High-Temperature Shock Tube Studies Using Multipass Absorption: Rate Constant Results for OH + CH3, OH + CH2, and the Dissociation of CH3OH

Abstract

The reflected shock tube technique with multipass absorption spectrometric detection has been used to study the reactions of OH radicals: (1) OH + CH 3 → 1 CH 2 + H 2 O, (2) OH + 3 CH 2 → CH 2 O + H, and the thermal dissociation of methanol, (3) CH 3 OH → CH 3 + OH. (1) has never been studied above 1000 K, (2) has never been studied, and (3) has been studied but with conflicting results. Depending on conditions, all three reactions can be important in combustion systems, and this realization supplies the motivation for the present study. tert-Butyl hydroperoxide, di-tert-butyl peroxide, methanol, and methyl iodide were used as pyrolytic precursors of hydroxyl and methyl radicals. Methylene was produced by the pyrolysis of ketene. The experiments were performed in single-shot experiments with low initial concentrations of hydroxyl radicals, [OH] 0 = (45-130) x 10 1 2 molecules cm - 3 . [OH] 1 was measured with resonance absorption around 308 nm. The measured rate constants are k, = 1.74 x 10 - 1 1 exp(915 K/T) (834-2383 K), k 2 = (2.6 ′ 1.6) x 10 - 1 1 (1841-2324 K), and k 3 = 4.39 x 10 - 8 exp(-31 938 K/T), all in cm 3 molecule - 1 s - 1 . In addition, the yield of OH radicals in the pyrolysis of methanol was determined, 0.94 ′ 0.09 (1841-2309 K). Where possible, these results are compared to earlier data and estimates. Existing theory is also reviewed and compared to the present results.