Construction of Potential Energy Surface for the PH2+ System and Quantum Dynamics Study of the P+ + H2 Reaction

A globally accurate potential energy surface for the 13A″ excited state of PH2+ is constructed by fitting extensive ab initio energies obtained from multireference configuration interaction calculations with the aug-cc-pV(Q+d)Z and aug-cc-pV(5+d)Z basis sets. The topographical features of the potential energy surface are examined in detail and are found to be in excellent agreement with previously reported results. Notably, when the reaction proceeds through the T-shaped geometry, intersystem crossing between the 13A″ and 21A′ potential energy surfaces, driven by spin–orbit coupling, gives rise to nonadiabatic reaction channel. Furthermore, dynamical calculations for the 13A″ state were carried out using the time-dependent wave packet method, showing that at a fixed temperature, increasing the initial rotational quantum number significantly raises the thermal rate constant. The newly developed potential energy surface provides a reliable foundation for investigating the reaction dynamics and for constructing larger phosphorus- and hydrogen-containing systems. Further nonadiabatic dynamical calculations are required to quantitatively assess the role of electronic transitions in the reaction mechanism.