Showing papers on "Raman spectroscopy published in 1973"

Raman gain in glass optical waveguides

Abstract: The small signal Raman gain in a single‐mode glass waveguide amplifier has been measured directly. The measured gain is in good agreement with that calculated from the Raman cross section. The cross section was determined by a comparison of the spontaneous Raman scattering of fused quartz and benzene.

Pressure and Temperature Dependences of the Raman-Active Phonons in Sn O 2

Abstract: The temperature (10-500 \ifmmode^\circ\else\textdegree\fi{}K) and pressure (0-4 kbar) dependences of the four Raman-active phonons ${B}_{1g}$, ${E}_{g}$, ${A}_{1g}$, and ${B}_{2g}$ as well as thermal expansion (93-700 \ifmmode^\circ\else\textdegree\fi{}K) and isothermal compressibility (0-3 kbar) in Sn${\mathrm{O}}_{2}$ were measured. These measurements allowed us to determine the mode Gr\"uneisen parameters for the Raman-active phonons and to separate the isobaric temperature dependence of each frequency into pure-volume and pure-temperature contributions. By this procedure the cubic and quartic anharmonicities responsible for the pure-temperature contributions to the mode frequencies were determined. The ${B}_{1g}$ mode in Sn${\mathrm{O}}_{2}$ exhibited anomalous temperature and pressure dependences in that $\ensuremath{\omega}({B}_{1g})$ increased with temperature and decreased with pressure. The remaining modes exhibited decreases in frequency with increasing temperature and increases in frequency with increasing pressure, characteristic of ionic crystals. The results are compared with the recent results on the isomorphic compound tetragonal Ti${\mathrm{O}}_{2}$.

Raman cross section of some simple gases

Abstract: The differential Raman cross sections of the main Raman-active vibrations have been measured in the gases N2, O2, H2, CO, NO, CO2, SO2, N2O, H2S, NH3, ND3, CH4, C2H6, and C6H6 using 488.0-nm laser light. The present results are compared with previous measurements made at other wavelengths. The Raman cross sections of the rotational lines in the diatomic gases were also measured, as were the vibrational-rotational lines of O2 and N2. Absolute measurement of the Raman cross sections were performed two ways: (i) by calibrating the Raman spectrometer, and (ii) by comparing the unknown against liquid benzene (for which the Raman cross section has been measured). Results of these measurements compare reasonably well with previous determinations for which corrections for the υ4 frequency dependence were made.

Assignment of ν2 (E) and ν4 (F2) of tetrahedral species by the calculation of the relative Raman intensities: The vibrational spectra of VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4

Abstract: A new method has been developed to assign the frequencies ν2(E) and ν4(F2) in tetrahedral molecules and ions. The method employs the calculation of the relative Raman intensities and has been applied to VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4. The assignment of the frequencies has been further confirmed by measuring the infrared and Raman spectra of some of the ions and molecules in the same solvent. A more complete spectrum of TcO4− than earlier reported in the literature has been given.

Infrared Reflectivity and Raman Scattering of Mg2SiO4 Single Crystal

Abstract: The lattice vibrations of Mg2SiO4 forsterite single crystal have been studied using infrared and Raman techniques. The site symmetry method allows to study the degeneracy lifting of the silicate ion vibrational levels and to assign the modes of vibration (45 infrared active modes and 36 Raman active modes), as internal or external. The analysis of the reflectivity data between 150 and 10000 cm−l by classical dispersion theory allows to find the oscillator parameter values. Most of the infrared lattice bands could be identified. All the predicted modes have been observed in the Raman spectra and the vl1 v2, and v4 lines have been identified. For some modes, specially in the low frequency range, the difference between internal and external modes is not obvious, taking into account the SiO4 tetrahedra deformation. Nous avons etudie, par reflexion infrarouge et diffusion Raman. les vibrations de reseau d'un monocristal de forsterite Mg,Si04. La mkthode du site nous a permis d'etudier la levee de degenbrescence des vibrations de l'ion silicate e t de classer les modes (35 actifs infrarouge et 36 actifs Raman) en internes e t externes. L'analyse des spectres de reflexion observks entre 150 et 10000 cm−l par les relations classiques de dispersion nous a permis de determiner les parametres associbs aux modes B1u, B2u B3u et Bsu. Nous avons interprkte la majeure partie des modes infrarouge. Par diffusion Raman, nous avons observe la totalite des raies prkvues e t nous avons identifik les modes issus de v1,v2 e t v4. Pour certains modes, notamment de basse frequence, la distinction entre modes externes et internes doit dtre nuanche, compte tenu de la deformation des tetraedres SiO4.

Disulfide bond dihedral angles from Raman spectroscopy.

