Solvent effect on the vibrational dephasing of the nu(2) (CN) and nu(4) (CC) stretching modes in liquid acetonitrile and acetonitrile-d(3)

The vibrational dynamics of CH,CN and CD3CN have been examined in pure subs tances and in mixtures with CCl4 at constant, room temperature, analysing t he band shapes and the frequency shifts of nu(2) (CN) and nu(4) (CC) stretc hing modes. The effective temperature of the scattering volume, instead of the thermostatic value, was used to calculate and eliminate some secondary structures present in all the examined profiles. By doing this, it has been possible to correctly extract the dynamic parameters from the Raman isotro pic profiles and from the relevant time correlation functions. The nonideal ity of the CH3CN/CCl4 mixture clearly emerges from the application of the K ubo theory in the frequency domain, following a calculation procedure previ ously developed in our laboratory. The concentration dependence of the bandwidths and the frequency shifts in nu(2) mode have been interpreted within the theory of the local concentrati on fluctuation. (C) 2000 Published by Elsevier Science B.V. All rights rese rved.