Perturbation treatment of doublet splittings in rotational spectra of molecules with two equivalent conformations separated by nonequivalent energy barriers

Abstract

A method is described for analyzing doublet splittings in rotational spectracaused by tunneling between two equivalent conformations, under the restriction that the tunneling motion be effectively aperiodic. The splittings can mainly be fitted with three parameters: the purely torsional doublet splitting ΔE and two Euler angles β and γ, which characterize the transformation between the principal-axis system and the Eckart-axis system. The method is numerically very fast when the splittings are small enough to allow the use of perturbation theory. Examples are given to show that a simple correlation between β and γ with the path of the tunneling process is possible.