Internal Rotation in Completely Asymmetric Molecules. III. Theory for Molecules with Twofold Potential Barriers

Abstract

The theory of internal rotation in asymmetric—asymmetric molecules is extended to planar molecules with twofold potential barriers. Two approaches utilizing a model with one degree of internal freedom are developed for solution of the problem. A framework-fixed-axis method is found to be best for medium barrier heights, where effects that arise from tunneling are important. The results of an internal-axis method are suitable for application in a high-barrier approximation, in which case simple, explicit functions are obtained for the torsional dependence of the moments of inertia and inertia defect. Finally, the theoretical results are discussed in relation to the experimental data from the microwave rotational spectra of phenol and nitrosobenzene.