  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.
