Temperature and Pressure-Dependent Rate Coefficients
for the Reaction of Vinyl Radical with Molecular Oxygen
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Abstract
State-of-the-art
calculations of the C<sub>2</sub>H<sub>3</sub>O<sub>2</sub> potential
energy surface are presented. A new method
is described for computing the interaction potential for R + O<sub>2</sub> 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 CH<sub>2</sub>O +
HCO at lower temperatures and CH<sub>2</sub>CHO + O at higher temperatures.
Above 10 atm, the collisional stabilization of CH<sub>2</sub>CHOO
directly competes with these two product channels. CH<sub>2</sub>CHOO
decomposes primarily to CH<sub>2</sub>O + HCO. The next two most significant
bimolecular products are OCHCHO + H and <sup>3</sup>CHCHO + OH, and
not C<sub>2</sub>H<sub>2</sub> + HO<sub>2</sub>. C<sub>2</sub>H<sub>3</sub> + O<sub>2</sub> 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 CH<sub>2</sub>CHO + O overtakes all other product channels