A theoretical study on the mechanisms of the N₂(X¹) + O⁺(⁴S_u) reaction involving the 1⁴A″ and X²Π states of the N₂O⁺ ion and the predissociation of the X²Π state

Abstract

The adiabatic path for the N₂(X¹ ) + O⁺(⁴S_u) → NO⁺(X¹Σ⁺) + N(⁴S_u) 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.

Keywords:

• CASPT2
• N₂O⁺
• reaction
• adiabatic and nonadiabatic paths
• predissociation

Acknowledgements

We appreciate the financial support of this work that was provided by National Natural Science Foundation of China through Contract No. 20773161.