXAFS

V-E. INSTRUMENTATION of investigation of chemistry in the surface domain. Sections IlI-A, IlI-B, and V-D show that both the economic and intellectual stakes are high. We must increase chemistry funding levels to place these powerful tools in the hands of those chemists working on catalysis. Only then can we expect to maintain a worId-leadership position in this crucial field. The United States cannot afford merely to watch with admiration as the field of catalysis is developed in properly equipped laboratories abroad. Surface Analysis As is always the case, sensitive measurement techniques can be regarded as analytical tools. This is the case in the surface sciences. Every one of the capabilities listed in the last column of Table V-1 can be put to analytical use in the pursuit of questions that may be only remotely connected to the surface sciences. As an example, a state-of-the-art laser microprobe device designed to desorb molecules from a solid surface can be used to detect the presence of a pesticide on the leaf of a plant. Such a capability was quite impossible only 10 years ago; today it permits us to contemplate tracking the amount, stability, weathering, and chemistry of a pesticide in field use. Of course, the analytical technique may, as well, be concerned with monitor- ing or clarifying chemical changes that take place on a surface or with a surface. Many of these analytical studies relate to catalysis. In Section V-D, examples were given of the use of EELS to determine the molecular structures that exist on a catalyst surface as it functions. Similarly, X-ray photoelectron spectroscopy (ESCA) studies of the cobalt molyb~ate catalyst show another facet of the chemical role of a catalyst. This catalyst (with 3 percent cobalt) is used commercially to remove sulfur from petro- leum (to reduce acid rain). In actual use, the catalyst surface is first prepared by chemical exposure to hydro- gen gas at a high temperature to reduce surface oxides. Then, the catalyst is "acti- vated" by exposing it to a hy- drogen sulfide/hydrogen mix- ture. Understanding how the catalyst has been chemically changed in each of these treatments is a crucial part of understanding how the cata- Tyst works. Present-day ESCA measurements clearly reveal the changes in the cobalt atoms as the oxide coating is removed by hydrogen and then as they are converted to the sulfide. 269 14. cat 1970 cat 1980 ~T - ~ -- 1 1 1 1 1 1 1 1 790 786 782 778 774 BINDING ENERGY (eV) /\ J Before _' A ter reduction in H2 After activation .} 'it ~ P with H2S In 1 1 1 1 1 1 1 1—1 790 786 782 778 774 BINDING ENERGY (eV) ESCA SHOWS HOW A COBALT CATALYST CHANGES ON ACTIVATION

270 C" a: :) cn CHEMISTRY AND NATIONAL WELL-BEING Fifteen years ago, the best ESCA equipment in existence was unable to distinguish these changes. The myriad of applications that lie somewhere between the two examples mentioned above has been made possible by the array of surface science instruments shown in Table V-4. These applications have given rise to surface analysis, a new subdivision of analytical chemistry. Applicability Surface analysis is quite different from bulk analysis; frequently, factors important for surface analysis are not important to bulk analysis. The most common distinguishing feature is the effective sampling depth of the analytical technique used. For each technique, the sampling depth of that technique defines the exact surface sampled. Sampling depth is important because the measuring technique should be appropriate to the phenomenon under study. For example, bonding to the surface, Nettability, and catalysis involve only a few atomic layers, whereas passivation and surface hardening treatments involve 10 to 1000 atomic layers. Typical sampling depths for the primary surface analytical techniques are one or two atomic layers for low energy in ion scattering, ~ A for static SIMS, 20 ~ for the ESCA and Auger techniques, and 100 ~ for dynamic SIMS. Laser mass spectrometry, the Raman microprobe, and scanning electron microscopy reach into the surface from 1000 to 10,000 ~ (i.e., to 1 micron). Another important matter is the microscopic heterogeneity or microcrystal- linity of the sample. The dis- O ~ OO ~ OOO LATERS tribution of the species across MEL - / a surface and its depth rlistri button inward from the sur- face can determine the behav- ior of the surface and must be known. The shallower the sampling depth of the tech- nique, the more finely it is able to define the depth pro- file of a sample. 8 ~3_~ ~~//////~/~/////////~//////~ WORE FUNCTION /////// __//// OPTICAL ABSORPTION ~ I, . CORROSION I _/////// _ ~ _ ISS SIMS ESCA SIMS LASER SEM (STATIC ) AUGER (DYNAMIC ) MS RAMAN HOW DEEP IS THE SURFACE? Developments Needed A major challenge in the development of surface ana- lytical instrumentation is the reinforcement of its quantita- tive dimension. Most of the examples given have been concerned with what is there. We must also be able to deter-

