Quantum Chemical Study of Ion−Molecule Reactions in N2 + + O2 System

We report a study of the ab initio quantum chemical calculations for an ion−molecule reaction in the N2 + + O2 system at the CCSD(T)/6-31G*//MP2(full)/6-31G* level augmented by multireference configuration interaction (MRCI) calculations. For the charge transfer (CT) reaction N2 + + O2 → N2 + O2 +, different mechanisms of electron transfer exist according to the electronic state of N2 +. Along the potential energy curve with C 2 v symmetry, electron transfer to N2 +(X2Σg +) occurs via a quartet T-shaped intermediate complex where positive charge has already been distributed on the O2 fragment, and the CT leads to O2 +(a4Πu) with large endothermicity. In contrast, electron transfer to N2 +(A2Πu) occurs via a doublet T-shaped intermediate complex, and the CT leads to O2 +(X2Πg) with large exothermicity. The doublet and quartet energy surfaces that connect the reactant systems, the intermediate complexes, and the product systems are examined in detail. The quartet CT reaction path contributes to the vibrational deactivation of N2 +(X2Σg +). Related characteristics of the reaction dynamics are also discussed.