Showing papers on "Raman spectroscopy published in 1968"

Molecular Vibration Spectra by Inelastic Electron Tunneling

Abstract: An experimental and theoretical study has been carried out on the process of inelastic tunneling between metal films. The experimental results show that this process gives rise to the observation of vibrational spectra for molecules contained in the junction region. The phenomena have been studied for a number of molecular species and at temperatures ranging from 1 to 300\ifmmode^\circ\else\textdegree\fi{}K. The principal effect of temperature is to broaden the observed spectral lines which can be accounted for quantitatively by considering the thermal smearing of the electron distribution in metals. Two detailed interaction mechanisms are discussed which can give rise to infrared dipole or Raman selection rules. None of the experiments carried out thus far can distinguish between these two processes, because of the low symmetry of the molecules used. In addition to the vibrational spectra, it appears that it should be possible to observe electronic transitions as well.

Raman Spectrum of Strontium Titanate

Abstract: The Raman spectrum of single‐crystal SrTiO3 has been investigated as a function of temperature down to about 25°K. The lattice dynamics of this crystal have been extensively studied in recent years primarily because of its unusual dielectric and acoustic properties. Both nominally pure and impure samples were examined since these properties seem to be sensitive to small amounts of impurities. An argon‐ion laser served as the exciting source and an in‐tandem grating spectrometer was used to disperse the scattered light. These instrumental techniques provided rather complete data including the polarization characteristics of the individual lines and peaks. The above data, together with the known phonon dispersion curves of SrTiO3, made it possible to obtain a reliable interpretation of the Raman spectrum. At room temperature we find the Raman spectrum to be entirely second order, in agreement with the selection rules for the cubic perovskite structure. Further, the phonons contributing to the second‐order s...

The vibrational spectra of vitreous silica, germania and beryllium fluoride

Abstract: Vibrational frequency spectra are presented for vitreous silica, germania and beryllium fluoride; these have been computed from atomic arrangements in physical models described in an earlier paper. The positions of bands in the computed spectra agree well with observed bands in the experimental infra-red and Raman spectra.

Raman Spectral Studies of HDO in H2O

Abstract: Argon‐ion‐laser and mercury‐excited photoelectric Raman spectra have been obtained from a 6.2M solution of D2O in H2O in the temperature range of 16°‐97°C and at frequencies from 2000‐3000 cm−1. Examination of the OD stretching contours observed near 2500‐2600 cm−1 revealed marked asymmetry, and a high‐frequency shoulder was apparent in all cases. In addition, an isosbestic point was found at 2570 ± 5 cm−1.The OD stretching contours were analyzed by means of a special‐purpose analog computer, and two Gaussian components near 2510‐2540 and 2630‐2660 cm−1 were found to provide adequate fits of the contours in the temperature range involved, although some indication of a third weak Gaussian Raman component was found, and three Gaussian components were employed to fit the infrared‐absorbance contours also obtained in this work. The integrated Raman intensities of the two principal Gaussian components were observed to have opposite temperature dependences, and the component intensities yielded a value of 2.5 ±...

Lattice Vibrations of Yttrium Vanadate

Abstract: The lattice vibrations of YV${\mathrm{O}}_{4}$ have been analyzed group-theoretically, and symmetry coordinates for the vibrations have been constructed The first-order Raman spectrum is reported in detail and preliminary results of infrared (IR) measurements are given Six of the seven allowed IR-active modes and nine of the twelve allowed Raman-active modes have been observed Symmetry assignments are given for all observed modes

Single Crystal Laser Raman Spectroscopy

Abstract: The chemical implications of single crystal Raman spectroscopy by means of laser excitation are briefly outlined. Unambiguous assignments are presented for PdCl 2- 4 , PtCl 2- 4 , PtCl 2- 6 , PdCl 2- 6 , GeCl 2- 6 and TeCl 2- 6 species. Detailed scattering equations are applied to mercurous chloride. The vibrational spectra of cassiterite, anataseand rutile are discussed in terms of the factor group. Gallium trichloride and aluminium tribromide spectra are discussed from the viewpoint of a perturbed D 2h Raman tensor. The complex spectrum of molybdenum trioxide is interpreted in terms of a site-factor group analysis. Problems of birefringence, crystal imperfection, dichroism, the resonance Raman effect, twinning, enantiomorphism, internal reflexion and dependence of relative intensity on physical state are noted. The methods discussed are applied to the first-order spectra of centrosymmetric crystals and rely on the validity of the Raman tensor predictions resulting from factor group analysis.

Raman and Infrared Studies of Coupled PO4−3 Vibrations

Abstract: The vibrations of PO4−3 ions in single crystals of hexagonal Ca10(PO4)6F2 have been observed by means of polarized Raman scattering and polarized infrared reflectance. The T2(ν3) and T2(ν4) Raman vibration frequencies are each observed to split in accord with the predictions of the factor group of the unit cell. The optically active vibrational modes are also observed, and the anisotropy of the extraordinary ray frequencies have been measured. The observations are analyzed in terms of dipole–dipole interionic forces using Ewald dipole summation techniques to account for the entire phosphate lattice. Qualitative agreement between the dipole model and experiment is achieved. The roles of short‐range forces and background dielectric shielding are discussed.

