Protons at Ice Surfaces

摘要

Ice surfaces play an important role in many chemical processes that occur in nature at low temperatures.Ice particles in the polar stratospheric clouds,for example,catalyze the heterogeneous reactions that lead to the seasonal depletion of the ozone layer,and prebiotic molecules detected in interstellar space are believed to form in the ice mantle of interstellar dust particles.The environmental and astrobiological importance of ice reactions has stimulated research on this subject in recent years.A critical issue in the study of ice reactions is the rate of proton transfer.Proton transfer is responsible for a variety of chemical reactions in the aqueous phase,ranging from acid-base neutralization to enzymatic reactions.Proton mobility is anomalously high compared to that of other ions in liquid water.This unique behavior is attributed to a proton relay (Grotthuss) mechanism in which the effective motion of a proton involves a sequence of proton tunnelings along the hydrogen-bonded chain of water molecules.This sequential proton transfer is promoted by the rearrangement of hydrogen-bond networks in liquid water in order to accommodate a proton in stable solvation structures.