Thermochemical and Kinetic Analysis of the Formyl Methyl Radical + O2 Reaction System

Abstract

Thermochemical properties for important species in the formyl methyl radical (C•H2CHO) + O2 reaction system are analyzed to evaluate reaction paths and kinetics in both oxidation and pyrolysis. Enthalpies of formation (ΔHf°298) are determined using isodesmic reaction analysis at the CBSQ composite and density functional levels. Entropies (S°298) and heat capacities [Cp°(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 formyl methyl radical adds to O2 to form a C(OO•)H2CHO peroxy radical with a 27.5 kcal/mol well depth. The peroxy radical can undergo dissociation back to reactants, decompose to CH2CO + HO2 via HO2 elimination, or isomerize via hydrogen shift to form a C(OOH)H2C•O. This C(OOH)H2C•O isomer can undergo β scission to products, CH2CO + HO2, decompose to CO + CH2O + OH, or decompose to a diradical, CH2O•C•O + OH via simple RO−OH bond cleavage. Rate constants...