Light scattering from molten alkali halides

We present results of a systematic, experimental study of Raman scattering from molten alkali halides. Melt spectra are compared with those of the solid alkali halides, and with those of inert-element liquids. The high-frequency region of the melt spectra is well approximated by an exponential [$\sim \exp \left(\frac{-\omega }{\Delta }\right)$], whose width $\Delta$ scales with the classical "plasma frequency" of the melt (${\omega }_p$). Specifically, we find $\Delta =(0.35+0.02)\mathrm{}{\omega }_p$. The depolarization ratio for the high-frequency, exponential scattering is found to vary inversely as the number density of ions. The prominent bands seen in the solid-state spectra persist into the melt in the form of a "shoulder." In melts with a large mismatch between the cation and anion masses, two distinct structures are seen. A qualitative discussion of the various spectral regions is given. Calculations based on dipole—induced-dipole, binary-dynamics approximations are presented. These reproduce the high-frequency exponential fairly well, but the low-frequency features, as well as the magnitude of the depolarization ratio, remain to be explained.