A novel thermal detection scheme has been developed and combined with the techniques of rapid scan Fourier transform infrared spectroscopy to make sensitive, high resolution measurements of the vibrational spectrum of carbon monoxide molecules on evaporated nickel films. Adsorbed molecules are detected by attaching a germanium resistance thermometer to the sample, cooling the assembly to liquid helium temperatures, and measuring the temperature changes which occur when infrared radiation is absorbed. Spectra are presented for a range of CO coverages on an evaporated nickel film and a film damaged by ion bombardment. The positions, shapes, and intensities of the spectral lines from linear and bridge bonded CO molecules give information about the surface structure of the metal films and about the different ordered phases of the adsorbed molecules.

Fourier transform infrared spectroscopy (FTIR) is a powerful tool for studying surface species present on supported catalysts during normal reaction conditions of high temperature and/or pressure. We have used a special high-throughput optical bench to optimize the sensitivity of the system for high optical density catalyst samples. The infrared cell is designed to operate at high vacuum for adsorption studies or as a recycle-flow reactor. Improvements in spectral subtractions have been obtained by the precise repositioning of samples in the IR beam. The enhanced performance resulting from these modifications has been instrumental in improving the sensitivity for infrared surface studies of the reactions C6H6 + 3H2 ⇔ C6H12 and 2C0 + 02 → 2CO2 over a Pt/A1203 catalyst. The bonding and geometry of benzene chemisorbed on the Pt surface have been determined from the infrared spectra. Simultaneous reaction rate and surface coverage measurements have also been made during CO oxidation on Pt/A1203. Hysteresis effects in both reaction rate and CO surface coverage are observed. The IR spectra indicate that islands of CO form on the Pt surface during reaction.

Infrared spectroscopy is one of the most widely used techniques for characterizing the molecular structures of species present on a catalyst surface. By using a Fourier-transform spectrometer, high quality spectra can be obtained in times as short as a few seconds, making it possible to investigate the dynamics of adsorption, desorption, and reaction of selected structures. This paper will illustrate several applications of this technique to studies of NO adsorption/desorption and CO hydrogenation over supported rhodium and ruthenium catalysts.

Low temperature matrix isolation spectroscopy has been developed over the past two decades into a powerful technique for the study of reactive chemical species. When reactive molecules, radicals or ions are trapped in low concentrations in a frozen film of an unreactive material such as argon, they may be studied spectroscopically without the use of rapid scanning instrumentation. This technique is especially suited to the study of vibrational spectra of trapped species. The sharp vibrational absorptions observed in the absence of complicated rotational structure are well suited for study by high-resolution Fourier-transform infrared spectroscopy, especially in studying compounds containing natural abundance or enriched isotopes. High resolution FTIR spectroscopy has been used recently in this laboratory to observe natural abundance chlorine isotope splittings in the IR spectra of ions produced by illuminating matrix isolated methylene chloride with 11 eV photons. Isotopic effects on complexes of hydrogen fluoride and ethylene in solid argon have also been successfully studied using high resolution FTIR techniques.

Polar molecules (such as acetonitrile, cyanoacetylene, acetone and nitromethane) imbedded in solid inert gas matrices give rise to different types of IR absorption bands in a spectral range where intramolecular vibrations may be excluded, i.e. below 150 cm^-1. Phonon bands of Ar, Kr and Xe are activated in the range below 72 cm^-1. Below 90 cm^-1 translational ("rattling") and librational modes of monomer molecules relative to the cage of inert gas atoms were observed. Between 80 and 130 cm^-1 the IR active intermolecular vibrations of antiparallel dimers appear. - Owing to the low energy throughput typical for the spectral range below 100 cm^-1 these studies had to be carried out using a Fourier spectrophotometer and not a dispersive system.

Low temperature matrix spectra of alcohols have been investigated in the region 50 cm^-1; to 400 cm^-1. Vibration frequencies associated with the hydrogen-bonded system R-OH...0 and the torsional modes have been assigned. From studies of the pure alcohols and from the concentration dependency of the observed bands it was found that the hydrogen bond stretching frequencies (ν_σ) appear in the 100 - 160 cm^-1; range. At higher M/A ratios the OH torsion modes (τ_OH) were identified in the 200 - 300 cm^-1; region. The influence of various matrix gases on the absorption frequencies has also been studied.

A double-beam optically compensated Fourier transform spectrometer is described. The sensitivity of the instrument is superior by a factor of 5 to 10 compared to the results obtained with a normal single-beam FTS using the same detector and measuring time. The instrument was used for the investigation of far-infrared vibrational spectra of amorphous Si and Ge and the crystalline alloy. The studies have been made on pure and hydrogenated amorphous Si and Ge, on deuterated and fluorinated amorphous Si, on phosphorus- or boron-doped amorphous Si and crystalline Si-Ge alloys. We found fine structure in the phonon spectra of the pure amorphous materials. By introducing lighter impurities, a resonant mode is also found, both in the amorphous and the crystalline cases. A strong increase of the TO band upon doping has also been found in the amorphous case. These spectra are compared with the vibrational density of states of the crystalline materials.

The amplitude and phase reflection spectra of InAs have been determined in the far infrared at room temperature by dispersive Fourier transform spectrometry and used to calculate the optical constants, dielectric response functions, and the anharmonic damping function of the q = 0 transverse optic mode. The overall features of the optical and dielectric functions are in good agreement with published work, but a number of new features associated with phonon combination bands are revealed for the first time, particularly in the damping function. The application of such measurements to the determination of improved values of critical point phonon frequencies in InAs and other zincblende structure crystals is discussed.

Of major technological importance is the need for high purity gallium arsenide, including the requirements to characterize and control the impurities in gallium arsenide. As a contribution to meet these goals, an extensive infrared investigation has been made on several wafers of semi-insulating GaAs:Cr at room and helium temperatures. Measurements were made around the plasma edge to search for carbon and oxygen impurities, while the near infrared results around the optical band edge of GaAs indicate the presence of a chromium acceptor at approximately 0.69 eV from the valence band. A comparison is also made with the neutron activated analysis of Martin et al.

Fl-IR spectra of Czochralski silicon crystals containing interstitial oxygen impurity have been recorded from 15K to room temperature. The major bands due to the oxygen impurity show intensity and frequency changes. These changes can be discussed in terms of a model for the oxygen atom moving in a potential with six-fold axis as described by Hrostowski and Adler.

Fourier transform infrared spectroscopy is shown to be a useful technique for structural studies on intercalates of iron oxychloride. Mid-infrared measurement yields information regarding the orientation of the guest molecule in the host lattice. Far-infrared studies reveal the effect of the guest molecule on the iron oxychloride lattice.

It has been shown that sample concentration fluctuations in rapid-scanning time-resolved experiments result in anomalies that can easily be misinterpreted as spectral features of transient species.¹ It is also known that these spectral features result from band displacement rather than aliasing. A quantitative explanation of the phenomenon will be presented which will discuss the origin and frequency of these spectral anomalies.

The development of Fourier transform infrared spectroscopic studies of pulsed transient phenomena, using rapid scanning interferometers is described. Early results obtained using this technique have been shown to have been misinterpreted. Some problems that have been encountered are described and systems of interest discussed.

Recently, we have explored the application of time resolved spectroscopy (TRS) to stretching and relaxing polymer films and we find TRS to be a very promising new diagnostic technique. Although the time interval, which is micro-seconds, is much slower than the observations made by researchers in the ultraviolet and visible regions, there exists several important experiments in this time frame which should yield important scientific information.

Complex heterogeneous reactions can be studied by a variety of techniques including on-line GC or GC--MS. These methods suffer from several problems including the need for sampling. The need for a separation and especially for GC-MS, a dependence of the "cleanliness" of the mixture to be analyzed.

The autoxidation reactions of hydrazine (HZ), monomethylhydrazine (MMH), and unsymmet-trical dimethylhydrazine (UDMH) at concentrations of 1 to 30 parts-per-million (ppm) were studied under simulated atmospheric conditions by long-path Fourier transform infrared spectroscopy in a 60-liter glass chamber. The observed reaction products for HZ were water and ammonia; for MMH they were methane, methanol, water and methyldiazene; and for UDMH it was formaldehyde dimethylhydrazone. Half lives were 133 minutes for HZ, 250 minutes for MMH, and 83.5 hours for UDMH.

