Dissociative electron attachment to supersonically cooled oxygen

Abstract

Formation of O⁻ and \({O}_{2}^{-}\) ions via DEA to a supersonic jet of O₂ having weakly bound van der Waals clusters is reported. The ion-yields show three peaks near 7, 11 and 16 eV electron energies where the 7 eV peak arises from the ²Π _u state of \({O}_{2}^{-}\). The 11 and 16 eV peaks are ascribed to two resonance states \({}^{2}\displaystyle \Sigma {}_{g}^{+}\) and \({}^{2}\displaystyle \Sigma {}_{u}^{+}\) respectively, through a violation of σ⁻ selection rule. Ar was used as a refrigerant carrier gas and cross-section dependence of the two new peaks on the proportion of carrier gas used is experimentally observed, eventually leading to an optimum O₂ : Ar ratio.