Resonant electron-stimulated desorption of O − ions from oriented O 2 on graphite

Abstract

We present measurements of the yield of O − ions in the resonant dissociative attachment reaction e −+O 2→O 2 −→O+O − in ζ-phase (upright) O 2 physisorbed on graphite. The yield of O − as a function of the electron impact energy shows three resonances at 8, 10, and 13 eV. Angular distribution measurements were performed on the O − ions desorbed from each resonance by rotating the substrate between the electron source and the ion detector. In each case we find that the desorbed O − ions are confined to an angular range close to the surface normal. Two important factors contributing to these angular profiles are: (i) the cross-section for capture of the incoming electron into the negative-ion resonance state, and (ii) the probability that the desorbing O − ion in emitted in the direction of the detector. In the present case, the narrow O − emission profile dominates the angular distributions.