Infrared spectroscopy is an excellent tool for examining the functional group changes occurring during photochemical reactions. Historically, this has been done by monitoring a single infrared wavelength during the irradiation. The development of interferometer hardware and software for rapid scanning and "on the fly" GC-IR have produced equipment equally applicable to the study of any time-dependant phenomenon where the requisite temporal resolution is .5 seconds or longer. We have used FT-IR spectroscopy to study several liquid and solid phase photochemical systems using both transmission and diffuse reflectance techniques. The multiplex nature of the experiment allows the simultaneous monitoring of any number of infrared frequencies related to products, reactants or intermediates.

The FT-IR spectra of liquid chromatographic fractions obtained using a flow-through liquid cell and an apparatus involving solvent-elimination and diffuse reflectance are compared. When working with complex mobile phase systems necessary for producing good LC separation, the diffuse reflectance method is capable of much higher sensitivity than the flow-cell technique. Examples of the sensitivity levels achievable with the diffuse reflectance method are presented.

In previous papers on HPLC/FT-IR from Ohio University, we have stressed the substantial reduction in detection limits that can be achieved if the mobile phase is completely removed from the solute prior to the measurement of the infrared spectrum of each solute (or "HPLC peak"). The most effective way of achieving this end which we have described to date^{1, 2}; has been to concentrate the solution eluting from the chromatograph by differential evaporation, and to deposit each peak onto a hollow cup containing KCl powder. After a final solvent elimination step, the diffuse reflectance infrared Fourier transform (DRIFT) spectrum of each peak is measured, with the operation of the entire HPLC/FT-IR interface being controlled by a microcomputer.

The development of a new, versatile beam condenser system for FT-IR spectrometers will be described. Primarily designed for use with the diamond-anvil high pressure cell, it also serves as a very convenient accessory for general microsampling. A major advantage of the system is the routine capability to visually observe the sample, using conventional optical microscopy, while the sample remains in place in the spectrometer. This adds a powerful tool to spectral studies of phase transitions, decompositions, kinetics, and distributions in microscopically heterogeneous samples. Applications of the system in high pressure studies of model lubricants will be discussed.

Most optical spectrometers can be readily used only for simple transmission measurements. The capability of these instruments for reflection (internal, external and diffuse) spectroscopy can be extended by providing adequate accessories. The versatility and ease for such measurements depends on the ingenuity of the design of the accessories. A variety of designs which enhance the spectrometers capability will be described. Beam condensers, which are playing an increasingly important role in all phases of optical spectroscopy, will also be discussed.

Absorbance subtract FT-IR suffers from weak intermolecular perturbations, which cause residual differences to remain after the constituents of the sample have been subtracted out. This problem can be redefined into a solution by using precisely these shifts as diagnostics for interesting sample features, in a manner similar to NMR shift reagents. Unlike the NMR case, however, the shifts are typically smaller than the bandwidth, and subtraction is required for their observation and that of the simultaneous intensity effects. The procedure has been demonstrated for a variety of applications, including optical isomer resolution, isolation of spectral features of one compound from those of a mixture, determination of site accessibility on a molecular scale, measuring physical cross linking in a polymer, and following chemical equilibria in samples.

We describe a compact, high resolution portable Fourier Transform Spectrometer for use at the Cassegrain focus of an astronomical telescope. The interferometer is dynamically aligned by continuously adjusting the tilt of the fixed mirror under the control of a servo system which monitors laser beams traversing the optical system. Resolution up to 0.02cm^-1 can be obtained in the spectral region 0.8 to 3 μm. Examples of astronomical spectra are given.

Spectroscopy of astronomical objects in the mid- and far-infrared region will contribute substantially to our understanding of basic astrophysical processes (e.g. formation of stars and galaxies). Therefore, a Michelson Interferometer is being built for line spectroscopy in the wavenumber range below 500 cm^-1 allowing a maximum spectral resolution of 0.03 cm^-1 for a field of view between 1 and 3 arcmin. Several specific components are used in the helium cooled environment (heat loss permitted ≈200 mW): (i) a special type of stepping motor driving a ball pivot, (ii) a corner cube reflector for tilt compensation, (iii) a diode laser measuring the path difference, (iv) piezoelectric transducers for mirror alignment, (v) high sensitivity photoconductors giving a NESR = 8 x 10^-13 W/(cm² sr cm^-1) which is orders of magnitude lower than for comparable astronomical instruments that exist. The instrument shall be used aboard the German Infrared Laboratory (GIRL) which is an infrared astronomy observatory on SPACELAB to be flown in 1986.

High resolution Fourier transform spectroscopy at the University of Oulu is based on the double-beam Fourier transform spectrometer constructed here. The instrument works between 20 and 1200 cm^-1 with a practical resolution of better than 0.010 cm^-1. The maximum optical path difference in the interferometer is 1.5 m giving a theoretical resolution of about 0.004 cm^-1. The wavenumber precision of the instrument was found to be ±0.0005 cm^-1. The practical resolution is limited by a signal-to-noise ratio accepted in spectral analysis. In the far infrared noise mainly originates in the detector and radiation source (black body radiator). Some new techniques aimed at eliminating these disadvantages will be presented. Also, some new computation methods will be pointed out.

An earlier paper described a family of two-beam interferometers in which path length scanning is accomplished by translating a wedge shaped refractive element across one of the interferometer arms. These refractively scanned interferometers (RSI's) were shown to have a number of theoretical advantages over conventional moving mirror Michelson interferometers. The present paper discusses the practical implications of these advantages, provides experimental confirmation of their magnitudes, and presents data illustrating the overall performance of one particular RSI design, the "TRANSEPT" interferometer.

This report describes the calibration procedures required for a Michelson Interferometer Spectrometer. Two separate calibration procedures are described, one for spectral radiant sterance (spectral radiance), and one for spectral radiant intensity measurements. The Michelson Interferometer Spectrometer is one of two primary sensors included in the Electro-Optical Target Signature Sensor System.

First order velocity variations in the moving mirror of typical interferometer spectrometers are usually compensated for by using a HeNe laser in the system to provide an accurate path difference monitor. The second order effects due to amplitude and phase distortion in the signal train analog band pass filter can be the dominant source of noise and distortion in the spectrum and, therefore, significantly effect the overall system design. Experimental studies of the important parameters effecting this distortion have been compared to the theoretical calculations of Zachor et al.

We have obtained infrared emission spectra (600-2000 cm^-1) from room temperature samples of reflective metal substrates with organic overlayers using a liquid nitrogen cooled interferometeroequipped with a liquid helium cooled Ge:Cu detector. Overlayer thicknesses as low as ≈10 Å have given good spectra. Spectra were obtained with a modified Digilab 14-B interferometer operating at 2 cm^-1 resolution. The viewing angle of the sample was usually ≈55° from the surface normal and a polarizer was used in some runs to obtain improved signal to noise. The spectra were corrected for instrument response function, substrate background and thermal populations and emission efficiencies of excited vibrational states.

The use of high frequency differential interferometry makes it possible to extract very weak signals from a large unmodulated background, as was first shown in transmission studies of circular vibrational dichroism. We have combined this technique with a liquid nitrogen cooled interferometer (modified Digilab Model 14B) and a liquid helium cooled Ge:Cu detector to detect the weak luminescence (≤10^-9 watt) between 1700-2000 cm^-1 emitted during bombardment by low energy electrons (0.8 mA @ 100 to 500 eV, frequency 10 KHz) of a single crystal of n-doped InSb (⪅ 10¹⁴-carriers/cm³) at 80K. For an absolute signal of 10^-10 watt, our signal-to-noise ratio for 100 scans is (≈1O-50 for respective resolutions of 2-16 cm^-1 while the overall background above 1000 cm^-1 is ≈10⁵ times larger. Without modulation the signal-to-noise ratio is one to two orders of magnitude lower. From our results it is clear that a substantial improvement in signal-to-noise ratio can be obtained in emission studies where the mechanism is fast enough to respond to high chopping frequencies such as electron or photon stimulated luminescence, field modulated emission and fast chemiluminescence.

A feasibility study performed with an unmodified FTIR spectrometer has shown that IR-emission spectroscopy is a potential analytical technique for studying surface layers. Thin layers give the best spectral contrast, while thick layers tend to resemble a black body. For quantitative analyses effects of saturation, selective reflection and self-absorption have to be taken into account.

