Investigation of the reaction of toluene with molecular oxygen in shock-heated gases

The reaction of toluene with molecular oxygen to yield benzyl and hydroperoxyl radicals has been studied using ultraviolet laser absorption of benzyl radicals at 266 nm in shock-heated gases. Test gas mixtures of toluene with excess oxygen diluted in helium and argon were heated in reflected shock waves to temperatures ranging from 1117 to 1366 K at total pressures around 1.7 bar. The growth in benzyl absorbance was monitored at 266 nm, allowing determination of the rate coefficient for the C6H5CH3 + O2 → C6H5CH2 + HO2, reaction (1). The high signal-to-noise ratio provided by laser absorption provides rate coefficient determinations with an estimated uncertainty of ±20%±20%. Fitting both these high-temperature shock tube results and the rate recommendation of Ingham et al. [Proc. Combust. Inst. 25 (1994) 767–774] at 773 K, the rate coefficient for reaction (1) can be described with a three-parameter Arrhenius expression by k1(T)=2.18×107T2.5exp(−46,045[cal/mol]/RT)[cm3mol−1s−1]. In addition, the measured benzyl time-histories can be used as experimental targets for the development and validation of detailed mechanisms for toluene oxidation.