Showing papers on "Raman spectroscopy published in 1977"

Anomalously intense Raman spectra of pyridine at a silver electrode

Abstract: Journal of the American Chemical Society is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Anomalously intense Raman spectra of pyridine at a silver electrode M. Grant Albrecht, and J. Alan Creighton J. Am. Chem. Soc., 1977, 99 (15), 5215-5217• DOI: 10.1021/ja00457a071 • Publication Date (Web): 01 May 2002 Downloaded from http://pubs.acs.org on March 5, 2009

Infrared and Raman spectra of the silicon-hydrogen bonds in amorphous silicon prepared by glow discharge and sputtering

Abstract: We have studied the number and nature of the silicon-hydrogen bonds in amorphous silicon films prepared in plasmas either of silane or of hydrogen and argon. The films from silane glow discharges have qualitatively different Raman and infrared spectra which depend on deposition parameters such as substrate temperature and silane gas pressure. Three main groups of spectral bands are seen associated with the Si-H bonds: the Si-H bond stretch bands, the bands due to relative bending of two or three Si-H bonds with a common silicon atom, and the "wagging" bands of Si-H bonds with respect to the Si matrix. These bands are split in a way suggestive of the presence of SiH, Si${\mathrm{H}}_{2}$, and Si${\mathrm{H}}_{3}$ complexes: the bond-bending bands are absent when only SiH bonds are present. All three types of complexes are identified in films deposited from glow discharges of silane at pressures \ensuremath{\sim} 1 Torr and room temperature. Higher substrate temperatures and/or lower pressures reduce the Si${\mathrm{H}}_{2}$ and Si${\mathrm{H}}_{3}$ concentrations: films deposited at 250\ifmmode^\circ\else\textdegree\fi{}C and 0.1 Torr contain only SiH groups. From the strength of the corresponding absorption bands, H concentrations as high as 35 to 52 atomic percent are estimated. Films sputtered at 200\ifmmode^\circ\else\textdegree\fi{}C in a 10% ${\mathrm{H}}_{2}$-90% Ar mixture contain all three groupings observed in the silane-derived samples. Deuterated sputtered films are used to confirm the analysis. The first- and second-order Raman scattering spectra of the Si-Si bonds in pure and hydrogenated $a\ensuremath{-}\mathrm{S}\mathrm{i}$ are also discussed. The scattering efficiency of $a\ensuremath{-}\mathrm{S}\mathrm{i}$ is found to be as much as 10 times that of crystal Si. The depolarization ratio of the $a\ensuremath{-}\mathrm{S}\mathrm{i}$ Raman spectrum has been remeasured. Finally, a picture is presented of when it is appropriate to refer to heavily hydrogenated $a\ensuremath{-}\mathrm{S}\mathrm{i}$ as still being a material describable by $a\ensuremath{-}\mathrm{S}\mathrm{i}$ network models.

Resonant Raman scattering in ZnO

Abstract: The resonance of the Raman scattering by ${E}_{2}, {A}_{1T}, {E}_{1L}$, and ${E}_{1T}$ phonons, and several second-order features, has been studied for ZnO for photon energies between 1.6 and 3 eV. The results are interpreted with a dielectric theory based on the first and second derivatives of the dielectric constant. By combining our results with absolute scattering cross sections previously determined by Arguello et al. at 2.41 eV absolute values of the deformation potentials of the band edge can be determined. The difference in strength between the longitudinal and the transverse modes provides the signs of these deformation potentials. The antiresonance around 1.6 eV suggested by the earlier work of Callender et al. and attributed to a cancellation of the deformation potential and electro-optical contributions to the Raman tensor is confirmed. The deformation potentials of the ${A}_{1}$ phonons at the band edge have been obtained from a pseudopotential calculation. While the sign of these deformation potentials agrees with the experimental determination, their magnitudes do not agree. This fact is attributed to difficulties with the pseudopotential of the ${\mathrm{O}}^{2\ensuremath{-}}$ ion. An estimate of the deformation potentials from the dependence of the band edges on uniaxial stress is also made.

