Bozzelli, J.W., and Dean, A.M. (1993)
Hydrocarbon Radical Reactions with O2: Comparison of Allyl,
Formyl, and Vinyl to Ethyl
J. Phys. Chem. 1993, 97, 4427.
Abstract
The reactions of allyl, formyl, and vinyl radicals with molecular oxygen have
been analyzed as addition reactions, in which the energized adduct has several
pathways available for further reaction. Rate constants for each of the reaction
channels are estimated using a chemical activation formalism based on the Quantum
Rice-Ramsperger-Kassel theory, along with thermodynamically consistent input rate
constants and falloff parameters. Results show good agreement with the limited
experimental data available. The well depth of the initially formed adduct is
shown to exert a major influence over the preferred reaction channels. In
particular, the shallow (~18 kcal/mol) well for the allyl addition results in
very little apparent reaction, and the major channel is simply redissociation to
initial reactants. The deeper wells for formyl and vinyl addition to oxygen (~40
kcal/mol) allow other reaction channels to open up even at low temperatures.
Predictions for the vinyl addition indicate HCO and CH2O are major products at
lower temperatures, while the vinoxy + O channel becomes more important at higher
temperatures. Formyl addition is shown to produce CO + HO2 as the major reaction
channel. Rate constants for the various reactions are presented over a wide range
of temperature and pressure. The good agreement between these calculations and
the experimental data supports the hypothesis that the reactions between
hydrocarbon radicals and oxygen proceed via chemically activated addition and
that one does not need to invoke a direct hydrogen abstraction pathway.
REACTION RATE COEFFICIENTS SUGGESTED IN THIS WORK:
GRI-Mech
Number
('-' sign
means
reverse) |
Reaction |
Rate Coefficient
A T^n exp(-E/RT) |
Temperature
Range
(K) |
A
(mol,cm3,s) |
n
(T in K) |
E
(cal/mol) |
| 168* |
HCO + O2 -> HO2 + CO |
1.29E+18 |
-1.97 |
885 |
900-2500 |
| A* |
HCO + O2 -> OH + CO2 |
1.12E+17 |
-1.97 |
885 |
900-2500 |
* at 1 atmosphere N2