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

Abstract

The basis for calculating the thermodynamic properties of the unsymmetrical internal rotator from energy levels derived from the old quantum theory is described, and a method is outlined for calculations with a potential energy function consisting of linked sections of cosine curve with the width of each section proportional to the barrier height. A table of values of a general quantum number index for the cosine function is presented and its application to the unsymmetrical internal rotator is illustrated. Thermodynamic properties are calculated for a double minimum system of optical isomers for which the forces restricting rotation must be repulsive. It is found that the entropy of such a system may be greater by nearly 0.5 unit than that of the limiting system with equal potential maxima, that is, with the symmetrical cosine potential function.