A review of the theory and application of coherent anti-Stokes Raman Spectroscopy (CARS)

Abstract: Coherent anti-Stokes Raman spectroscopy (CARS) is a relatively new kind of Raman spectroscopy which is based on a nonlinear conversion of two laser beams into a coherent, laser-like Raman beam of high intensity in the anti-Stokes region. The emission is often many orders of magnitude greater than normal Raman scattering and, because of the coherent and anti-Stokes character of radiation, the method is very useful for obtaining Raman spectra of fluorescing samples, gases in discharges, plasmas, combustion, atmospheric chemistry. In this paper we outline the basic theory behind CARS and describe its unusual effects and drawbacks. We review the research to date on various materials, and indicate the possible future direction, utility and applications of CARS such as surface studies, fluctuation phenomena, reaction dynamics, photochemistry, kinetics, relaxation, and energy transfer.

A Raman and far-infrared investigation of phonons in the rhombohedral V2–VI3 compounds Bi2Te3, Bi2Se3, Sb2Te3 and Bi2(Te1−xSex)3 (0 < x < 1), (Bi1−ySby)2Te3 (0 < y < 1)

Abstract: The Raman-active lattice vibrations of Bi2Se3, Bi2Te3, Sb2Te3, and their solid slutions, whose symmetries correspond to the R3m space group, are investigated by Raman scattering. Three of the four expected Raman modes, Eg and A1g, could be determined. The FIR optical properties of Bi2Te3 crystal surfaces of improved quality (E ∥ c and E ⟂ c) and Bi2Se3 (E ⟂ c) are re-examined near helium and room temperature with a Fourier spectrometer, allowing a determination of the infrared-active mode frequencies with higher accuracy. The results for Bi2Te3 are compared to the predicted frequencies from the lattice dynamical model, given by Jenkins et al. The frequncy shifts of the Raman-active modes in the mixed crystals show single-mode and two-mode behaviour, which is in agreement with simple models for the substitution of antimony and selenium atoms for bismuth and tellurium, respectively, in Bi2Te3.

Infrared and Raman spectra of the IV-VI compounds SnS and SnSe

Abstract: The results of Raman scattering and infrared reflectivity measurements on the IV-VI layer-type semiconductors SnS and SnSe are presented. The infrared-active TO, the associated LO-phonon frequencies, and the dielectric constants for all three principal polarizations have been determined from a Kramers-Kronig analysis of the reflectivity data. The symmetries of the zone-center phonons observed in the different polarization configurations are in agreement with the group-theoretical analysis of the ${D}_{2h}^{16}$ space group of these compounds. Despite the center of inversion symmetry in this structure, some infrared- and Raman-active modes are found to be nearly degenerate, suggesting the importance of the layerlike character in these compounds as in the isomorphic GeS and GeSe. A comparison of the phonon frequencies of the corresponding modes in the spectra of SnS and SnSe, or GeS and GeSe, indicates that the frequencies vary as a power (-2.2) of the lattice constant.

The Rayleigh depolarization ratio and rotational Raman spectrum of water vapor and the polarizability components for the water molecule

Abstract: This paper describes the observation and computer simulation of the rotational Raman spectrum of water vapor and the measurement of the depolarization ratio for Rayleigh scattering from water vapor, which was found to be (3.0±1.4) ×10−4. These results were combined with the value of the mean polarizability to calculate the principal polarizability components of the water molecule. At 514.5 nm, they are (in units of 10−24 cm3): αxx=1.468±0.003, αyy =1.415±0.013, and αzz=1.528±0.013, where the x axis is the dipole axis and the y axis is perpendicular to the molecular plane.

Resonance Raman studies of the purple membrane

Abstract: The individual resonance Raman spectra of the PM568 and M412 forms of light-adapted purple membrane from Halobacterium halobium have been measured using the newly developed flow technique. For comparison purposes, the Raman spectra of the model chromophores, all-trans- and 13-cis retinal n-butylamine, both as protonated and unprotonated Schiff bases, have also been obtained. In agreement with previous work, the Raman data indicate that the retinal chromophore is linked to the purple membrane protein via a protonated. Schiff base in the case of the PM568 and an unprotonated Schiff base for the M412 form. The basic mechanism for color regulation in both forms appears to be electron delocalization. The spectral features of the two forms are different from each other and different from the model compound spectra.

