RECONSTRUCTION OF THE ORIENTATIONAL PAIR-CORRELATION FUNCTION FROM NEUTRON-DIFFRACTION DATA - THE CASE OF LIQUID-HYDROGEN IODIDE

An analysis of partial-structure-factor information on molecular liqui ds is described which uses the spherical harmonic expansion of the sit e-site structure factors to extract an estimate of the orientational p air-correlation function between molecules. Recently published neutron -diffraction data on the site-site partials in liquid hydrogen iodide at 210 K are used as the input data to this technique. The results, wh ich are presented as a map of the orientational pair-correlation funct ion, g(r,omega1,omega2), show the occurrence of pronounced relative or ientational correlations between molecules at this temperature, even t hough the same orientations are apparently only weakly correlated with the molecular center of mass. The same spherical harmonic expansion p rocedure can be applied to a number of other molecular liquids where d iffraction data are available.