V-E. INSTRUMENTATION mine how much. Relative quantitative surface analysis measures a species of interest against a component already present. To quantify surface species without resorting to such internal standards is a difficult problem whose solution will expand surface analysis to many applications, particularly those . . . . . nvo. ~vlng organic species. Another important problem is the development of microprobes that can provide both chemical and spatial information about surface species. Currently, Auger and ion microprobes are useful in this respect for probing elemental composition, such as the presence and location of the trace contaminants phosphorus and lead in silicon chips. However, they are not able to probe for large organic molecules such as carcinogens or therapeutic drugs. Thus, development of new organic microprobes is an urgent need. Characterization of small particles is another important challenge for surface analysis: this is ~ · ~ ~ · ~ ~ - ~ ~ ~ , particularly important in environmental monitoring where the analysis of carcinogenic hydrocarbons on particulates is a current problem. Finally. devel- ~ ~ ~ · · 1 1 ~ ~ 1 _ _ 1 _ ~ ~ -—.~ 7 -- - -— opment of new hardware IS Important. An example has been mentioned earlier: it is important to interface high-vacuum surface spectroscopic techniques with samples at atmospheric pressure. Development of cells to permit real time examination of surfaces in contact with a reactive gas is a challenging instrumental problem. Costs The cost listed in Table V-5 are applicable in analytical uses as well. Just as for research applications, surface analytical problems are seldom solved by a single, stand-alone technique. Instead, the more interesting problems require a combination of instrumental approaches. Therefore, an effective surface ana- lytical laboratory will have to be equipped with several instruments. A considerable capital investment is implied, again approaching or exceeding $500K. Chromatography Chromatography separates molecules or ions by partitioning species between a moving and stationary phase. The technique exploits small differences in properties such as solubility, adsorbability, volatility, stereochemistry, and ion exchange, so that understanding the fundamental chemistry of these interac- tions is basic to progress in the field. Liquid chromatography has shown an impressive growth since 1970. The current $400M annual sales are mainly by U.S. manufacturers. The growth has come through innovations, such as high pressure and gradient moving phases to give greater speed and resolution, bonded-molecule stationary phases to give greater selectivity and column life, and electrochemical, fluorometric, and mass spectrometric detectors sensitive to as little as 1o-~2 g. Although gas chromatography is a more mature field by perhaps a decade, important advances continue to appear. High-speed separa- tions can now be accomplished in a few tenths of a second; portable instruments 271

272 CHEMISTRY AND NATIONAL WELL-BEING the size of a matchbox are in use. A complex mixture can be separated into literally thousands of components using fused silica capillary columns that are a direct spin-off from optical fiber technology for communications. It is even possible to separate compounds that differ only in isotopic composition. Despite this well established record of success, chromatography is still expanding its horizons. High-performance liquid chromatography and capillary column chromatography provide convincing examples of new concepts advanc- ing the field. High-Performance Liquid Chromatography (HPI~CJ During the 1970s, theoretical understandings of the complex flow and mass transfer phenomena involved in chromatographic band dispersion helped opti- mization of column design. During this same period, small diameter (3 to 10 micron) silica particles with controlled porosity were introduced and synthetic advances in silica chemistry led to tailoring of particle diameter, pore diameter, and pore size distribution. Today, 15-cm columns with efficiencies exceeding 10,000 theoretical plates are routine. The instrumentation ancillary to these high-performance columns required development of specialized pumps to drive liquid flows with high precision and low pulsation through the small particle columns. Detector advances occurred as well. First UV and refractive index, then more selective detectors based on fluorescence and amperometry/coulometry, were developed for HPEC. Still another major advance of the 1970s was the introduction of chemically bonded phases in which surfaces of porous silica are functionalized with organosilanes. Especially important is the use of hydrocarbonaceous phases (such as n-octy] and n-octadecyI) in which the mobile liquid phase is typically an organic-aqueous mixture. This is called reversed phase chromatography (RPEC), and it currently provides well over 50 percent of all HPEC separations. It is especially well suited to substances at least partially soluble in water (e drugs, biochemically ::3nd nolvn,~rl~r ~rom~t.ir.~) _' ~ or-- ^ Am. ____ ~ . .. . ~ .. ... . ~ _ ·= 7 1nus no IS a vlorant new wltn new crevelopments continually affecting many disciplines. New small particle supports based on silica and organic polymeric materials have recently been introduced for the ion exchange and reversed phase HPEC separation of biopolymers. Whereas separations previ- ously required days for completion, today it is becoming possible to accomplish 1 1 1 ~ · - · . ~ - ~ · . ~ ~ even netter resolutions within a tew minutes. (column design is improving as well. Instead of the conventional 4- to 5-mm diameters, narrower bore columns from .6-2-mm i.d. are providing routes to sensitive analyses even when the amount of sample is limited. Also, the lower flow rates at the same linear velocity permit coupling of LC to powerful vapor phase detectors, such as mass spectrometry and flame ionization. Open tubular capillary IN columns of 1- to 10-micron inner diameter are being investigated for the potential of generating high resolving power in the separation of extremely complex mixtures (e.g.,

