Perturbation theoretical study of resonance Raman intensities: Contribution of forbidden electronic states

An equation which describes vibrational resonance Raman intensities was derived using the non‐adiabatically expanded (to the second order) state vector and the damped Kramers‐Heisenberg‐Dirac dispersion equation. The equation obtained includes the terms which correspond to the equation previously proposed by Albrecht, by Zgierski and by Korenowski et al. Forbidden electronic states may contribute to Raman intensities through the second‐order terms. The Raman excitation profile is predicted to show a characteristic pattern for a system where one of these second‐order terms plays an important role. The physical meanings of these higher order terms are discussed.