Kinetics of the OH + CO reaction under atmospheric conditions

The pulsed laser photolysis‐pulsed laser‐induced fluorescence technique has been employed to study the kinetics of the reaction, OH + CO → k 1 products, as a function of temperature and pressure in N 2 , air, and O 2 buffer gases. At pressures of 1 atm and below, k 1 is found to increase linearly with increasing pressure. Within experimental uncertainty, both the rate constant in the low‐pressure limit and the slope of the k 1 versus pressure dependence are found to be the same at 262 K as at 299 K. From our data we obtain the expression k 1 = (1.47 ± 0.08) × 10 −13 1 + (0.59 ± 0.10) P independent of temperature, where P is in units of atmospheres and k 1 is in units of cubic centimeters per molecule per second. Within experimental uncertainty, the pressure dependence of k 1 at 299 K is the same in N 2 buffer gas as in O 2 buffer gas. In 700‐torr air at 299 K, k 1 is found to be independent of water vapor concentration over the range 0.01–20 torr. Our results will have little effect on current panel recommendations of k 1 values for use in atmospheric models. However, uncertainties in the temperature dependence under atmospheric conditions, the third body efficiency of O 2 , and the effect of water vapor on k 1 are now greatly reduced.