Models of orientational correlations in fluids: applications to liquid fluorine

Abstract

A new method of analysing the experimental atom-atom pair distribution functions gaa(r), based on the corresponding state principle, is presented. The method is first rested on nitrogen and chlorine liquids via computer simulations by exploiting intermolecular potentials that reproduce the experimental data satisfactorily. It is then applied to liquid fluorine to explain the large discrepancies we found when experimental and simulated gaa(r) were compared. Different models involving various degrees of microscopic orientational correlation are built up; among them, only one implying no appreciable orientational order agrees with the experimental data for fluorine. This model also fits liquid nitrogen well and fails in the case of liquid chlorine; consequently, the microscopic structure of liquid fluorine must be very different from that of other liquid halogens. However, some discrepancies between model and experimental gaa(r) of fluorine around 5 AA and spurious oscillations below 2 AA indicate that significant experimental uncertainties could affect the experimental data. The results of other models, which imply different degrees of orientational order, reported here can provide a useful guide for interpreting new experimental data.