Abstract
A large broadening (∼0.4meV) of quasielastic neutron scattering (QENS) signal in H2O ice Ih at T=5K was observed by Bove et al. [Phys. Rev. Lett. 103, 165901 (2009)] and explained by a model of concerted proton tunneling. This result was rather unexpected, as prior studies never showed significant mobility in water at low temperatures and ambient pressure. There were a few attempts of theoretical understanding of the effect. Recent path-integral simulations as well as quantum lattice-gauge theory supported the possibility of the collective tunneling of protons in ice Ih, however other studies stated that concerted tunneling in ice Ih should have very low frequency. Here, we report on QENS measurements of H2O ice Ih at 1.8 and 5 K by using neutron scattering spectrometers with the energy resolution similar to and four times better than the energy resolution in the original experiment of Bove and co-workers. We did not observe any QENS broadening, and the measured spectra for the ice Ih and the reference vanadium sample were almost identical. Therefore, we conclude that there is no proton tunneling in ice Ih at temperatures down to 1.8 K measurable on an energy scale of 3.5 μeV and above. The literature data on low-temperature heat capacity of ice Ih support this conclusion.
