Oxidation of Methyl Radicals Studied in Reflected Shock Waves using the Time-of-Flight Mass Spectrometer

Abstract

The oxidation of methyl radicals has been investigated using a shock tube coupled to a time-of-flight mass spectrometer between 1100 and 1400°K. The effect of varying the temperature and oxygen concentration is reported. Formaldehyde was observed as a product of the oxidation reaction. For a 10-fold excess of O₂ at 1350°K the concentration—time profiles for the following principal species: CH₃, C₂H₆, C₂H₄, CH₄, CH₂O, H₂O, and CO have been obtained over the reaction time scale of 350 μsec. Numerical integration calculations have been performed using a mechanism and rate data compounded from two earlier studies in this laboratory to describe the present methyl radical oxidation data. Good agreement between all the experimental and calculated profiles is obtained, with the inclusion of one additional reaction in the integrated mechanism, $$\mathrm{O}+{\mathrm{C}}_2{\mathrm{H}}_4\to {\mathrm{CH}}_3+\mathrm{H}+\mathrm{CO},$$ with a rate coefficient $k_{13}{\text{=8.3× 10}}^{\text{−12}}\hspace{0.17em}\mathrm{cc}/\mathrm{particle}·\sec$ at 1350°K as quoted in the literature, and if the following reactions: $${\mathrm{CH}}_3+{\mathrm{O}}_2\to {\mathrm{CH}}_2\mathrm{O}+\mathrm{OH},$$ $${\mathrm{CH}}_3+\mathrm{O}\to {\mathrm{CH}}_2\mathrm{O}+\mathrm{H},$$ take on the rate values $k_5{\text{=3.3× 10}}^{\text{−14}}\hspace{0.17em}\mathrm{cc}/\mathrm{particle}·\sec$ and $k_6{\text{=4.2× 10}}^{\text{−11}}\hspace{0.17em}\mathrm{cc}/\mathrm{particle}·\sec$ at 1350°K which are factors of 2 greater than in the earlier studies.