DENSITY-DEPENDENCE OF ROTATIONAL RELAXATION OF SUPERCRITICAL CF3H

Polarized and depolarized Raman scattering measurement and molecular dynamics (MD) calculations have been performed for supercritical CF3H at various densities along an isotherm higher than T-c by about 6 K in order to investigate the density dependence of rotational relaxation. The rotational autocorrelation functions obtained from both methods, which are in satisfactory agreement with each other, showed liquid-like diffusional decay for the fluid at densities higher than rho(c). The function changed in shape continuously to a nearly free-rotor-like one at the lowest density going through the oscillatory ones at intermediate densities. The detailed analysis based upon the MD trajectories has been done in order to clarify the relaxation mechanism at each density. Applicability of the J-extended diffusion model was also examined. They showed that the density dependence of the rotational relaxation may be explained in terms of the states of molecular aggregation in the fluid. (C) 1995 American Institute of Physics.