Temperature and Pressure-Dependent Rate Coefficients for the Reaction of Vinyl Radical with Molecular Oxygen

State-of-the-art calculations of the C₂H₃O₂ potential energy surface are presented. A new method is described for computing the interaction potential for R + O₂ reactions. The method, which combines accurate determination of the quartet potential along the doublet minimum energy path with multireference calculations of the doublet/quartet splitting, decreases the uncertainty in the doublet potential and thence the rate constants by more than a factor of 2. The temperature- and pressure-dependent rate coefficients are computed using variable reaction coordinate transition-state theory, variational transition-state theory, and conventional transition-state theory, as implemented in a new RRKM/ME code. The main bimolecular product channels are CH₂O + HCO at lower temperatures and CH₂CHO + O at higher temperatures. Above 10 atm, the collisional stabilization of CH₂CHOO directly competes with these two product channels. CH₂CHOO decomposes primarily to CH₂O + HCO. The next two most significant bimolecular products are OCHCHO + H and ³CHCHO + OH, and not C₂H₂ + HO₂. C₂H₃ + O₂ will be predominantly chain branching above 1700 K. Uncertainty analysis is presented for the two most important transition states. The uncertainties in these two barrier heights result in a significant uncertainty in the temperature at which CH₂CHO + O overtakes all other product channels