Reaction dynamics for the NH3+ + H2 → NH4+ + H reaction on a full-dimensional accurate potential energy surface.

The NH3+ + H2 reaction is one of the crucial steps for understanding the chemical network of nitrogen in the interstellar medium. The dynamics and kinetics of this reaction are studied using the quasi-classical trajectory method and microcanonical optimized multidimensional tunneling corrected-canonical variational transition state theory on a newly developed potential energy surface (PES). The PES is fitted by the fundamental invariant-neural network approach, giving a total root mean square error of 0.066 kcal mol-1. Dynamics calculations show that exciting the low-frequency umbrella mode of NH3+ promotes the reactivity remarkably more than exciting the high-frequency stretching modes over the collision energy studied. This special dynamical behavior can be rationalized by the enlarged attractive interaction between reactants, which increases the chance of H2 being captured by NH3+, along with the enhancement of direct rebound mechanisms at low collision energies and stripping mechanisms at high collision energies. In addition, the calculated rate coefficients of the reaction agree reasonably well with the available experimental results.