V-E. INSTRUMENTATION fossil energy fuels). In all these examples, specially designed instruments are needed to accommodate the small sample sizes. Finally, the microprocessor/computer is playing an increasing role. "Smart" HPEC instruments are under development that use statistical optimization schemes. Semi-empirical solvent and stationary phase characterization schemes have been developed to enhance the power of these approaches. New detectors of greater sensitivity and selectivity are on the horizon. In particular, laser spectroscopy promises to yield highly sensitive devices for subpicogram detection. Because of these performance improvements, HPEC is having a major impact on diverse fields of biochemistry, biomedicine, pharmaceutical development, environmental monitoring, and forensic science. Today, peptide analysis and isolation requires HPEC because of its separating power and speed. Analysis of PTH-amino acids in protein/peptide sequencing is conventionally accomplished by RPEC. In clinical analysis, therapeutic drug monitoring can be accomplished by HPEC. The analysis of catecholamines is typically accomplished by RPEC with electrochemical detection. Isoenzyme analysis, important, for example, in assessment of damage after heart attack, can be rapidly accomplished by HPEC. Analysis of parent drugs and their metabolites in a pharmoco-kinetic study is typically accomplished by HPI,C. The isolation of synthesized drugs in purified form is typically achieved by HPEC. The analysis of polar and high-molecular- weight organic species in waste streams can be performed by EPIC, while the separation and analysis of phenols by RPEC is recommended. Analysis of narcotics, inks, paints, and blood represent only a few of the samples of forensic relevance. Capillary Chromatography This version of chromatography dispenses with the granular materials normally packed into the column. Instead, it uses an open capillary tube with a thin retentive layer on its inner wall. It began with capillary gas chromatog- raphy and now is being transferred to use with liquids. Although many satisfactory GC columns are available today, surface inves- tigations are continuing to improve the general understanding of thin liquid films and related superficial interactions. Glass as an inert material for the preparation of GC capillary columns carried with it a fragility that discouraged many potential users. Now we have flexible, fused-silica capillaries with a polymer overcoat; these columns are a spin-off of fiber-pntics technolo~v. The . . ... . . . . . . ,& ~" advances In capillary column recnno~ogy lea to intensive commercialization during the 1970s. Today's capillary columns exhibit efficiencies between 105 to 106 theoretical plates and are capable of separating literally hundreds of components within a narrow boiling-point range. As the corresponding chro- matographic peaks are separated by seconds or less, the sample input and output measurements must be comparably rapid. Direct introduction of samples at the nanogram levels has been developed, and much effort has been spent on 273

274 CHEMISTRY AND NATIONAL WELL-BEING optimization of gas-phase ionization detectors. Among these detectors are some of the most sensitive measurement devices known. Combined advances in the column and detector areas now make feasible trace analytical determinations below 10-~2-gram levels by capillary gas chromatography. The highly sensitive electron capture detector and element-specific detectors, in conjunction with capillary GC, currently find numerous applications in environmental and biomedical research. Of particular note is the combination of capillary GC with powerful identifi- cation methods, such as mass spectrometry and Fourier transform infrared spectroscopy, as mentioned in Section V-D. The combined techniques are now routinely capable of identifying numerous compounds of interest that are present in complex mixtures in only nanogram quantities. They have been used to identify new biologically important molecules, as well as in drug metabolism studies, forensic applications, and identifications of trace environmental pollu- tants. During the last decade, microcolumn high-performance liquid chromatogra- phy (HPEC) has been under intensive development. Two advantages are the reduced consumption of the expensive and often environmentally undesirable mobile phase and the possibility of exploring new detection methods. Open tubular columns and partially packed columns of"capilIary dimensions" have been tried. The open tubular columns for GC typically have 200- to 300-micron inner diameters to obtain optimal solute mass-transfer processes between the two chromatographic phases. Because of radial diffusion rates, liquid chroma- tography in open tubular columns necessitates considerably smaller column dimensions, as small as ~ to 10 microns, and nanoliter volumes are needed for both sample introduction and detection volumes. Packed capillary columns of dimensions ranging from 40 to 300 microns have now been developed that perform satisfactorily: several hundred thousand theoretical plate performance can now be achieved in several hours' time, and resolution of quite complex mixtures has been demonstrated. Microcolumn technology has recently found yet another application in capil- lary high-voltage zone electrophoresis. The small diameters (typically 60 microns) of open tubular columns permit application of voltages in excess of 30,000 volts without overheating. Very efficient separations of certain charged species were already demonstrated, but improvements are still needed. Capillary supercritical fluid chromatography has recently emerged as a promising approach to the analysis of complex nonvolatile mixtures. As the solute diffusion coefficients and viscosities of supercritical fluids are more favorable than those observed in the normal condensed phase, chromatographic performance is substantially enhanced. Furthermore, the relative optical trans- parency of supercritical fluids makes them attractive for certain optical detec- tion techniques. Besides its analytical potential, supercritical fluid chromatog- raphy appears to be an ideal method for measuring physicochemical parameters in the vicinity of the critical point.

