The structure of liquid and supercritical benzene as studied by neutron diffraction and molecular dynamics

The local ordering in benzene has been investigated under isothermal and is obaric conditions from the liquid to the supercritical domain using neutron diffraction. The experimental results have been analyzed at the light of m olecular dynamics simulation. A progressive evolution of local ordering is observed when the density decreases when going from liquid to gaslike value s in the supercritical domain. The translational ordering, which is charact erized by three well-defined shells of neighboring molecules at ambient con ditions, is gradually weakened, and extends only to the first shell as the density decreases in the supercritical domain (under isothermal compression ). In the same way, the orientational ordering of benzene, which exists und er ordinary conditions where parallel and perpendicular configurations of n eighboring molecules are slightly favored, is lost in the supercritical sta te and is found to be almost completely isotropic. (C) 2000 American Instit ute of Physics. [S0021-9606(00)51933-3].