Electron-impact ionization of low-temperature water ice leads to H+, H+2, and H+(H2O)(n=1-8) desorption. The 22 eV H+ desorption threshold is correlated with localized 2-hole 1-electron and 2-hole final states which Coulomb explode, while the 22 eV H+2 threshold is due to H2O+ unimolecular dissociation. The 70 eV primary cluster ion threshold is consistent with holes in the 2a(1) level and secondary ionization channels. All cation yields are sensitive to local structural changes and probe surface acidity. The cluster size distribution indicates hole-hole screening distances of 1-2 nm.

Electron beam induced production and desorption of H + , H 2 + , OH + , and H + (H 2 O) n has been studied from water-covered zirconia surfaces. The proton yield is strongly dependent upon the form of water present with large yields mainly from multilayers or clusters. The high proton kinetic energy distributions and the linear yield vs dose are indicative of proton formation and desorption by 2-hole and 2-hole, 1-electron final states. These localized states are produced either directly or via Auger decay pathways, and desorption occurs from the vacuum surface interface as a result of a Coulomb explosion. The proton yield increases from 80 to 150 K and then drops dramatically as the temperature exceeds 150 K. The increased yield is associated with structural and physical changes in the adsorbed water and longer excited-state lifetimes. The decreased yield is correlated with water desorption. Above 180 K, a small proton signal is observable which we associate with electron-stimulated dissociation of hydroxyl groups present on the zirconia surface. At temperatures above 225 K, this yield drops and gives rise to electron-stimulated desorption of OH + ions. H 2 + is also formed from adsorbed water and involves direct dissociative ionization channels. Some reactive scattering of energetic protons and 2-hole Coulomb interactions produce H 3 O + and other higher mass clusters such as H + (H 2 O) n , where n ) 2-8. Though this is a minor channel, it yields information concerning 2-hole screening distances.

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