Fuel and lubricant deposits on solid surfaces, though often of similar visual appearance, differ in composition, depending on the nature of the deposit formers and the circumstances of deposition. To help establish these relations an Infrared Emission Fourier Polarization Microspectrophotometer was constructed to record infrared spectra from the deposits on their original support. By focussing on small aggregates with a reflecting microscope objective and by discriminating against the randomly polarized blackbody radiation with a rotating polarizing filter phase-locked to an amplifier, excellent Fourier emission spectra of polarized bands could be obtained. In many instances, the microscope objective was adequate without the polarizer. The analysis was calibrated against a very thin film of polyethylene terephthalate attached to a highly reflective aluminum mirror on the sample positioner.

Photoacoustic FT-IR spectra recorded using a new photoacoustic cell are described. The study of the photoacoustic spectra of cast films of Plexiglas of different thicknesses shows that the depth of penetration of the FT-IR photoacoustic experiments is of the order of a few micrometers and that photoacoustic saturation effects play a key role in the qualitative appearance of the spectra. These differences can be misinterpreted as due to structural changes in different layers of the sample.

The photoacoustic effect, discovered a century ago, has only recently been developed as a viable analytical tool in the industrial laboratory. PAS in the UV/visible region is well established and commercial instruments are available which use conventional lamp sources. PAS has been less successful in the mid-IR region, which is the most important for analytical purposes and is the domain of classical IR spectroscopy. With the advent of Fourier transform infrared spectrometers and their powerful multiplex ability, photoacoustic FT infrared spectroscopy (FT-PAS) is becoming a more routine analytical tool.

Photoacoustic infrared spectroscopy has been used to study the interactions of a carbamate insecticide with a clay carrier. The ability of photoacoustic infrared spectroscopy to measure infrared spectra from opaque samples non-destructively, is particularly valuable in this study where weak bonds might be destroyed by sample grinding. The results of this study show that the strong N-H stretching modes, which appear at approximately 3300 cm^-1 in in the pure insecticide, are missing in the subtraction of the N-H group spectrum. This suggests that the hydrogen attached to the nitrogen of the carbamate is forming a reasonably strong bond with the hydrated silicate structure of the clay carrier. This interaction may effect the release rate of the pesticide upon application.

Measurement of the spectrum of certain types of solid samples has always presented infrared spectroscopists with a problem. Although some solids can be pressed into a KBr disk, ground into a mineral oil mull, contacted with an internal reflection element, or even pressed into a self-supporting wafer, by no means all samples fall into one of these categories. For example, recognizable spectra of chunky polymer samples which are not easily ground or dissolved, and which are too hard to afford good contact with an ATR plate, are always difficult to measure. Similarly the problems of measuring the spectra of species adsorbed on the surface of catalysts and other adsorbents have usually given surface chemists some difficulty. If the sample is pressed into a self-supporting wafer and the transmittance spectrum is measured after the fashion first described by Eischens, scattering at high wavenumber and absorption by the adsorbent (typically below 1200 cm^-1 for silica and alumina) severely reduce the signal-to-noise ratio (SNR) of the measured spectrum. Another less commonly recognized problem with this type of sampling technique is that once the wafer is pressed, the surface area available to the adsorbate is considerably reduced.

The diffuse reflectance FT-IP spectra obtained using three different accessories are compared and discussed. The presence of specularly reflected radiation in the diffuse radiation can lead to distortions of the relative band intensities in the recorded spectra. Spectral subtractions can be performed on the diffuse reflectance spectra, when the spectra are presented in the Kubelka-Munk format.

Diffuse reflectance (DR) sampling techniques for FT-IR spectroscopy are finding increasing use as an alternative to pressed halide disks of powdered materials. Recently, the diffuse reflectance technique has been applied to FT-IR microsampling and to recalcitrant materials.

The vast majority of infrared spectrometry of surface species is currently performed using the same type of sampling technique described by Eischens et al. in 1956, in which the transmittance of a very thin disk of the adsorbent is measured. Although a wealth of data on surface species has been obtained in this way, the transmittance of the samples is quite low across the spectrum, especially at very high wavenumber (where scattering is greatest) and at low wavenumber (where most adsorbents exhibit strong absorption bands). Other techniques which have been studied include reflection-absorption (R-A) spectrometry, for which only very weak bands due to adsorbed species at monolayer or partial monolayer coverage can be observed, and emission spectrometry, which is plagued by severe emission from the adsorbent and the effect of temperature gradients.

In the few years of its existence, diffuse reflectance infrared Fourier transform (DRIFT) spectrometry has been applied to the qualitative analysis of a wide variety of samples. These include coals, adsorbed molecules, HPLC effluents, biopolymers and synthetic polymers. Far fewer quantitative determinations have been performed by DRIFT spectrometry. Nevertheless, it is our belief that there is no insurmountable reason why DRIFT should not become a powerful tool for the quantitative analysis of powdered samples.

Infrared reflection-absorption spectroscopy is a technique that can be used to study molecules adsorbed in monolayer and submonolayer concentrations on low-area metal surfaces. The results from four experimental approaches, each involving polarized light reflected off flat metal surfaces at near-grazing angles of incidence, have been compared. The approaches are (1) an optical-null experiment on a double-beam dispersive spectrometer, (2) a fixed-polarizer experiment using FTIR, (3) a polarization-modulation single-heam experiment on a dispersive spectrometer, and (4) a polarization-modulation experiment using FTIR. A thin film of cellulose acetate on copper is examined. The polarization-modulation FTIR approach gives the best results for this system.

Fourier Transform Infrared Spectroscopy (FT-IR) has already been used for determining many characteristics of polymers. We have combined several different techniques, which were used independently of each other on the FT-IR, to determine the glass transition temperature of polymeric films. Recently a microprocessor temperature programmer has been interfaced to our Nicolet 7199 FT-IR spectrometer. This allows us to easily follow chemical reactions by infrared as a function of temperature. Changes in the infrared spectrum as the sample goes through phase transitions can be easily detected. The samples of interest in this study are epoxy polymers cured onto fiberglass fabric. The samples are approximately 200μ thick. Infrared characterization of these samples had been obtained using variable angle ATR. In order to determine the glass transition temperature of these polymeric materials, our ATR accessory was modified so that the polymer sample could be heated while ATR spectra were being obtained. The experimental details and results from this study are presented.

A brief comparison of different FT-IR techniques for analysis of a polymer film on a me-tal surface is made. DRIFT (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is used to obtain spectra of thin films of polystyrene on metal and glass substrates. Band intensities measured for different thicknesses of free polystyrene films are found to follow correctly the Kubelka-Munk theory relating concentration and band intensity.

The "on-the-fly" acquisition of infrared spectra from the vapor eluting from a gas chromatograph has become a routine analytical technique. From the spectroscopic viewpoint, GC/IR appears to be a very simple experiment, and yet in many ways, the technique places the greatest demands on both the hardware and the software of any infrared experiment. The fact that the gas chromatograph vaporizes and ideally separates the sample means that the spectrometer is observing vapor phase, ambient pressure and pure compounds. While this may seem ideal, the sensitivity requirements and data acquisition rates required for real time GC/IR can be obtained only with an optimally designed system.

Selected tradeoffs involved in the design of Gas Chromatography/Fourier Transform Infrared Spectroscopy (GC/FT-IR) software are discussed. The merits of saving absorbance spectra rather than interferograms are presented. Three different methods of chromatogram reconstruction are evaluated and compared with each other. Finally, automated methods for detecting peaks and constructing component spectra are discussed.

The evolution of GC/FT-IP over the past ten years has seen the technique grow from a novel curiosity into a powerful analytical tool. The detection limits of the technique, a prime factor in many analyses, has decreased from many micrograms in the early days down into the low nanogram range over the past few years. Similarly, capillary column gas chromatography has evolved into a very powerful separation technology. GC/MS workers have taken advantage of this advance in separations technology yet capillary CC/FT-IF, has recently just started to be seriously explored.

The GC/FT-IR experiment is analyzed to determine the requirements for an effective system, including the types of information it should provide and the data processing this implies. To emphasis the special problems and advantages of GC/FT-IR, a comparison is made to the more mature technology of GC/MS. The particular solutions developed for Digilab's new generation of GC/FT-IR systems are examined in detail.

