Local orientational correlations in fluid CO2 in a wide range of thermodynamic parameters

In this paper we present a thorough study of the local microscopic structure of carbon dioxide in a wide thermodynamic region, coveting both undercritical and supercritical states. From neutron diffraction measurements we derive accurate information an the neutron weighted distribution function, g(nw) (r), which allows us to single out a realistic interaction potential to be used in Molecular Dynamics (MD) simulations. These MD simulations are then performed to supplement the information obtained from the neutron scattering experiments. In such a way we determine appropriate averages of the molecular distribution function, g(R, omega(1),omega(2)). The presence of preferred relative orientations between neighbouring molecules is evident. We find that, among first neighbouring molecules, T-shaped configurations are largely preferred in all the investigated thermodynamic states and that electrostatic interactions play a crucial role in determining the local structure of the fluid.