Electron stimulated desorption of O− and O2− from condensed ozone: Possible implications for the heterogeneous photochemistry of stratospheric O3

Abstract

We have studied the desorption of negative ions following low energy electron impact (0–15 eV) to ozone condensed in multilayer amounts on a cryogenically cooled gold surface. Intense desorption of O⁻ is observed at low electron energies (below 4 eV) ia pronounced resonances with an estimated desorption cross section of the order of 10⁻¹⁸ cm² (peak value). The resonant features in the ion yield indicate that O⁻ desorption is driven by dissociative electron attachment to O₃ molecules at or near the surface. While dissociative electron attachment (DA) from gas phase ozone generates the fragment ions O⁻ and O₂⁻ at comparable intensities, desorption of O₂⁻ from condensed ozone is strongly suppressed, being only weakly observed within a resonance located at 7 eV. Possible implications for the heterogeneous chemistry of ozone on polar stratospheric cloud (PSC) particles, namely photo-induced dissociative electron transfer from the substrate, are discussed in the light of the effective O⁻ desorption observed at low electron energies.