Temperature dependences for the reactions of O2− and O− with N and O atoms in a selected-ion flow tube instrument

Abstract

Rate constants for the reactions of O2(-) and O(-) with N and O atoms have been measured for the first time as a function of temperature from 173 to 500 K for O(-) reactions and 173 to 400 K for O2(-) reactions. Room temperature rate constants for O2(-) reacting with N and O are 3.1 × 10(-10) and 1.7 × 10(-10) cm(3) s(-1), respectively, and the corresponding O(-) rate constants are 1.7 × 10(-10) and 1.5 × 10(-10) cm(3) s(-1), in good agreement with previous values. Temperature dependences are about T(-1.7) for both O2(-) reactions and T(-0.6) and T(-1.3) for the reactions of O(-) with N and O, respectively. Branching for the O2(-) reaction with N is found to predominantly form O(-) (>85%) in contrast to previous measurements, which reported NO2 + e(-) as the main channel. Calculations point to the present results being correct. The potential energy surface for this reaction was calculated using density functional theory, coupled cluster with singles, doubles (triples), complete active space self-consistent field, and complete active space second-order perturbation methods and is found to be quite complex, with agreement between the calculated surface and the observed kinetic data only possible through the inclusion of dynamical correlation.