Ab Initio Chemical Kinetics of Radical–Radical Reaction of CH3O with NO2

Abstract This work theoretically investigated the ab initio chemical kinetics of the radical–radical reaction between the methoxy (CH3O) and nitrogen dioxide (NO2), which represents a key C–N interaction in ammonia/hydrocarbon cocombustion. The stationary-point energies were determined at the CCSD(T)/CBS//M06–2X/def2-TZVPP level of theory. For the barrierless reaction pathways, potential energy scans were performed using the multireference CASPT2(14e,9o) method to account for the evolving multireference character along the reaction coordinate. The kinetic calculations were focused on the barrierless path leading to the CH3ONO2 formation. The temperature- and pressure-dependent rate constants and product branching of the path were determined by using the RRKM/Master Equation analysis combined with the conventional transition state theory (CTST) and the variable reaction coordinate transition state theory (VRC-TST). Another path leading to the CH3OONO formation was identified, and it is found to involve an inner transition state likely caused by the internal conformational change of NO2.