Ab initio and quasiclassical trajectory study of the N(2D) plus NO(X 2Π)→O(1D)+N2(X 1Σg+) reaction on the lowest 1A′ potential energy surface

In this work we have carried out ab initio electronic structure calculations, CASSCF/CASPT2 with the Pople's 6-311G(2d) basis set on the ground singlet potential energy surface (1 (1)A' PES) involved in the title reaction. Transition states, minima and one 1 (1)A'/2 (1)A' surface crossing have been characterized, obtaining three NNO isomers with the energy ordering: NNO ((1)Sigma (+))< cyclic-C-2v NON((1)A(1))< NON((1)Sigma (+)(g)). Approximately 1250 ab initio points have been used to derive an analytical PES which fits most of the stationary points, with a global root-mean-square deviation of 1.12 kcal/mol. A quasiclassical trajectory study at several temperatures (300-1500 K) was performed to determine thermal rate constants, vibrational and rovibrational distributions and angular distributions. The dynamics of this barrierless reaction presents a predominant reaction pathway (96% at 300 K) with very short-lived collision complexes around the NNO minimum, which originate backward scattering and a similar fraction of vibrational and translational energy distributed into products. At higher temperatures other reaction pathways involving NON structures become increasingly important as well as the N-exchange reaction (3.02% of the branching ratio at 1500 K), this latter in accord with experimental data. It is concluded that the physical electronic quenching of N(D-2) by NO should be negligible against all possible N(D-2)+NO reaction channels. (C) 2000 American Institute of Physics. [S0021-9606(00)30448-2].