Rotational motion of methane within the confines of zeolite NaCa A: molecular dynamics and ab initio calculations.

Molecular dynamics simulation of a five-site model of methane within zeolite NaCaA and ab initio calculations have been reported. Methane shows a preferential orientation during its passage through the eight-ring window. Partial freezing of certain rotational degrees of freedom is observed during the passage of methane through the eight-ring window, which acts as a bottleneck for diffusion of methane. Both the orientation and the rotational motion of methane and its experimental verification can indicate the accuracy of the intermolecular potential between methane and zeolite employed in this study. Intracage motion of methane shows that methane performs a rolling motion rather than a sliding motion within the supercage.