Thermochemistry and Reaction Kinetics of Secondary Ethyl Radical of Methyl Ethyl Sulfide, CH 3 SCH•CH 3 , with 3 O 2 to CH 2 SCH(OO•)CH 3

The quantum Rice-Ramsperger-Kassel (QRRK) theory is used to analyze the reaction between the activated CH3S CH•CH3 and molecular oxygen to account for further reaction and collisional and deactivation. hydroxyl radicals initiate the oxidation of Methyl ethyl sulfide (CH3SCH2CH3) and MES (methylthioethane) under combustion conditions. The CBS-QB3 and G3MP2B3 composite and M062X/6-311+G(2d, p) DFT methods was used to study the thermochemical properties of reactants, products and transition states. These thermochemical properties are used for the calculations for kinetic and thermochemical parameters. Under high pressure and low temperature, isomerization and stabilization of the CH3SCH(OO•)CH3 adduct is of importance. Under atmospheric pressure and at temperatures between above 600 ~ 800 K reactions of the chemically activated peroxy adduct become important relative to stabilization. The reaction between CH3SCH•CH3 and O2 forms an energized peroxy adduct CH3SCH(OO•)CH3 with a calculated well depth of 30.2 kcal/mol at the CBS-QB3 level of theory. Kinetic parameters are calculated using the thermochemical properties of products, reactants and transition states obtained using under CBS-QB3 method of calculation. At temperature below 500 K, Stabilization of CH3SCH(OO•)CH3 adduct is of importance. Temperature of 500-900 K, is optimal for intramolecular hydrogen shift and the isomerization of CH3SCH(OO•)CH3 adduct. At temperature above 800 K, all of the subsequent reaction paths are of importance. For a reaction to move forward under pressure 1-4 atm, the recommended optimal temperature is between 600-800 K. A new pathway for the CH3SCH(OO•)CH3 adduct is observed, the attachment of peroxyl oxygen radical to sulfur followed by carbon-sulfur bond dissociation and formation of oxygen-sulfur and oxygen-carbon double bonds.