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 isobaric conditions from the liquid to the supercritical domain using neutron diffraction. The experimental results have been analyzed at the light of molecular dynamics simulation. A progressive evolution of local ordering is observed when the density decreases when going from liquid to gaslike values in the supercritical domain. The translational ordering, which is characterized by three well-defined shells of neighboring molecules at ambient conditions, 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 under ordinary conditions where parallel and perpendicular configurations of neighboring molecules are slightly favored, is lost in the supercritical state and is found to be almost completely isotropic. (C) 2000 American Institute of Physics. [S0021-9606(00)51933-3].