CALCULATION OF ROTATIONAL STATES OF METHANE MOLECULES IN A SQUARE LATTICE

Abstract Methane molecules in a square lattice perform hindered rotation due to the molecular interaction. First, the one-body term in the interaction gives the new pattern of rotational energy level scheme. In the case of strong interaction, this scheme becomes similar to tunneling levels calculated from the pocket state formalism. Secondly, the two-body term produces a potential with lower symmetry. We investigate the case of a ferro-orientational phase. Four levels remain in the lowest part of rotational energy spectrum under the field strength estimated from the sum of atom–atom pair potentials. This small number of levels approaches to more realistic systems.