Abstract: Raman spectra of several compounds containing the CS-SC moiety were obtained (in the solid phase) from 450-800 cm(-1) to investigate the S-S and C-S stretching behavior. The S-S stretching frequency varied linearly with the CS-SC dihedral angle (obtained from either x-ray or neutron diffraction or ultraviolet absorption) for compounds whose CC-SS dihedral angles were not very different. The ratio of the intensities of the S-S and C-S stretching bands exhibited no recognizable correlation with either the CS-SC dihedral angle or the CSS bond angle, probably because this ratio is sensitive to the crystalline environment. The linear dependence of the S-S stretching frequency on dihedral angle leads to a dihedral angle for the plant hormone, malformin A, that is in excellent agreement with that estimated from the longest wavelength CS-SC ultraviolet absorption band.

The Growth of a GaAs–GaAlAs Superlattice

Abstract: An ultra high vacuum epitaxy system is described, including special features such as computer control. The system is capable of preparing sophisticated structures requiring a high degree of precise control. GaAlAs films have been grown and evaluated by various techniques; He-ion backscattering and Raman spectroscopy have been shown to be particularly valuable for periodic structures. A structure with a very narrow period has been made, and its transport properties measured and interpreted by the superlattice mechanism.

Nonlinear Behavior of Stimulated Brillouin and Raman Scattering in Laser-Irradiated Plasmas

Abstract: Both analytic theory and inhomogeneous plasma simulations are presented to show the nonlinear development of the Brillouin and Raman backscatter instabilities. Nonlinear fluid behavior predicts a backscatter energy on the order of the incident laser energy, but particle trapping and heating effects associated with the excited electrostatic wave can significantly reduce this.

Binary transition metal dinitrogen complexes. I. Matrix infrared and Raman spectra, structure and bonding of Ni(N2)n and Pd(N2)m(n = 1-4 and m = 1-3)

Abstract: The products of the cocondensation reactions of Ni and Pd atoms with N2 at 4.2-10'K are investigated by matrix isolation infrared and Raman spectroscopy and are shown to be binary dinitrogen complexes of the form of Ni(N2), and Pd(N2)m. Examination of the reaction products in pure 14N2,in 14N2/15N2, in dilute Ar/14N2, Ar/14N2/15N2 and Ar/14N5N matrices establishes the stoichiometries of the complexes to be respectively n = 1-4 and m = 1-3. Structural assignments can be made for most of the complexes on the basis of infrared and Raman activities and are found to be similar to the analogous carbonyls. Isotopic frequencies and integrated infrared absorption intensities, computed for the NN stretching modes of the individual dinitrogen complexes on the basis of the Cotton-Kraihanzel force field approximation and on isotopic intensity sum rules, are found to be in close agreement with the observed values. Ni(N2)4 in argon is a regular tetrahedral molecule with “end on bonded” dinitrogen. In nitrogen, however, it is slightly distorted. Calculations show that a substitutional site symmetry C2 for Ni(N2) satisfactorily accounts for all of the spectral lines observed for the complex in nitrogen.

Temperature Dependence of the Raman Spectrum and the Depolarization Spectrum of Amorphous As 2 S 3

Abstract: The polarized Stokes and anti-Stokes Raman spectrum of amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ has been measured at several temperatures in the range 20-448 \ifmmode^\circ\else\textdegree\fi{}K with a He-Ne laser, and at room temperature with a c.w. dye laser. Using the Shuker-Gammon data-reduction method, the approximate density of vibrational states has been determined from the Raman spectra and has been found to be temperature independent. A new type of spectrum, the depolarization spectrum, has been measured for amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$. The depolarization spectrum has been defined to be the dispersion of the Raman depolarization ratio. The measured Raman and depolarization spectra have been used to test the validity of the two structural models of vitreous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ proposed to date, namely: the planar-random-network model of Bermudez and the molecular model of Lucovsky and Martin. It has been shown that both models can be used to calculate Raman spectra in reasonable agreement with experiment while only the molecular model is compatible with the observed depolarization spectrum. Further, it has been demonstrated that the depolarization spectrum, not the Raman spectrum, provides a test of the applicability of the Shuker---Gammon data-reduction technique to a given amorphous solid. The low-temperature ($\ensuremath{\sim}20$ \ifmmode^\circ\else\textdegree\fi{}K) Raman and room-temperature infrared transmission spectra of orpiment, the crystalline form of ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, have been measured. Several lines unresolved in previously reported room-temperature Raman spectra of orpiment have been resolved in the low-temperature spectra. The envelope of the approximate density of vibrational states of orpiment has been found to resemble remarkably the approximate density of vibrational states of amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$. This resemblance has been explained using the molecular model.

