Reactions of small negative ions with O₂(a ¹Δ_g) and O₂(X ³Σ_g^-)

The rate constants and product ion branching ratios were measured for the reactions of various small negative ions with O₂(X ³Σ_g^-) and O₂(a ¹Δ_g) in a selected ion flow tube (SIFT). Only NH₂^- and CH₃O^- were found to react with O₂(X) and both reactions were slow. CH₃O^- reacted by hydride transfer, both with and without electron detachment. NH₂^- formed both OH^-, as observed previously, and O₂^-, the latter via endothermic charge transfer. A temperature study revealed a negative temperature dependence for the former channel and Arrhenius behavior for the endothermic channel, resulting in an overall rate constant with a minimum at 500 K. SF₆^-, SF₄^-, SO₃^- and CO₃^- were found to react with O₂(a ¹Δ_g) with rate constants less than 10^-11 cm³ s^-1. NH₂^- reacted rapidly with O₂(a ¹Δ_g) by charge transfer. The reactions of HO₂^- and SO₂^- proceeded moderately with competition between Penning detachment and charge transfer. SO₂^- produced a SO₄^- cluster product in 2% of reactions and HO₂^- produced O₃^- in 13% of the reactions. CH₃O^- proceeded essentially at the collision rate by hydride transfer, again both with and without electron detachment. These results show that charge transfer to O₂(a ¹Δ_g) occurs readily if the there are no restrictions on the ion beyond the reaction thermodynamics. The SO₂^- and HO₂^- reactions with O₂(a) are the only known reactions involving Penning detachment besides the reaction with O₂^- studied previously [R.S. Berry, Phys. Chem. Chem. Phys., 7 (2005) 289-290].