THE STRUCTURE OF FLUID CARBON-DIOXIDE BY NEUTRON-DIFFRACTION AT HIGH-PRESSURE AND BY RISM CALCULATIONS

High-pressure neutron diffraction measurements on fluid carbon dioxide are reported. At the supercritical temperature of 380 K, the density of the fluid was varied by almost a factor of two from 0.5 to 0.9 g cm-3. Some aspects of the experiment and the data evaluation are mentioned, and the intramolecular structural parameters are given. The measurements were performed to assess the usefulness of some three-centre pair potentials reported in the literature by means of reference-interaction-site-model (RISM) calculations with regard to their applicability to reproduce the short-range order of that polar liquid. The hyper-netted-chain (HNC) and Percus-Yevick-Allnatt (PYA) closure relations were tested by comparison with the results of molecular dynamics calculations. The density dependent measurements proved to be useful for assessing the individual potentials.