College Park, Maryland      June 6 - 10 , 2004

WP65: Proton Tunneling in Supercritical Water

G.F. Reiter (Physics Department, University of Houston), J.C. Li (Physics Department, University of Manchester), J. Mayers, T. Abdul-Redah (ISIS, Rutherford Appleton Laboratory), P. Platzman (Bell Labs-Lucent Technologies)

Neutron Compton Scattering measurements can give a detailed measurement of the momentum distribution of light ions in solids and liquids. We present the momentum distribution in ice, room temperature water, supercritical water, and confined supercritical water. While the ice and room temperature water data can be interpreted in terms of nearly harmonic potentials, the supercritical water data shows clear evidence of tunneling, apparently along the bond, over distances of about 0.3 Angstroms. Confinement by hydrophobic surfaces of C60 reduces slightly that distance. The data is consistent with vapor phase at the hydrophobic surfaces, and inconsistent with ice phase formation. The strong anharmonicity makes classical simulations of dubious value in describing supercritical water. We interpret the data in terms of 'inherited tunneling' from the motion transverse to the bond.

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