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

The reactivity, energetics and dynamics of the bimolecular reactions between Ar2+ and O-2 have 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+ + O-2(+), Ar+ + O+, ArO+ + O+ and O+ + O+. The formation of Ar+ + O-2(+) is a minor channel, involving forward scattering, and generates O-2(+) 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 O-2, 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 O-2(+)* 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 O-2 by 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 ((2)pi). The formation of O+ + O+ results from dissociative double electron transfer via an O-2(2+) intermediate. The exoergicity of the dissociation of the nascent O-2(2+) intermediate is in good agreement with previous work investigating the unimolecular dissociation of this dication.