The effects of signal-averaging in Fourier transform infrared spectrometry (FT-IR) have been well characterized and are well known. In some applications, such as aas chromatography/Fourier transform infrared spectrometry (GC/FT-IR), it may be necessary to collect single-scan interferograms. There is considerable interest in the direct processing of interferometric data as opposed to spectral domain data processing. Areas of study to which interferometric data handling have been directed are chromatogram reconstruction, search systems and compound classification. Any instability in the interferometer leads to noise in the interferogram. The character of this noise and its effects have been investigated.

Earlier work in this laboratory has shown matrix isolation Fourier transform infrared spectrometry (MI FTIR) to possess several advantages over conventional sampling techniques for the qualitative analysis of complex samples. The ability to obtain very sharp spectra using MI makes it possible to distinguish between very similar compounds, including isomers, present in a sample. Instrumentation to couple capillary column gas chromatography (GC) to MI FTIR has been developed as an alternative to on-the-fly gas-phase GC FTIR measurements. This technique allows leisurely study of chromatographic fractions at medium resolution (1 cm^-1). A gold-plated disk is cooled to 15K with a closed-cycle helium refrigerator and used to collect compounds eluting from the GC. Nitrogen is used as both GC carrier gas and matrix material. Beam condensing optics and KRS-5 rods are used to reflect the IR beam from the individual sample deposition surfaces.

Laboratory mixtures of terpenoid compounds and crude fractions extracted from native plants have been subjected to analysis by GC-FTIR. Positive identification is relatively straightforward for compounds whose relative retention times are sufficiently different, and proper choice of the stationary phase in the GC column can ensure satisfactory results for this class of compounds. Preliminary work with capillary GC columns has also been carried out, and the results of the various experiments are discussed.

After pesticides in bait formulation have been applied in the field, it is important that the fate of that amount of toxicant which has not been consumed by the pest is known. Many of these substances are not compatible with the environment and it is also important that their biodegradation be understood and controlled to a certain extent. In efforts to monitor and direct these reactions GC-IR has been found to be an invaluable tool.

A GC/MS has been interfaced to an FT-IR so that real time MS and IR spectra are recorded on the identical sample. After much effort at optimizing the match between the GC and the IR, it was found that a nearly optimum trade-off between resolution and sensitivity was obtained using a SCOT column. To preserve the CC resolution, a makeup gas flow was used with a standard light pipe to optimize flow rates and conditions in the FT-IR. Further steps in this optimization include small sized detectors and matched light pipes which are currently being prepared. The GC/MS and GC/IR are coupled in parallel by a constriction splitter operating in Mach limited flow, with about 90% of the sample going to the infrared system. Initially, the computer library search outputs of both systems were integrated manually, but the output from the separate HP21MX (GC/MS) and Nova 3 (FT-IR) mainframes is being gradually integrated for combined data processing. Further integration of GC retention times into the qualitative interpretation is being planned. The ternary GC/MS/IR hyphenated instrument has shown the following advantages over its binary ancestors: (1) Added resolvability of overlapping peaks, particularly those involving isomers. (2) Simpler end searches by comparing the hit lists from the IR and MS spectral searches. (3) Complementary structural information on samples where library searches were unsuccessful.

A GC/FT-IR interface is described which operates with the small FX-6200 FT-IR spectrometer manufactured by Analect Instruments. The packed column GC/FT-IR instrumentation is coupled in series to a MS to demonstrate the major analytical capabilities of GC/FT-IR/MS. Infrared and mass spectra of a standard mixture separated and identified by GC/FT-IR/MS is shown. A MS total-ion reconstructed gas chromatogram (RGC) demonstrates separation efficiency of the coupled instrumentation.

FT-IR spectroscopy has been used to study micelle formation in aqueous sodium alkanoate systems. The critical micelle concentration ranges of sodium propionate through to sodium decanoate and the Krafft transitions of sodium laurate and sodium oleate were investigated. It is shown that FT-IR is a sensitive technique for such studies.

The lipid components of the plasma membrane of the microorganism A. laidlawii B undergo a temperature induced phase transition. The biosynthetic incorporation of deuterated fatty acids into these membranes has allowed, via the C-D stretching vibrations, a detailed study of the lipid organization and dynamics, and the effect of the intrinsic membrane proteins on the transition. A number of fatty acids, of different chain lengths, have been incorporated biosynthetically in the presence or absence of avidin, a fatty acid synthesis inhibitor. In this manner the membranes are enriched solely in the added deuterated fatty acid up to high levels of homogeneity, providing an excellent system for the study of lipid-protein interactions. Detailed data regarding the lipid thermal behaviour will be presented and compared with results obtained by means of other techniques.

The influence of sterilization on the bulk and surface morphologies of a copolyether-urethane-urea was studied. The bulk morphology was altered due to annealing by autoclaving and ethylene oxide sterilization. Radiation sterilization did not significantly alter the morphology. Surface morphology was not significantly altered by any of the sterilization procedures. Changes in chemical structure as the result of sterilization were not observed.

FTIR spectroscopy of biological macromolecules provides structural information about single vibrating groups and their interactions with nearest neighbors.

In recent years peptide chemists have made available a wider variety of pure peptides whose structures were described by techniques such as amino acid sequencing and ¹³C and ¹H nuclear magnetic resonance. With the advent of fourier transform infrared spectroscopy (FTIR), the natural course of events is to determine if FTIR data treatment can contribute significantly to enhance I.R. spectral applications to these compounds.

Research at our labs concerning studies of protein adsorption onto surfaces was just beginning when we presented a paper at the 1977 International FT-IR Meeting. Since that time, a quantum leap has occurred in our ability to study protein adsorption from flowing protein solutions (including whole blood) onto various surfaces. The work we will present involves using ATR in conjunction with FT-IR to study adsorption of blood proteins in real time as it adsorbs onto polymer coated ATR crystals. Through multiple subtraction and other data reduction techniques, meaningful data concerning how proteins interact with surfaces and with each other is obtained. Polymers have been found to influence protein adsorption patterns, and FT-IR is being used to study these effects. This type of study is assisting in the development of theory concerning the fabrication of surfaces with enhanced biocompatibility.

Aqueous solutions of the major blood proteins were studied using FT-IR in transmission and ATR mode. Studies concerning the spectral effects of concentration, pH, time and flow rate on individual proteins and mixtures of model proteins will be discussed. Conformational and structural changes demonstrated in the transmission spectra have been related to variations seen in adsorbed species studied by ATR of flowing systems. By various data manipulation techniques such as deconvolution, spectral subtraction and derivative spectra, components of a mixture can be identified.

The characterization of the surface of elemental carbon (soot) generated by the combustion of hexane, taken as a model for petroleum fuel, has been accomplished with Fourier transform infrared (FT-IR) spectroscopy combined with thermal desorption measurements. Carbon-oxygen functionalities on the fresh carbon surface include acid anhydride, a carbonyl conjugated with an aromatic segment, an alkyl ketone, and aryl ether linkages. Also present, confirmed by isotopic substitution, is a quantity of unsaturated C-H dependent upon the conditions of soot formation. The reactivity of this surface toward some oxides of sulfur and nitrogen also has been studied by FT-IR. SO2 reacts selectively with surface groups in the absence of 02 to form sulfate. The formation of carboxylate and nitro groups, through the reaction of NO2 with the functional groups of the soot surface, has been observed.

Specular reflectance Fourier transform infrared (FT-IR) spectroscopy has been used to study the chemical interaction and molecular structure and orientation of thin coatings of model carboxylate-containing organic compounds on coupons of highly polished SAE 1010 steel. The aim of this work has been to study the extent and nature of the coating molecule/steel substrate interaction and to utilize polarized incident radiation to examine the orientation of the coating molecule with respect to the steel surface at or near the coating/steel interface. The results of this model study demonstrate the potential of specular reflectance techniques for studying systems of interest in the coatings industry.

An experimental approach to the study of polymer film photodegradation by Fourier transform infrared (FT-IR) spectroscopy, with simultaneous UV irradiation under varying thermal and environmental parameters, has been developed. Reflection spectra from metal-backed polycarbonate films undergoing irradiation in a test chamber illustrate the system's capability. Early degradative events in polycarbonate are revealed by differences in these spectra.

