The temperature dependence of equilibrium, as well as the dynamic properties of SF6 in NaY zeolite, were investigated using molecular dynamics simulations. At about 200K, SF6 began to exhibit increased mobility. Strong orientational preference was exhibited by SF6 during its passage through the 12-ring window, which was a bottleneck for diffusion. The preference was for orientation with the C3 followed by C2 and then C4 molecular symmetry axes perpendicular to the window plane. The translational motion was diffusive, with an activation energy of 5.5kJ/mol. The rotational-diffusion coefficient had an activation energy of 2.83kJ/mol. Rotational motion was easy within the α-cage. Translational motion was hindered during passage through the 12-ring window, when C4 was perpendicular to the window plane. Orientational correlation functions around C2, C3 and C4 were reported. Only the long-term decay of C4 exhibited oscillations. This was attributed to hindered rotation during intercage migration when passing through the 12-ring window.

Translational and Rotational Diffusion of SF6 in Zeolite NaY. P.K.Ghorai, S.Yashonath: Journal of Chemical Physics, 2004, 120, 5315