ROTATIONAL MOTION OF SF6 INSIDE SMALL PORES OF SILICA GLASS

Raman spectra of the v2 and v5 vibrational modes of SF6 confined within pores of silica gels of average diameter 12 angstrom are recorded at pressures varied between 84 and 1827 bars and at temperatures 296, 353, and 398 K. The experimental correlation functions for SF6 inside the pores are compared with the theoretical functions obtained from the extended diffusion model and the Fokker-Planck-Langevin model in order to find relaxation times for the angular momentum. It is shown that although experimental correlation functions of SF6 for neat liquid and inside the pores exhibit similar time and density dependence, the mechanisms of reorientational relaxation are different. At low densities molecules collide mainly with the walls and it is suggested that those collisions are less effective in changing the angular momentum.