The structure of fluid carbon dioxide by neutron diffraction at high pressure and by RISM calculations

Inelastic neutron scattering and molecular dynamics determination of the interaction potential in liquid CD4

Anisotropic interactions of liquid CD4 are studied in detail by comparison of inelastic neutron Brillouin scattering data with molecular dynamics simulations using up to four different models of the methane site-site potential. We demonstrate that the experimental dynamic structure factor S(Q,omega) acts as a highly discriminating quantity for possible interaction schemes. In particular, the Q evolution of the spectra enables a selective probing of the short- and medium-range features of the anisotropic potentials. We show that the preferential configuration of methane dimers at liquid densities can thus be discerned by analyzing the orientation-dependent model potential curves, in light of the experimental and simulation results.

Orientational correlations in liquid, supercritical and gaseous carbon dioxide

Neutron and x-ray diffraction results obtained for liquid CO(2) have been modelled by means of the reverse Monte Carlo method. Partial pair correlation functions, centre-centre pair correlation functions and relative orientations of molecular axes as a function of distances between molecular centres have been calculated from the models. It was found that well defined orientational correlations exist in the liquid state. Close to the critical point, these correlations seem to disappear, but further away from the critical point, in the high density supercritical state, they reappear. Using large particle configurations, the density fluctuations close to the critical point could be visualized.