A Shock Tube Study of the CO + OH Reaction Near the Low-Pressure Limit

Rate coefficients for the reaction between carbon monoxide and hydroxyl radical were measured behind reflected shock waves over 700 – 1230 K and 1.2 – 9.8 bar. The temperature/pressure conditions correspond to the predicted low-pressure limit of this reaction, where the channel leading to carbon dioxide formation is dominant. The reaction rate coefficients were inferred by measuring the formation of carbon dioxide using quantum cascade laser absorption near 4.2 µm. Experiments were performed under pseudo-first order conditions with tert-butyl hydroperoxide (TBHP) as the OH precursor. Using ultraviolet laser absorption by OH radicals, the TBHP decomposition rate was measured to quantify potential facility effects under extremely dilute conditions used here. The measured CO + OH rate coefficients are provided in Arrhenius form for three different pressure ranges: kCO+OH (1.2 – 1.6 bar) = 9.14 x 10-13 exp(-1265/T) cm3 molecule-1 s-1 kCO+OH (4.3 – 5.1 bar) = 8.70 x 10-13 exp(-1156/T) cm3 molecule-1 s-1 kCO+OH (9.6 – 9.8 bar) = 7.48 x 10-13 exp(-929/T) cm3 molecule-1 s-1 The measured rate coefficients are found to be lower than the master equation modeling results by Weston et al. [J. Phys. Chem. A, 117 (2013) 821] at 819 K and in closer agreement with the expression provided by Joshi and Wang [Int. J. Chem. Kinet., 38 (2006) 57].