Showing papers on "Raman spectroscopy published in 1970"

Raman Spectrum of Graphite

Abstract: Raman spectra are reported from single crystals of graphite and other graphite materials. Single crystals of graphite show one single line at 1575 cm−1. For the other materials like stress‐annealed pyrolitic graphite, commercial graphites, activated charcoal, lampblack, and vitreous carbon another line is detected at 1355 cm−1. The Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k‐selection rule. The intensity of this band allows an estimate of the crystallite size in the surface layer of any carbon sample. Two in‐plane force constants are calculated from the frequencies.

Raman Spectrum of Diamond

Abstract: The first- and second-order Raman spectra of diamond were studied using the 4880 \AA{} and 5145 \AA{} lines of an Ar ion laser and the 6328 \AA{} line of a He-Ne laser. The spectra were recorded at room, liquid-nitrogen, and liquid-helium temperatures. In addition to the second-order spectrum previously reported by Krishnan, a new weaker second-order spectrum was observed in the range 1600-2100 ${\mathrm{cm}}^{\ensuremath{-}1}$. Polarization studies were carried out on both the first- and second-order spectra. From such studies it was established that the 1332-${\mathrm{cm}}^{\ensuremath{-}1}$ Raman line is the zone-center optical phonon with ${\ensuremath{\Gamma}}^{(25+)}$ (${F}_{2g}$) symmetry. The prominent features in both the second-order Raman spectra reported here and the second-order infrared spectra are interpreted in terms of the critical points of the phonon dispersion curves established from neutron spectroscopy and on the basis of space-group selection rules.

Temperature Dependence of Raman Scattering in Silicon

Abstract: We have measured the linewidth and the frequency of the q=0 optical phonon in silicon over the temperature range of 20-770\ifmmode^\circ\else\textdegree\fi{}K. The temperature dependence of the linewidth has been interpreted as arising from the decay of the optical phonon to two LA phonons at half the optical frequency. From the observed temperature variation, we deduce an absolute half-width $\ensuremath{\Gamma}$ of 2.1 ${\mathrm{cm}}^{\ensuremath{-}1}$ at 0\ifmmode^\circ\else\textdegree\fi{}K. This value is considerably smaller than that obtained theoretically by Cowley on the basis of numerical calculations which include decay to phonons throughout the Brillouin zone. His numerical calculations also predict a temperature dependence of the linewidth which does not agree with experiment. However, the observed change in frequency with temperature correlates very well with Cowley's theory. We have also studied the relative intensities of Stokes and anti-Stokes components of Raman spectra. The observed temperature dependence of the relative intensities is compared with that predicted on the basis of the Bose-Einstein population factor for the optical phonon.

Characterization of Graphite Fiber Surfaces with Raman Spectroscopy

Abstract: Raman spectroscopy is used to characterize the fiber surface of graphite and carbon fibers. A correlation exists between the Raman spectrum of the fiber surface and the shear strength of the com po...

Atomic vibrations in vitreous silica

Abstract: Frequency spectra and normal modes of vibration have been computed for vitreous silica. They have been calculated from atomic arrangements in physical models based on the random network theory. The positions of bands in the computed spectra agree well with observed features in the experimental infra-red and Raman spectra of the glass. Detailed analysis of the normal modes indicates that the bands at 1050, 750 and 400 cm–1 are associated with bond-stretching, bending and rocking motions, respectively, of the oxygen atoms. Atomic vibrations in the glass are, on the whole, less extended in space than the plane wave-like modes which prevail in perfect crystals. The spatial localization tends to be greatest at high frequencies and near band edges. If non-bridging oxygen atoms are present in the structure, the frequenncy spectrum exhibits an additional band of very intense localization, associated with bond-stretching vibrations of the non-bridging atoms.

Variable Temperature Sample Holder for Raman Spectroscopy

Abstract: This note describes a simple, convenient sample holder for laser Raman spectroscopy of liquids and powders at any temperature between −196° and +200°C. It was designed for the Spex Ramalog system, which uses 90° viewing. With this system a liquid or powdered sample is contained in a thinwalled melting point tube which is oriented crosswise to the slit, i.e., parallel to the plane of the slit jaws and perpendicular to the long axis of the slit.1 The laser beam impinges on the sample vertically, and the tattered radiation is viewed horizontally.

