Shock Compression of Argon. II. Nonadditive Repulsive Potential

Abstract

By means of the Monte Carlo method the shock Hugoniots of argon have been analyzed for an effective pair potential. This effective pair potential for the low-density Hugoniots closely agrees with the potential derived from molecular beams indicating the high accuracy of the pair-wise additivity approximation besides confirming the consistency of two complex experiments. For the high-density Hugoniot, however, the effective pair potential is considerably stiffer than the pair-wise potential at high compression. For liquid argon compressed twofold, the nonadditivity effect in the potential is about 30%. The theoretically derived pair-wise potential is only a few percent softer than this nonadditive potential. This theory might be improved further by allowing for distortions of the outer electron shell in a direction away from the contact region of the interacting pair of atoms. At high density the surrounding medium inhibits this distortion which leads to the observed stiffening and to the close agreement with the theory of spherical atoms.