Vibronic structure of MCD spectra. I. Non-Condon effects in molecules with nondegenerate electronic states

Abstract

A model is formulated for calculation of MCD spectra of molecules with nondegenerate electronic states. It takes into account differences between nuclear equilibrium configurations of the excited electronic states that are coupled by the magnetic field. These differences lead to the appearance of new (‘‘non-Condon’’) terms in the expression for the B term describing magnetic optical activity. It is shown that these terms have a strong effect on the vibrational structure of MCD spectra. They cause this structure to differ from the vibrational structure of the corresponding absorption spectra and can lead to sign changes within a single, isolated electronic manifold. It is argued that the experimental MCD spectra of planar aromatic hydrocarbons and their derivatives show clear signs of the presence of such non-Condon effects.