Bond-forming and electron-transfer reactivity between Ar2+and O2

Abstract

The reactivity, energetics and dynamics of the bimolecular reactions between Ar2+and O2have been studied using a position sensitive coincidence methodology at a collision energy of 4.4 eV. Four bimolecular reaction channels generating pairs of product ions are observed, forming: Ar++ O2+, Ar++ O+, ArO++ O+and O++ O+. The formation of Ar++ O2+is a minor channel, involving forward scattering, and generates O2+in its ground electronic state. This single electron transfer process is expected to be facile by Landau-Zener arguments, but the intensity of this channel is low because the electron transfer pathways involve multi-electron processes. The formation of Ar++ O++ O, is the most intense channel following interactions of Ar2+with O2, in agreement with previous experiments. Many different combinations of Ar2+and product electronic states contribute to the product flux in this channel. Major dissociation pathways of the nascent O2+* ion involve the ion's first and second dissociation limits. Unusually, the experimental results clearly show the involvement of a short-lived collision complex [ArO2]2+in this channel. The formation of O+and ArO+involves direct abstraction of O−from O2by Ar2+. There is scant evidence of the involvement of a collision complex in this bond forming pathway. The ArO+product appears to be formed in the first excited electronic state (2Π). The formation of O++ O+results from dissociative double electron transferviaan O22+intermediate. The exoergicity of the dissociation of the nascent O22+intermediate is in good agreement with previous work investigating the unimolecular dissociation of this dication.