Reaction of the N Atom with Electronically Excited O Revisited: A Theoretical Study.

The kinetics of the reaction of N with electronically excited O (singlet aΔ and bΣ states), potentially relevant for NO formation in nonthermal air plasma, is theoretically studied using the multireference second-order perturbation theory. The corresponding thermodynamically and kinetically favored reaction pathways together with possible intersystem crossings are identified. It has been revealed that the energy barrier for the N + O(aΔ) → NO + O reaction is approximately twice the barrier height for the counterpart process with O(Σ). The molecular oxygen in the bΣ state, in turn, proved to be even less reactive to atomic nitrogen than O(aΔ). Appropriate thermal rate constants for specified reaction channels are calculated by the variational transition-state theory incorporating corrections for the tunneling effect, nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. The corresponding three-parameter Arrhenius expressions for the broad temperature range ( = 300-4000 K) are reported. At last, post-transition-state molecular dynamics simulations indicate that the N + O(aΔ) reaction produces vibrationally much colder NO molecules than the N + O(Σ) process.