Vibronic effects in the chiroptical spectra of dissymmetric trigonal systems

Abstract

The influence of vibronic interactions on the chiroptical spectra associated with nearly degenerate E (doubly degenerate) and A (non-degenerate) electronic states in dissymmetric trigonal systems is examined on a formal theoretical model. The model considers both Jahn-Teller (JT) interactions within the E state and pseudo Jahn-Teller (PJT) interactions between the E and A states originating with (A + E) coupling to a single doubly degenerate vibrational mode (e). Formal expressions are developed for the rotatory strengths of individual vibronic states derived from (A + E) ⊗e coupling. Calculations based on the model are carried out for a large number of parameter sets representative of various vibronic coupling strengths, energy spacings between the unperturbed E and A electronic states, oscillator (vibrational mode) frequencies, and electronic rotatory strengths. The calculated results demonstrate the profound influence of vibronic interactions on the sign patterns and intensity distributions within the rotatory strength spectrum associated with the coupled E and A states, and upon the energy spacings between the vibronic levels which arise from (A + E) × e coupling. The implications of these results for interpretations of circular dichroism spectra of trigonal systems are discussed.