Dynamic structure factors and neutron scattering in molten salts

A simple form for the partial dynamic structure factors in a molten binary salt, based on Mori's memory function formalism and satisfying the usual moment sum rules, is proposed and applied in numerical calculations for a rigid-ion model of molten sodium chloride. Suitable linear combinations of the partial density fluctuations, having the character of acoustic- and optic-type collective motions at long wavelength and of independent particle behaviour of the two components at short wavelength and of independent particle behaviour of the two components at short wavelength, lead to an approximate diagonalization of the matrix of dynamic structure factors. The corresponding longitudinal current spectra, at any given wavevector, peak at different frequencies even though no well defined structure corresponding to optic-type motions would be present in the neutron scattering spectrum for wavevectors q>or approximately=1AA -1 .