Translational and rotational diffusion of SF6 in zeolite NaY

Temperature dependence of equilibrium as well as dynamical properties of SF6 in zeolite NaY have been investigated by molecular dynamics simulation. By about 200 K, SF6 begins to have increased mobility. Strong orientational preference is exhibited by SF6 during its passage through the 12-ring window, the bottleneck for diffusion. The preference is for orientation with C-3 followed by C-2 and then C-4 molecular symmetry axis perpendicular to the window plane. Translational motion is diffusive with an activation energy of 5.5 kJ/mol. Rotational-diffusion coefficient has an activation energy of 2.83 kJ/mol. Rotational motion is facile within the alpha-cage. Translational motion is hindered during passage through the 12-ring window when C-4 is perpendicular to the window plane. Orientational correlation functions P-1 and P-2 around C-2, C-3 and C-4 are reported. Only the long time decay Of C-4 shows oscillations. This is attributed to the hindered rotation during intercage migration while passing through the 12-ring window. (C) 2004 American Institute of Physics.