Showing papers on "Infrared spectroscopy published in 1976"

Electronic structure, spectra, and properties of 4:2-coordinated materials. I. Crystalline and amorphous SiO 2 and GeO 2

Abstract: A two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed. The parameters, a covalent and a polar energy, are fitted to the optical absorption spectra. The valence energy bands and density of states are calculated. In terms of these a consistent interpretation of all the observed photoemission and x-ray-emission spectra of ${\mathrm{SiO}}_{2}$ is obtained. The x-ray-absorption spectra are also analyzed. A bond-orbital approximation allows a simple calculation of the refractive index (or dielectric constant) of the various allotropic forms of silica and germania. Finally, the variation in total energy and charge distribution with local distortion is analyzed in order to study structural stability, elastic rigidity, and the effective charges (including dynamic contributions) which determine the piezoelectric constants and infrared absorption intensities.

Interstellar H$sub 2$: The population of excited rotational states and the infrared response to ultraviolet radiation

Abstract: Molecular hydrogen in interstellar clouds absorbs ultraviolet radiation in lines of the Lyman and Werner systems. The subsequent fluorescence leads to dissociation or to the population of excited rotational-vibrational levels of the ground electronic state. The rotational-vibrational levels decay by means of quadrupole transitions which result in the emission of infrared photons and populate excited rotational levels of the lowest vibrational state. An additional input into the cascade is provided by the formation of molecules on grain surfaces. A concise tabular description of the rotation-vibration cascade is presented. Calculations of the infrared emission spectrum of H$sub 2$ are given for an illustrative cloud model which includes the processes of fluorescence and hot molecule formation. In favorable circumstances, some of the infrared lines may have detectable intensities. Due to distribution of lines, it may prove possible to detect interstellar H$sub 2$ using narrow-band filter photometry at a wavelength of 2.4 $mu$. (AIP)

Laser Spectroscopy of Atoms and Molecules

Abstract: Atomic and molecular spectroscopy with lasers.- Infrared spectroscopy with tunable lasers.- Double-resonance spectroscopy of molecules by means of lasers.- Laser Raman spectroscopy of gases.- Linear and nonlinear phenomena in laser optical pumping.- Laser frequency measurements, the speed of light, and the meter.

Infrared absorption spectra of carbon monoxide in rare gas matrices

Abstract: Medium and high resolution infrared spectra of CO trapped in solid Ne, Ar, Kr and Xe are presented. Spectra of low optical density samples are identical to those previously observed but a different assignment is proposed. Monomeric absorption is clearly identified by double doping experiments and by sample deposition through a nitrogen cold trap. In addition other broad weak bands are observed on the spectra of high optical density samples. These bands are assigned to combinations between internal vibration, libration and lattice vibrations. The barrier hindering rotation due to site distortion is estimated to 30–50 cm −1 . Librational motion is strongly perturbed by coupling with lattice motion. Carbon monoxide is also an efficient probe to study the dynamical properties of rare gas lattices.

Surface Chemistry of Oxides

Abstract: The chemistry of the surface of oxides depends to a large extent on the quantity and type of both physically and chemically (OH groups) absorbed water. Infrared spectroscopy coupled with a variety of chemical exchange processes has provided useful information on the nature and stability of the adsorbed species, and on the interaction of the surface hydroxyl groups with adsorbates at the solid/vapour and solid/liquid interfaces. Electrochemical techniques are used to study the oxide/aqueous solution interface to provide surface charge data and establish zero points of charge, both of which are related to the character of the hydroxyl group and its environment. This paper briefly reviews the application of these methods to the oxides of titanium, silicon and aluminium, in both the pure and mixed forms, and to the study of the deposition of one oxide on the surface of another.

Aggregation effect on the infrared absorption spectrum of small ionic crystals

Abstract: The frequency spectrum of clusters of small ionic particles is calculated when the particle mutual interaction is described by a dipole-dipole interaction Hamiltonian. The crystallites are spheres of known bulk dielectric properties. The actual geometry of the cluster is taken into account. Clusters of increasing size (pair, triplet, quadruplet, etc.) have been solved analytically. As expected, the dipolar broadening of the frequency spectrum of (optically active or inactive) surface modes increases with cluster size and compactness. From the spectrum of few-particle clusters, one obtains the long-wavelength modes of large linear or planar aggregates of such clusters by application of the Bloch-Floquet theorem.Application is made to ir optical absorption of NiO. The present approach is intermediate between the continuum model of a structureless powder on the one hand and microscopic calculations for single microcrystals of prescribed shape on the other hand.

Vibrational constants and force field of sulfur hexafluoride

Abstract: The infrared-active combination bands of SF/sub 6/ gas were remeasured and the band origins estimated. These data were combined with the Raman frequencies of Bosworth et al., and with the spectrum of SF/sub 6/ in cryogenic liquid oxygen solutions reported by Bertsev et al., to obtain estimates for the 21 anharmonicity constants X/sub ij/. The resulting harmonic vibrational frequencies were used in a calculation of the general quadratic harmonic force field of SF/sub 6/. The most useful constraint in the F/sub 1//sub u/ symmetry block was the Coriolis constant zeta/sub 3/ = 0.693 +- 0.004 obtained from an analysis of ..nu../sub 3/ resolved with tunable diode lasers; but zeta/sub 4/ estimated from a similar analysis of ..nu../sub 4/, and the /sup 32/S--/sup 34/S isotope frequency shifts reported by Brunet and Perez for these fundamentals, are all in general agreement. The more important valence force constants are f/sub r/ = 5.45 +- 0.03, f/sub rr/(cis interaction) = 0.36 +- 0.01, f/sub rr'/ (trans interaction) = -0.02 +- 0.03, and f/sub ..cap alpha../ approximately 0.83, all in mdyn/A. From the absolute band intensities of Schatz and Hornig and the present force field, the S--F bond moment and its derivative are estimated tomore » be ..mu../sub 0/ = 2.44 +- 0.12 D and delta ..mu../delta r = 4.2 +- 0.3 D/A.« less

Uses of Raman Spectroscopy in Cement Chemistry

Abstract: Laser-Raman spectroscopy is largely complementary to ir spectroscopy, but spectral interpretation is simpler. Lack of homogeneity in clinker minerals, direct study of white portland cement hydration, characterization of clinker minerals, identification of the various calcium sulfate forms, and effects of carbonation are discussed.

