Liquid Water: Atom Pair Correlation Functions from Neutron and X-Ray Diffraction

Neutron diffraction data for heavy water at 25°C, together with results derived from x-ray scattering, show that the orientational correlation between pairs of molecules is of a much shorter range (5Å) than the positional correlation between molecular centers (8 Å). The neutron diffraction pattern is completely described by a model which assumes preferred average orientation between neighboring molecules and no orientational correlation between second and higher neighbors. The structure of an average D2O molecule in the liquid is not significantly different from that of an isolated molecule in the dilute gas. Atom pair correlation functions derived from the data and the model are in good qualitative agreement with results derived from molecular dynamics studies.