D−, O− and OD− desorption induced by low-energy (0-20 eV) electron impact on amorphous D2O films

We report measurements of low-energy electron stimulated desorption of D−, O− and OD− anions from multilayer amorphous D2O films physisorbed on a Pt substrate. The 0-20 eV incident energy dependence (i.e., the yield function) of the desorbed D− yield reveals the presence of a strong peak located at 7.2 eV with a shoulder near 9 eV, which are due to dissociation of the transient states 2B1 and 2A1 of D2O, respectively. The O− and OD− yield functions each exhibit a single broad structure between 5 and 12 eV which also result from dissociative electron attachment (DEA). Due to the weakness of the O− and OD− signals, three possible processes involving DEA must be considered to explain their yield functions, i.e., direct DEA, reactive scattering and DEA to a new product in the film synthesized by the electron beam. It is concluded that at large electron doses (>7.5×1014 electrons/cm2), these broad peaks arise from DEA to a new product, whereas at lower dose the possibility of direct DEA (i.e., e−+D2O→D2O−→O−+D2 and OD−+D) cannot be entirely discounted. Above 15 eV, all anion yield functions exhibit a monotonic rise due to direct dipolar dissociation.