Observation of Negative Ion Resonances in Amorphous Ice via Low-Energy (5–40 eV) Electron-Stimulated Production of Molecular Hydrogen

The $D_2({}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$, $v=0\mathrm{}–2$, $J=0\mathrm{}–2$) desorbates produced during low-energy (5–40 eV) electron-beam irradiation of amorphous ${\mathrm{D}}_2$O ice were monitored using resonance-enhanced laser ionization spectroscopy. We attribute the structure in the ${\mathrm{D}}_2$ yield as a function of the incident electron energy to core-excited negative ion resonances. These resonances, or the excited states produced after electron autodetachment, decay via molecular elimination to yield $D_2\left({}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}\right)$ directly. ${\mathrm{D}}_2$ is observed with $v=0\mathrm{}$ or 2 but not $v=1\mathrm{}$, suggesting a symmetry propensity in the excitation or decay of the resonances.