Theoretical study of mechanism and kinetics for OH-initiated oxidation of o-cresol in the troposphere

Reaction mechanisms for the OH-initiated oxidation of o-cresol in the troposphere were investigated using B3LYP hybrid density functional method with the 6-311++G(2df,2pd) basis set. Single-point energy calculations with the same basis set were performed using the coupled cluster method with single, double, and perturbative triple configurations, CCSD(T). The equilibrium geometries, energies, and thermodynamics properties of all the stationary points along the addition reaction pathway and hydrogen abstraction reaction pathway were calculated. The rate constants and the branching ratios of each pathway were evaluated using classical transition state theory (TST) in the temperature range of 200-360 K, to simulated temperatures in all parts of the troposphere. The ortho (at position ortho- to the hydroxyl group) addition pathway was found dominant, accounting for 95.3-75.0% of the overall products from 200 to 360 K. The calculated rate constants are in good agreement with available experimental values. The addition reaction and hydrogen abstraction reaction are both thermodynamically irreversible.