Showing papers on "Raman spectroscopy published in 1982"

Adsorption and surface-enhanced Raman of dyes on silver and gold sols

Abstract: Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SERS nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine.

Advances in Infrared and Raman Spectroscopy

Abstract: Infrared Spectroscopy of the Electrode-Electrolyte Solution Interface Infrared Spectral Studies of DNA Conformations Vibrational Analysis of the Retinal Isomers A Unified View of Raman, Resonance Raman and Fluorescence Spectroscopy (and their Analogues in Two-Photon Absorption) Magnetic Raman Optical Acitivity The Resonance Raman Effect and Depolarization in Vibrational Raman Scattering Low Frequency Depolarized Light Scattering from Liquids and Solutions.

Surface selection rules

Abstract: The modification of the absorption, emission, and Raman scattering intensities of molecules near metal surfaces is discussed with emphasis on the last. These modifications are usually referred to as surface selection rules. We show that in Raman scattering, the ‘‘rule,’’ which states that only those modes will be active which belong to the irreducible representation to which α′zz also belongs, is only approximately obeyed. The circumstances under which modes which are represented by nondiagonal derived polarizibility tensors are ‘‘surface‐active’’ are considered, as well as the geometrical strategies which should be followed in studying the Raman spectra of molecules adsorbed on flat, metal surfaces.

Growth of diamond particles from methane-hydrogen gas

Abstract: Microcrystals of diamond were grown on non-diamond substrates including silicon, molybdenum and silica, as well as on diamond by chemical vapour deposition. Deposition was carried out by passing a mixture of hydrocarbon and hydrogen gases through a heated reaction chamber in which a hot tungsten filament was held near the substrates. The deposit was identified by reflection electron diffraction and Raman spectroscopy. The effects of experimental conditions on the growth features were studied.

Raman and infrared spectra on silica gel evolving toward glass

Abstract: Infrared and Raman spectra of gels obtained from specially prepared solutions of Si(OC2H5)4 (TEOS) which have been thermally treated in the 40–800°C temperature range, are reported and discussed with reference to the spectra of fused quartz. The results show that the gel to glass transformation is an hydrolytic polycondensation process, which takes plase gradually and is practically completed in the samples treated at 800°C. Particularly revealing is the behaviour of the bands due to OH (associated and/or unassociated H-bonded) stretching modes, including those of water, which are weakened by increasing temperature; the behaviour of the band due to the SiOH stretching mode; the behaviour of the network bands, some of which become more intense with increasing temperature, due to asymmetric and symmetric stretching and the bending SiOSi modes. In the Raman spectra of gels heated at different temperatures two peaks also appear at ≈600 and ≈490 cm−1, which are also present in the Raman spectrum of fused quartz, they are related to network defects of the glass structure, for which no definite interpretation has yet been given in the literature.

Scanning coherent anti-Stokes Raman microscope

Abstract: We have constructed a spatially scanning coherent anti-Stokes Raman spectroscopic (CARS) apparatus that allows us to image the distribution of distinct chemical species in a microscopic sample region. Images of onion-skin cells have been obtained by using the CARS signal produced by the 2450-cm−1 band of deuterated water. Future applications will be discussed.

Raman scattering from hydrogenated microcrystalline and amorphous silicon

Abstract: Raman scattering measurements on hydrogenated microcrystalline silicon prepared in a hydrogen plasma at deposition temperatures between approximately=65 and 400 degrees C are presented and discussed. The shifts of the crystalline (c) and 'amorphous-like' (a) components of the spectra to lower frequencies with decreasing crystallite size have been correlated with the lattice expansion and the finite dimensions of the crystallites in these films. The roles of hydrogen and of the compressive stress in the samples have been investigated by annealing experiments and a deposition of the samples under negative bias of the substrate, respectively. These results point to a probable mechanism of the crystalline-amorphous transition in silicon. The data presented allow an assignment of the amorphous-like feature in the Raman spectra to surface-like modes at grain boundaries of the crystallites. Strong arguments are given that suggest that the 480 cm-1 peak in the Raman spectra of X-ray amorphous silicon is of the same origin and is hence associated with some shearing modes of Si clusters rather than a broadened density of states. Results on the depolarisation ratio of Raman scattering in the microcrystalline and X-ray amorphous films are also presented and discussed.

