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

The D₂(¹Σg⁺, v0ex0ex=0ex0ex0--2, J0ex0ex=0ex0ex0--2) desorbates produced during low-energy (5--40 eV) electron-beam irradiation of amorphous D₂O ice were monitored using resonance-enhanced laser ionization spectroscopy. We attribute the structure in the D₂ 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 D₂(¹Σg⁺) directly. D₂ is observed with v0ex0ex=0ex0ex0 or 2 but not v0ex0ex=0ex0ex1, suggesting a symmetry propensity in the excitation or decay of the resonances.