Reactions of small negative ions with O2(a 1Δg) and O2(X 3Σg−)

The rate constants and product ion branching ratios were measured for the reactions of various small negative ions with O2(X 3Σg−) and O2(a 1Δg) 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 1Δg) with rate constants less than 10−11 cm3 s−1. NH2− reacted rapidly with O2(a 1Δg) 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 1Δg) 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].