Dynamics of molecular reorientational motion and vibrational relaxation for symmetric top molecules in the liquid phase

Abstract

Detailed studies of the molecular relaxation processes in pure liquid t-butyl chloride (TBC) and t-butyl bromide (TBB) and in solutions in carbon tetrachloride and in n-hexane have been made using several experimental techniques. Single particle reorientational motions perpendicular to the symmetry axis were studied using Raman scattering and a comparison of these results with those obtained from depolarized Rayleigh scattering allowed an evaluation of the importance of correlations in orientation between pairs of molecules in the two systems, also, collision induced scattering was not found to be significant. Additional cross comparisons of related data obtained using infrared absorption and dipolar absorption were made. In all cases, the original experimental data were subjected to Fourier transform analyses so that the time evolution of the resulting correlation functions could be studied. In general, at short times the reorientational motions are inertial, but at long times exponential decay of the correlation functions is observed. The mechanism of vibrational relaxation in TBC and TBB was also studied by analysis of the correlation functions corresponding to the isotropic Raman scattering in the pure liquids and in solution. In addition, an efficient computational model for the theoretical calculation of any orientational vectorial correlation function has been developed. The theoretical correlation functions could be compared directly with those determined experimentally.