Breakup of the Hydrogen Bond Network In Water:The Momentum Distribution of the Protons

TL;DR

This study uses neutron Compton scattering to investigate how the hydrogen bond network in water disintegrates from ice to supercritical phase, revealing increased anharmonicity and potential gas phase formation at boundaries.

Contribution

It provides the first detailed measurement of proton momentum distribution across water phases, highlighting the transition from harmonic to anharmonic potentials.

Findings

Proton motion shifts from harmonic in ice to anharmonic in supercritical water.

Supercritical water exhibits a double well potential with ~0.3 Å separation.

Confinement in C60 enhances anharmonicity and suggests gas phase formation.

Abstract

Neutron Compton Scattering measurements presented here of the momentum distribution of hydrogen in water at temperatures slightly below freezing to the supercritical phase show a dramatic change in the distribution as the hydrogen bond network becomes more disordered. Within a single particle interpretation, the proton moves from an essentially harmonic well in ice to a slightly anharmonic well in room temperature water, to a deeply anharmonic potential in the supercritical phase that is best described by a double well potential with a separation of the wells along the bond axis of about .3 Angstroms. Confining the supercritical water in the interstices of a C60 powder enhances this anharmonicity. The changes in the distribution are consistent with gas phase formation at the hydrophobic boundaries.