Spin-orbit transitions in the N + (PJ A 3)+H 2 → NH + (X 2 Π, 4 Σ - ) + H( 2 S) reaction, using adiabatic and mixed quantum-adiabatic statistical approaches.

The cross section and rate constants for the title reaction are calculated for all the spin-orbit states of N(PJ3) using two statistical approaches, one purely adiabatic and the other one mixing quantum capture for the entrance channel and adiabatic treatment for the products channel. This is made by using a symmetry adapted basis set combining electronic (spin and orbital) and nuclear angular momenta in the reactants channel. To this aim, accurate ab initio calculations are performed separately for reactants and products. In the reactants channel, the three lowest electronic states (without spin-orbit couplings) have been diabatized, and the spin-orbit couplings have been introduced through a model localizing the spin-orbit interactions in the N atom, which yields accurate results as compared to ab initio calculations, including spin-orbit couplings. For the products, 11 purely adiabatic spin-orbit states have been determined with ab initio calculations. The reactive rate constants thus obtained are in very good agreement with the available experimental data for several ortho-H fractions, assuming a thermal initial distribution of spin-orbit states. The rate constants for selected spin-orbit J states are obtained, to provide a proper validation of the spin-orbit effects to obtain the experimental rate constants.