Orientational correlations in liquid and supercritical CO2: neutron diffraction experiments and molecular dynamics simulations

Neutron diffraction data from sub- and supercritical CO₂, collected over three different experimental runs, are analysed together, in order to investigate the evolution of the microscopic structure with the thermodynamic parameters. The relative orientations of neighbouring molecules are analysed also in terms of the angular radial correlation function, obtained by molecular dynamics simulation runs compatible with the total neutron weighted radial distribution function. Orientational correlations between neighbouring molecules are seen to persist across the whole thermodynamic range investigated. However, these are limited to the first neighbouring shell, and mainly ascribable to the quadrupolar interaction.