Search results for "raman scattering"
showing 10 items of 284 documents
Experimental and theoretical study of line mixing in methane spectra. III. The Q branch of the Raman ν1 band
2000
The shape of the ν1 Raman Q branch of CH4 perturbed by Ar and He at room temperature has been studied. Stimulated Raman spectroscopy (SRS) experiments have been made in the 2915–2918 cm−1 spectral region for total pressures from 0.4 to 70 atm and mixtures of ≈5% CH4 with He and Ar. Analysis of the spectra demonstrates that the shape of the Q branch is significantly influenced by line mixing and much narrower than what is predicted by the addition of individual line profiles. For the first time, a model is proposed for the calculation and analysis of the effects of collisions on the considered spectra. In this approach, the rotational part of the relaxation matrix is constructed, with no adj…
Collisional shifting and broadening coefficients for the rovibrational anisotropic lines of the ν1/2ν2 fermi dyad in CO2 gas studied by stimulated Ra…
1998
High-resolution stimulated Raman spectroscopy was applied to the study of collisional broadening and shifting for rovibrational anisotropic Raman lines of the Fermi dyad of molecular carbon dioxide. The O(J) lines of the ν1 band and the S(J) lines of the 2ν2 band were recorded at 295 K. The pressure-induced line shifts were obtained and compared with the overall shift of the high-density Raman Q-branch. A rotational quantum number dependence of the rovibrational line broadening coefficients was observed. The experimental line broadening coefficients were used in order to check the ability of two theoretical methods (random phase approximation and sum rule) for calculating the line broadenin…
The infrared and Raman spectra of solid tridehydropeptides : influence of ΔAla and ΔPhe on the spectral profile
2012
Abstract A series of solid tripeptides Boc-Gly-X-Gly-OMe (X = dehydroalanine (ΔAla), dehydrophenylalanine (ΔPhe)) was investigated by Raman scattering and Fourier transform infrared spectra to examine the conformational marker bands of the unsaturated residue. The observed fundamental modes gave us the opportunity to analyze structural features that change due to the substitution of Ala by ΔAla and due to the different spatial arrangement of ΔPhe ( Z and E isomers). In addition, we showed the alteration of the spectral profile when the large size residue (Phe) is introduced into the backbone of the peptide with ΔPhe (in Boc-Gly-Δ (Z) Phe-Phe-OMe). The frequency ranges of interest included t…
Raman and theoretical study of the solvent effects on the sizable intramolecular charge transfer in the push-pull 5-(dimethylamino)-5'-nitro-2,2'-bit…
2006
In this paper, we analyze the degree of intramolecular charge transfer in a push-pull π-conjugated system, 5-(dimethylamino)-5'-nitro-2,2'-bithiophene, from changes in frequencies and relative intensities of its strongestRaman scatterings in a bunch of solvents with different polarities. Density functional theory (DFT) was used as a support of the experimental study. Solvent effects on the molecular and electronic structures and on the vibrational properties were estimated by performing B3LYP/6-31G** calculations within the framework of the polarized continuum model (PCM) developed by Tomasi. Calculations reveal that the molecule is highly polarized in the ground state and behaves as a very…
Sorting of Single Biomolecules based on Fourier Polar Representation of Surface Enhanced Raman Spectra
2016
AbstractSurface enhanced Raman scattering (SERS) spectroscopy becomes increasingly used in biosensors for its capacity to detect and identify single molecules. In practice, a large number of SERS spectra are acquired and reliable ranking methods are thus essential for analysing all these data. Supervised classification strategies, which are the most effective methods, are usually applied but they require pre-determined models or classes. In this work, we propose to sort SERS spectra in unknown groups with an alternative strategy called Fourier polar representation. This non-fitting method based on simple Fourier sine and cosine transforms produces a fast and graphical representation for sor…
Inelastic neutron scattering due to acoustic vibrations confined in nanoparticles: theory and experiment
2008
The inelastic scattering of neutrons by nanoparticles due to acoustic vibrational modes (energy below 10 meV) confined in nanoparticles is calculated using the Zemach-Glauber formalism. Such vibrational modes are commonly observed by light scattering techniques (Brillouin or low-frequency Raman scattering). We also report high resolution inelastic neutron scattering measurements for anatase TiO2 nanoparticles in a loose powder. Factors enabling the observation of such vibrations are discussed. These include a narrow nanoparticle size distribution which minimizes inhomogeneous broadening of the spectrum and the presence of hydrogen atoms oscillating with the nanoparticle surfaces which enhan…
Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constan…
2011
We investigate the low-frequency enhancement of vibrational excitations ('boson peak') in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150?cm ? 1. A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio.
Raman Scattering in CuCl under Pressure
1999
Raman spectra of CuCl were measured under hydrostatic pressures up to 14 GPa at low temperatures (T = 5 K). The anomaly in the Raman lineshape of zincblende CuCl at frequencies near the transverse-optic (TO) mode, which consists of a broad structure with several maxima, disappears at a pressure near 3 GPa. This effect is well reproduced by a model calculation of the anharmonic coupling of the TO mode to acoustic two-phonon states (Fermi resonance). Alternative interpretations of the TO Raman anomaly in terms of local vibrational modes of Cu atoms in off-center positions are not supported by the present results. Raman spectra indicate the existence of the phase CuCl-IIa in a narrow pressure …
Pressure dependence of optical phonons in ZnCdSe alloys
2003
5 páginas, 2 figuras, 2 tablas.-- PACS 62.50.+p, 63.20.Dj, 78.30.Fs, 78.66.Hf.-- et al.
Lattice dynamics of the fluoride scheelite CaZnF4
2000
The lattice dynamics of the fluoride scheelite CaZnF4 have been investigated by means of infrared reflectivity and Raman scattering. The measured phonon modes have been assigned to the various irreducible representations of the point group of the crystal. The phonon dispersion curves, density of states and sound velocities have been calculated within a rigid-ion model based on experimental zone-centre phonons.