Resonance Raman Effect and Resonance Fluorescence in Halogen Gases

Abstract: The various output frequencies of the argon ion laser at 5145, 5017, 4965, 4880, and 4765 A lie in the absorption bands of the heavier halogen gases. With the appropriate choice of exciting line, either resonance Raman effect or resonance fluorescence can be observed. The difference between the two types of spectra are discussed in some detail. In the case of a strong resonance Raman effect, overtone sequences up to the 14th harmonic could be observed. Raman frequencies, depolarization ratios, and relative scattering cross sections are given for the fundamentals and overtones of Cl2, Br2, I2, BrCl, ICI, and IBr at 4880 A excitation.

Raman Spectra of Polycrystalline Solids; Application to the Pb Ti 1 − x Zr x O 3 System

Abstract: It is shown that Raman scattering from polycrystalline piezoelectric solids contains all of the essential features of Raman single-crystal spectra even when the crystal spectrum is quite anisotropic As an illustration of the Raman powder technique, the ceramic ferroelectric-antiferroelectric system PbTi${\mathrm{O}}_{3}$-PbZr${\mathrm{O}}_{3}$ has been investigated and the "soft" $E(\mathrm{TO})$ optical phonon modes measured in the tetragonal ferroelectric region

Raman Studies of Underdamped Soft Modes in PbTi O 3

Abstract: Unlike other ferroelectric perovskites, PbTi${\mathrm{O}}_{3}$ displays temperature-dependent Raman spectra consisting of underdamped modes, including the "soft" transverse-optical (TO) modes. Moreover, the softest TO mode shows linewidth divergence at the ferroelectric-to-paraelectric transition. Also in contrast to previously studied perovskites, Raman selection rules are rigorously obeyed in both the ferroelectric and paraelectric states.

The single-crystal Raman spectra of nearly opaque materials. Iron(III) oxide and chromium(III) oxide

Abstract: A technique for studying orientation effects on nearly opaque single crystals with laser Raman spectroscopy is described in detail. The instrument used in these studies is a Spex monochromator. The scattering equations derived are applied to a study of iron(III) oxide and chromium(III) oxide.

Raman Spectral Studies of the Effects of Perchlorate Ion on Water Structure

Abstract: Raman contours corresponding to the OD and OH stretching vibrations from HDO, as well as from H2O and D2O, were obtained at 25°C from a series of ternary aqueous solutions containing HDO, ClO4− (Li+, Na+, K+), and H2O or D2O. The Raman spectra were obtained photoelectrically using 4880‐A argon‐ion‐laser excitation, as well as conventional 4358‐A mercury excitation. Quantitative Raman data were obtained from ternary solutions having NaClO4 concentrations from 1 to 4M, and stoichiometric concentrations of 5.51M D2O (H2O as solvent), or 5.53M H2O (D2O as solvent). Raman spectra were also obtained from solutions having lower (and higher) HDO or NaClO4 concentrations. In addition, binary solutions of NaClO4 and H2O or D2O were examined. Addition of ClO4− to solutions containing HDO, and H2O or D2O produces a pronounced splitting of the OD and OH stretching contours from HDO, as well as from D2O and H2O. The splittings are directly observable in the Raman spectra. Two principal peaks or components, having frequ...

Raman spectra of poly(ethylene glycols) in solution

Abstract: Raman spectra have been obtained from poly(ethylene glycol) (PEG) in the solid and molten phases and in aqueous and chloroform solutions. Several new lines are observed or resolved in the Raman spectrum of the solid state as a result of using a high-power argon-ion laser as a source. The Raman spectra of the molten polymer and the chloroform solutions are indicative of a disordered structure, since additional Raman lines appear as a result of the additional rotational isomers. The Raman spectrum of the aqueous solution shows that considerably less structural change occurs upon dissolution in water.

Developments in the Theories of Vibrational Raman Intensities

Abstract: The theory of light scattering from an individual particle involving the “summation-over-states” problem of second-order perturbation theory, was offered first in 1925 by Kramers and Heisenberg1 by analogy to the classical theory of dispersion. The same expression was verified later by Dirac2 based on the radiation-field theory. And from this expression Van Vleck3 derived the basic selection rules for the vibrational Raman effects in molecules. For the nonresonance case, special simplifications are possible. When the frequency of the incident light is far from the resonance region, and the initial and final states of the molecule are both in the ground electronic state, it was shown by Placzek4 that the intensity of molecular Raman scattering arises from the dependence of the ground-state polarizability on nuclear vibrations. This so-called polarizability theory of Placzek has led to the bond polarizability theory commonly used by chemists to analyze vibrational Raman spectra in terms of ground-state properties of the molecules. (The bond polarizability theory is reviewed in the first volume of this book.) The object of the present chapter is to review the recent developments of Raman intensity theories, beginning, more or less, at the stage subsequent to the material treated in the first volume and continuing to the most recent work which has appeared in the literature (1960–1968).

