Translational–orientational coupling during passage of methane through the bottleneck in zeolite A

Diffusion of a five-site model of methane within porous zeolite A has been investigated by molecular dynamics simulation using potential available in the literature. Equilibrium and dynamical quantities especially those relating to the orientational degrees of freedom of methane have been computed. Methane exhibits interesting orientational preference during intercage diffusion through the eight-membered window which is the rate determining step for diffusion. A predominance of (2+2) orientation in place of (1+3) orientation is seen suggesting a strong translational–orientational coupling. This suggests that orientational motion might strongly influence the translational diffusivity of methane.