Thermal decomposition of toluene: Overall rate and branching ratio

The two-channel thermal decomposition of toluene, C6H5CH3 → C6H5CH2 + H (1) and C6H5CH3 → C6H5 + CH3 (2), was investigated in shock tube experiments over the temperature range of 1400–1780 K at a pressure of 1.5 (±0.1) bar. Rate coefficients for reactions (1) and (2) were determined by monitoring benzyl radical (C6H5CH2) absorption at 266 nm during the decomposition of toluene diluted in argon and modeling the temporal behavior of the benzyl concentration with a kinetic model. The first-order rate coefficients determined at a pressure of 1.5 bar are expressed by k1(T) = 2.09 × 1015 exp (−87510 [cal/mol]/RT) [s−1] and k2(T) = 2.66 × 1016 exp (−97880 [cal/mol]/RT) [s−1]. The resulting branching ratio, k1/(k1 + k2), ranges from 0.8 at 1350 K to 0.6 at 1800 K.