Neutron diffraction study of high density supercritical water

New neutron diffraction data on supercritical water are presented, from which the site–site radial distribution functions are calculated, with the aim of providing additional experimental evidence about the degree of hydrogen bonding in bulk water under these thermodynamic conditions. Compared to water under ambient conditions severe modifications to the three site–site radial distribution functions are found, with little evidence for a distinct hydrogen bond peak in the OH function, at densities in the range $\text{0.58}$ ${\mathrm{g/cm}}^3$ $\text{⩽ρ⩽0.78}$ ${\mathrm{g/cm}}^3,$ along the isotherm at $\text{T=673}$ K. The results highlight the loss of tetrahedral coordination in supercritical water, thus confirming the conclusions of a previous neutron diffraction experiment. These new results are relevant to the current debate about the suitability of rigid body, pairwise additive, effective potentials for predicting the behavior of water far away from ambient conditions.