Franck-Condon analysis of photoelectron and electronic spectra of small molecules

Currently available methods for the simulation of Franck-Condon envelopes of electronic and photoelectron spectra of small to medium-sized molecules are reviewed and discussed. The advantages of combining ab initio molecular orbital calculations with Franck-Condon calculations to simulate vibrationally resolved electronic and photoelectron spectra are outlined and the ability of such calculations to assign the vibrational components observed in these spectra and to derive excited or ionic state geometries is emphasized. Simulation of the emission spectrum of CF2 is taken as an example where a harmonic oscillator model has been used for each electronic state to derive vibrational eigenvalues and eigenvectors and hence calculate Franck-Condon factors. The possibility of improving this model by the use of anharmonic potentials is identified as a likely future development. (C) 1998 Elsevier Science B.V. All rights reserved.