Showing papers on "Fourier transform spectroscopy published in 1987"

Molecular line parameters for the atmospheric trace molecule spectroscopy experiment

Abstract: During its first mission in 1985 onboard Spacelab 3, the ATMOS (atmospheric trace molecule spectroscopy) instrument, a high speed Fourier transform spectrometer, produced a large number of high resolution infrared solar absorption spectra recorded in the occultation mode. The analysis and interpretation of these data in terms of composition, chemistry, and dynamics of the earth's upper atmosphere required good knowledge of the molecular line parameters for those species giving rise to the absorptions in the atmospheric spectra. This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results. With over 400,000 entries, the linelist catalogs parameters of 46 minor and trace species in the 1-10,000/cm region.

Pulsed beam Fourier transform microwave measurements on OCS and rare gas complexes of OCS with Ne, Ar, and Kr

Abstract: A pulsed molecular beam Fourier transform microwave spectrometer, which has been recently constructed at NBS, was employed for measurements on several monomer and van der Waals species of OCS. The absorption–emission cell consists of a Fabry–Perot resonant cavity inside a high vacuum chamber. A pulsed nozzle is used to generate a supersonic molecular beam of a seeded inert gas. New spectra of Ne–OCS, Ar–OC34S, and for four Kr isotopes of Kr–OCS are reported, as well as structure analyses of each species. The nuclear electric quadrupole hyperfine structure of 83Kr–OCS has been resolved and yields eQqaa=1.601(7) MHz and eQqbb=−1.857(3) MHz.

The à 2Π–X̃ 2Σ+ transition of HC2 isolated in solid argon

Abstract: Fourier transform absorption spectra have been obtained between 700 and 7900 cm−1 at a resolution of 0.2 cm−1 for Ar:C2H2 samples codeposited at 12 K with a beam of argon atoms that had been excited in a microwave discharge. Detailed isotopic substitution studies have confirmed that the predominant product species is HC2, which contributes not only the absorptions previously assigned to its two stretching fundamentals but also several weaker absorptions in the 2000–3600 cm−1 spectral region and a prominent, complicated pattern of absorptions between 3600 and 7800 cm−1. The previous assignment of the 3611 cm−1 HC2 absorption as the CH‐stretching fundamental is reviewed, and the assignment of an absorption at 2104 cm−1 as ν2+ν3 of ground‐state HC2 is discussed. The near infrared absorption band system has been assigned to the A 2Π–X 2Σ+ transition of HC2, extensively perturbed by interaction with high vibrational levels of the ground state. The position of the transition origin could not be definitively e...

High precision fourier transform spectrometry: The critical role of phase corrections

Abstract: In high precision Fourier transform spectrometry, proper handling of the phase correction is essential if the full potential wave number accuracy of the data is to be preserved. One-sided interferograms are shown to be especially sensitive to phase error, and this sensitivity is quantitatively related to the signal-to-noise ratio. The role of the truncation/apodization function used to obtain the phase correction is also discussed, as is the special problem of emission spectra.

Fourier Transform Raman Spectroscopy of Long-Chain Molecules Containing Strongly Absorbing Chromophores

Abstract: Fourier transform Raman spectroscopy shows considerable promise as a new characterization technique for molecules which contain chromophores which absorb in the visible region, the region where conventional Raman measurements are made. With the use of near-infrared excitation, spectra in the absence of fluorescence and resonance enhancement are obtained. These advantages can be further enhanced if the collection of data using this technique becomes routine, requiring a level of complexity comparable to that of conventional Raman scattering. Toward that end, the implementation of a 90° scattering geometry in our FT-Raman measurements was undertaken, and the results are shown to be at least comparable to those obtained with the use of reflective optics in a 180° geometry. A number of results on both liquids and solids have also been obtained in order to compare FT-Raman with conventional scanning Raman measurements.

Fourier transform Raman spectroscopy

Abstract: The basic experimental aspects of Fourier transform Raman Spectroscopy are reviewed with an emphasis on detector technology. The sensitivity is comparable to dispersive Raman Spectroscopy using visible lasers. The ease of spectral subtraction is demonstrated and examples are given showing the elimination of fluorescence.

Laboratory methods in vibrational spectroscopy

Abstract: Introduction Terminology and Definitions in Vibrational Spectroscopy Group Frequency Correlation Table Selected Properties of Infrared Transmitting Materials Spectra of Solvents and Frequently Encountered Contaminants The Dispersive Infrared Spectrometer Mid Infrared Fourier Transform Spectrometry Quantitative Analysis from the Infrared Spectrum Simple Sampling Preparation of Polymer Samples for IR Examination Reflection Spectroscopy Micro-Sampling Methods in Infrared Spectroscopy Techniques for Vibrational Spectroscopic Measurements under High Pressures Matrix Isolation Modern Methods for GC/IR and GC/FTIR Capillary GC/FT-IR Species Adsorbed at Surfaces Reactive, Unstable, Explosive and Energetic Materials Infrared Spectroscopy of Inorganic Compounds Methods of Obtaining Spectra at High and Low Temperatures The Infrared Emission Spectrum Raman Instrumentation Raman Sampling Concise Theory of Infrared Spectroscopy.

