Resonance Raman Spectroscopy as a Test of Ab Initio Methods for the Computation of Molecular Potential Energy Surfaces

The use of ab initio quantum chemical methods to aid in the interpretation of resonance Raman spectra is illustrated with examples where the resonant electronic absorption spectra are unstructured. In such cases only the gradient of the excited electronic state potential energy surface at the ground electronic state geometry is important in determining the upper state dynamics that are relevant to the Raman scattering process. The use of ab initio methods for which analytic gradients are available permits application to large molecular systems and to cluster models of molecules in solution. This procedure eliminates possible ambiguities in the empirical interpretation of resonance Raman spectra. These same ab initio methods may be used to provide descriptions of the groundstate normal modes and the effect of isotopic substitution on the form of the normal modes.