Substrate dependence of electron-stimulated O− yields from dissociative electron attachment to physisorbed O2

Abstract

We present measurements of O⁻ electron stimulated desorption yields obtained under identical experimental conditions from 0.15 monolayers (ML) of O₂ deposited onto disordered substrates consisting of 4 ML of either Kr, Xe, C₂H₆, C₂H₄, N₂O, CH₃Cl, or H₂O, all condensed on Pt (polycrystalline). The resulting O⁻ yield functions, for incident electron energies below 20 eV, are compared to that obtained from the O₂/Kr solid; this allows us to assess the order of magnitude effects of the local substrate environment on dissociative electron attachment (DEA) via the ²Π_u and gas phase forbidden ²Σ⁺_g,u resonances of O⁻₂. We note that, in addition to electron energy losses in the substrate prior to DEA to O₂ and post‐dissociation interactions of the O⁻ with the substrate molecules, charge or energy transfer from the O⁻₂ transient anion to a substrate molecule, and capture of the incident electron into a dissociative anion resonance of the substrate molecule may contribute to a reduced O⁻ yield from the physisorbed O₂. In the case of O₂ deposited on amorphous ice, we find that the O⁻ signal from DEA to O₂ is completely absent for electron energies below 14 eV; we attribute this to a complete quenching of the dissociative O⁻₂(²Π_u, ²Σ⁺) resonances by the adjacent water molecules.