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College Park, Maryland      June 6 - 10 , 2004

M3-D2 (2:00 PM): Recent Progress in the Measurement of Proton Momentum Distributions in Hydrogen Bonded Systems

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

Recent progress in Neutron Compton Scattering (Deep Inelastic Neutron Scattering) has made possible the detailed measurement of the momentum distribution of the proton in a variety of hydrogen bonded systems. The distribution is determined almost entirely by quantum localization effects, and hence the measurements provide a detailed picture of the localizing potential. Quantum effects such as tunneling are easily observed. We will provide an overview of the method and discuss the measurements in ice, room temperature water, supercritical water, water in confined geometries, and water with acid, base and salt impurities added. The supercritical water data exhibits a dramatic tunneling motion and provides additional evidence that water near a hydrophobic surface is in the vapor, not ice phase. The impurity measurements provide a direct observation of the localization of the acid proton and base hydroxyl groups. We will also discuss the ferroelectrics KDP, DKDP and the structural spin glass RDP-ADP, in which the tunneling motion of the hydrogen bonds that hold the crystal together are an essential feature of the observed structural phase transitions.

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