Inelastic neutron scattering study of water in the subcritical and supercritical region

Inelastic neutron scattering measurements have been carried out at high-energy transfers on ${\mathrm{H}}_2\mathrm{O}$ water in the subcritical and supercritical region. The results were compared to estimated values of the kinetic energy of a hydrogen atom in a water molecule in the gas and liquid states. It was found that the increase in kinetic energy with temperature was more than expected from the harmonic approximation. It is concluded that about half the hydrogen bonds in water with density of $\rho =0.85\mathrm{}{\mathrm{g}/\mathrm{c}\mathrm{m}}^3$ are broken at $400°\mathrm{C}.$ It was also found that there was a further decrease in the number of hydrogen bonds on decreasing the density at $400°\mathrm{C}.$