A neural network potential energy surface for the NaH 2 system and dynamics studies on the H( 2 S) + NaH(X 1 Σ + ) → Na( 2 S) + H 2 (X 1 Σ g + ) reaction.

In order to study the dynamics of the reaction H(2 S) + NaH(X1 Σ+ ) → Na(2 S) + H2 (X1 Σg + ), a new potential energy surface (PES) for the ground state of the NaH2 system is constructed based on 35 730 ab initio energy points. Using basis sets of quadruple zeta quality, multireference configuration interaction calculations with Davidson correction were carried out to obtain the ab initio energy points. The neural network method is used to fit the PES, and the root mean square error is very small (0.00639 eV). The bond lengths, dissociation energies, zero-point energies and spectroscopic constants of H2 (X1 Σg + ) and NaH(X1 Σ+ ) obtained on the new NaH2 PES are in good agreement with the experiment data. On the new PES, the reactant coordinate-based time-dependent wave packet method is applied to study the reaction dynamics of H(2 S) + NaH(X1 Σ+ ) → Na(2 S) + H2 (X1 Σg + ), and the reaction probabilities, integral cross-sections (ICSs) and differential cross-sections (DCSs) are obtained. There is no threshold in the reaction due to the absence of an energy barrier on the minimum energy path. When the collision energy increases, the ICSs decrease from a high value at low collision energy. The DCS results show that the angular distribution of the product molecules tends to the forward direction. Compared with the LiH2 system, the NaH2 system has a larger mass and the PES has a larger well at the H-NaH configuration, which leads to a higher ICS value in the H(2 S) + NaH(X1 Σ+ ) → Na(2 S) + H2 (X1 Σg + ) reaction. Because the H(2 S) + NaH(X1 Σ+ ) → Na(2 S) + H2 (X1 Σg + ) reaction releases more energy, the product molecules can be excited to a higher vibrational state.