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 14001780 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 k(1)(T) = 2.09 x 10(15) exp(-87510 [cal/mol/RT) [s(-1)] and k(2)(T) = 2.66 x 10(16) exp(-97880 [cal/mol]/RT) [s(-1)]. The resulting branching ratio, k(1)/(k(1) + k(2)), ranges from 0.8 at 1350 K to 0.6 at 1800 K. (C) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.