MOLECULAR-REORIENTATION IN LIQUID ACETONITRILE STUDIED BY DEPOLARIZED LIGHT-SCATTERING EXPERIMENTS

Time correlation functions from depolarized light scattering experiments at several temperatures were examined by biexponentials that simultaneously account for the unique axis molecular reorientations (an the picosecond time-scale) and collisional processes (on the subpicosecond time-scale). The first are found to be systematically slower than those obtained in previous studies. The important role played by dipolar interactions on the molecular organization in the liquid is confirmed. Comparison with dielectric relaxation times indicates that rotational diffusion provides only an approximate description of molecular reorientation in liquid acetonitrile. Application of the J-diffusion model shows that the exponential decay of the observed orientational correlation functions cannot be taken as evidence of rotational diffusion in liquid acetonitrile.