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, OH+H2→H2O+H,k6=4.0±0.2×109,OH+CO→CO2+H,k7=8.9±0.9×1010, OH+CH4→H2O+CH3,k1=5.3±0.2×109,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.