Spectral moment method versus least-squares Franck-Condon analysis for vibrationally resolved absorption spectra

Abstract

An accurate, back-of-the-envelope spectral moment method is described to obtain molecular parameters of excited state molecules and ions from vibrationally resolved absorption spectra. Since it is not an iterative procedure, the spectral moment method is clearly much faster than the least-squares Franck-Condon analysis for obtaining molecular parameters, and the procedure described here can even be implemented on a hand-held calculator. Some of the drawbacks of Franck-Condon analysis are overcome by the spectral moment method. Comparison of molecular parameters for a diverse range of excited state molecules and ions obtained by the spectral moment method versus Franck-Condon analysis or rotational spectroscopy reveal the high accuracy of the procedure here. Simulations of vibrationally resolved absorption spectra show that the spectral moment method with the Morse potential approximation gives an envelope that matches very well the observed spectra. © 1991 American Institute of Physics.