The reaction of allyl radicals with oxygen atoms-rate coefficient and product branching

The primary product formation of the C(3)H(5) + O reaction in the gas phase has been studied at room temperature. Allyl radicals (C(3)H(5)) and O atoms were generated by laser flash photolysis at lambda = 193 nm of the precursors C(3)H(5)Cl, C(3)H(5)Br, C(6)H(10) (1,5-hexadiene), and SO(2), respectively. The educts and the products were detected by using quantitative FTIR spectroscopy. The combined product analysis of the experiments with the different precursors leads to the following relative branching fractions: C(3)H(5) + O -> C(3)H(4)O + H (47%), C(2)H(4) + H + CO (41'%), H(2)CO + C(2)H(2) + H (7%), CH(3)CCH + OH and CH(2)CCH(2) + OH (<5%). The rate of reaction has been studied relative to CH(3)OCH(2) + O and C(2)H(5) + O in the temperature range from 300 to 623 K. Here, the radicals were produced via the fast reactions of propene, dimethyl ether, and ethane, respectively, with atomic fluorine. Laser-induced multiphoton ionization combined with TOF mass spectrometry and molecular beam sampling from a flow reactor was used for the specific and sensitive detection of the C(3)H(5), C(2)H(5), and CH(3)COCH(2) radicals. The rate coefficient of the reaction C(3)H(5) + O was derived with reference to the reaction C(2)H(5) + O leading to k(C(3)H(5) + O) = (1.11 +/- 0.2) x 10(14) cm(3)/(mol s) in the temperature range 300-623 K. The C(3)H(5) + O rate and channel branching, when incorporated in a suitable detailed reaction mechanism, have a large influence on benzene and allyl concentration profiles in fuel-rich propene flames, on the propene flame speed, and on propene ignition delay times. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.