Although water ice has been widely accepted to carry a positive charge via the transfer of excess protons through a hydrogen-bonded system, ice was recently found to be a negative charge conductor upon simultaneous exposure to electrons and ultraviolet photons at temperatures below 50 K. In this work, the mechanism of electron delivery was confirmed experimentally by both measuring currents through ice and monitoring photodissociated OH radicals on ice by using a novel method. The surface OH radicals significantly decrease upon the appearance of negative current flow, indicating that the electrons are delivered by proton-hole (OH) transfer in ice triggered by OH production on the surface. The mechanism of proton-hole transfer was rationalized by density functional theory calculations.
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