Opportunities in Chemistry (1985) / Chapter Skim
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V. Chemistry and National well-Being
V. Chemistry and National well-Being
Pages 193-278
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From page 193... ...
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.
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From page 194... ...
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.
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There are innumerable examples to prove that this is not a generally applicable premise. Consider carbon monoxide (CO)
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From page 196... ...
For example, an active research area is connected with separation techniques to allow rapid and unequivocal analysis 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
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From page 197... ...
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.
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From page 198... ...
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)
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From page 199... ...
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.
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From page 200... ...
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.
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From page 201... ...
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 revolutionized by some of the recent advances in analytical chemistry.
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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.
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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)
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Problems are sometimes encountered in extrapolating from laboratory experiments and computer-based models to actual field conditions. 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.
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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.
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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
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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)
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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.
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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.
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The time scale of the recently perceived decline is short, and projections are risky. The only prediction that is easily made is that changes are inevitable.
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V-B. CONTINUED ECONOMIC COMPETITIVENESS energy sources.
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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.
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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.
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Increasingly, progress depends upon a deep understanding 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.
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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.
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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.
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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.
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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.
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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.
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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.
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V-B. CONTINUED ECONOMIC COMPETITIVENESS research that maintains the knowledge base from which we derive our competitive edge.
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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.
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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 resistance all of which contribute to and determine the electiveness, cost, and useful life of weapons systems.
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From page 224... ...
and from each other. It has applications in such diverse areas as the nuclear fuel cycle, analytical chemistry, and biochemistry.
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Future availability of such elements as chromium, the platinum group elements, and others may depend critically upon developing chemical separations pro225 TABLE V-2 U.s. Import Dependence, Selected Elements (Imports as Percent of Apparent Consumption)
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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 surveillance 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.
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From page 227... ...
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.
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From page 228... ...
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 production and destruction, efficiency of use of the fissionable material, and breeding capabilities.
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From page 229... ...
A solution is provided by tuned laser excitation in a mass spectrometer. At the resonant laser frequencies at which lutecium can be photoexcited to ionization, the ytterbium back229 THERMAL Ytterbium Background Yb J he in T I Yb~ r 1 j ~ 1 1 ~ .
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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)
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From page 231... ...
Detonation Chemistry Conventional condensed-phase explosives yield detonation waves with velocities 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.
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From page 232... ...
Somewhat analogous to the studies of detonation and explosion 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 unravel rapid, complex chemistry at the molecular level is considerably more advanced and pervasive in the study of propellants than it is in the study of explosives.
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From page 233... ...
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.
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From page 234... ...
In operation, the atmospheric sample flows continuously through an electrical discharge, and the ions produced 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)
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From page 235... ...
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)
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From page 236... ...
Furthermore, periodically, stores of obsolete munitions containing chemical agents must be destroyed. Methods currently available are prohibitively costly and hazardous.
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From page 237... ...
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.
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From page 238... ...
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From page 239... ...
Slowly, this papermaker'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 *
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From page 240... ...
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.
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From page 241... ...
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 chemistry and chemical engineering.
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From page 242... ...
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.
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From page 243... ...
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.
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From page 244... ...
The characteristic 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.
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From page 245... ...
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.
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From page 246... ...
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.
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From page 247... ...
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.
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From page 248... ...
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.
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From page 249... ...
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.
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From page 250... ...
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.
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From page 251... ...
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.
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From page 252... ...
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.
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The more powerful computers of the future will digest the huge volumes of data from spectroscopic methods (especially Fourier transform and two-dimensional methods) much more efficiently.
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From page 254... ...
N2O . 1150 1200 1250 1300 FOURIER TRANSFORM INFRARED N IGHT SKY SPECTRUM over 1 mile; fluorescence excitation and pulsed laser Raman with time-resolved ranging are particularly prom· ~ slng.
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From page 255... ...
Secondary Ion Mass Spectrometry (SIMS)
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From page 256... ...
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)
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From page 257... ...
Understanding surface chemistry demands unusual information, 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)
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From page 258... ...
The increasing 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 methodology 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.
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From page 259... ...
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.
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From page 260... ...
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)
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From page 261... ...
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 nuclear reaction mechanisms, and even the discovery of new modes of radioactive decay (proton emission and 2-neutron emission)
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From page 262... ...
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.
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From page 263... ...
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.
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From page 264... ...
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.
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From page 265... ...
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.
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From page 266... ...
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)
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From page 267... ...
inert gas ions. Ton scattering spectroscopy determines the surface composition by the energy change of inert gas ions upon surface scattering.
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From page 268... ...
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)
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From page 269... ...
Surface Analysis As is always the case, sensitive measurement techniques can be regarded as analytical tools. This is the case in the surface sciences.
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From page 270... ...
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.
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From page 271... ...
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 .
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From page 272... ...
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.,
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From page 273... ...
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.
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From page 274... ...
Of particular note is the combination of capillary GC with powerful identification 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.
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From page 275... ...
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.
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From page 276... ...
Because these motions are sensitive to bond strengths and molecular architecture, infrared spectroscopy has become one of the routine diagnostic tools of chemistry. A large, research-oriented chemistry department might operate five to ten such instruments with capabilities ranging from rugged, low-resolution instruments for instruction in an advanced first-year chemistry course to highresolution Fourier transform instruments (FTIR)
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From page 277... ...
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 oligonucleotides 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 usewith the high performance described above that they are becoming ubiquitous.
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From page 278... ...
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.
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