Ab initio study of the role of vibronic coupling in the ultraviolet valence/Rydberg spectrum of formaldehyde: Handling of vibronic interaction between three electronic states

Abstract

Two approaches were developed to calculate vibronic coupling between three electronic states: the first one is based on adiabatic potential, the other on diabatic ones. The methods were applied to the three lowest excited 1A1 states of formaldehyde, coupled through the C-O stretch vibrational mode. Using expansions of sufficient length, excellent agreement between vibrational energies calculated independently by the two approaches were obtained. Similarly good agreement was found for the calculated transition moments.