A shock tube study of CO + OH ? CO2 + H and HNCO + OH ? products via simultaneous laser absorption measurements of OH and CO2

The rate coefficients for the reactions were determined using mixtures of HNO3/CO/Ar and HNO3/HNCO/Ar in incident shock wave experiments. Simultaneous OH and CO2 absorption time-histories were obtained via cw uv narrow-linewidth absorption at 32606.56 cm−1 (λ = 306.687 nm) and cw infrared narrow-linewidth absorption at 2380.72 cm−1 (λ = 4.2004 μm), respectively. The measurements of k1 determined from measured CO2 time-histories are in good agreement with those determined from previous measurements of OH time-histories at this laboratory. The rate coefficient for the overall reaction of HNCO + OH → Products was determined from analysis of OH data traces. The uncertainty in k2 was found to be +22% −16%. By incorporating data from a previous low-temperature study, the following empirical expression was determined for the bimolecular reaction: over the temperature range 620–1860 K. From analysis of CO2 data traces, an upper limit on the branching fraction (α = k2a/k2) for reaction (2a) of 10% was found, independent of temperature over the range 1250–1860 K.