| Abstract
| - Thermochemical properties for important species in the formyl methyl radical (C•H2CHO) + O2 reactionsystem are analyzed to evaluate reaction paths and kinetics in both oxidation and pyrolysis. Enthalpies offormation (ΔHf°298) are determined using isodesmic reaction analysis at the CBSQ composite and densityfunctional levels. Entropies (S°298) and heat capacities [Cp°(T)] are determined using geometric parametersand vibrational frequencies obtained at the HF/6-31G(d‘) level of theory. Internal rotor contributions areincluded in S and Cp(T) values. The formyl methyl radical adds to O2 to form a C(OO•)H2CHO peroxyradical 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. Rateconstants are estimated as a function of pressure and temperature using quantum Rice−Ramsperger−Kassel(QRRK) analysis for k(E) and master equation for falloff. Important reaction products are stabilization of theC(OO•)H2CHO peroxy adduct at low temperature and CO + CH2O + OH products via intramolecular Hshift at high temperature. ΔHf°298 values are estimated for the following compounds at the CBSQ level: C•H2CHO (3.52 kcal/mol), C(OOH)H2CHO (−56.19 kcal/mol), C(OO•)H2CHO (−21.01 kcal/mol), C(OOH)H2C•O (−19.64 kcal/mol). A mechanism for pyrolysis and oxidation of the formyl methyl radical is constructed,and the reaction of the formyl methyl radical with O2 versus unimolecular decomposition is evaluated.
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