Theoretical studies on the gas phase reaction mechanisms and kinetics of glyoxal with HO2 with water and without water

The quantum chemical methods are employed to investigate the reactions of glyoxal with the HO2 radical and the HO2 and H2O. There are twelve complexes found herein, whose stabilized energies are in the range of −3.8 kcal/mol to −12.3 kcal/mol. The calculated results predict that the proton coupled electron transfer process is the most favorable in the reactivity of the HO2 radical with glyoxal due to the low energy barrier of 5.4 kcal/mol. In addition, the barriers in the reaction glyoxal with the formed HO2⋯H2O complex are so high that the processes are unlikely to occur in the atmosphere, whereas the energy barriers of the HO2 reaction with the complexes formed between glyoxal and water are decreased. Additionally, the rate constant of the proton coupled electron transfer process is computed to be 2.83 × 10−16 cm3 molecule−1 s−1 at 298 K using the transition state theory with Eckart correction, which agrees well with the experimental data. It is noted that the rate constants of the water-catalyzed glyoxal reaction with HO2 is increased about 10 times greater than the naked reaction HO2 + (CHO)2.