Ultraviolet-photon exposure stimulates negative current conductivity in amorphous ice below 50 K

Abstract

Water ice is known to carry positive charge via transfer of excess protons through a hydrogen-bonded system. In contrast, constant negative charge conductivity in ice has neither been confirmed experimentally nor theoretically. Here, we report that ultraviolet-photon irradiation stimulates negative current conductivity in amorphous ice at temperatures below 50 K, where hitherto known proton transfer from the surface through the bulk ice is inhibited. Quantum chemical calculations imply that the negative current conductivity results from almost barrier-less proton-hole transfer processes that neither requires intrinsic defects, doped species, nor reorientation of H2O molecules in ice.