In lower atmosphere, the tropopause and the stratosphere, the infrared emission radiance level directly relates to temperature and concentration of the molecules responsible for the emission. Our experiment was planned to obtain high precision data on altitude profiles of various atmospheric parameters (temperature, chemical composition, etc.) by measuring the infrared emission spectrum of the atmosphere from a balloon-borne platform. The emission measurement distinguished itself from the absorption measurement on the following aspects. A major distinction is derived from the fact that no definite source is required. The interferometer can point to any direction through the atmosphere, thereby not dictated by the diurnal change in the solar position. The atmospheric pollutant detection sensitivity can be made high in our experiment, because all lines are observed through a very long path in the atmosphere. Weak lines are observable in a well defined line structure, while strong lines show a saturation with respect to a corresponding black-body radiance. The diurnal variations, if they exist, are readily observable in the data.

Whole band analysis - a method of obtaining band parameters from spectra by nonlinear least-squares fitting of calculated to observed spectra - has been applied to bands of N20 and CO2. The retrieved N2 broadened widths of the 02°0-00°0 and 12°0-00°0 bands of N20 suggest that the air broadened widths on the AFGL listing are about 10% high. The intensities and ¹²C¹⁶02 broadened widths of the 20002-00001 and 21102-01101 bands of ¹²C¹⁶O¹⁸O and the 20002-00001 band of ¹²C¹⁶0¹⁷0 have also been determined.

Utah State University and Air Force Geophysics Laboratory have been developing field-widened interferometer systems since the late 1960's. These instruments have been developed primarily to remotely sense spectral emissions from the night sky in the near infrared. However, the systems also have application for making measurements of any dim extended source.

A commercial Fourier transform spectrometer is being used to collect 0.06cm^-1 2-14μm slant path atmospheric spectra using the sun as the source of radiation. Using a Lambert plot approach, 10-15 spectra are collected at different air masses. The logarithm of the intensity versus air mass is used to calculate the extinctance for the atmosphere at arbitrary frequencies within the bandwidth. Over the past three years, spectra have been collected on over 120 days at White Sands Missile Range, New Mexico. This data base is being used to study seasonal variation of atmospheric extinction for CO2 and DF laser frequencies. Up to a factor of ten variation in the atmospheric extinction is observed at many CO2 laser frequencies which correlate with atmospheric water vapor measurements. Variations in the atmospheric extinction for DF frequencies are smaller and do not correlate with the water vapor measurements.

We studied the capability of a Fourier spectrometer system to remotely detect trace gases in localized clouds, e.g., stationary source effluents. Detection is based on the degree to which the observed IR spectral radiance contrast between the cloud and adjacent background is correlated with a computed reference spectrum. It is shown that trace gases can be reliably detected when spectral features are well below the noise level. The minimum detectable quantities (MDQ's) for various trace gases at one atmosphere total pressure are given. The MDQ's determine the combinations of gas column thickness and gas-background temperature difference that correspond to 95 percent detection probability and one percent false detection probability when an FTS system with modest-size foreoptics views the target through a path equivalent to approximately one air mass.

When spectra of simple gases are measured at moderate resolution, the rotational fine structure of bands may be resolved but the effect of convolving the true shape of each line with the instrument line shape (ILS) function of the spectrometer leads to decreased band intensity. We have studied the feasibility of fitting the peak intensities of lines in absorption and emission vibration-rotation spectra to theoretical values computed by convolving the true spectrum with the sinc² ILS function of an FT-IR spectrometer. Early work showed that absorption spectra of CO at room temperature gave an excellent fit but the fit became poorer at elevated temperature. Subsequent work has shown that part of the reason for this behavior was an inaccurate knowledge of the temperature dependence of collision-broadened line widths, and we will present more accurate data for self-broadened CO. The current state of this technique for determining the temperature and concentration of remote hot gases from FT-IR emission spectra will then be summarized.

A Michelson interferometer with on-line data processing has been used to obtain infrared emission spectra of carbon monoxide under the non-equilibrium conditions present in a low pressure gas discharge. The advantages of a Fourier Transform Spectrometer over a conventional IR spectrometer make it ideally suited for rapid acquisition of the weak, broad band emission spectra encountered in this type of experiment. A nonlinear least-squares analysis together with a multiple linear regression analysis have been used to derive both the rotational temperature and the non-equilibrium vibrational populations from the low resolution first overtone CO spectrum. Under some discharge conditions emission is observed from 36 vibrational levels of molecule.

Experiments were conducted to determine the chemical fate of four toxic chemicals. The compounds studied were: formaldehyde, acrylonitrile, trichloroethylene, and vinylidene chloride. These chemicals were irradiated in the presence of nitrous acid and oxides of nitrogen in an N2/O2 700 Torr matrix. The nitrous acid serves as a source of OH radicals. Reactant and product concentrations were determined using long path Fourier transform infrared spectroscopy. The results of these experiments which include OH rate constants and atmospheric chemical mechanisms are discussed.

FT-IR absorption measurements of gas phase species in highly sooting hydrocarbon flames are presented. These measurements were made in linear propane/air, methane/air and methane/ propane/air flames supported on a modified surface-mixing burner. In addition to the usual products of combustion (H2O, CO2, and CO), we have observed broad bands indicative of long chain aliphatic and olefinic hydrocarbons. Rotational temperatures computed from the CO spectrum, and hydrocarbon absorbances are presented as a function of distance above the burner surface. CH4, C2H4, and C2H2 have also been identified as decomposition products in propane/air flames.

High resolution (0.007 cm^-1) spectral measurements of ¹³C¹⁶O2 and ¹³C¹⁶O¹⁸O at 600°K and 300°K taken with the Air Force Geophysics Laboratory (AFGL) Fourier Transform Spectrometer are reported. Vibration-rotation constants which predict line positions to within 0.001 cm^-1 are presented for several bands of these two isotopes. The CO2 sample contained in the high temperature absorption cell consisted of 88% ¹³C¹⁶02, 11% ¹³C¹⁶O¹⁸O, and 1% various other isotopes.

Search algorithms based on the time (or distance) domain representation of the infrared absorption spectrum were constructed and demonstrated. Preliminary results indicate significant advantages in speed, reliability, and efficiency of the search systems over the traditional spectrum-based method. A direct interferogram-based search system with a high degree of reliability was demonstrated for the first time and the requirements for an instrument-independent data were delineated.

A recent major advance in the field of gas chromatography/Fourier transform infrared spectrometry (GC/FT-IR) is the availability of a search system and digitized vapor phase infrared library. This paper presents the results of the application of this search system to a real-world sample. Examples are shown of correct matches and an incorrect match. Overall, the search performs very well with good quality unknown spectra, but cannot differentiate between a spectrum and background. These results indicate that visual comparison of the unknown and standard are required for all but the most routine identifications.

During the past couple of years, spectral searching in the infrared has come of age. What a few years ago was a relatively slow technique (whether performed manually using Sadtler's Spec-Finder books or done using a computer such as the ASTM card-based system) is now offered as part of every FT-IR system and even some dispersive instruments.

Historically, infrared spectra libraries have been used mainly for qualitative analysis and functional group assignments with some limited use for quantitative analysis. The latter application mainly uses reference libraries for selecting an absorption band free from other interfering bands for quantitative methods development. The marrying of digital computers to infrared spectrometers has expanded the uses of reference libraries. In addition to the above applications, requirements now include computerized searches for reducing the task of unknown identification, rapid recall of reference spectra for viewing, and even digitized spectrum recall for spectral subtraction when a sample is not available for actually measuring the reference spectrum. All of these applications for spectral libraries cannot necessarily be achieved with the same data base, but for a library to be useful for qualitative analysis, it certainly needs to contain as large a number of reference compounds as it possibly can. In addition, the library user must be able to view the full reference spectra as rapidly as possible.

