The nature of molecular vibrations selected by various excitation processes

Abstract

Local modes of vibration have been clearly identified in infrared absorption, but sofar not in other kinds of optical spectroscopy. We have investigated the reason for this through model calculations on a simple, but realistic, double Morse oscillator model of the stretch vibrations of a CH 2 radical, excited by various optical processes involving a change of electronic state. The general result is, that the resulting spectrum is determined mainly by the excitation operator, and is normal-mode-like for excitation processes dominated by Franck-Condon factors. The specific form of the spectrum depends on the details of the excitation operator, and we investigate how the characteristics of the normal-mode-like spectrum depend on the difference in the equilibrium distance of the two potential surfaces.