Validating Experiment for the Reaction H2 + NH2- by Dynamical Computations on an Accurate Full-Dimensional Potential Energy Surface

Abstract

Ion-neutral molecular reactions play key roles in the field of ion related chemistry. As a prototypical multi-channel ion-molecular reaction, the reaction H2 + NH2- → NH3 + H- has been studied for decades. In this work, we develop a globally accurate potential energy surface (PES) for the title system H2 + NH2- based on nearly hundreds of thousands points over a wide dynamically relevant region. The permutational invariants polynomials neural network (PIP-NN) method is used for fitting and the total root mean squared error (RMSE) is extremely small, only 0.026 kcal mol-1. Extensive dynamical and rate coefficient calculations are carried out on this new PIP-NN PES by the quasi-classical trajectory (QCT) method. The calculated rate coefficients for H2 / D2 + NH2- agree well with the experimental results that show a inverse temperature dependence from 50 to 300 K, consistent with the capture nature of this barrierless reaction. A significant kinetic isotope effect has been well reproduced by the QCT computations. In addition, we report a unique phenomenon of significant reactivity suppression by exciting the rotational mode of H2, particular at low collision energies. Further analysis shows that the excitation of rotational mode of H2 would prevent the formation of the reactant complex and thus suppress reactivity.