Absolute Rate Constant of the OH + ClO Reaction at Temperatures between 218 and 298 K

Abstract

The total absolute rate constant (k1a + k1b) for the reactions OH + ClO → Cl + HO2 (k1a) → HCl + O2 (k1b) has been determined in the temperature range from 218 to 298 K at a total pressure of 1 Torr of helium. Pseudo-first-order conditions were used with ClO in large excess over initial OH. ClO was produced by reacting Cl atoms with an excess of O3; both ClO and O3 were quantitatively determined by UV spectrophotometry between 210 and 310 nm. Two sources of OH were used: the reaction of F atoms with excess water vapor and the reaction of H atoms with an excess of NO2. OH was monitored by resonance fluorescence near 308 nm. The absolute rate constant was determined from plots of ln [OH] vs time and absolute ClO concentrations. At 298 K, the result is (2.22 ± 0.33) × 10-11 cm3 molecule-1 s-1. The temperature dependence expressed in Arrhenius form is (7.2 ± 2.2) × 10-12 exp[(333 ± 70)/T] cm3 molecule-1 s-1. The uncertainties are at the 95% confidence limits and include statistical errors from the data analy...