V-E. INSTRUMENTATION Field-Flow Fractionation (FFF) Chromatography becomes more difficult to apply as molecular size grows and becomes ineffectual in separating macromolecules and colloidal particles in the size range .01 to 1 micron in diameter. A recent innovation, field flow fractionation, may fill this need. In FFF, a liquid sample is injected into a thin (.1-.3 mm), ribbon-like flow channel. A thermal, sedimentation, or electric field gradient is applied through the ribbon. Each constituent in the sample distributes itself in a steady-state concentration gradient that is determined by its response to the gradient and its diffusional properties. Since flow through the channel is fastest near the middle of the ribbon, constituents that are pulled close to the wall move more slowly through the ribbon than constituents that reside near the middle of the flow channel. Separations are thus achieved. A useful aspect of this technique is that the strength of the applied field can be varied in a deliberate and programmed way during the course of the separation. Thermal gradients are effective in separating most synthetic polymers. Sedimentation gradients separate large colloids, and electrical fields are appro- priate for charged species. Because of the range of operating parameters, FFT has proven capable of separating both charged and uncharged species in either chain or globular configuration. The method works both in aqueous and nonaqueous media. The mass range of molecules and particles to which FFF has been applied extends from molecular weights of 1000 up to 10~8, that is, up to particle sizes of about 100-micron diameters FFF appears to be applicable to nearly any complex molecular or particulate material within that vast range. Because the channel geometry and flow are well characterized, the rate of displacement of a given constituent can be related rigorously to such properties as mass, size, diffusivity, density, charge, and thermal diffusion rates. Hence, the above properties can be determined by measuring displacement rates, and FFT becomes an accurate tool for particle characterization. Applications of FFF have so far included macromolecules and particles of biological and biomedical relevance (proteins, viruses, subcellular particles, liposomes, artificial blood, and whole celIs), of industrial importance (both nonpolar and water soluble polymers, lattices, coal liquid residues, emulsions, and colloidal silica), and of environmental significance (waterborne colloids and fly ash). Costs Chromatography is an essential too] to every synthetic chemist and to analytical chemists in a variety of fields. An advanced analytical gas chromato- graph might cost $20K, an HPEC about the same, and a preparative (large volume) chromatograph somewhat more, perhaps $30K. While each item has only a modest cost, three or four such instruments will be needed as dedicated 275