Effects of laser-modulated particulate incandescence on Raman scattering diagnostics

Abstract: Laser‐modulated particulate (soot) incandescence has been studied by measuring the laser‐driven particle surface temperature in a propane diffusion flame as a function of laser focal flux. The experimental results display fair agreement with an analytical model of the process. Quite importantly, the absolute incandescence level displays a saturation behavior with increasing laser pulse energy. For laser Raman scattering diagnostics, this behavior means that the S/N ratio will increase with increasing laser flux level. Thus, for highest S/N ratio, it is preferable to operate at the highest possible flux short of gas breakdown and/or optical‐component damage levels.

Polarized Raman Scattering Studies of Orientational Order in Uniaxial Liquid Crystalline Phases

Abstract: The measurement of vibrational Raman depolarization ratios has been used to study molecular orientational order in uniaxial single domain nematic and smectic liquid crystal samples. This technique is demonstrated to obtain the same microscopic order parameter 〈P2〉=1/2 〈3 cos2ϑ−1〉, where ϑ is the angle between a molecular long axis and the uniaxial direction, as other existing methods. In addition, the next higher moment of the orientational distribution function 〈P4〉=1/8 〈35 cos4 ϑ−30 cos2ϑ+3〉 has been measured for the first time. The physical basis, theoretical apparatus, and experimental methods necessary for the application of this technique are thoroughly detailed in this paper. Measurements are presented of the temperature dependence of 〈P2〉 and 〈P4〉 of N‐ (p′‐butoxybenzylidene) ‐p‐cyanoaniline (BBCA) dissolved in N‐ (p′‐methoxybenzylidene) ‐p‐cyanoaniline (MBBA) and of pure MBBA in the isotropic and nematic phases, and in the isotropic, nematic, smectic A, and smectic B phases of N‐ (p′‐butoxybenzyl...

Raman spectroscopic investigation of the structure of silicate glasses (II). Soda-alkaline earth-alumina ternary and quaternary glasses

Abstract: Raman spectra of some ternary and quaternary glasses in the system Na2OCaOMgOAl2O3SiO2 are presented. The spectra are interpreted in terms of the structural alteration of the glass as the composition is altered from the binary end members to more complicated glasses. Addition of CaO and MgO to soda-silica glasses act only to increase the disorder of the network slightly. Addition of Al2O3 greatly modifies the network. In some soda-lime-aluminosiliscate compositions an estimate can be made of the amount of aluminum in four- and six-fold coordination. It is shown that the amounts of four- and sixfold coordinated aluminum depend on the glass composition.

Raman scattering studies of SnS2 and SnSe2

Abstract: The Raman spectra of 2H and 4H-SnS2 and 6Hb-SnSe2 have been studied at room and liquid nitrogen temperatures. Interpretation of the observed Raman modes is given in terms of the different symmetries of these polytypes and the more important short-range forces involved in determining the energies of the higher-energy phonon modes are identified by the use of a simple force-constant model.

Calculations of resonance Raman spectra of conjugated molecules

Abstract: A method for calculations of the complete resonance Raman (RR) spectrum of large conjugated molecules is presented. The method is based on calculations of the Franck–Condon factors and on differentiation of the electronic transition moments with respect to the vibrational normal modes. This approach is more simple and practical than previous treatments which are based on the Herzberg–Teller expansion. It allows one to evaluate quantitatively the contributions of the A and B terms to the RR intensity pattern. This paper gives the detailed derivation of the calculation scheme and examines different possible approximations. The multimode nature of the RR process is considered in detail and the effect of combination levels is taken into account explicitly. It is shown that in cases of resonance with strong electronic transitions the A term is much more important than the B term. The calculations are demonstrated by the evaluation of the Raman spectra of butadiene and 1,3,5‐hexatriene in the nonresonance regio...

A detailed assignment of the O–H stretching bands of ice I

Abstract: A detailed assignment of the infrared and Raman O–H stretching bands of disordered ice Ih and Ic is proposed. It is based on the assumptions that the spectra of disordered ice Ic are closely relate...

