Diffusion in liquid mixtures of isotopes

Molecular dynamic calculations of the velocity autocorrelation functions and self-diffusion coefficients in two-component liquid mixtures consisting of the argon isotope of mass 40 and, in order to obtain a clear isotope effect, fictitious argon isotopes of one of the masses 32, 80 and 200 have been made. A perturbation theory, in principle being an expansion in powers of the mass difference of the two isotopes in the mixtures, has been developed and used for the analysis of the results for the velocity autocorrelation functions, permitting also the calculation of isotope effects for the mass differences occurring in mixtures of real isotopes. The connection between the mutual and self-diffusion coefficients and the relation of the results to binary collision and hydrodynamic theory has been briefly considered.