Collective atomic dynamics in mixtures of liquid alkali metals and molten alkali halides

First results from the most recent investigation of the temperature dependence of the dynamic structure factor of Rb₈₀(RbBr)₂₀ using cold-neutron time-of-flight spectroscopy are compared with the dispersion relations of collective excitations in Rb(RbCl) and Rb(RbBr) mixtures. Dispersion curves are obtained from the maxima in the longitudinal current correlation function that extend the information on the collective atomic dynamics in this mixture to considerably larger momentum transfers than were covered by the dispersions determined from the fits to S(Q, omega ) in the previous investigations of the same mixture. A small minimum is found in the dispersion near 22 nm^-1, which can be related to a maximum in the partial static structure factor S_MX(Q) and which could be caused by an interaction of optic and acoustic modes in this region of momentum transfers, where S_NN(Q) and S_CC(Q) have comparable weights, demonstrating a change in the interatomic interaction due to the addition of 20 mol% salt to the metal.