High level theoretical characterization of the vinoxy radical (•CH2CHO) + O2 reaction

Numerous processes in atmospheric and combustion chemistry produce the vinoxy radical (center dot CH2CHO). To understand the fate of this radical and to provide reliable energies needed for kinetic modeling of such processes, we have examined its reaction with O-2 using highly reliable theoretical methods. Utilizing the focal point approach, the energetics of this reaction and subsequent reactions were obtained using coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] extrapolated to the complete basis set limit. These extrapolated energies were appended with several corrections including a treatment of full triples and connected quadruple excitations, i.e., CCSDT(Q). In addition, this study models the initial vinoxy radical + O-2 reaction for the first time with multireference methods. We predict a barrier for this reaction of approximately 0.4 kcal mol(-1) . This result agrees with experimental findings but is in disagreement with previous theoretical studies. The vinoxy radical + O-2 reaction produces a 2-oxoethylperoxy radical which can undergo a number of unimolecular reactions. Abstraction of a ) beta-hydrogen (a 1,4-hydrogen shift) and dissociation back to reactants are predicted to be competitive to each other due to their similar barriers of 21.2 and 22.3 kcal mol(-1) , respectively. The minimum-energy ) beta-hydrogen abstraction pathway produces a hydroperoxy radical (QOOH) that eventually decomposes to formaldehyde, CO, and (OH)-O-center dot. Two other unimolecular reactions of the peroxy radical are alpha-hydrogen abstraction (38.7 kcal mol(-1) barrier) and HO2 center dot elimination (43.5 kcal mol(-1) barrier). These pathways lead to glyoxal + (OH)-O-center dot and ketene + HO2 center dot formation, respectively, but they are expected to be uncompetitive due to their high barriers. Published by AIP Publishing.