Formation Mechanisms of Electronically Excited Nitrogen Molecules from N + N 2 and N + N + N Collisions Revealed by Full-Dimensional Potential Energy Surfaces.

This work reports six new full-dimensional adiabatic potential energy surfaces (PESs) of the N 3 system (four 4 A″ states and two 2 A″ states) at the MRCI + Q/AVQZ level of theory that correlated to N 2 ( X 1 Σ g + ) + N( 4 S ), N 2 ( X 1 Σ g + ) + N( 2 D ), N 2 ( A 3 Σ u + ) + N( 4 S ), N 2 ( B 3 Π g ) + N( 4 S ), N 2 ( W 3 Δ u ) + N( 4 S ), and N( 4 S ) + N( 4 S ) + N( 4 S ) channels. The neural networks with a proper account of the nuclear permutation invariant symmetry of N 3 were employed to fit the PESs based on about 4000 ab initio points. The accuracy of the PESs was validated by excellent agreement on the equilibrium bond length, vertical excitation energy, and dissociation energy with experimental values. Two possible mechanisms of the formation of N 2 ( A ) were found. One is that the collision occurs between N 2 ( X ) and N( 4 S ) in the 1 4 A ″ state, followed by a nonadiabatic transition through the conical intersection with the 2 4 A ″ PES, resulting in the formation of the N 2 ( A ) + N( 4 S ) product. The other takes place in the collision among three N( 4 S ) atoms in the adiabatic 2 4 A ″ state, and then, N 2 ( A ) + N( 4 S ) is formed. This is the first systematical research of the N 3 system focusing on the formation of the excited states of N 2 via both adiabatic and nonadiabatic pathways.