MOLECULAR-REORIENTATION IN LIQUID ACETONITRILE STUDIED BY DEPOLARIZEDLIGHT-SCATTERING EXPERIMENTS

Time correlation functions from depolarized light scattering experimen ts at several temperatures were examined by biexponentials that simult aneously 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 tho se 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 reori entation in liquid acetonitrile. Application of the J-diffusion model shows that the exponential decay of the observed orientational correla tion functions cannot be taken as evidence of rotational diffusion in liquid acetonitrile.