Rate constants for the abstraction reactions RO2 + C2H6; R = H, CH3, and C2H5

The thermal dissociation of hydroperoxides to form alkoxy and hydroxyl radicals is thought to play an important role in the low temperature oxidation of alkanes. One possible source of these species is the hydrogen abstraction from alkanes by alkylperoxy radicals. Motivated by a special interest in the oxidation chemistry of ethane, we performed transition state (TST) calculations with tunneling corrections of the rate constants for the reactions of HO2, CH3O2, and C2H5O2 with C2H6. The required input data were obtained from CBS-QB3 ab initio calculations. Complementary to these calculations we obtained rate constants for the same reactions based on empirical estimation rules. The agreement between both sets of rate constants is within a factor of 2 for the 'Negative Temperature Coefficient' region. Based on the TST results, we recommend HO2 + C(2)H6 reversible arrow H2O2 + C2H5 k(9) = 261 T-3.37 exp(- 15.9 kcal/mol/RT) cm(3)/mol/s CH3O2 + C2H6 reversible arrow CH3OOH + C2H5 k(10) = 19.4T(3.64) exp(-17.1 kcal/mol/RT) cm(3)/mol/s C2H5O2 + C2H6 reversible arrow C2H5OOH + C2H5 k(11) = 8.6T(3.76) exp(-17.2 kcal/mol/RT)cm(3)/mol/s By performing simulations of a 50:50 C2H6/O-2 mixture using a low temperature ethane oxidation mechanism with and Without the C2H5O2 + C2H6 reaction included, we demonstrate that this reaction has a significant impact on predicted ignition times. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.