Frequency Dependence of Relative Intensities and Depolarization Ratio for Resonance Raman Scattering

Abstract

Theoretical expressions for the frequency dependence of the intensities of Raman lines in the pre-resonance and rigorous resonance Raman scattering are derived on the basis of a new approach. In this effort the main contribution to the change in polarizability is obtained from the derivative of electronic transition moment with respect to the vibrational normal coordinates. Therefore, this approach differs from previous approaches which suggested that the main contribution to the Raman intensities (polarizability derivative) comes from the derivative of electronic frequency with respect to the normal coordinate. This new approach leads to excellent agreement between the derived theoretical expressions and several recently reported experimental studies. In this paper the effective absorption frequencies and damping terms are determined from the excitation profile rather than the electronic absorption spectrum. To extend these studies to non-totally symmetric modes by considering the scattering due to nondiagonal polarizability tensor components, we have attempted to derive the depolarization ratios by calculating the contribution to the scattered intensity from the quadrupole and magnetic dipole terms. An anomalous depolarization ratio results from the angular distribution of the magnetic dipole vibration at a certain spectral location.