Isotopic quantum effects in water structure measured with high energy photon diffraction

High energy electromagnetic radiation scattering techniques have been used to measure the structural differences between light and heavy water: we hav e studied both intra- and intermolecular effects. These methods and our dat a analysis are described in detail. We have observed a maximum isotopic eff ect of 1.6% relative to the magnitude of the x-ray structure factor. Our un certainties are an order of magnitude smaller than those of previous gamma- ray measurements (Root J H, Egelstaff P A and Hime A 1986 Chem. Phys. 109 5 164) and this has permitted us to test accurately the available quantum sim ulation results on water. The SPC and TIP4P potentials reproduce the measur ed results in r-space moderately well for intermolecular effects at distanc es greater than 2.5 Angstrom. These results show that H2O is a slightly mor e disordered liquid than D2O at the same temperature.