State-to-state dynamics of P(2D) + H2(X1Σg+) reactions based on the new neural network potential energy surface

To investigate the state-to-state dynamics of the P(D2) + H2(XΣg+1)(v = 0, j = 0) reaction, we reconstructed the PH2(X2B1) potential energy surface (PES) using the permutation invariant polynomial neural network (PIP-NN) method based on 40 595 ab initio points. The aug-cc-pVQZ basis sets with Davidson correction were employed throughout the calculations. The reference wave function for the multi-reference configuration interaction calculations was constructed from a full valence complete-active-space self-consistent field wave function. To achieve higher PES accuracy, the double many-body expansion-scaled external correlation (DMBE-SEC) method was applied to extrapolate to the one-electron complete basis set limit, yielding a total root-mean square deviation of 2.4 meV for the final NN-PES. Based on the refined PH2(X2B1) NN-PES, geometries, energies, and harmonic frequencies of stationary points were obtained and analyzed in detail, showing excellent agreement with other theoretical results. Subsequently, quantum time-dependent wave packet (TDWP) and quasi-classical trajectory (QCT) methods were utilized to compute reaction probability, integral cross section (ICS), differential cross section (DCS), product rovibrational distribution, and rate constant on the developed NN-PES. The TDWP results reveal rich resonant structures, while the QCT calculations provide a qualitatively correct description of the coarse-grained reaction cross sections. These results also demonstrate a threshold-type microscopic reaction mechanism characterized by dominant forward-backward scattering, attributable to long-lived collision complex formation. Collectively, these findings provide fundamental mechanistic insights into the microscopic reaction mechanism and dynamics of phosphorus chemistry in interstellar environments.