FT-IR offers a unique method of inorganic compound speciation. Particularily in environmental samples, inorganic information has previosuly been limited to elemental or at best anion/cation information. Using FT-IR, a relatively small amount of sample (about 1 mg) can yield inorganic compound identifications. Of central importance to this technique is the availability of a good computerized reference library of pure inorganic compounds in common hydration states. This library should cover both mid- and far IR. In our laboratory, this library is being amassed using X-ray crystallography to comlement infrared results. A computer search system for the identification of inorganic compounds in mixtures has been developed which uses the above library as well as spectral knowledge of the user. Second derivative spectra are used to establish exact peak frequencies. The combination of good reference spectra and the ability to locate the exact position of overlapping bands by the use of the 2nd derivative, allows the identification of specific inorganic compounds in complex mixtures.

There are now several commercially available computer routines for identifying unknowns by a spectral search and match procedure. These routines work well if the match is perfect, however they can be frustrating when the data base does not contain the unknown as one of its entries. An alternative method for identifying an unknown is to establish the IR active funtionalities that are presnt. This can be done by a classification-matching method or by an interpretation method that tries to mimic how the chemist/spectroscopist thinks. The latter has been discussed in several papers and forms the starting point for our studies.

In rapid scanning FT-IR, several sources of errors can lead to reduced photometric accuracy and faulty results, especially in the area of spectral subtraction. Poor phase correction is one and can lead to misleading features such as false residuals in the subtraction spectra. The most common algorithm employed for phase correction is the Mertz method where a phase error array is calculated from a short double sided interferogram and the correction applied to the results of a complex Fourier transform. An alternative method discussed by Forman, Steel and Vanasse2 used the phase error array to generate a convolution function which "symmetrizes" the interferogram. The spectrum is then calculated with a real Fourier transform. This method has several advantages; i.e., less sensitivity to the location of the center burst and the ability to easily iterate on the phase error. The results with both methods will be discussed for ideal asymmetric interferograms and actual instrumental data.

Photometric accuracy in Fourier spectroscopy depends not only on instrumental factors, but also on the method used to produce the spectrum from the interferogram. Almost all FT-IR instruments compute the spectrum by means of apodization, complex FFT and multiplicative phase correction steps. When the contribution of the apodization and phase correction steps to photometric inaccuracy is examined, two classes of error are found: error in computing the reference transform and error resulting from the contrast correction function. Means of eliminating of minimizing these errors are considered. Alternate methods of phase correction are discussed.

The frequency scale of commercial FT-IR instruments is precise to within ≤ 0.005 cm^-1, regardless of the resolution employed in the measurement. Consequently, given adequate S/N ratios, frequencies and bandwidths of spectral lines can be determined down to this limit, provided the data are treated correctly. Although appropriate techniques are routinely utilized in high resolution gas phase studies they are not generally employed in studies of relatively low resolution (0.5^-8 cm^-1) condensed phase spectra. A comparison will be made of several different methods of data reduction, and it will be demonstrated that frequencies and bandwidths can be routinely determined with uncertainties of less than 0.1 cm^-1, even with low instrumental resolutions. This permits the monitoring of extremely small changes in condensed phase spectra.

The general principles of Fourier self-deconvolution are presented. Self-deconvolution reduces the intrinsic widths of lines by a factor K which is limited by the noise in the spectrum. A formula for computing changes in the signal-to-noise ratio, S/N, of the spectrum as a function of K resulting from Fourier self-deconvolution is derived. Examples of the application of the method to synthetic and experimental infrared spectra are presented and it is shown that lines having moderate S/N ratios (1000-10000) can readily be reduced in width by a factor of four.

Several methods can be used to resolved overlapped bands in the spectra of mixtures. For most of these methods an estimate of the number of components in the mixture must be made as the first step. The number of components can sometimes be deduced using factor analysis or the absorbance ratio technique, but the answers given by these techniques are often ambiguous. When the number of components is known, the spectrum of each individual component may be obtained using absorbance subtraction routines; however, for this technique to be successful the spectroscopist should have some knowledge of the composition of his sample, and he needs the spectra of at least as many samples of different composition as there are components in the mixture. The problem of mixture analysis is therefore often reduced to the problem of estimating the number of components present in the sample.

Recent developments in far infrared, laser spectrometry and dispersive Fourier transform spectrometry have allowed the direct determination of the optical constants of some aqueous salt solutions in the spectral range between 25 and 450 cm^-1. The following salts were studied by these methods LiC1, LiC1O4, NaCl, NaC1O4, NaI , KCl, Kbr, KI, KF, MgCl2, Mg(ClO4)2 and Bu4NBr (tetrabutylammonium). The results show that in the presence of some electrolytes the optical constants of the solution can differ significantly from those of pure water, and that in localised spectral regions the absorption can be many times less than that of pure water.

Many molecules with two internal C3v rotors have been shown to have "rich" far infrared spectra. Barriers calculated in early studies used approximation methods derived from theoretical work done in the field of microwave spectroscopy. At most, only two Fourier coefficients of the potential function could be determined which allowed interpretation and assignment of only a few of the usually large number of spectral features found in the far infrared region. It is apparent that this approach of treating the semi-rigid model, based on the use of tabulated perturbation sums, is not at all sufficient to explain the commonly very "rich" torsional far infrared spectra. These early methods were not capable of extracting all of the information about the potential functions of these molecules. In a recent series of papers, we have demonstrated how far infrared interferometry and laser Raman spectroscopy may be combined with modern computing techniques to determine three or more Fourier coefficients of the potential function in two variables and to interpret most or all of the features observed in the far infrared spectral region of such two-top molecules. We have recorded the far infrared spectra of dimethylsulfide, dimethylselenide, 1-chloro-2-methylpropene, cis-dimethyloxirane, and trans-dimethyloxirane on a far infrared interferometer at a resolution of 0.25 cm-1. A large amount of torsional data have been obtained and the observed transitions have been assigned on the basis of the semi-rigid model. The barriers to internal rotation have been calculated and, for several of the molecules, both the cosine-cosine and sine-sine coupling terms have been obtained.

The far infrared (450 to 50 cm-1) spectrum has been recorded for gaseous methyl vinyl ketone. The asymmetric torsion for the s-trans conformer was observed at 116 cm-1 in the infrared spectrum of the gas with two accompanying hot bands and the corresponding torsion of the s-cis conformer was observed at 87 cm-1 with an additional hot band occurring at 84 cm-1. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V1 = 180±9, V2 = 827±107, V3 = 113±8, and V4 = 150±34 cm-1. From these data it has been determined that the s-trans conformer is the predominant form at ambient temperature and the enthalpy difference between the s-trans and s-cis conformers is 280 cm-1 (800 cal/mol) for the vapor. The calculated trans-cis barrier is 827 cm-1 (2.36 kcal/mol) and the cis-trans barrier is 547 cm-1 (1.56 kcal/mol). These results are compared to similar quantities in related molecules.

The inherent resolution capability and frequency precision of FTIR spectroscopy has led to renewed interest into several "conventional" infrared investigations, one of these being the determination of the energy barrier hindering free internal rotation of molecules with two or more internal rotors.

The vibrational spectra of 1,2-difluoroethane, 1,1,2-trifluoroethane, and 1,1,2,2-tetra-fluoroethane have been recorded in the gaseous, liquid, and solid states. The conformational preferences have been studied as a function of temperature and physical state. Transitions arising from the torsional vibration for the stable form of each molecule have been observed in the far infrared. Using these and other data, torsional potential functions have been developed. Trends in the conformational characteristics of the fluoroethanes are discussed.

The infrared spectra of gaseous vinylsilane, cyclopropylsilane, vinyltrichlorosilane, cyclopropyltrichlorosilane, and silacyclopentane have been recorded. Barriers to internal rotation have been calculated for vinylsilane and cyclopropylsilane from an analysis of combination and difference bands associated with the Si-H stretches. Vibrational assignments have been made for vinyltrichlorosilane and cyclopropylsilane. High resolution spectra of the combination and difference bands involving the Si-H stretches and the ring-puckering vibration in silacyclopentane have been analyzed, and the new assignment is found to be completely consistent with existing low-frequency data. The structural implications of the results are discussed.

The vapor spectra of the title compounds were recorded between 50 and 700 cm-1 with an evacuable FT-IR spectrometer by transmission and emission techniques. Special vapor cells were made of nickel and fitted with windows of diamond. Quite analogous spectra were recorded in absorption and emission. At tempratures higher than 300°C the emission spectra had the better quality above 100 cm-1. The equilibria between the dimer and monomer species were studied as a function of temperature. Seven of eight IR active dimer (D2b) bands were assigned. For AlI3 and GaC13 monomers (D3h), the three IR active modes were found. Force fields for the dimers were derived by combination with Raman vapor data.

