Theoretical characterization of the reactions CH3XCH2O2 + NO (X = O, S)

The reactions of NO with the peroxy radicals CH3SCH2O2 and CH3OCH2O2 are investigated using ab initio and DFT electronic structure methods. The peroxy nitrite association adducts, CH3XCH2OONO, and the isomeric nitrate compounds, CH3XCH2ONO2, X = O, S, are theoretically characterized and the heat of formation parameters are evaluated. The formation of the products, the oxy radical and nitrogen dioxide, CH3XCH2O + NO2, take place in both cases, through the dissociation of the reaction intermediate, cis- CH3XCH2OONO, via low activation barriers located late in the exit valley. The negligible activation energies are in good agreement with the large rate coefficients observed experimentally.