Molecular reorientational motion in liquid acetonitrile: Raman band shapes, diffusion constants and activation energy of reorientation

Abstract: Isotropic I α(ω) and anisotropic I β(ω) Raman band shape analyses of the ν1(a1) fundamentals in liquid CH3CN and CD3CN are reported. The ν2 and ν4 fundamentals are complicated by secondary structure and therefore were not studied in detail. Values of the perpendicular rotational diffusion constants D⊥, derived from the ν1(a1) fundamentals of both isotopic species are in good agreement with those obtained using NMR relaxation and dielectric methods and in addition agree closely with values calculated from microviscosity theory. The latter is based upon a model which involves a connection between the rotational and translational motions in liquids. In this model, reorientations perpendicular to the C3 axis proceed by small step Brownian diffusion and D⊥ (Raman) for CD3CN yields an activation energy for liquid state molecular reorientations perpendicular to the C3 symmetry axis of 2.0 ± 0.3 kcal/mole, in good agreement with existing NMR and microviscosity values. Comparison of Raman data and results reported here with available infrared results reveals that the D⊥(ir) values are too high by a factor of 2. The source of the infrared errors is discussed.Isotropic I α(ω) and anisotropic I β(ω) Raman band shape analyses of the ν1(a1) fundamentals in liquid CH3CN and CD3CN are reported. The ν2 and ν4 fundamentals are complicated by secondary structure and therefore were not studied in detail. Values of the perpendicular rotational diffusion constants D⊥, derived from the ν1(a1) fundamentals of both isotopic species are in good agreement with those obtained using NMR relaxation and dielectric methods and in addition agree closely with values calculated from microviscosity theory. The latter is based upon a model which involves a connection between the rotational and translational motions in liquids. In this model, reorientations perpendicular to the C3 axis proceed by small step Brownian diffusion and D⊥ (Raman) for CD3CN yields an activation energy for liquid state molecular reorientations perpendicular to the C3 symmetry axis of 2.0 ± 0.3 kcal/mole, in good agreement with existing NMR and microviscosity values. Comparison of Raman data and results reported...

The effect of the internal field on Raman scattering cross sections

Abstract: The increase in amplitude of incident and Raman scattered radiation brought about by the dielectric nature of liquids is known as the internal field effect and is responsible for increasing scattering cross section with increasing refractive index. This effect has been investigated quantitatively by independent measurements of corresponding liquid and gas phase cross sections of 53 Raman bands, or groups of bands, from 14 different organic compounds. Agreement with proposed theory is obtained in most cases, notable exceptions occurring with hydrogen bonded liquids.

Dielectric parameterization of raman lineshapes for GaP with a plasma of charge carriers

Abstract: We have studied the Raman lineshapes of several samples of GaP with appreciable carrier concentrations. There is no feature identifiable as a plasma resonance, but there are pronounced effects of interaction with the LO phonon resonance. For analysis we have developed a model along lines laid down by Barker and Loudon, employing Nyquist relations to calculate infrared fluctuations which scatter light. We introduce a response matrix α(ω) withseveral resonances; and we uncover some points which seem to be new, for coupled-mode scattering systems in general. In the GaP-plasma problem the data do not necessitate inclusion of the scattering amplitude from the plasma; we ascribe this to large plasma damping rates (ωτ≲1). This provides an account for the lack of any apparent plasma resonance in the scattering and for the modified appearance of the LO phonon, relative to the pure crystal. We emphasize that the following parameters suffice: Lorentz parameters measured in linear infrared experiments, the nonlinear parameterC from a visible-infrared mixing experiment, and the plasma frequency and damping fit to each sample. Beyond treatment of the plasma problem, the theory bears more generally on the conditions under which an LO Raman lineshape measures locally the shape of 〈E 2〉ω. Also it bears upon the analysis of polariton linewidths to infer the variation of the phonon damping Γ(ω).

Evidence for short-range orientation effects in dipolar aprotic liquids from vibrational spectroscopy. Part 1.—Ethylene and propylene carbonates

Abstract: The CO stretching frequency of liquid ethylene and propylene carbonates is higher in the infrared than in the Raman spectrum. The difference amounts to 13 cm–1 for ethylene carbonate at 313 K. This effect is explained as the consequence of a coupling between the transition dipoles of neighbouring molecules, which is made possible by some degree of alignment of molecular dipoles due to the high dipole moment of these molecules (about 16 × 10–30 C m). A study of dilution and temperature effects confirms this interpretation.

The preparation, properties, and vibrational spectra of complexes containing the AuCl2–, AuBr2–, and AuI2– ions

Abstract: The preparation and isolation of the complexes [Et4N][AuX2] and [Bun4N][AuX2], where X = Cl, Br, or I, are described. The i.r. and Raman spectra of the salts have been interpreted in terms of linear anions in each case. The fundamental frequencies of each anion are compared with those of the structurally similar HgX2 molecules, and appropriate force constants are given.

Effects of Free Carriers on Zone-Center Vibrational Modes in Heavily Doped p -type Si. I. Acoustical Modes

Abstract: We have performed a systematic study of free-carrier effects on the elastic constant ${C}_{44}$ (this paper) and on the Raman spectrum (a succeeding paper) of heavily doped $p$-type Si. We have considered samples with a wide range of impurity (boron) concentrations, with and without the application of uniaxial stress. The data on the acoustical modes are compared with Keyes's theory, and extensions of this containing the effects of an external uniaxial stress. In particular, we have found satisfactory agreement between experiments and theory in the regions of high and low impurity concentrations. The various calculations were based on models for the valence bands, yielding information as to their applicability to problems of this nature. More generally, we have found a number of similarities between the effects of doping on the acoustical and optical zone-center vibrational modes, suggesting that both effects are produced by the same basic mechanism.