Theoretical Calculations of the Raman Intensities by the Vibronic Method

The values of the transition moment of Raman scattering have been calculated according to the formula derived from the vibronic expansion approach. The calculations have been performed for the symmetry coordinates of several small molecules and for the normal vibrations of methane. The electronic wave functions were calculated by the CNDO/2-CI method. The calculated results are large in comparison with the experimental ones. The calculated Raman intensities for the symmetric stretching vibrations were almost all contributed by the term A in the vibronic expansion theory. From the calculated results for the normal vibrations of methane, it was found that the vibronic method used in this work leads to more appropriate values than those obtained from the polarizability theory which was used in the previous paper.