X-ray and neutron diffraction from diatomic liquids

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Abstract
The analysis of x‐ray and neutron diffraction data for studying the structure of diatomic liquids is critically examined. Using calculated pair distribution functions for a model diatomic fluid, ``experimental'' x‐ray and neutron intensity scans are constructed. The importance of the orientational correlations to the scattering intensity, and its effect on the interpretation of the intensity, is considered in detail. A method of assessing the orientational correlation contribution to experimental diffraction data is suggested, and the circumstance for which this contribution may be large is identified. It is found that approximate Fourier inversion procedures, and simple models of the liquid state which neglect the coupling between radial and orientational correlations, cannot be used to extract accurate information about the center‐of‐mass radial distribution function from diffraction data. The limited utility of the atomic radial distribution function for polyatomic molecules, and a problem which arises in calculating this function from diffraction data, are both discussed. A method is suggested for unfolding the structure of a dense molecular fluid from x‐ray and neutron diffraction data which is based upon a theory of molecular fluids proposed by Steele and Sandler [preceding paper]. A test of this method indicates that it yields reasonably accurate information about both the radial and orientational correlations in diatomic liquids.