Fast Proton Hopping Detection in Ice I_h by Quasi-Elastic Neutron Scattering

Abstract

Quasi-elastic neutron scattering was employed on samples of HCl-doped polycrystalline ice Ih. The analysis of the scattering signal provides the excess proton hopping time, τhop, in the temperature range of 140–195 K. The hopping time strongly depends on the temperature of the sample, and the activation energy of a hopping step is 17 kJ/mol. The values of τhop of the current experiment are in good agreement with calculated values derived from previous photochemical experiments,(1) in which we found that the proton hopping time at T > 242 K is on the order of 200 fs, roughly 10 times shorter than in liquid water at room temperature.