Mean square force in liquid argon and separation factor of isotopes

Abstract

The relationship between the separation factor in isotopic phase equilibria and the mean square force in the two phases is applied to the liquid-vapour equilibrium of argon isotopic mixtures and a comparison is made with mean square forces theoretically deduced from potentials and distribution functions. It is found that only distribution functions obtained from Percus and Yevick's and hypernetted chain integral equations or from Monte Carlo calculations give a satisfactory temperature dependence. A residual 20% discrepancy between theory and experiment is tentatively attributed to the Lennard-Jones potential and the possibility that varying the potential could improve the agreement is considered. The results generally indicate either a less steep variation of the potential between zero and the minimum, and therefore a smaller σ, or a substantial contribution of three-body forces.