Kinetic study of the reaction of HO2 with ozone

The reaction HO2+O3→OH+2O2 has been studied using a discharge-flow system with laser magnetic resonance detection. The rate constant for the reaction was determined directly by monitoring the first-order decay of isotopically labeled H18O2 in excess 16O3. The data give a curved Arrhenius plot over the temperature range 243<T<413 K: k(T)=(3.8±2.4) ×10−14 exp[−(820±190/T)] cm3 s−1. A more representative fit is obtained with a three parameter expression: k(T)=(3.2±5.8)×10−13 exp[−(1730±740)/T] + (1.2±0.5)×10−15 cm3 s1. The error limits are the 95% confidence limits on the coefficients while the accuracy of the measurements is estimated to be about ±20% at each temperature. An analysis of the OH radical product indicates that 16OH is formed predominately (75±10)%. The scrambling reactions H18O2+16O3→H16O2+18O18O16O (1c) and H18O2+16O2→H16O2+18O2 (8) were also examined and found to be slow. Their rate constants are k1c<2×10−17 cm3 s−1 at 297 and 333 K and k8<3×10−17 cm3 s−1 at 297 and 413 K.