Raman scattering properties of amorphous As and Sb

Abstract: Raman scattering measurements on bulk amorphous As and thin-film sputter-deposited amorphous As and Sb indicate differences in the vibrational character of the systems. The polarization properties of amorphous As indicate quasimolecular character with differences between the bulk and sputtered material attributed to local variations in structure beyond nearest neighbors. The Raman spectra of sputtered amorphous Sb, in contrast, indicate nonmolecular character as in group-IV amorphous systems. A comparison of neutron-scattering measurements with the Raman spectra has been used to gain information about the frequency dependence of the Raman coupling parameter. The approximate form of the coupling parameter near the lowest peak in the density of phonon states, which is also found to hold for amorphous Se and Ge, is used to estimate the form of the density of states of amorphous Sb. The low-frequency phonon spectrum in amorphous Sb differs appreciably from the crystalline rhombohedral form reflecting changes in the second of higher neighbor distributions.

Phonons in amorphous silica

Abstract: A new theory of lattice vibrations in amorphous silicon dioxide is presented in which the randomness of the solid is treated separately from its chemistry. The theory attributes all measurable properties of phonons in silica to the nearly crystalline nearest-neighbor geometry of the lattice and to the disruptive effects of bondangle disorder. Neutron, infrared, and Raman spectra are calculated and compared with experiment. The theory is an application of the recently developed cluster-Bethe-lattice approach to studying amorphous solids.

Low-frequency inelastic light scattering from chalcogenide glasses and alloys

Abstract: Polarized low-frequency Raman and Brillouin spectra of the chalcogenide glasses ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, Ge${\mathrm{S}}_{2}$, Ge${\mathrm{Se}}_{2}$, and ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$ and the glass alloy system ${({\mathrm{As}}_{2}{\mathrm{S}}_{3})}_{1\ensuremath{-}x}{(\mathrm{Ge}{\mathrm{S}}_{2})}_{x}$ have been measured using the near infrared 7525 or 7993 \AA{} lines of a krypton laser. The low-temperature $T\ensuremath{\sim}10$ K spectra of the four binary glasses indicate that the Raman coupling constant exhibits an ${\ensuremath{\omega}}^{2}$ frequency dependence in the limit $\ensuremath{\omega}\ensuremath{\rightarrow}0$. In addition it is demonstrated that the spectral distribution of the low-frequency low-temperature Raman coupling constant can be described by a model proposed by Martin and Brenig. By fitting the predicted spectra of the model to the experimentally obtained spectra, the structural correlation ranges of the glasses have been determined. It is found that the structural correlation ranges of the ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ and ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$ glasses are 6.5 \ifmmode\pm\else\textpm\fi{} 1 \AA{}, while those of the Ge${\mathrm{S}}_{2}$ and Ge${\mathrm{Se}}_{2}$ glasses are 8.5 \ifmmode\pm\else\textpm\fi{} 1 \AA{}. These results are compared with values of structural correlations obtained from x-ray diffraction spectra and optic-mode Raman spectra. The depolarization spectra predicted from the Martin and Brenig model are found to deviate significantly from the observed low-frequency depolarization spectra of the chalcogenide glasses. At higher temperatures the low-frequency Raman spectra of all samples exhibit a feature apparently centered at 0 frequency shift which cannot be described by the model of Martin and Brenig. A similar feature termed the light scattering excess has been reported for the low-frequency Raman spectrum of fused silica. A recent model by Theodorakopoulos and J\"ackle describes the light scattering excess in terms of two-level defect states. The temperature dependence, depolarization ratio, and spectral distribution of the light-scattering excess are interpreted using this model and recent ultrasonic attenuation measurements. The composition dependence of both the structural correlation range and the light-scattering excess is presented for the alloy system of ${({\mathrm{As}}_{2}{\mathrm{S}}_{3})}_{1\ensuremath{-}x}{(\mathrm{Ge}{\mathrm{S}}_{2})}_{x}$.

Temperature Dependence of the Raman Spectra of ZrO2

Abstract: Raman spectra of ZrO/sub 2/ were measured in the range 300 to 1600/sup 0/K. Irreducible components of the Raman spectra were obtained from polarization measurements at room temperature, and the symmetries of the Raman-active modes in the monoclinic phase were determined. The temperature dependence of the spectra shows a hysteresis. In the temperature range of phase change, two kinds of Raman lines coexist. Six Raman-active mode frequencies were found in the tetragonal phase at high temperatures. Analysis of the spectra showed that the Raman-active modes in the tetragonal phase are affected by strain introduced into the crystals during the phase transformation.

