A single- and multireference study on CH (X2Π) reaction with O2 (X3Σg-)

This study focuses on the dynamics of the reaction of CH (X-2 Pi) radicals with O-2 (X-3 Sigma(-)(g)) in the presence of N-2, as the bath gas molecule. A general description of the reaction mechanism was investigated by employing molecular dynamics simulations with an implanted reactive force field under a realistic system that could account for both reactive and nonreactive collisions. This tool helped to provide an initial guess for the reaction mechanism to unravel some information about the potential reaction paths and secondary products. The initial guess was used to explore the detailed reaction mechanism quantum mechanically over the lowest doublet and quadruplet surfaces at the single-reference level of CCSD(T)/aug-cc-pVTZ and the multireference level of CASPT2/aug-cc-pVTZ. The theoretical bimolecular reaction rate constants were computed by solving a master equation over the lowest doublet single- and multireference potential energy surfaces. The calculated rate constant for loss of the reactants and formation of the HCO and CO products declared noticeable agreement with the available experimental rate constants. HCO, CO, and CO2 are identified as the main products along with the following single-reference (multireference)-based product branching ratios at 450 K: [triangular (CO2)-C-1 + H-2 and linear (CO2)-C-1 + H-2]: 69.1% (79.3%); (CO)-C-1 + (OH)-O-2: 18.2% (15.0%); (HCO)-H-2 + O-3: 12.7% (5.7%). Both single- and multireference calculations demonstrated reliable chemical kinetics results, in the context of the available experimental rate constants and resulted in fair agreement with the experimentally reported branching ratios.