Infrared Spectroscopy of Polymers

Abstract: Since 1945 inrared (IR) spectroscopy has become one of the most important methods for characterizing and studying the chemical and physical structure of compounds. Especially in the polymer field, IR spectroscopy and Raman spectroscopy have proved valuable for analytical and structural investigations. An IR spectrum of a polymer sample provides the following qualitative and quantitative information about the chemical and physical structure of the polymer under consideration: Chemical nature of the polymer: type and degree of branching, nature of end groups, impurities, etc. Steric order: cis-trans isomerism, stereoregularity, etc. Conformational order: physical arrangement of a polymer chain, planar zigzag conformation, helix conformation, etc. Crystallinity: number of chains per unit cell, intermolecular forces, etc.

An infrared spectroscopic study of sealants.

Abstract: – The aim of this work was to determine the quantity of remaining unreacted methacrylate groups in polymerized dental sealants. Eight brands of sealants were investigated by means of a grating infrared spectrophotometer. The infrared absorbance measurements were made before polymerization and repeated after the sealants had been polymerized at 37°C for 24 h. The quantities of remaining unreacted methacrylate groups were determined and the data expressed as percentages of the total amount of methacrylate groups in the unpolymerized materials. The results demonstrate that commercially available sealants exhibit different degrees of conversion 24 h after the start of polymerization. The quantities of remaining methacrylate groups after polymerization under conditions comparable with optimal clinical conditions range from approximately 15 % to approximately 35 % in the different brands.

Theory of the infrared spectra of the hydrogen bond in molecular crystals

Abstract: A general model for the vibrational interactions of the hydrogen bonds in molecular crystals is presented. The energy and the intensity distributions of the IR spectra of the 1-methylthymine and uracil crystals are correctly reproduced.

The solution conformation of poly(L-lysine). A Raman and infrared spectroscopic study.

Abstract: The Raman and infrared spectra of poly(L-lysine) and poly(DL-lysine) in solution are reported and the effects of various salts are investigated. The results demonstrate that α-helix formation in solution is induced by specific salts and the spectral data support the hypothesis of regions of local order for poly(L-lysine) in aqueous solutions of low ionic strength.

The predicted infrared spectrum and the structure of the isolated UF5 molecule

Abstract: The infrared absorption spectrum by the fundamental modes of UF5 is calculated using force constants transferred from UF6 to predict the wavenumbers and using the F atom polar tensor from CH3F to predict the intensities. Calculations are made for several assumed geometrical configurations of UF5. Comparison of the predicted spectra with the recently observed spectrum, in the UF‐stretching region, of a photolysis product of UF6 isolated in an Ar matrix suggests strongly that the structure is square pyramidal (C4v) with the U atom above the F atom equatorial plane. Although the model for the intensities is simple, the calculated spectrum is expected to predict the correct order of magnitude of the intensities of the fundamentals, first overtones, and binary combination bands of UF5, and the approximate wavenumbers for the expected absorption. Some comparisons are given between the calculations for the several structures of UF5 and observed spectra of other XF5 molecules, including PF5, BrF5, and IF5.

Evidence for a second kind of trapped electron in some deuterated aqueous glasses at low temperatures. A pulse radiolysis study

Abstract: Several deuterated aqueous glasses have been pulse-irradiated at 76 K. In addition to the well known visible absorption band of et−, a second intense infrared absorption band, with λmax > 3200 nm, has been found in (a) 50% by volume ethylene glycol, (b) 9.5 M LiCl, and (c) 2.5 and 4 M MgCl2 glasses. Electron scavengers decrease the intensities of both bands, but to different extents. An increase in temperature decreases the intensity of the infrared band, but not that of the visible band. These and other features lead us to conclude that the infrared band is due to shallowly trapped electrons which are distinctly different from trapped electrons which absorb in the visible region.The decay of the infrared band extends over several orders of magnitude in time and, unlike that of the visible band, is independent of wavelength. In the two chloride glasses the decay of the infrared band is accompanied by emission (λmax ≈ 410 nm) and is probably due to a spur reaction between an electron and hydroxyl radical t...

Vibrational spectroscopy of matrix‐isolated UF6 and UF5

Abstract: The vibrational spectrum of UF6 molecules isolated in Ar, Xe, and CO matrices is reported. Also, the ir spectrum of monomeric UF5 molecules produced in these matrices by photolysics with uv radiation is reported. (AIP)

Elimination of Thin Film Infrared Channel Spectra in Fourier Transform Infrared Spectroscopy

Abstract: Thin samples in spectroscopy often show disturbing "channel spectra" due to interference fringes produced by reflections at the sample surface. These fringes will be characterized by a set of peak wavenumbers, vm as Vm = m/2nd (1) where m = 0, 1, 2, ... ; n is the sample refractive index, and d, its thickness. The intensity of these peaks, ΔT, is given by ΔT = 4 (n − 1/n + 1)2 (2) for thin film solid samples and ΔT = 4 (n − n0/n + n0)2 (3) for samples contained between windows of index n0.