Compton scattering study of water versus ice Ih: intra- and intermolecular structure.

The hydrogen-bond geometries in water and polycrystalline ice Ih are studied using synchrotron radiation-based Compton scattering data of unprecedented statistical accuracy and consistency. By combining the experimental data with model calculations utilizing density functional theory, we show that the technique provides unique and complementary information on hydrogen bonding in water. The comparison of water and ice indicates the necessity of including a local intra-intermolecular geometric correlation for water, relating the intramolecular O-H bond length to the corresponding hydrogen-bond geometry. By using the hydrogen-bond geometries obeying this correlation, we demonstrate a further constraint on the angular distortions of the hydrogen bonds in water.