Raman study of vibrational dephasing in liquid CH3CN and CD3CN

Abstract: The Raman line shapes of the ν1(a1) C–H and C–D fundamentals in liquid acetonitrile and acetonitrile‐d3 have been measured as a function of pressure up to 4 kbar within the temperature interval 30–120 °C. Densities have also been determined. From the isotropic component of the vibrational Raman band shape the vibrational relaxation times have been obtained as a function of temperature and pressure (density). The experimental results can be summarized as follows: (i) as T increases at constant density ρ, the vibrational relaxation rate (τvib)−1 increases; (ii) at constant T as density is raised τvib−1 increases; (iii) at constant pressure the T increase produces higher τvib−1, however, the change is more pronounced for the CD3CN liquid. Isotopic dilution studies of the CH3CN/CD3CN mixtures shows no significant effect on (τvib−1). The experimental data are interpreted in terms of the Kubo stochastic line shape theory and the dephasing model of Fischer and Laubereau. The results based on Kubo formalism indic...

Saturation effects in laser induced fluorescence spectroscopy

Abstract: Laser based spectroscopic diagnostic tools offer the possibility of spatially and temporally resolved measurements of species concentrations in complex reacting gas flows of engineering interest. The major problem associated with such measurements is the effect of quenching reactions on the fluorescence signal. To overcome this difficulty operating in the saturation mode is proposed. For suitable systems the fluorescence signal is then no longer a function of quenching rates or laser power. Very low detectability limits appear possible.

Resonance Raman spectra of metalloporphyrins. Effects of Jahn–Teller instability and nuclear distortion on excitation profiles of Stokes fundamentals

Abstract: Excitation profiles of depolarized modes (blg, b2g) in Ni etioporphyrin I exhibit marked 0–0 resonance Raman intensity upon Q‐band excitation. By contrast, inversely polarized Raman scattering (a2g) is stronger with 0–1 excitation. Within the crude Born–Oppenheimer approximation, a theoretical model is presented which explains the 0–0 enhancements of depolarized modes as arising from interference of intermanifold (Q –B) and intramanifold (Q –Q) vibronic coupling. Comparison of computed and observed excitation profiles shows that a weak Jahn–Teller distortion is present in the Q state. The vibronic model predicts behavior of Raman intensity in the B (Soret) electronic state. Evidence of increased vibronic coupling of both 400 and 1365 cm−1 polarized vibrations (a1g) is found in chromium tetraphenylporphyrin with the appearance of a supernumerary peak at 1400 cm−1 in the excitation profile of the 400 cm−1 vibration. Excitation profiles of a2g modes in the chromium complex exhibit an apparent decrease in exc...

Analysis of torsional spectra of molecules with two internal C3v rotors. II - Far infrared and low frequency Raman spectra of dimethylether isotopes

Abstract: The torsional far infrared and Raman spectra of gaseous CH3OCH3, CD3OCH3, and CD3OCD3 are presented. They are analyzed using a computer program which is based on the results of an extensive investigation of the isometric groups and of the symmetry groups of the rotation–internal rotation Hamiltonians of a series of semirigid two‐top models. Four or more Fourier coefficients of the potential functions in two variables could be determined for each isotope. Strong evidence was found for Fermi‐resonance‐type interactions with the COC bending mode.

Vibrational spectra of the alkaline earth double carbonates

Abstract: Raman spectra and mid-range and far infrared spectra have been measured on polycrystalline norsethite [BaMg(COs)], barytocalcite IBaCa(COr)r], the high-temperature modification of barytocalcite, huntite [CaMgr(CO.)o], benstonite [CatBa"(CO3)tr], and alstonite [CaBa(COr)r]. Factor-group calculations permit the assignment of the internal modes of the known structures. Effects of ordering in these derivative structures appear mainly in the IR spectra. A degree of translational disorder in the high-temperature modification of barytocalcite and in alstonite appears as a line broadening of the symmetric stretching mode in the Raman spectra.