Reaction dynamics of P(⁴S) + O₂(X ³Σ^-) → O(³P) + PO(X ²Π) on a global CHIPR potential energy surface of PO₂(X ²A₁): implication for atmospheric modelling

Abstract. Reaction dynamics of P(⁴S) + O₂(X ³Σ^-) → O(³P) + PO(X ²Π) is thought to be important in atmospheric and interstellar chemistry. Based on the state-of-the-art ab initio energy points, we analytically constructed a global potential energy surface (PES) for the ground state PO₂(X ²A₁) using the combined-hyperbolic-inverse-power-representation (CHIPR) method. A total of 6471 energy points are computed by the multireference configuration interaction method with the Davidson correction and aug-cc-pV5Z basis set. The analytical CHIPR PES reproduces ab initio energies accurately with a root-mean-square deviation of 91.5 cm^-1 (or 0.262 kcal/mol). The strongly-bound valence region of the PES has complicated topographical features with multiple potential wells and barriers. The attributes of the important intermediates are carefully validated with our geometry optimization results and previous computational results. Finally, the reaction probability, integral cross sections and rate constants for P(⁴S) + O₂(X ³Σ^-) → O(³P) + PO(X ²Π) are calculated using the quasi-classical trajectory and time-dependent wave packet methods. The trends of probability and integral cross section versus the collision energy can be divided into three stages, which are governed by the entrance barriers or exothermicity of the reaction. The rate constant demonstrates strong Arrhenius linear behavior at relatively low temperatures, but it deviates from this pattern at high temperatures. The calculated cross sections and rate constants are helpful for modelling the P chemistry in atmosphere and interstellar media.