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

摘要

The primary product formation of the C_3H_5 + O reaction in the gas phase has been studied at room temperature. Allyl radicals (C_3H_5) and O atoms were generated by laser flash photolysis at λ = 193 nm of the precursors C_3H_5Cl, C_3H_5Br, C_6H_(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_3H_5 + O → C_3H_4O + H (47%), C_2H_4 + H + CO (41%), H_2CO + C_2H_2 + H (7%), CH_3CCH + OH and CH_2CCH_2 + OH (<5%). The rate of reaction has been studied relative to CH_3OCH_2 + O and C_2H_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 multipho-ton 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_3H_5, C_2H_5, and CH_3COCH_2 radicals. The rate coefficient of the reaction C_3H_5 + O was derived with reference to the reaction C_2H_5 + O leading to k(C_3H_5 + O) = (1.11 ± 0.2) × 10~(14) cm~3/(mol s) in the temperature range 300-623 K. The C_3H_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.