REACTION OF HO2 WITH O-3 AND THE EFFECT OF WATER-VAPOR ON HO2 KINETICS

Photolysis of H2-O2-O3 mixtures at 253.7 nm has been used to measure the ratio k1/k21/2 in the temperature range -42.5 to +61 °C, at atmospheric pressure: HO2 + O3 → OH + 2O2 (k1), HO2 + HO2 → H2O2 + O2 (k2). The result is k1/k21/2 = 6.4 × 10-8 exp(-1220/T) cm3/2 s-1/2, which is in excellent agreement with recent absolute measurements of k1 and k2. Addition of water vapor causes a reduction in the measured k1/k21/2. The magnitude of the effect is in agreement with the observations of Hamilton showing an increase in k2 in the presence of water vapor. The ratio k1/k21/2 was also measured at 25 °C by the photolysis of H2O-O2-N2 mixtures at 184.9 nm. The resulting value of k1/k21/2 is in good agreement with that obtained from the first type of experiment, when the water vapor effect is taken into account. The 184.9-nm experiments also yield information on the rate constant k11: OH + HO2 → H2O + O2 (k11). As in previous experiments by DeMore and Tschuikow-Roux, the results are compatible only with k11 values in excess of 10-10 cm3 s-1, which is higher than k11 values measured by others in low pressure systems. These results suggest a possible dependence of k11 on reaction conditions such as pressure. © 1979 American Chemical Society.