Dynamics of the N(4Su) + NO(X2Π) → N2(1Σg+) + O(3Pg) atmospheric reaction on the 3A'' ground potential energy surface. I. Analytical potential energy surface and preliminary quasiclassical trajectory calculations

The N(4Su)+NO(X 2Π)→N2(X 1Σg+)+O(3Pg) reaction plays an important role in the upper atmosphere chemistry and as a calibration system for discharge flow systems. Surprisingly, very little theoretical and experimental work has been devoted to the characterization of the dynamical features of this system. In this work a Sorbie-Murrell expression for the lowest 3A' potential energy surface (PES) connecting reactants in their ground electronic states based upon the fitting of an accurate ab initio CI grid of points has been derived. The PES fitted shows no barrier to reaction with respect to the reactants asymptote in accordance with experimental findings and becomes highly repulsive as the NNO angle is varied away from the saddle point geometry. The results of preliminary quasiclassical trajectory calculations on this surface reproduce very well the experimental energy disposal in products, even though the vibrational distribution derived from trajectories seems to be a bit cooler than the experimental data. Moreover, thermal rate constants derived from trajectories are in excellent accordance with experimental values