Rate constant for the OH + CO reaction: Pressure dependence and the effect of oxygen

The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N 2 , and SF 6 over the pressure range 200–730 torr. All experiments were at room temperature. The method involved laser‐induced fluorescence to measure steady‐state OH concentrations in the 184.9 nm photolysis of H 2 O‐CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O 2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N 2 and SF 6 , but not for Ar, within an experimental error of about 10%. The pressure effect for N 2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF 6 a factor of two enhancement was seen at 730 torr. In each case it was found that O 2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.