Anharmonic Lattice Vibrations and the Temperature Shift of Raman Spectral Lines

Abstract The temperature dependence of the average lattice mode frequency of a molecule undergoing librational motion in a quasi-harmonic potential has been calculated with the purpose of finding an explicit relationship between the observed shift of Raman spectral lines with temperature and the anharmonic term in the rotational potential. Calculations were carried out both for uncoupled and coupled oscillators. The equations obtained with this model provide good fittings for solid Cl2 and benzene data. This result can be applied to the analysis of the temperature dependence of NQR frequencies in molecular crystals.