Atomic radical-molecule reaction N (4S)Â +Â NO2 (2A1): Mechanistic study

The reaction of atomic radical N (4S) with NO2 was explored theoretically using density functional, coupled cluster, and Møller-Plesset perturbation theory. The triplet electronic state potential energy surface (PES) was calculated at the G3B3 and CCSD(T)/cc-pVTZ//B3LYP/6-311+G(d,p) levels of theory. Various possible reaction pathways, including the N-adduct-O-shift and four-center ring formation-decomposition reactions, are considered. On the PES of the title reaction, it is shown that the most favorable pathway should be the atomic radical N attacking the N-atom of NO2 firstly to form the adduct 1 NN(OO), followed by one of the NO bonds breaking to give intermediate 2 NNOO, and then leading to the major products P2 (O2 + N2). As efficient routes to the reduction of NO2 to form N2 and O2 are sought, both kinetic and thermodynamic considerations support the viability of this channel. The transition states involved in the generation of products P1 (2NO), P2 (O2 + N2), and P3 (3O + N2O) lie much lower than the reactants. Thus, the novel reaction N + NO2 can proceed effectively even at low-temperature and it is expected to play an important role in both combustion and interstellar processes. The reaction heats of formation calculated are in good agreement with that obtained experimentally.