Hydroxyl-Radical Kinetics by Kinetic Spectroscopy. I. Reactions with H2, CO, and CH4 at 300°K

Abstract

Gas‐phase reactions of OH radicals with H₂, CO, and CH₄ have been studied at total pressure of up to 200 mm. Hydroxyl radicals were generated rapidly in the presence of the reactant by flash photolysis of H₂O—reactant mixtures in a quartz system, and the subsequent decrease in OH concentration was followed by quantitative kinetic spectroscopy (KS). Rate constants at 301°±1°K were found to be, in cubic centimeters per mole·second, $$\begin{array}{cc}\hspace{0.17em}\mathrm{OH}+{\mathrm{H}}_2\to {\mathrm{H}}_2\mathrm{O}+\mathrm{H},& k_6{\text{=4.0±0.2×10}}^9,\\ \mathrm{OH}+\mathrm{CO}\to {\mathrm{CO}}_2+\mathrm{H},& k_7{\text{=8.9±0.9×10}}^{10},\\ \mathrm{\hspace{0.17em}\hspace{0.17em}}\mathrm{OH}+{\mathrm{CH}}_4\to {\mathrm{H}}_2\mathrm{O}+{\mathrm{CH}}_3,& k_1{\text{=5.3±0.2×10}}^9,\end{array}$$ over 25‐fold ranges of [OH] and > fivefold ranges of [H₂], [CO], and [CH₄]. These results confirm recently reported values obtained at pressures of ∼1 mm with a flow‐system—ESR technique and extend the range of reactant concentration studied by factors of up to 125.