Profiting from the example of Fourier transform spectroscopy, a number of possible other transform spectroscopies, such as Hadamard, Walsh, and Laplace transforms, have been investigated. A number of other transforms show spectroscopic promise in the IR. (1) CHIRP. Here a tunable laser is coupled via a beamsplitter to a spatially extended sample and a heterodyne detector. The audio frequency output of the latter after chirp transformation yields a range resolved signal useful for remote measurements or nonuniform sample measurements. (2) KRAMERS-KRONIG. This transform, for which a simplified fast calculating procedure has evolved in the Fourier domain, interconverts refraction and absorption spectra. Refractive index spectra offer advantages for tunable laser work, can be used for absorption spectrum correction, and can be conveniently obtained by asymmetric FT-IR. (3) ABSORBANCE NONLINEARITY. Particle size or shape, thickness, or concentration distributions within an inhomogeneous sample can be calculated from line shape distortions produced by the energy nonlinearity of the absorption process. Other transforms of potential ability, such as the Hankel, the equiabsorbance, and two dimensional Fourier transforms, will be briefly mentioned.

Prior work by Lehr and McClellan and Lehr, based on chemical, crystallographic, and x-ray diffraction studies, showed the relationship between phosphate (P) and substituted carbonate (C) in francolite apatite to be P+C = 6.00 ± 0.04 and the generalized apatite formula to be (Ca,Na,Mg) 10(PO4)6-x(CO3)xFy(F,OH)2, in which y ranges from 0.33x to 0.5x. Using the FTIR, the ratio of the area of the absorption curve for C-0 (bands in the region 1375 to 1550 cm-1) versus the area of the absorption curve for P-0 (bands in the region 530 to 690 cm-1), the "CO2 index," was found to be proportional to the mole ratio of CO3:PO4 in francolites. Stripping methods allowed the subtraction of spectral contributions of silicate and carbonate minerals and water, which would ordinarily interfere with such a determination. The study was based on 65 mineral samples and the formula was found to be: CO2 index = 0.0678 + 4.184(mole ratio CO3:PO4) (1) The correlation factor, r2, was 0.938 and the standard error of the slope ±0.136. The probability of the null hypothesis for the model was less than 0.0001.

The SP-250 epoxy resin/glass fiber prepreg system is one of the basic organic materials of prime importance to the U.S. Army and U.S. Navy. It is presently being used in the rotor blades for the CH-46 and CH-47 helicopters. Present quality control analytical methods involve complex and time-consuming HPLC or GPC procedures. In the present work, Fourier Trinsform Infrared Spectroscopy (FT-IR) spetra were interpreted quantitatively with relative absorbances 1140cm-1 C-0-C, 1080cm-1 aromatic Cl, and 915cm-1 epoxide peaks. These frequencies were normalized to the 1510cm-1 aromatic peak. Quantitative absorbances were determined using the baseline method. FT-IR allows reproducible quantitative absorbance determinations with statistically good reproducibility. Spectra were obtained from thin films of THF/DMF extracts from the epoxy/glass prepreg cast on KBr plates. Quantitative absorbance determination from FT-IR provides enough information from a single spectrum, with five functional group peak absorbances being measured, to allow acceptance or rejection of lots of prepreg.

The design and fabrication of capacitative metal-mesh-dielectric (MMD) mirrors are described. An outline of their expected theoretical behavior in the far infrared region in terms of the mesh parameters, g the grid periodicity, 2a the width of the gap between the metallized regions, and n the refractive index of the supporting substrate, is given. The frequency response of various MMD mirrors has been measured using a Fourier transform interferometer and is shown to agree with a suitably modified theory which takes account of the high index substrate.

Three auarters of a century after its inception, a generation after its advantages were recognized, and a decade after its first commercialization, FT-IR dominates the growth of the IR market, and reigns alone over its high performance end. What lies ahead for FT-IR now? On one hand, the boundary between it and the classical scanning spectrometers is becoming fuzzy, as gratings attempt to use as much of FT-IR's computer technology as they can handle, and smaller FT systems invade the medium cost instrument range. On the other hand, technology advances in IR detectors, non-Fourier interference devices, and the often announced tunable laser are at long last getting set to make serious inroads in the field (although not necessarily in the manner most of us expected). However, the dominance of FT-IR as the leading edge of IR spectroscopy seems assured for a good many years. The evolution of FT-IR will be dominated by demands not yet fully satisfied such as rapid sample turnover, better quantitation, automated interpretation, higher GC-IR sensitivity, improved LC-IR, and, above all else, reliability and ease of use. These developments will be based on multiple small advances in hardware, large advances in the way systems are put together, and the traditional yearly revolutionary advances of the computer industry. The big question in the field will, however, still be whether our ambition and our skill can continue to keep up with the advances of our tools. It will be fun.

Atmospheric spectroscopists have for some time been using FT methods to overcome some of the difficulties involved in making high resolution studies of the upper atmosphere. For limb absorption measurements from balloon platforms, the critical requirement is the need to record the interferogram in short enough time to prevent distortion of the spectrum by the changing line-of-sight air mass. Here, the time available is typically 100 seconds, and current instruments can record the entire near and mid-IR spectrum at about 0.01 cm-1 resolution within this interval. To increase the altitude and latitude coverage of such measurements, however, by making the observations from space platforms, the process must be speeded up by two orders of magnitude. The Atmospheric Trace Molecules Spectroscopy (ATMOS) experiment, which uses a shuttle-borne Connes-type interferometer covering the two to sixteen micron range, is described. The measurements will provide the first opportunity to obtain simultaneously the vertical profiles of all of the infrared active trace constituents with relative concentrations as low as 10-12, throughout the stratosphere and mesosphere. In addition to problems in the instrument design, the experiment presents major challenges in data management.

While perhaps the most familiar form of thermal analysis where FT-IR has been utilized is GC-FT-IR, there are a variety of other forms of thermal analysis where FT-IR is usable to advantage. By considering the destructive or non-destructive nature of the analysis coupled with isothermal or non-isothermal and time dependent or independent criteria an assortment of experiments are describable. The scope of experiments extends from the analysis of multicomponent equilibrium adsorption to defining pyrolytic reaction mechanisms. In this paper, a survey of some of the diverse applications where FT-IR can be employed are discussed with particular emphasis on the Fourier Transform Infrared Evolved Gas Analysis (FT-IR-EGA) technique. The application of this technique in material comparison and in pyrolysis mechanism elucidation are illustrated and several other applications are cited.

The development of interferometry and Fourier transform interferometry with its application to many problems shall be discussed by several of the lecturers; however, it should be noted that the first chemical applications of FT-IR spectroscopy were made in the far infrared region of the spectrum (approximately 400-10 cm-1) because the instrumentation required to study this region was much simpler than that needed for the mid-infrared or near infrared regions. The instrumental advantages in the far infrared region included a lower tolerance for the mirror drive of a Michelson interferometer, a smaller dynamic range of the interferogram, and a longer sampling time which resulted in a reduced number of data points. However, far infrared spectroscopy also had its apparent difficulties such as low-energy sources, poor detectors, a lack of suitable optical materials, and spectral interference of water. Researchers in this area have overcome most of these difficulties and therefore investigations in the far infrared spectral region have become widespread. In this presentation some of the applications of Fourier transform far infrared spectroscopy will be examined. The three areas in which research was initially carried out using Fourier transform far infrared spectroscopy were investigations of pure rotational spectra, studies of molecules in the solid state, and studies of heavy atom vibrations and skeletal bending modes. These initial studies did not show a significant departure from the mainstream of far infrared research since a majority of them could be carried out utilizing dispersive instrumentation, but in the field of solid state research, the interferometrically obtained spectra provided data which were not easily obtained by grating instruments. Thus, physicists have put interferometers to use in the study of the solid state to determine optical constants such as the index of refraction, complex indices, phase angle transmission coefficients, and the electronic processes in insulating crystals, as well as the intermolecular vibrations of molecular crystals. Such studies have been important in the development of interpretative theories of solid state behavior. For the sake of brevity I shall mainly discuss current uses of far infrared interferometry for the study of molecules in the gas phase which contain very anharmonic vibrations, such as torsional vibrations and ring-puckering motions in some small ring compounds, and for conformational analyses by the spectral assignment of the asymmetric rotor transitions. The interpretation of the far infrared data for several molecules will be illustrated and many examples will be provided.

