Studies of molecular motions and vibrational relaxation in acetonitrile

Abstract

Far-infra-red spectra in the 2–200 cm^-1 region of dilute solutions of CH₃CN in CCl₄ solution have been employed to test the various analytical models available for the description of rotational motions of a symmetric top dipole in the liquid phase. It is found that none of the various approximants of the Mori continued fraction description of reorientational correlation function fit the experimental data satisfactorily. This implies that, although the data (from this and other techniques) may appear to be properly described by a simple rotational diffusion model at long times, the short time dynamics are too complicated to be reproduced even by much more sophisticated models. The data are able to clearly discriminate between the various models tried and, in addition, give valuable information about the nature and extent of the mean square torques acting on the probe molecule.