Some aspects of hydrogen bonding in the phases of water

Abstract This paper reviews four aspects of hydrogen bonding in both the vapour and the solid phases of water. 1. The first aspect is the dimerization of H 2 O and D 2 O molecules in the vapour phase, as measured by their second virial coefficients. The difference of the second virial coefficients of H 2 O and D 2 O is 15 cm 3 mol −1 at 150°C, about 5 cm 3 mol −1 at 200°C, and about 1 cm 3 mol −1 at 300°C and a significant difference seems to persist up to 500°C. It is caused by the difference of the zero-point and thermal energies of the monomers and dimers of H 2 O and D 2 O vapour. 2. The equilibrium lines between the liquid and ice VI and between ice VI and ice VIII have been extrapolated towards high pressure and high temperature to the metastable triple point at which the liquid, ice VI and ice VIII are at equilibrium. The metastable liquid-VIII line was extrapolated approximately to zero pressure at about 60 K, and it was predicted that when ice VIII at zero pressure and 77 K was heated it would transform to a low-density amorphous ice. The prediction was correct. 3. The configurational entropies of both high-density and low-density amorphous ice relative to ice Ih have been inferred from an analysis of what we know about the course of the ice-I-liquid line, its extrapolation to low temperatures, and the measured enthalpies of the transformations. The configurational entropies are 2±≈1 J K −1 mol −1 and 1±≈0.5 J K −1 mol −1 respectively, which is much smaller than the existing theoretical estimates of about 6 J K −1 mol −1 . 4. The incoherent inelastic scattering of neutrons by the phases of H 2 O ice, in particular by high-density and low-density amorphous ice and by ice Ih and Ic, has been measured in order to determine the densities of vibrational states. From these measurements, the first accurate determination of the anharmonic contribution to the heat capacity of ice Ih has been obtained.