Since the last International Conference on Fourier Transform Spectroscopy considerable experience has been gained in the use of automatically aligned interferometric spectrometer systems. Features of these systems will be discussed in relation to a general purpose FTIR system with special emphasis on those areas which are most important in defining the performance of such systems. These will include alignment, phase characterization, spectral resolution, wavelength coverage, throughput and sensitivity.

In the last dozen years spaceborne Fourier Transform Spectrometers have obtained infrared emission spectra of Earth, Mars, Jupiter, Saturn and Titan as well as of the Galilean and other Saturnian satellites and Saturn's rings. Intercomparisons of the properties of planetary atmospheres and of the characteristics of solid surfaces are now feasible. The principles of remotely sensing the environment on a planetary body are discussed. Special consideration is given to the most recent results obtained by the Voyager infrared investigation on the Saturn system.

Very sensitive Fourier transform spectrometers (FTS's) have been developed for infrared measurements utilizing advanced technology to achieve stable operation at very low temperatures. All of the structural, optical, and detector components used to construct these spectrometers are cryogenically cooled to improve the sensitivity of their detectors and to eliminate unwanted background emission signals from the components. Various designs of cooled FTS systems which have been successfully used and tested by USU and AFGL are presented in the paper. The performance specifications, the advantages, and the limitations of each technique are discussed. Also, general evaluations of the advantages and the limitations of cooling an FTS are given.

After discovering the photoacoustic effect, Alexander Graham Bell predicted its use in spectrometers, and that it would find its greatest utility "in the ultra-red." More than ninety years were required to fulfil his first prediction, and the second is still a prophecy. There is no record whether he ever imagined that an invention being developed that same winter by a young protege of his named Albert Michelson would ever be combined with his photoacoustic effect. A century later, the combination was made by Farrow Burnham, and Eyring, using a visible-range interferometer spectrometer of their own design. Soon afterwards, Rockley and myself, working independently, applied the technique to infrared measurements of solid samples. Photoacoustic cells are now commercially available as FT-IR accessories, and the technique is in use in the field.

A review is presented of recent developments in the methods of dispersive Fourier transform spectrometry that have demonstrated the unique value of the technique in providing accurate determinations of both optical constants of a material at millimetre and submillimetre wavelengths. These developments are illustrated by reference to the results of measurements on gases, liquids and solids that would not have been possible with more conventional spectrometric techniques, and which have improved our knowledge and understanding of the microscopic behaviour of such systems.

After a brief review giving an account of the life of FTS in France, the latest interactions between infrared Doppler limited molecular spectroscopy and FTS are presented. Recent results on vibration rotation spectra together with the description of the new method allowing cancellation of systematic distortions on Fourier spectra to be compared are given. Particular application of the new method on pressure-shift experiment on the 1-0 12C16O vibration rotation band demonstrates an improvement of two orders of magnitude over the best previous results. Shifts due to 5 torr of CO are detectable between spectra having a S/N of about 200. Comparison between identical spectra experimentally shows under such S/N conditions no evidence of remaining differential systematic errors, within 10-6 cm-1 (30 KHz). The 50 lines of the band of CO taken as a test are extracted from 300,000 spectral elements spectra. Various aspects of these preliminary results are discussed.

Since the first FT spectrometer was constructed at Osaka University, FT spectroscopy began to become popular in Japan, even though it was behind in world's competition. This review is to introduce a brief story on the domestic growth of the FT spectrometer and its current aspect in the field of application.

After reviewing the FT-IR activity in the Federal Republic of Germany, the paper will report on various FT-IR measurements made at the Max-Planck Institut filr Festkorperforschung in Stuttgart. Among these are far-infrared investigations on films or layers of bio-molecules and of amorphous semiconductors. Several new techniques, developed in Stuttgart, are reviewed.

The possible applications of Fourier transform spectroscopy in the submillimeter region are briefly reviewed, stressing the importance of measurements with high resolution. Recent measurements with a resolution of 0.003 cm-1 (unapodized) both of stratospheric emission at balloon altitudes and of individual molecular species in the laboratory are presented and discussed.

The explosive growth of the use of Fourier Transform Infrared Spectrometers during the last decade has been due in large part to both revolutionary and evolutionary advances in software developments related to the implementation, practice and applications of FT-IR. Clearly the trends of performance-to-price ratio of digital technology has played a fundamental role in enabling the forward progression of software development but major independent developments have had fundamental impact in their own right. The history of these developments in acquisition and control, spectral recovery, and data processing and their implication on spectrometer hardware design and use are reviewed and critiqued.

With use of the technique of Fourier spectroscopy, we are able to conduct a high quality measurement (high resolution and high S/N) on a very large number of spectral lines which spread over a wide spectral region. As a consequence, the Fourier spectroscopists are challenged with a problem of analyzing extremely complex spectral data containing a large number of lines. This paper reviews the numerical processing technique required for such spectral analysis.

The term unconventional is relative in both time and the area of application. Today's unconventional processing may become tomorrow's common practice if it proves to be of sufficient utility. Also, workers in one area may be unaware of methods in another which could be useful. Processing techniques in both of these categories are discussed. Time and space do not permit the inclusion of all of the specialized forms of processing now practiced in FT-IR. However, several processing topics of special interest to remote sensing but which should be of interest to other applications of spectroscopy are discussed. These are: radiometric calibration, interferogram dynamic range reduction and correlation interferometry.

A summary of the research and development efforts of FT-IR applications and operational software is presented. The efforts of the 1971-81 time period forms the central theme of the discussion. A cursory review of the preceeding work of 1955-'71 is outlined as background for these developments. Conclusions along two themes of recent research are derived. The evolution of low cost, high performance FT-IR spectrometers and their operating software is discussed. Recent developments of FT-IR search algorithms and data bases are also presented. Conclusions indicate a very promising future for the application of FT-IR technology to an ever widening sphere of applications.

Although rapid-scanning interferometers giving very high sensitivity were first developed more than twenty years ago, these instruments were not well accepted by chemical spectroscopists because of their low resolution and poor capability for data manipulation. It was not until 1969 with the development of laser-referenced rapid-scan interferometers which could generate spectra of at least 0.5 cm-1 resolution that the chemical community really started to recognize FT-IR spectrometry as a genuinely useful analytical technique. Even so, it has still taken a further decade to get the technique unequivocally accepted.

The EPA Remote Optical Sensing of Emissions (ROSE) System, which consists of a commercial FT-IR system and associated components installed in a van, has now been in use for over three years. The system is used in either the absorption mode with a remotely located light source (long paths through the atmosphere or short paths across industrial stacks) or in the single-ended emission mode to quantify the gaseous pollutants emitted from various types of sources. Spectra are usually obtained at a resolution of 0.125 cm-1 over the range 700 to 6000 cm-1. On two recent measurement programs the ROSE system was used to characterize the emissions from an aluminum refinery potroom and from a cement plant. The major potroom emission specie was HF; varying amounts of CF4, COS, CO, and SO2 were also observed. In addition to H2O and CO2, the cement plant emissions included NO, CO, HC1, NH3, SO2, and H2C0; a comparison was made between species concentrations deter-mined by cross-stack absorption and by single-ended emission.

The principles of double modulation FT-IR circular dichroism are presented. This approach to the measurement of infrared circular dichroism is compared to other methods and the advantages of the double modulation technique are explained. Examples of FT-IR vibrational circular dichroism (VCD) are presented and compared to the same VCD spectra measured with a conventional dispersive instrument. Procedures for calibrating the FT-IR-VCD spectra are noted and the performance of the instrument is evaluated for signal-to-noise ratio and interfering polarization artifacts.

An ex vivo FT-IR/ATR experiment for studying blood protein adsorption at the molecular level is described. This experiment involves the use of live dogs pumping the blood through a arterial-veinal shunt to the ATR cell and back into the animal. The results from these live dog experiments are compared to results obtained using donated whole blood. These experiments demonstrate that FT-IR can be used to study aqueous, physiological, flowing solutions in real time with the sensitivity necessary to detect minor changes.