A shock tube study of CO + OH → CO 2 + H and HNCO + OH → products via simultaneous laser absorption measurements of OH and CO 2

The rate coefficients for the reactions $$\rm CO + OH\ \longrightarrow CO_2 + H \eqno{(1)}$$ $$\rm HNCO + OH\ \longrightarrow Products \eqno{(2)}$$ $$\rm HNCO + OH\ \longrightarrow CO_2 + NH_2 \eqno{(2a)}$$ were determined using mixtures of HNO 3 /CO/Ar and HNO 3 /HNCO/Ar in incident shock wave experiments. Simultaneous OH and CO 2 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 k 1 determined from measured CO 2 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 k 2 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: $$k_2=3.63\times 10^{7} T^{1.5} \exp(-1809/T)[{\rm cm^3\ mol^{-1}s^{-1}}]$$ over the temperature range 620–1860 K. From analysis of CO 2 data traces, an upper limit on the branching fraction (α = k 2a / k 2 ) for reaction (2a) of 10% was found, independent of temperature over the range 1250–1860 K. © 1996 John Wiley & Sons, Inc.