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

Quasi-elastic neutron scattering was employed on samples of HCl-doped polycrystalline ice I-h. The analysis of the scattering signal provides the excess proton hopping time, tau(hop), 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 tau(hop) 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.