276 an a: o CHEMISTRY AND NATIONAL WELL-BEING . instruments by each research group. Thus the total may approach $100K, a capital investment that must be available for effective research. Infrared Spectroscopy The infrared spectral region reveals molecular vibrational motions. Because these motions are sensitive to bond strengths and molecular architecture, infrared spectroscopy has become one of the routine diagnostic tools of chemis- try. A large, research-oriented chemistry department might operate five to ten such instruments with capabilities ranging from rugged, low-resolution instru- ments for instruction in an advanced first-year chemistry course to high- resolution Fourier transform instruments (FTIR) suited to molecular structure determination and specialized research use. Computer-Aided Spectrometers Modern research infrared spectrometers incorporate dedicated computer capability for programmed operation, data collection, and data manipulation. The major impact of computers, however, has been their influence on the accessibility and reliability of Fourier transform interferometers. As mentioned earlier in Section TTT-E, the perfection of the Fourier transform algorithm plus the reduction in accompanying computer costs brought the interferometer from a trouble-plagued, research-only instrument to a routine, high-performance workhorse. Spectral resolutions of .25 cm-i are readily obtained over a long scan range (e.g., 4000 to 400 cm- in 20 or 30 minutes. A notable capability is the ease and accuracy with which difference spectra can be displayed. One important application relates to infrared spectra of biological samples in which evidence of a chemical change associated with a localized biological function can be completely masked by the heavy infrared spectrum of the inactive substrate. The digitized data permit pre- cise spectral subtraction so that the background spectrum can be virtually eliminated to reveal the spectral changes of interest. Another vivid display of the value of the difference capability is provided by photolysis of molecules suspended in a cryogenic solid ("matrix isolations. If the digi- tized spectrum before photolysis is subtracted from the spectrum after photolysis, only the fea- tures that change are seen. Any molecule that is DIFLUOROPROPENE IN SO L I D KRYPTON, 12 4~ cis gauche hL`11 ~ 1 41 I gaucbet | ~rA4, cis1 1 400 1200 1000 V(cm l) s~ BEFORE PBOTOLTSIS (hi) Ha_ ~ DETER (hi)— BEEORE (hi) ~ __0 FTIR DIFFERENCE SPECTROSCOPY SHOWS ROTAMER INTERCONVERSION

V-E. INSTRUMENTATION being consumed presents its spectral features downward, while the product spectral features extend upwards. This has been used, for example, to distin- guish the two rotameric forms (cis- and gauche-) of 2,3,-difluoropropene in the cluttered spectrum of a complex mixture. Interconversion is caused by laser irradiation of one of the adsorptions of one rotamer. Applications The coupling of FTIR with gas chromatographic separations in a variety of analytical uses has been discussed in Section V-D. This coupling is facilitated by computerized data collection, and it is made possible by the reduced scan time that accompanies the high-performance characteristics of FTIR instruments. Also as noted in Sections V-A and V-D, infrared spectroscopy is a specially effective method for monitoring and studying atmospheric chemistry. This is because gaseous molecules of Tow molecular weight are important, including formaldehyde, nitric acid, sulfur dioxide, acetaldehyde, ozone, oxides of chlorine and nitrogen, nitrous oxide, carbon dioxide, and the freons. These substances are influential participants in photochemical smog production, acid rain stratospheric disturbance of the ozone layer, and the greenhouse effect. TABLE V-6 Additional Instrumental Techniques in Modern Chemistry Instrument Information Obtained Approximate Cost ($) Ion cyclotron resonance spectrometer Laser magnetic resonance spectrometer Laser-Raman spectrometer Fluorimeter Circular dichroism spectrometer Flow cytometer Protein sequencer Oligonucleotide synthesizer Electron diffraction Scintillation counter Reaction rates of gaseous molecular ions Precise molecular structures of gaseous free radicals Vibrational structure of molecules or of chromophores in complex Energies and lifetimes of electronically excited molecules Stereoconformations of complex molecules Laser-activated cell sorter Automated analysis of protein sequence Automated synthesis of design oligonucle- otides Molecular structures of gaseous molecules Tracking radio-tracers through chemical reactions 125K 75K 60K 40K 50K 150K 120K 40K 150K 50K Costs Fourier transform infrared spectrometers are now sufficiently easy to use- with the high performance described above that they are becoming ubiqui- tous. In 1983, perhaps 200 such instruments were sold by U.S. companies, and foreign instruments are appearing (from West Germany and Canada). Costs 277

278 CHEMISTRY AND NATIONAL WELL-BEING currently range from $140K to $200K, depending upon the resolution and scan range. Accessories permit long-wavelength spectroscopy to 10 cm-i and near- infrared spectroscopy reaching into the visible. Other Instrumentation In Sections IlI-E, IV-E, and V-E, there has been explicit discussion of more than a dozen different classes of instrumentation that are important in defining and advancing the current frontiers of chemistry. By no means, however, is the list all-inclusive. Table V-6 lists additional types of equipment, what kinds of chemical information each one provides, and approximate current costs. Plainly, these, too, contribute to the capital investment needed to sustain frontier research in chemistry.

Next: VI. Manpower and Education »
Opportunities in Chemistry Get This Book
×
Buy Hardback | $60.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Opportunities in Chemistry is based on the contributions of hundreds of American chemists in academia and industry and should be taken as the best available consensus of the chemical community regarding its intellectual frontiers and the economic opportunities that lie beyond them," says Science. This volume addresses the direction in which today's chemical research is heading, including recent developments, technological applications, and the ways advances in chemistry can be used to improve the human condition. In addition, the book examines economic and political implications of chemical research and lists resources for basic research and education in the chemical sciences.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!