Interaction of Atomic Nitrogen with Electronically Excited Molecular Oxygen: a Theoretical Study
Under conditions of violation of the thermodynamic equilibrium between the internal degrees of freedom of particles, the kinetics of the ongoing physicochemical processes can differ significantly from the equilibrium case. One of the important reactions responsible for the formation of nitrogen oxides in air is the reaction of a nitrogen atom with an oxygen molecule, which can be in the ground state as well as in the electronically excited states under the influence of a nonequilibrium electric discharge, resonant laser radiation or behind the front of a strong shock wave. Quantum chemical calculations were performed using the extended multi-configuration quasi-degenerate perturbation theory to study the reaction of the interaction of a nitrogen atom with an electronically excited molecule O<sub>2</sub> molecule in the electronic states a<sup>1</sup>D<sub>g</sub> and b<sup>1</sup>S<sub>g</sub><sup>+</sup>, quantum-chemical calculations were performed using the extended multi-configuration quasidegenerate second-order perturbation theory. Energetically favorable reaction paths, minimum energy crossing points, and the corresponding quenching channels were found. It was shown that the activation barrier of the reaction N(<sup>4</sup>S)+O<sub>2</sub>(a<sup>1</sup>D<sub>g</sub>) is 2.3 times larger than the barrier of the reaction of a nitrogen atom with O<sub>2</sub> in the ground state, however, for an accurate estimate of the constant of this process, it is also necessary to take into account the probability of a nonadiabatic transition N(<sup>4</sup>S)+O<sub>2</sub>(a<sup>1</sup>D<sub>g</sub>)→N(<sup>4</sup>S)+O<sub>2</sub>(X<sup> 3</sup>S<sub>g</sub><sup>-</sup>). It was shown for the first time that the reaction of atomic nitrogen and O<sub>2</sub>(b<sup>1</sup>S<sub>g</sub><sup>+</sup>) leads to the formation of a molecule NO(X<sup> 2</sup>P<sub>r</sub>) and an atom O(<sup>3</sup>P). Besides, the quenching process N(<sup>4</sup>S)+O<sub>2</sub>(b<sup>1</sup>S<sub>g</sub><sup>+</sup>)→N(<sup>2</sup>D)+O<sub>2</sub>(X<sup> 3</sup>S<sub>g</sub><sup>-</sup>) is also possible. In the future, the rate constants of these processes will be estimated within the variational and non-adiabatic transition state theories.