MODELS OF ORIENTATIONAL CORRELATIONS IN FLUIDS - APPLICATIONS TO LIQUID FLUORINE

A new method of analysing the experimental atom-atom pair distribution functions g(aa)(r), based on the corresponding state principle, is pr esented. The method is first tested on nitrogen and chlorine liquids v ia computer simulations by exploiting intermolecular potentials that r eproduce the experimental data satisfactorily. It is then applied to l iquid fluorine to explain the large discrepancies we found when experi mental and simulated g(aa)(r) were compared. Different models involvin g various degrees of microscopic orientational correlation are built u p; among them, only one implying no appreciable orientational order ag rees with the experimental data for fluorine. This model also fits liq uid nitrogen well and fails in the case of liquid chlorine; consequent ly, the microscopic structure of liquid fluorine must be very differen t from that of other liquid halogens. However, some discrepancies betw een model and experimental g(aa)(r) of fluorine around 5 angstrom and spurious oscillations below 2 angstrom indicate that significant exper imental 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 experim ental data.