Mass dependence of the ionic dynamics in molten salts

The dynamical properties of condensed media are studied on the basis of molecular dynamics in a two component system of charged particles. The short-time behavior of the particle motion is described in terms of velocity autocorrelation functions. In order to get a better understanding of the mechanism of the transport process the effect of isotope substitution is examined. It is shown that the collision theory does not provide a suitable model; the results are interpreted within the framework of perturbation theory. Expressions are derived which give a correct representation of the influence of a mass change on the self-diffusion coefficients; this approach is used to calculate the isotope effects in naturally occurring systems. Comparisons with experimental results are interpreted by introducing strongly correlated motions.