Electron-stimulated desorption of D- (H-) from condensed D2O (H2O) films

The electron-stimulated desorption (ESD) of D- and H- ions from condensed D2O and H2O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of B-2(1), (2)A(1) and B-2(2) dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a(1) orbital. The ion yield resulting from excitation of the B-2(1) resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited stales that lead to desorption. (C) 1997 Elsevier Science B.V.