| Abstract
| - In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associatedwith engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenylradical oxidation at low to intermediate temperature range were computationally studied, focusing on boththe first and the second O2 addition to the isobutenyl radical. The geometries of reactants, importantintermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at theB3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined onthe basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for severalimportant intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. Thekinetic analysis of the first O2 addition to the isobutenyl radical was performed using enthalpies at the CBS-QB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can bestabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the2-hydroperoxymethyl-2-propenyl radical that further undergoes another O2 addition. The reaction channelsfor isomerization and cyclization and further dissociation on this second O2 addition were analyzed usingenthalpies at the DFT level with energy corrections based on similar reaction channels for the first O2 addition.The high-pressure limit rate constants for each reaction channel were determined as functions of temperatureby the canonical transition state theory for further kinetic model development.
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