Ab initio, VTST and QCT study of the 1 2A'' potential energy surface of the N(2D) + O2(X3 Σg-) → O(3P) + NO(X2Π) reaction

Abstract

An ab initio study based on the CASSCF ~Complete Active Space Self-Consistent Field! and CASPT2 (Second-Order Perturbation Theory on a CASSCF wave function) methods has been carried out on the ground 2A' potential energy surface (PES) involved in the relevant atmospheric reaction between N(2D) and O2 to produce O(3P) and NO. Also, some intersections between PES have been studied. The stationary points have been characterized and a grid of more than 800 points have been fitted to an analytical function. This analytical representation of the PES has been used to obtain kinetic and dynamic properties of the reaction. The rate constant of this reaction has been calculated at different levels of theory [variational transition state theory (VTST) and quasiclassical trajectory (QCT) methods] and has been compared with the experimental values (overall rate constant including physical electronic quenching) obtaining a good agreement. The QCT method has also been employed to study the properties of products from both the abstraction and insertion microscopic mechanisms. The vibrational distribution of NO arising from the reaction at 100 K has also been calculated and compared with the experimental ones. In this case, the agreement between the theoretical and the experimental results is not so good, the experimental vibrational distribution being less excited. Future work is necessary to determine the origin of this difference