Repulsive double many-body expansion potential energy surface for the reactions N(⁴S) + H₂ ⇌ NH(X³Σ⁻) + H from accurate ab initio calculations

A single-sheeted DMBE potential energy surface is reported for the reactions N(⁴S) + H₂ ⇌ NH(X³Σ⁻) + H based on a fit to accurate multireference configuration interaction energies. These have been calculated using the aug-cc-pVQZ basis set of Dunning and the full valence complete active space wave function as reference, being semi-empirically corrected by scaling the two-body and three-body dynamical correlation energies. The topographical features of the novel global potential energy surface are examined in detail, including a conical intersection involving the two first ⁴A″ potential energy surfaces which has been transformed into an avoided crossing in the present single-sheeted representation.