Temperature Dependence of Second-Order Raman Scattering in Potassium and Rubidium Halides

The second-order Raman-scattering spectra of KCl, KBr, KI, RbCl, RbBr, and RbI have been recorded at 300, 90, and 23 K. A symmetry analysis for reducing phonon pairs into irreducible representations has been employed, in conjuction with a knowledge of the one-phonon densities of states derived from neutron-diffraction data, to identify the two-phonon combinations that give rise to features in these second-order Raman spectra. The temperature dependence of a given spectrum is dominated by the phonon occupation numbers which appear in the final-state density-of-states factor in the scattering cross section. In addition to a description of the general features of the second-order spectra, the results for each substance are described and discussed individually in some detail.