Thermodynamic Properties of the Internal Rotator. Double Minimum with Attractive Forces

Abstract

A previously outlined general method of calculating thermodynamic properties for an unsymmetrical internal rotation is applied to a double minimum with attractive forces, for which the potential energy has two maxima at the same height and two minima at different heights. The entropy is lower than that of the system of two equal potential valleys or that for a single valley, and can be lower than the former by as much as R ln2 when the potential barriers are high. This decrease tends to disappear in the region of close approach to free rotation, when the barriers are lower than RT. For very high potential barriers, if one of two equal minima is raised, the system acquires the properties of a simple harmonic oscillator.