Lattice-dynamical model for graphite

Abstract: The lattice dynamics of pristine graphite is presented with the use of a Born---von K\'arm\'an model. With the consideration of interactions to fourth neighbor both intraplane and interplane, good agreement is simultaneously obtained with ir, Raman, and inelastic neutron scattering measurements of lattice modes and with the measured elastic constants. The second-order Raman spectrum is also calculated and compared with experiment.

Electrochemical properties of small clusters of metal atoms and their role in the surface enhanced Raman scattering

Abstract: Starting with equations for the shift of the reversible redox potential of small metal particles with size, the electrochemical properties of these particles are discussed. Approximate equations are given for the relationship between the particle size and the surface charge, the potential of zero charge, the surface potential, work function and quantities related to this function. The influence of these properties on redox reactions, electrosorption, and chemisorption are discussed. The results are used to explain experimental observation in connection with the surface enhanced Raman effect. 2 figures, 1 table.

Lightning rod effect in surface enhanced Raman scattering

Abstract: The electromagnetic model of Gersten and Nitzan1 of the surface enhanced Raman scattering is discussed. The ’’lightning rod’’ effect is taken up in some detail. (AIP)

Measurement of the Crystallographically Transformed Zone Produced by Fracture in Ceramics Containing Tetragonal Zirconia

Abstract: During fracture of ceramics containing tetragonal zirconia particles, a volume of zirconia material on either side of the crack irreversibly transforms to the monoclinic crystal structure. Transformation zone sizes, measured using Raman microprobe spectroscopy, are presented for three sintered ceramics. In a single-phase ZrO2−3.5 mol% Y2O3 material, an upper bound measurement of 5 μm is obtained for the zone size. In the Al2O3/ZrO2 composites studied, the zone size is deduced to correspond to ∼1 grain in diameter. On the basis of the monoclinic concentrations derived from the Raman spectra it is further concluded that only a fraction of the ZrO2 grains within the transformation zone transform, providing indirect evidence for the effect of particle size on the propensity for transformation.

The structures and vibrational spectra of crystals and glasses in the silica-alumina system

Abstract: Solar furnace melting and fast-quench techniques have been used to prepare SiO2Al2O3 glasses to high alumina content (near 60 mol% Al2O3), which have been studied by Raman spectroscopy. These spectra may not be simply interpreted. The structures of crystalline compounds in the SiO2Al2O3 system are discussed in relation to their vibrational spectra. On the basis of this discussion and other considerations, a structural model for the silica-alumina glass system is proposed, which is consistent with the stable or metastable immiscibility suggested along this join. The essential features of this model include a modified silica structure at low alumina content, and “structure-broken” regions at high alumina compositions, with silicon in tetrahedral coordination, but aluminium assuming a variety of bonding geometries. These are proposed to include aluminate tetrahedra with higher polymerization than simple corner-sharing, and less well-defined polyhedra of higher average coordination number.

Resonance Raman spectra of bacteriorhodopsin's primary photoproduct: evidence for a distorted 13-cis retinal chromophore.

Abstract: We have obtained the resonance Raman spectrum of bacteriorhodopsin's primary photoproduct K with a novel low-temperature spinning sample technique. Purple membrane at 77 K is illuminated with spatially separated actinic (pump) and probe laser beams. The 514-nm pump beam produces a photostationary steady-state mixture of bacteriorhodopsin and K. This mixture is then rotated through the red (676 nm) probe beam, which selectively enhances the Raman scattering from K. The essential advantage of our successive pump-and-probe technique is that it prevents the fluorescence excited by the pump beam from masking the red probe Raman scattering. K exhibits strong Raman lines at 1516, 1294, 1194, 1012, 957, and 811 cm-1. The effects of C15 deuteration on K's fingerprint lines correlate well with those seen in 13-cis model compounds, indicating that K has a 13-cis chromophore. However, the presence of unusually strong "low-wavenumber" lines at 811 and 957 cm-1, attributable to hydrogen out-of-plane wags, indicates that the protein holds the chromophore in a distorted conformation after trans leads to cis isomerization.