Raman studies on rock-forming minerals. Part II. Minerals containing MO3, MO4, and MO6 groups

Abstract: Raman spectra of a number of carbonate, phosphate, arsenate, vanadate, niobate, tantalate, sulphate, chromate, molybdate, and tungstate minerals have been measured over the range 140–1200 cm.–1(600–1600 cm.–1 for carbonates). The internal modes of the (MOn) groups in these minerals have been assigned, and the validity of factor group and site symmetry analyses discussed. The use of Raman spectroscopy for mineral studies is discussed.

Phonon and Electronic Raman Spectra of Cubic Rare-Earth Oxides and Isomorphous Yttrium Oxide*

Abstract: Laser-excited Raman spectra have been observed in single crystals of Y2O3, Y2O3(Eu3+), Er2O3, and YB2O3 at 10, 80, and 300 K. In Y2O3(Eu3+) the symmetries of the excited levels have been determined. The optically active phonons can be separated into two groups; in one group (above 300 cm−1) the internal vibrations of (R.E.-O6) octahedrons are preponderant, whereas in the other group (below 200 cm−1) the translational motions of these octahedrons and the R.E. ions are dominant. In Y2O3(Eu3+) electronic transitions (2F0 → 2F2) of the Eu ions in C3i-site symmetry have been observed and the symmetries of the crystal-field-split levels have been determined. Other effects, which may also be attributed to electronic Raman transitions, have been observed in Er2O3 and Yb2O3.

LOW‐POWER QUASI‐cw RAMAN OSCILLATOR

Abstract: Quasi‐cw stimulated Raman emission in the visible has been obtained from an oscillator cavity with a pump‐power input of less than 5W. This large reduction of oscillator threshold is achieved with the use of a liquid‐core optical waveguide structure. Significant conversion of pump to Stokes light has been observed. Extension of the system to continuous operation and to the study of other nonlinear effects is suggested.

Raman Spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 in the Vapor State

Abstract: Raman spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 have been observed for the gaseous state using laser excitation Some assignments of fundamental frequencies have had to be revised from previously accepted values The overtone 2ν6 was observed for all these gaseous hexafluorides and several other overtones were observed for some of the molecules Considerable broadening of the eg and f2g fundamentals was observed for TcF6 and for ReF6 This broadening is attributed to dynamic Jahn–Teller coupling The best currently available measured values of fundamental frequencies for all 15 hexafluoride molecules of known Oh symmetry are tabulated

Resonance Raman Scattering of Laser Radiation by Vibrational Modes of Carotenoid Pigment Molecules in Intact Plant Tissues

Abstract: WE report here the detection of resonance Raman (RR)1–11 scattering of laser radiation from vibrational modes in the molecules of the carotenoid pigments12–14 lycopene and β-carotene in intact plant samples (Figs. 1a and b). Resonance enhancement is obtained in the Raman spectra of pigments excited at wavelengths in the region of electronic absorption. The effect is manifest in a conspicuous gain in the scattering efficiency from some of the vibrational modes of the pigment. The scattered light becomes sufficiently intense to overcome the increased absorption losses of both the exciting and the scattered radiation. In this study we have demonstrated this effect in heterogeneous (tissue) samples, in which the pigment is just one constituent.

Raman spectra and lattice dynamics of the α phases of nitrogen and carbon monoxide crystals

Abstract: The Raman spectra of polycrystalline α-nitrogen and α-carbon monoxide have been recorded at 18 °K, using argon–ion and helium–neon laser excitation. Previously undetected peaks at 60 cm−1 for N2 an...

Raman Spectra and the Phonon Dispersion of Polyglycine

Abstract: The Raman spectra of the two crystalline modifications of polyglycine, I and II, and of N‐deuterated polyglycine II have been recorded. The results of a normal‐coordinate analysis of polyglycine II and N‐deuterated polyglycine II are presented along with the phonon dispersion curves of polyglycine II. Assignments are made on a number of bands not observed in the infrared. Some previous band assignments are found to be inconsistent with the Raman data.