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

Abstract

The primary product formation of the C3H5+O reaction in the gas phase has been studied at room temperature. Allyl radicals (C3H5) and O atoms were generated by laser flash photolysis at λ=193nm of the precursors C3H5Cl, C3H5Br, C6H10 (1,5-hexadiene), and SO2, 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: C3H5+O→C3H4O+H (47%), C2H4+H+CO (41%), H2CO+C2H2+H (7%), CH3CCH+OH and CH2CCH2+OH (<5%). The rate of reaction has been studied relative to CH3OCH2+O and C2H5+O in the temperature range from 300 to 623K. 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 C3H5, C2H5, and CH3COCH2 radicals. The rate coefficient of the reaction C3H5+O was derived with reference to the reaction C2H5+O leading to k(C3H5+O)=(1.11±0.2)×1014cm3/(mols) in the temperature range 300–623K. The C3H5+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.