Rate constants of OH with HO2, O2-, and H2O2+ from hydrogen peroxide formation in pulse-irradiated oxygenated water

Abstract

The rate constants for the reactions of OH with HO2, O2-, and H2O2+ are calculated from measurements of G(H2O2) in oxygenated water irradiated at 25° with a pulsed electron beam in the pH range 0.46-6.75 and at dose rates between 500 and 5000 rads/pulse. At these dose rates, HO2 remains in equilibrium with its ionized and protonated forms during these reactions. Above pH 2.74, G(H2O2) decreases, owing to the dissociation of HO2. Based on k(OH + OH) = 0.60 × 1010 M-1 sec-1, we obtain k(OH + HO2) = 0.71 × 1010 M-1 sec-1, k(OH + O2-) = 1.01 × 1010 M-1 sec-1, and pK = 4.45 ± 0.10 for HO2 ⇄ H+ + O2-. Results at pH 1.51 and 0.46 support Bielski and Allens's suggestion that HO2 protonates in this pH region and give a pK = 1.20 ± 0.30 for H2O2+ ⇄ HO2 + H+ and the rate constant k(OH + H2O2+) = 1.27 × 1010 M-1 sec-1.