Excited state geometry changes from preresonance Raman intensities: Isoprene and hexatriene

Abstract: A method is presented for using a single preresonance Raman spectrum and an absorption spectrum to obtain changes in equilibrium geometry upon electronic excitation. The relative displacements along each of the vibrational normal coordinates are obtained from the Raman intensities, while the overall scaling of the displacements is determined by the absorption band shape. The absorption spectra, as well as Raman excitation profiles, are calculated using either a sum over vibronic states or a formally equivalent time‐dependent method [S.‐Y. Lee and E. J. Heller, J. Chem. Phys. 71, 4777 (1979)]. The time‐dependent method is computationally much faster than the vibronic sum for large multidimensional systems. Our analysis, which assumes isolated molecules and separable, harmonic surfaces, yields a good fit to the vapor phase absorption spectrum of trans‐hexatriene with a Lorentzian linewidth of 175 cm−1. However, the diffuse absorption spectrum of isoprene cannot be adequately reproduced using Lorentzian line...

Infrared and Raman study of amorphous V2O5

Abstract: Amorphous V2O5 can be obtained by cooling from the melt. This amorphous oxide is very sensitive to water vapour and can even be dissolved in water to give a vanadium pentoxide gel. The hydration process has been followed by infrared and Raman spectroscopy between 20 and 4000 cm−1. Short-range order in the amorphous oxide appears to be almost the same as in orthorhombic V2O5. The amorphous phase could even be described as made of small crystallites about 100 A in diameter. The structure of amorphous V2O5 does not seem to be modified by water adsorption, at least during the first stages of the hydration process. However, a drastic modification occurs when enough water is added to give a gel. A general shift to lower frequencies is observed, indicating a weakening of the VO bonds, presumably associated with the formation of new VOH2 bonds. Two different water species have been identified, one of which seems to be almost free of hydrogen bonding. Short-range order in the gels seems to be quite well defined and the spectra could be interpreted either in terms of crystallites, as in amorphous V2O5, or in terms of molecular (or macromolecular) species containing V2O5, (H2O), groups.

Observation of Ramsey Fringes Using a Stimulated, Resonance Raman Transition in a Sodium Atomic Beam

Abstract: Ramsey fringes have been observed using a stimulated, resonance Raman transition at 1772 MHz excited by two dye lasers in a sodium atomic beam. The width of the central fringe is 650 Hz (half width at half maximum), corresponding to a 30-cm interaction-region separation. The fringes are free from laser jitter because the jitters in both laser beams are correlated. Applications to frequency standards as well as to high-resolution spectroscopy in the microwave to far-ir regions are discussed.

Optical switching in semiconductor organic thin films

Abstract: Semiconducting organometallic films such as copper tetracyanoquinodimethane (CuTCNQ) have been observed to switch between two stable states when exposed to optical radiation. Observations of switching between two states in these films have been made by Raman spectroscopic methods and direct observation of electrical resistance changes. Line or pattern generation is observed for exposure above certain threshold levels. These effects are observed in a wide range of Cu and Ag organometallic compounds.

Charge transfer effects in surface‐enhanced Raman scatteringa)

Abstract: Surface enhanced Raman scattering (SERS) due to charge transfer interactions between the adsorbed molecule and the metal surface is analyzed using the semiempirical Wolfsberg–Helmholz method1 to relate the moleculesurface interactions and the resulting charge transfer states to the overlap integrals between the metal conduction–band orbitals and an acceptor or donor molecular orbital of the molecule. Calculations for the model system of ethylene adsorbed on silver (approximated as a simple cubic metal with tight binding wave functions constructed from Ag 5s valence orbitals), with charge-transfer excitation of an electron from the metal to the antibonding ethylene π orbital, show that charge-transfer Raman enhancements of the order of 10 to 1000 are possible if the charge-transfer band is partially resonant with the exciting radiation. The net enhancement is the product of the charge–transfer gain and the electrodynamic enhancement due to plasmon resonances at surface roughness elements. Symmetric vibrations usually will be enhanced substantially more than nonsymmetric ones by charge–transfer because, in contrast to non–resonant Raman scattering, the vibrational coupling is primarily Franck–Condon (due to differences in the equilibrium nuclear configurations of the ground and excited charge transfer states and the resulting nonorthogonality of different vibrational sublevels of these states) rather than Herzberg–Teller (due to vibrationally induced changes in the electronic wave functions). The charge–transfer mechanism is selective with the most enhanced vibrations involving those atoms which experience the greatest change in electron density between the ground and excited charge–transfer state. A recent report of SERS for benzene on platinum, strongly suggests charge–transfer enhancement because the electromagnetic–fieldenhancing plasmon resonances are strongly damped in this metal. The complete paper will be published in the December 1, 1982 issue of the Journal of Chemical Physics.