Relaxation of Vibrational Excitons in Molecular-Ionic Crystal s Measured by Picosecond Time-Resolved CARS

The decay times of the internal vibrations in K2S04, KCl04, NaN03 and CaC03 single crystals have been measured at different temperature s by picosecond time-resolved CARS. The low temperature experimental data and their temperature dependence are interpreted on the basis of an energy relaxation mechanism, involving two-phonon and higher order decay processes

ELECTRIC FIELD-INDUCED SPECTRA AND DIPOLE MOMENT OF THE A1A2A^{1}A_{2} STATE OF FORMALDEHYDE.

$^{1}$ A. D. Buckingham and D. A. Ramsay, J. Chem. Phys. 42, 3721 (1965). $^{2}$ N. J. Bridge and D. A. Dows, paper 16, Columbus Symposium 1966. $^{3}$N. J. Bridge, D. A. Haner, and D. A. Dows, J. Chem. Phys. 43, 3128 (1966).Author Institution: Department of Chemistry University of Southern California, Los Angeles, California, 90007``Electric field spectra'' are obtained by modulating the ultraviolet absorption spectrum of a gas by an alternating electric field applied to the $sample,^{1,2,3}$ A lock-in amplifier detects the signal induced at even harmonics of the applied field frequency. The amplitudes and line shapes of the EFS lines depend on the molecular dipole moments in both electronic states. A quantitative treatment of the EFS phenomenon has been applied to lines of the $3390 {\AA}$ band of formaldehyde, and the excited state moment obtained at $\mu^{\prime}=1.52 = .05D$. The method can be applied with slight modification to spectra which contain overlapping lines, and some results will be described. This research was supported by the National Science Foundation

PRESSURE DEPENDENCE OF THE LATTICE VIBRATIONS OF CRYSTALLINE BENZENE

Author Institution: Chemistry Department, University of California; Chemistry Department, University of Southern CaliforniaThe Raman spectrum of crystalline benzene has been studied at temperatures between $77^{\circ} K$ and $300^{\circ} K$ and pressures up to 35 kbar. Lattice and internal vibrations have been observed for the orthorhombic and the monoclinic (high-pressure) phases. This paper reports primarily the results for the pressure-dependence of the gerade lattice vibrations in the orthorhombic phase at $77^{\circ} K$ . Theoretical calculations, based on an atom-atom intermolecular potential, are discussed. They include calculation of equilibrium crystal structure, elastic constants and pressure-dependence of structure and lattice frequencies. This work was supported in part by the Army Research Office (Durham) and by the United States Atomic Energy Commission