Fourier transform infrared spectroscopy of molecular clusters: The structure and internal mobility of clustered carbon dioxide

Abstract: Infrared spectra of supersonic jets of carbon dioxide seeded in helium are reported: Features assignable to clusters were observed for the ν2, ν3, ν1+ν3, and 2ν2+ν3 bands A detailed study was made of the ν3 band, from which it was concluded that the clusters do not adopt the face‐centered cubic crystal structure of solid carbon dioxide The observed spectra indicate that the cluster geometry is largely determined by pairwise interactions between adjacent molecules Furthermore, expansions of pure carbon dioxide produced clusters whose spectra indicate motional averaging: such clusters seem to be fluid on a picosecond time scale

Calibration of the photoluminescence technique for measuring B, P and Al concentrations in Si in the range 1012 to 1015 cm-3 using Fourier transform spectroscopy

Abstract: Calibrations are reported for measuring boron, phosphorus and aluminium concentrations in silicon by comparing the intensities of bound-exciton and free-exciton luminescence features. Particular attention has been directed towards investigating the effects of excitation density and instrumental resolution. The luminescence spectra have been corrected for the system response so that the calibrations are independent of the equipment used and are hence transferable. Fourier transform rather than dispersive spectroscopy has been employed to measure the luminescence spectra. Since Fourier transform photoluminescence spectroscopy is a relatively new technique, it is described in some detail.

An investigation of the hydrogen‐bonded dimer H3N⋅⋅⋅HBr by pulsed‐nozzle, Fourier‐transform microwave spectroscopy of ammonium bromide vapor

Abstract: The ground‐state rotational spectrum of a dimer of ammonia and hydrogen bromide has been detected by using the technique of Fourier‐transform microwave spectroscopy in a Fabry–Perot cavity to examine a supersonically expanded gas pulse composed of ammonium bromide vapor entrained in argon. The spectroscopic constants B0, DJ, DJK, χ(14N), χ(79Br), and χ(81Br) have been determined (where appropriate) for the four symmetric‐top type isotopic species (14NH3, H79Br), (14NH3, H81Br), (15NH3, H79Br), and (15NH3, H81Br) and for the first of these the values are as follows: B0=3226.862(1) MHz, DJ=9.0(2) kHz, DJK=142.2(6) kHz, χ(14N)=−3.183(8) MHz, and χ(79Br)=361.245(6) MHz. The spectroscopic constants have been interpreted in terms of a hydrogen‐bonded dimer of C3v symmetry, having r(N⋅⋅⋅Br)=3.255 A and the hydrogen‐bond stretching force constant kσ=13.4 N m−1. A detailed analysis has demonstrated that χ(79Br) is consistent with a model of the dimer in which only a small electrical rearrangement in the HBr subuni...

Dispersive Fourier Transform Spectroscopy

Abstract: A review is presented of recent developments in the methods of dispersive Fourier transform spectroscopy that have demonstrated the unique value of this broad band method for determining the optical constants of gases, liquids and solids.

Fourier transform infrared spectroscopy of a single aerosol particle

Abstract: Throughout this thesis, the phenomenon of radiation-induced particle size change is studied both on a theoretical as well as experimental level. The thrust of this study is aimed at using the size changes due to heat absorption to develop a technique for obtaining the particle chemical composition. The experiments here involve charged particles, generated with an impulse jet, and trapped by the electric field of an electrodynamic balance. The particles under study are all aqueous solutions of non-volatile salts, where upon heating a partial evaporation of water occurs. The evaporation and subsequent condensation processes are modeled in both the continuum and the transition regimes. The models developed are tested and the agreement between theory and experimental results is demonstrated. The models are also used to extract the values of the water, thermal, and mass accommodation coefficients from the data. The results for the thermal accommodation show that its value is near unity, however the corresponding results for the mass accommodation are not conclusive. A method is developed for obtaining the molecular composition of a single suspended microparticle by Fourier transform infrared spectroscopy. The particle is irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The laser is tuned to an edge of an optical resonance of the particle while the IR beam is chopped. Through evaporation and condensation the chopped IR beam causes a size modulation of the droplet, which in turn induces a fluctuation in the laser light scattered from the particle. The scattered light is detected at 90° with a photomultiplier, and the amplitude of the light fluctuation is measured with a lock-in amplifier. The lock-in signal is then inverted by a discrete fast Fourier transform routine (FFT), to yield the particle absorption spectrum. Spectra of (NH4)2SO4 droplets at different solute concentrations are presented.

