Thermochemical and Kinetic Analysis of the Acetyl Radical (CH3C•O) + O2 Reaction System

Abstract

Thermochemical properties for reactants, intermediates, products, and transition states important in the acetyl radical (CH3C•(O)) + O2 reaction system are analyzed with density functional and ab initio calculations, to evaluate reaction paths and kinetics in both oxidation and pyrolysis. Enthalpies of formation (Δ ) are determined using isodesmic reaction analysis at the CBSQ composite and density functional levels. Entropies ( ) and heat capacities ( (T)) are determined using geometric parameters and vibrational frequencies obtained at the HF/6-31G(d‘) level of theory. Internal rotor contributions are included in S and Cp(T) values. The acetyl radical adds to O2 to form a CH3C(O)OO• peroxy radical with a 35 kcal/mol well depth. The peroxy radical can undergo dissociation back to reactants, decompose to products, CH2CO + HO2 via concerted HO2 elimination (Ea = 34.58 kcal/mol), or isomerize via hydrogen shift (Ea = 26.42) to form a C•H2C(O)OOH isomer. This C•H2C(O)OOH isomer can undergo β scission to prod...