Product Channels in the Reaction of the CH3SO Radical With NO2: DFT and Ab Initio Studies

The stationary points involved in the CH3SO + NO2 radical-radical reaction were examined at the B3LYP/6-311++G(2df,2pd) and CCSD/cc-pVDZ levels of theory. Singlet potential energy surface was calculated using the CCSD(T)/aug-cc-pVTZ//CCSD/CC-pVDZ single-point calculations and the CBS-QB3 composite method. The association between radicals is confirmed to be a barrierless process and resulted in the two low-energy intermediates, CH3S(O)NO2 and CH3S(O)ONO. The CH3S(O)ONO intermediate decomposes directly to the CH3SO2 + NO products with the N-O bond dissociation energy of 7.9 kcal mol(-1). Although the dissociation of the C-S bond in the CH3SO2 requires an energy of 16.3 kcal mol(-1), the formation of final CH3 + SO2 + NO products is very likely, because their energy level is by 3.4 kcal mol(-1) still lower relative to that of the reactants. The formation of the CH2SO + HONO products from CH3S(O)ONO can proceed through the three-center transition state, but it is not important due to significant barrier well above the energy level of reactants. Eventually, CH2SO + HONO may be generated in the direct H-abstraction from CH3SO radical by NO2. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 112: 1904-1912, 2012