Rate constant of the elementary reaction of carbon monoxide with hydroxyl radical

Abstract

Using a supersonic molecular beam sampling technique coupled with a mass spectrometer, the concentrations of all stable and unstable species have been measured in the reaction zone of a lean carbon monoxide-hydrogen-oxygen flame (9.4%CO, 11.4%H2, 79.2%O2) burning at 40 Torr. Reaction (1) CO+OH→CO2+H is the main process for CO conversion to CO2. From radical concentration profiles, it was determined that reaction (4) CO+HO2→CO2+OH is negligible as compared to (1). The rate constant k1 was determined from the CO2 mole fluxes over a large temperature range (400°–1800°K). The experimental data exhibit a marked and significant curvature in the plot of logk1 vs 1/T. From 400° to 800°K, k1 (8×1010 cm3 mole−1s−1) increases only slightly but above 1000°K the Arrhenius expression k1=2.32×1012 exp (−5700/RT) cm3 mole−1s−1 up to 1800°K. The rate constant of reaction (9) H2+OH→H2O+H was determined similarly and found to be 7×1012 exp (−4400/RT) cm3 mole−1s−1 in the temperature range of 600° to 1300°K. A curvature, less pronounced than for k1, was observed.