A theoretical study on the mechanisms of the N2(X1[image omitted]) + O+(4Su) reaction involving the 14A'' and X2Π states of the N2O+ ion and the predissociation of the X2Π state.

The adiabatic path for the N2(X1 [image omitted]) + O+(4Su) → NO+(X1Σ+) + N(4Su) reaction is presented based on the CASPT2 O- and N-loss dissociation potential energy curves (PECs) of the 14A'' (not 14Σ-) state of N2O+ and it has a small barrier of 0.45 eV (0.34 eV with the CASSCF zero-point energy corrections) in good agreement with the experimental value of 0.33 ± 0.08 eV. Based on the CASPT2 O- and N-loss dissociation PECs of the X2Π state of N2O +and the calculated energies and spin-orbital coupling values at the located MECPs (minimum energy crossing points) for the X2Π/14A'' state pairs, a nonadiabatic path via the 14A''/12A'' O-loss MECP, X2Π minimum, and 12A''/14A'' N-loss MECP is presented. The CASPT2 energetic results indicate that this nonadiabatic process can occur without external energy. Based on the adiabatic and nonadiabatic paths, we explain the experimental facts for the reaction: small cross-section at low energy and an onset of a strong increase in cross-section at a certain energy value. Mechanisms for O- and N-loss predissociation of the X2Π state by 14A'' via the 12A''/14A'' O- and N-loss MECPs, respectively, are described, and the experimental facts are explained using the results of our energetic and spin-orbit coupling calculations. [ABSTRACT FROM AUTHOR]