BRILLOUIN SPECTRA AND VIBRATIONAL-TRANSLATIONAL ENERGY-EXCHANGE IN LIQUID ACETONITRILE

Polarized light scattering experiments in the GHz frequency range (Ray leigh-Brillouin spectra) are reported for liquid acetonitrile. Hyperso nic velocities and absorption coefficients have been measured as a fun ction of temperature and of transferred wave vector. The plots of thes e quantities versus frequency show characteristic dispersion which is indicative of relaxation phenomena. The occurring relaxation has been interpreted as due to a thermal process in which the translational ene rgy of molecules is transferred, during the collisions or through dipo lar interactions, into internal degrees of freedom of low quanta vibra tional motions. The quite strange behavior of the relaxation time with the temperature has been interpreted and compared with the behavior o f the relaxation time in liquid chloroform. (C) 1998 American Institut e of Physics.