Ab initio, VTST, and QCT study of the 1(2)A('') potential energy surface of the N(D-2)+O-2(X-3 Sigma(-)(g))-> O(P-3)+NO(X-2 Pi) reaction

An ab initio study based on the CASSCF (Complete Active Space Self-Consiste nt Field) and CASPT2 (Second-Order Perturbation Theory on a CASSCF wave fun ction) methods has been carried out on the ground (2)A" potential energy su rface (PES) involved in the relevant atmospheric reaction between N(D-2) an d O-2 to produce O(P-3) and NO. Also, some intersections between PES have b een studied. The stationary points have been characterized and a grid of mo re than 800 points have been fitted to an analytical function. This analyti cal representation of the PES has been used to obtain kinetic and dynamic p roperties of the reaction. The rate constant of this reaction has been calc ulated at different levels of theory [variational transition state theory ( VTST) and quasiclassical trajectory (QCT) methods] and has been compared wi th the experimental values (overall rate constant including physical electr onic quenching) obtaining a good agreement. The QCT method has also been em ployed to study the properties of products from both the abstraction and in sertion microscopic mechanisms. The vibrational distribution of NO arising from the reaction at 100 K has also been calculated and compared with the e xperimental ones. In this case, the agreement between the theoretical and t he experimental results is not so good, the experimental vibrational distri bution being less excited. Future work is necessary to determine the origin of this difference. (C) 2001 American Institute of Physics.