HIGH-RESOLUTION RAMAN-STUDY OF PHONON AND VIBRON BANDWIDTHS IN ISOTOPICALLY PURE AND NATURAL BENZENE CRYSTAL

The frequency and the bandwidth of the 12 Raman active lattice modes a nd of more than 45 internal vibrons of natural and C-12 isotopically p ure benzene have been measured under high resolution with the aid of a tandem interferometer-spectrometer system or alternatively of a two m eter focal length grating Sopra spectrometer. For five lattice phonons and for several vibrons the measurements were extended to a sufficien t temperature range to study the relaxation processes in terms of anha rmonic phonon-phonon and phonon-vibron coupling processes. The effect of the isotopic impurities on the phonon lifetime has been shown to be very important for some vibrons, in particular, for those resonant wi th the impurity level. The bandwidth evolution with temperature has be en interpreted in terms of down- and up- three- and four-phonon as wel l as of dephasing processes. (C) 1998 American Institute of Physics. [ S0021-9606(98)00637-0].