Photodissociation of water in crystalline ice: a molecular dynamics study

Ultraviolet irradiation of ice is of great interest for understanding the chemistry in both atmospheric and astrophysical environments. In interstellar space, photodissociation of H2O molecules can be a driving force behind the chemistry on icy dust grains in dense, cold molecular clouds even though the flux of UV photons is extremely low. The mechanisms of such photoinduced processes are poorly understood, however. In this work the photodissociation dynamics of a water molecule in crystalline ice at 10 K is studied computationally using classical molecular dynamics. Photodissociation in the first bilayer leads mainly to H atoms desorbing (65%), while in the third bilayer trapping of H and OH dominates (51%). The kinetic energy distribution of the desorbing H atoms is much broader than that for the corresponding gas-phase photodissociation. The H atoms on average move 11 Angstroms before becoming trapped, while OH radicals typically move 2 Angstroms. In accordance with experiments a blueshift of the absorption spectrum is obtained relative to gas-phase water.Comment: 23 pages, 5 figure

INVESTIGATION OF THE PROTON-EXCHANGE PROCESSES AT THE ICE - METAL INTERFACE

La présence d'une atmosphère d'hydrogène exerce une grande influence sur les courants continus de volume et de surface dans le cas d'un échantillon de glace maintenu entre des électrodes de Pd et d'alliages de Pd. La charge automatique de Pd et de ses alliages est peut-être une possibilité pour produire une électrode ohmique protonique permanente.Strong influence of the hydrogen atmosphere on steady volume and surface currents has been observed in ice samples with Pd and Pd alloys electrodes. Possible mechanisms of this phenomenon have been discussed. Automatic charging of Pd and its alloy electrodes may be one of the ways of producing "eternal" ohmic proton electrodes