Measurements on the raman component of laser atmospheric backscatter

Abstract: Density profiles of the gaseous atmosphere up to 3 km have been measured using laser backscatter. The ambiguity in the return at the laser frequency (6943 A) due to the aerosol scatter component was avoided by monitoring the frequency‐shifted Raman vibrational‐rotational band of the nitrogen component centered at 8285 A.

Raman Scattering from InSb Surfaces at Photon Energies Near the E 1 Energy Gap

Abstract: We have observed surface electric-field-induced and resonance-enhanced Raman scattering by $q\ensuremath{\approx}0$ LO phonons in the spectra obtained from InSb surfaces. The data indicate that excitons are responsible for the resonance enhancement. The effects of temperature and externally applied electric fields are discussed. The results suggest the possibility of studying the surface electronic properties by Raman spectroscopy.

Laser-Excited Rotation–Vibration Raman Scattering in Ultra-Small Gas Samples*

Abstract: The focused beam of an argon–ion laser was used as a light source for Raman-scattering experiments in gases. Photoelectric recording of rotation–vibration Raman spectra has been observed from about 1011 gas molecules in the focal region of the laser beam. The focusing geometry used to illuminate the gas samples is discussed and the important parameters of the optical system for collecting the Raman-scattered light from the small volumes are considered. The pulse-counting detection system is described and the new experimental results are presented.

cis-Dioxo- and trioxo-complexes

Abstract: Raman and infrared spectra have been measured of a number of transition-metal complexes of the form [MO2X4]n–(M = MoVI, WVI, or VV; X = F, Cl, or ½ Ox), and a cis configuration of the oxygen ligands has been found for these d0-species. The results are compared with those obtained for trans-dioxo-complexes and the differences explained in terms of the oxygen–metal bonding involved. The vibrational spectra of a number of trioxo-species and some polymeric oxyfluorides have also been measured.

Infrared and raman investigation of condensed phases of methylamine and its deuterium derivatives.

Abstract: IR and Raman spectra of solid and matrix isolated methylamine and deuterium derivatives, locating amine twisting vibration in solid phase IR spectra

Vibrational Assignment of Carbazole from Infrared, Raman, and Fluorescence Spectra

Abstract: The infrared, Raman, and fluorescence spectra of carbazole are reported with as complete polarization information as possible An experimental assignment of fundamentals is given and is reliable only for A1 species, being incomplete or uncertain for the other symmetry species Some lattice modes of the carbazole crystal were found both in the infrared and Raman spectra, and a partial assignment made A crude normal‐coordinate calculation was made using a force field transferred from phenanthrene for the in‐plane problem and from benzene and anthracene for the out‐of‐plane problem The observed and calculated frequencies are compared, and good agreement is found for the A1 fundamentals

Raman Spectrum of Crystalline Sodium Nitrate

Abstract: Raman scattering from crystalline NaNO3 has been observed in all polarization orientations. Except for small intensity contributions in some orientations which are probably due to depolarization effects in the birefringent crystal, the polarizability activities of both internal and external modes follow the expected symmetry selection rules. From relative intensity considerations, the bands at 185 and 98 cm− 1 have been designated as the Raman‐active librational and translational lattice modes, respectively. This assignment has been confirmed by the comparison of the lattice spectra of Na14NO3 and Na15NO3 at 35°K, where an isotope shift is observed only on the lower frequency band. No evidence of mixing between these Eg lattice modes has been observed.

Intrachain Force Field and Normal Vibrations of Polyethylene Glycol

Abstract: Normal vibrations of polyethylene glycol and the perdeuterated species were treated. Intrachain force field was expressed in terms of local-symmetry coordinates. Force constants were adjusted by the method of least squares, with reference to observed infrared and Raman frequencies. A set of force constants was obtained, which reproduces the observed frequencies with an r. m. s. deviation of 0.9%. The values of the force constants thus refined were discussed in comparison with corresponding values of related molecules. Vibrational assignments of the observed infrared absorption bands and Raman lines were revised on the basis of potential-energy distributions refined in the present treatment.

Raman Spectrum of α Quartz at High Pressures

Abstract: Raman spectra of single crystals of α quartz at pressures as high as 40 kbar are reported The frequencies of the Raman lines located at 128, 207, 265, 464, 697, 795, and 807 cm−1 at atmospheric pressure increase with increasing pressure by about 06, 18, 05, 09, 08, 08, and 08 cm−1·kbar−1, respectively, with a probable accuracy of about 20% due to an uncertainty about the pressure scale These frequencies of the α‐quartz spectrum also are significantly sensitive to temperature The frequencies of all other Raman lines of α quartz, except three at 145, 450, and 509 cm−1 that could not be studied, are independent of pressure

Dicke narrowing and collisional broadening of the S0(0) and S0(1) Raman line of H2

Abstract: The width of the rotational Raman lines of H2 was studied in the region of density from 1 to 100 amagats at room temperature. Collisional narrowing and collisional broadening of the lines is observed with a minimum in the width of the lines occurring near a density of 10 amagats. A comparison of the width of the S0(0) and S0(1) lines indicates that collisions which produce the broadening and the collisions which produce the narrowing are uncorrelated. The observations are only qualitatively in agreement with the theory of the width of the lines.

Photon, spin, and Raman echoes

Abstract: The general technique of the excitation of a system into a linear superposition of states is reviewed. Recent results in ruby are presented together with a simple theory which predicts Raman echoes.