Hydrated protons at the surface of water ice are of fundamental importance in a variety of physicochemical phenomena on earth and in the universe. Hydrated protons can be introduced by the autoionization of water molecules; thus, the autoionization and subsequent proton transfer processes determine the proton activity inherent to water molecular systems. A recent experimental study on the H/D isotopic exchange of water molecules reports markedly enhanced proton activity at the surface of crystalline ice.
