The lowest doublet and quartet potential energy surfaces involved in the N(4S) + O2 reaction. II. Ab initio study of the C2v-symmetry insertion mechanism

Abstract

In the present work we have carried out ab initio complete active space self-consistent field (CASSCF) and second-order perturbation theory on CASSCF wave function (CASPT2) calculations and also some density functional theory calculations with the aug-cc-pVTZ Dunning's basis set on the lowest A1, B1, A2 and B2 doublet and quartet potential energy surfaces (PESs) that could be involved in the title reaction. Thus, several minima, transition states and surface crossings have been found for the C2v-insertion reaction mechanism. The results agree very well with available experimental data (i.e., for NO2 (2A1), MIN2 (2B2), NO2 (2∏u)) and with other previous ab initio calculations. Six A' / A' and four A' / A' type surface crossings were located and classified for these PESs, whose only one (i.e., 2B2 / 2A1) has been previously reported in theoretical and experimental studies. High-energy barriers were found for the direct C2v-insertion mechanism (3.11 and 2.54 eV for the lowest doublet and quartet PESs at the CASPT2/aug-cc-pVTZ level, respectively), clearly showing that this competitive mechanism is much less favorable than the direct Cs-abstraction or the indirect Cs-insertion reaction mechanisms reported in paper I.