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.