Hadamard transform visible Raman spectrometry

Abstract: The successful application of LC-SLM Hadamard transform spectrometry as a simultaneous multiwavelength detection system to Raman spectroscopy is presented. Multiplexed Raman data are obtained with the use of an Ar+ laser lasing at 514.5 nm and a room-temperature silicon photodiode. A conventional 90° scattering geometry is employed for measurements. It is demonstrated that the LC-SLM Hadamard transform Raman spectrometer possesses the capability of performing spectral subtraction and the ability to obtain depolarization ratios of Raman bands, and can function as a selectively tunable optical filter for both Rayleigh line rejection and optical band notching. It is also demonstrated that, for the Hadamard transform Raman experiment, the silicon photodiode used as the detector produces spectra with slightly better signal-to-noise ratios than those obtained with the photomultiplier tube (PMT) used as the detector, although the PMT shows an increase in sensitivity.

Near-Surface Analysis and Depth Profiling by FT-IR Photoacoustic Spectroscopy:

Abstract: Fourier transform photoacoustic spectroscopy (FT-IR/PAS) has proven to be a powerful technique for the near-surface characterization of solid materials. The effective sampling depth of FT-IR/PAS can be varied by using different interferometer mirror velocities, so that nondestructive depth profiling can be performed. In this research, sized cotton yarns, treated glass fibers, chemically modified poly(ethylene terephthalate) fibers, and a naturally weathered poly(vinyl chloride) composite were investigated with the use of FT-IR/PAS at different mirror velocities. Penetration of the chemical additives in these materials was studied. It was demonstrated that FT-IR/PAS has the ability to investigate the changes in chemical nature within the detectable surface layers of solid samples.

High resolution interferometric Fourier transform infrared absorption spectroscopy in a supersonic free jet expansion

Abstract: The absorption spectrum of CHF3 in a free jet expansion has been recorded at a resolution of 0·004 cm-1 in the 8–9 μm region. The line width is found to be essentially Doppler limited. An approximate rotational temperature of 40K has been determined from the spectrum. Relative intensities and transition moments for the interacting bands are discussed.

The dynamics and microscopic kinetics of the reactions of O(1D2) atoms with CHCl3 and CHF3

Abstract: The energy disposal and branching ratios in the reactions of O(1D2) with CHCl3 and CHF3 have been measured using an implementation of time‐resolved Fourier transform spectroscopy in this laboratory. The infrared emission from the products of the reactions is measured as a function of time after the creation of the O(1D2) atom by UV photolysis of ozone. The reaction with CHCl3 produces OH, HCl, and CO as primary products. The OH vibrational excitation indicates simple abstraction dynamics. The HCl has much lower vibrational excitation, characteristic of a longer‐lived insertion‐elimination process, which also produces CO in the decomposition of the internally excited Cl2CO product. Only HF is observed in the reaction with CHF3. In this case the vibrational distribution is nonmonotonic, indicating contributions from two microscopic channels, possibly associated with the formation of F2CO in both the ground (X 1A1) and first excited (A 1A2) states.

Determination of dissociation energies and thermal functions of hydrogen-bond formation using high resolution FTIR spectroscopy

Abstract: A technique which employs high resolution Fourier transform infrared spectroscopy is demonstrated for evaluation of hydrogen bond dissociation energies D0 and De. Results for HCN‐‐HF give a D0=20.77(22) and De =28.77(45) kJ/mol which are compared with previously determined values obtained from microwave absolute intensity measurements and ab initio molecular orbital calculations. Rovibrational band information available for HCN‐‐HF also permits evaluation of thermal functions of dimer formation in kJ/mol: ΔU○298.2 =20.1(2), ΔH○298.2 =22.6(2), ΔG○298.2 =59.4(2), ΔS○298.2 =−0.1235.

FTIR spectra of the HF−2 and H2F−3 anions isolated in solid argon and neon

Abstract: Argon diluted samples of HF were bombarded by low energy electrons (150–400 eV) from a thermionic electron source during condensation at 12 K. Several polyfluoride anions, which have extremely strong hydrogen bonds, were characterized using matrix infrared spectroscopy. Three principal ions were trapped in the argon matrix: HF−2 (1377 cm−1), H2F−3 (1815 cm−1), and ArnH+ (904 cm−1). Electron impact experiments performed with HF/DF mixtures gave counterpart absorptions: DF−2 (965 cm−1), HDF−3 (1707 cm−1), D2F−3 (1391 cm−1), and Arn D+ (644 cm−1). The 1377 cm−1 matrix band is assigned to ν3 of linear, centrosymmetric HF−2, based on agreement with solid state and matrix ion pair spectra, and ab initio calculations, and a proper H/D ratio (1.427) for a linear centrosymmetric species. However, this assignment challenges the recent 1848 cm−1 gas phase assignment to ν3 of HF−2 using laser spectroscopy; the 1848 cm−1 absorption exhibits an H/D ratio (1.323) that is too low for the ν3 vibration of centrosymmetric H...