Theoretical and experimental studies of the second-order Raman spectra of CsCl, CsBr, and CsI

Measurements of the second-order Raman spectra of CsCl, CsBr, and CsI have been made at both 300 and 80 °K. From these the three independent spectral components, $A_{ 1g}$, $E_{ g}$, and $T_{ 2g}$, have been determined for all three crystals at both temperatures. A theoretical interpretation of these data has been carried out using the phenomenological Born-Bradburn model to describe the Raman polarizability tensor and the deformation-dipole model to provide the lattice-dynamical eigendata. We have found it possible to obtain an excellent description of the observed spectra retaining 16 of the first- and second-neighbor polarizability derivatives in the Born-Bradburn expressions for the elements of the polarizability tensor. We have also found that only three of these need be retained to obtain a good semiquantitative fit to the observed spectra.