C. T. Walker

Resonance Raman scattering study of azulene. II. Nonzero temperature multimode model calculations

In a recent paper (Az I), well‐structured T=300 K resonance Raman (RR) profiles for the 1400, 1260, 900, and 2×825 cm−1 lines of azulene in CS2 and for the 825 cm−1 line of azulene in methanol were reported. Previously developed transform techniques were used to (1) compute RR profile line shapes directly from measured optical absorption spectra, and (2) extract ratios of Stokes loss parameters from the line shape scale factors. The transform analysis indicated that (1) our model assumptions (adiabatic and Condon approximations, harmonic phonons, atomic equilibrium position shifts, and small vibrational frequency shifts upon excitation to a single electronic state) are basically correct allowing forminor modifications, and (2) any deviations from these assumptions are likely to be larger for the 900 cm−1 mode and smaller for the 1400 and 1260 cm−1 modes. In this paper (Az II), we report model calculations of the optical absorption spectra, RR profile line shapes, and relative RR intensities. In these calc...

Raman scattering from CuBr and CuI

Abstract Detailed temperature-dependent Raman spectra of CuI and CuBr are reported for the first time. Spectra have been recorded between room temperature and 6K. Peaks arising from scattering by the zone-center optic phonon modes have been identified and their frequencies compared with those determined by neutron scattering and infrared measurements. The LO phonon energy in CuBr is found to reflect the negative thermal expansion at low temperatures while the TO phonon frequency does not follow this behavior. Second-order features of the CuI spectrum are identified using available phonon dispersion curves.

Resonance Raman scattering study of azulene. I. Experiment and theoretical analysis via transform techniques

Room temperature resonance Raman (RR) profiles for the 1400, 1260, 900 and 2×825 cm−1 lines of azulene in CS2 and for the 825 cm−1 line in methanol are reported. These profiles display pronounced multimode interference effects within the measured spectral range (570–720 nm). Using previously developed transform techniques, we analyze our RR data by calculating profile line shapes directly from our measured optical absorption data. The calculated and measured profile line shapes are in good agreement for all of the modes studied. These results are consistent with the model assumptions upon which the transform analysis rests. To further test our model assumptions, we extract ratios of the RR Stokes loss parameters from the scale factors of our profile line shape fits. RR Stokes loss parameters estimated from these ratios are found to be in good correlation with published 2K emission intensity ratios. However, their correlation with published 4K absorption intensity ratios indicates the presence of some inte...

Temperature‐dependent resonance Raman profiles of β‐carotene in carbon disulfide

Resonance Raman (RR) profiles of the 1005, 1155, and 1525 cm−1 modes of β‐carotene dissolved in carbon disulfide have been measured at room temperature and at 172 K. Previous studies, based upon room temperature measurements, have indicated that inhomogeneous (i.e., site) broadening may be important for this system. Our measurements are the first RR data for this system at two temperatures. Such data are necessary in order to study the relative importance of inhomogeneous broadening and thermal broadening. Using previously developed transform techniques, we analyze our RR data by calculating profile line shapes directly from our measured optical absorption data for each temperature. The assumptions underlying this analysis do not include inhomogeneous broadening, and the calculations yield profile line shapes which are in quite good overall agreement with the measured profile line shapes for all three modes at both temperatures. We have also extended the transform calculations in order to incorporate inho...

Brillouin and ultrasonic study of the temperature dependence of the elastic constants in NaCN

Abstract The temperature dependence of the elastic constants of NaCN has been studied by propagation of ultrasonic waves at 15 MHz and by Brillouin scattering at 3 GHz over the temperature range from 287K to 355K. c 44 is observed to soften linearly with temperature as the order-disorder phase transition at 284K is approached from above. The other elastic constants also soften, except for c 12 which stiffens. Considerable dispersion is seen in the values of c 44 obtained ultrasonically and by Brillouin scattering. Measurements of the temperature dependence of the density are also reported.

Pressure dependence of the Raman scattering in the ordered phase of NH4Cℓ

Abstract We have observed Raman scattering in NH 4 Cl from 105K to 295K and up to 7kbar hydrostatic pressure, including the disordered phase II and the ordered phase IV. The pressure dependences of internal and lattice modes are reported, as well as that of the libration mode. The results are applied to several theories of the potential barrier to rotation.

Raman scattering in NH4Br and NH4I under hydrostatic pressure

Raman spectra are reported for NH4Br and NH4I from 86 to 295 K under hydrostatic pressures from 1 bar to 7 kbar. Phases II, III, and IV were studied. The pressure dependence is reported for the lattice modes, for the librational mode and its harmonics, and for certain combination bands. Several theoretical models for the librational potential are discussed and compared with the data.

Brillouin Scattering at High Pressures

Pressure and temperature dependences of the Brillouin spectra for KCN and NaCN are shown for pressures of 0 to 7 kbar and temperatures of 178 K to 295 K for KCN and of 285 K to 340 K for NaCN. Dispersion of c44 and c’ = (c11 + c12 + 2c44)/2 and strong pressure dependence of To, the temperature where c44 would vanish, has been found for NaCN, whereas there is no dispersion for c44 and c’ and no pressure dependence of To in KCN. On the other hand it is shown for both substances that multiphonon interactions, which increase approaching the phase transition, are the dominant anharmonic effect for the zone center acoustic phonons. A review of current theories for the order-disorder transition of the CN--ion system is given.

Impurity-induced raman scattering studies of pure crystal anharmonicity in KBr☆

Abstract Raman spectra for Tl+-doped KBr are reported as functions of hydrostatic pressure at 30, 85 and 300 K, and as functions of temperature at zero pressure. The experiments can be understood in terms of the volume dependence of phonon frequencies alone, with no multiphonon effects. Peak shifts, calculated on the basis of pure crystal phonons and bulk anharmonicity, are seen to be in good agreement with experiment.

Raman Scattering Studies of Anharmonicities in Potassium Halides

In recent years, Raman scattering has become a widely accepted technique for investigating phonons in crystals. In this paper we demonstrate its use for studying anharmonicities in potassium halides. It has been shown1 that, for dilute concentrations of a particular dopant, namely T1+, the observed defect-induced first-order spectra of these crystals at low temperatures are best understood by assuming that essentially zero force-constant perturbations are induced by T1+. Since the even parity type (Alg, Eg, and T2g) Raman active modes involve no defect motion, the observed spectra reflects the projected densities of states of these host crystals.