Ab intio Investigation of the Thermochemistry and Kinetics of the SO2 + O3- → SO3- + O2 Reaction in Aircraft Engines and the Environment

In the present work, the mechanisms, thermochemistry and kinetics of the reaction of SO2 with O-3(-) have been studied using the CCSD(T)/6-31G(d) + CF method. It has been shown that there exist two possible pathways A and B of the SO2 + O-3(-) -> SO3- + O-2 reaction. The two pathways' A and B barrier heights are 0.61 kcal mol(-1) and 3.40 kcal mol(-1), respectively, while the energy of the SO2 + O-3(-) -> SO3- + O-2 reaction is -25.25 kcal mol(-1). The canonical variational transition state theory with small-curvature tunneling (CVT/SCT) has been applied to study the reaction kinetics. The CVT/SCT study shows that the rate constants K for pathways A and B, K-A = 1.11 x 10(-12) exp(-2526.13/T) and K-B = 2.7 x 10(-14) exp(-1029.25/T), respectively, grow as the temperature increases and are much larger than those of the SO2 + O-3 -> SO3 + O-2 reaction over the entire temperature range of 200-1500 K. This indicates that ionization of O-3 and high temperatures are favorable for the SO2 oxidation via the reaction with ozone. The new data obtained in the present study can be utilized directly for the evaluation of experiments and model predictions concerning SO2 oxidation and kinetic modeling of gas-phase chemistry of pollutants/nucleation precursors formed in aircraft engines and the Earth's atmosphere.