Juxtaposition of descriptions of Raman and resonance Raman scattering by classical and mixed quantum– classical theories

Abstract

AbstractRaman scattering (RS) is described by a classical model for molecular electronic and nuclear subsystems coupled by one of the simplest cubic non‐linear couplings. The corresponding system of classical non‐linear equations for the motion of electrons and nuclei of a molecule in an electric field of low‐intensity incident light is compared with the system of equations for a mixed quantum– classical model that describes the quantum dynamics of a two‐state electronic molecular subsystem and classical dynamics of a nuclear subsystem of the molecule. Here the classical dynamics are defined by the Born– Oppenheimer quadratic potential with consideration of the equilibrium position shift of the nuclei when an electronic subsystem transition from the basic state to the excited state occurs. A simple relationship, for which non‐resonance RS line intensities for both models of molecule are nearly equal, was established between the shift and the parameter characterizing the effectiveness of the coupling of electronic and nuclear oscillators in the classical molecule's model. Capabilities for comparing the description of resonance Raman scattering by the considered models and the question of the occurrence of a background in resonance RS spectra due to non‐linear coupling between electronic and nuclear subsystems of the molecule are also examined. Copyright © 2001 John Wiley & Sons, Ltd.