Reactions of H2O3 in the Pulse-Irradiated Fe(II)–O2 System

$\mathrm{G[}\mathrm{Fe}\mathrm{(III)]}$ is measured in pulse‐irradiated O₂‐saturated solutions of 20 to 160 μMFe(II), at the pH's 0.46, 1.51, and 2.74 H₂SO₄ and HClO₄ and with dose rates between 1 and 8 krad/1 μsec pulse. Based on homogeneous kinetics, the results are interpreted by a system of 18 reactions. The formation of the hydrogen sesquioxide H₂O₃ as an intermediate in the reaction OH + HO₂→H₂O₃→H₂O + O₂ is confirmed. In the absence of Fe(II), $\mathrm{G(}{\mathrm{H}}_2{\mathrm{O}}_3)$ varies from 2.04 at pH 0.46 to 1.57 at pH 2.74. The rate constant $\mathrm{k[}{\mathrm{H}}_2{\mathrm{O}}_3+\mathrm{Fe}{\text{(II)]\hspace{0.17em}=\hspace{0.17em}6.0\hspace{0.17em}×\hspace{0.17em}1}}^4{M}^{\text{−1}}·{\sec }^{\text{−1}}$ at the pH's studied. The direct reaction, OH + HO₂ = H₂O + O₂, does not take place. In H₁SO₄, at pH 0.46, 151, and 2.74 and in HClO₄ at pH 0.46 and 1.51, the complexes of Fe(III) produced by the radiation reach equilibrium before they react with HO₂. However, equilibrium is not reached in HClO₄ at pH 2.74, where the effective rate constant $\mathrm{k(}{\mathrm{HO}}_2+\mathrm{Fe}\mathrm{(III)]}$ is 6.2 times its value when Fe(III) is in its equilibrium form. This ratio is constant over the dose rate range studied. With dose rates up to 64 krad/1.4 μsec pulse $\mathrm{G[}\mathrm{Fe}\mathrm{(III)]}$ and $\mathrm{G(}{\mathrm{H}}_2)$ were measured in the air saturated 1‐mM FeSO₄ dosimeter and $\mathrm{G[}\mathrm{Fe}\mathrm{(III)]}$ in the O₂ saturated 10‐mM FeSO₄ dosimeter, each in $\text{0.4M}{\mathrm{H}}_2{\mathrm{SO}}_4$ . $\mathrm{G[}\mathrm{Fe}\mathrm{(III)]}$ decreases in both dosimeters less rapidly with increasing dose rate than was found by earlier workers. The principal reason for the decrease is the failure of O₂ to scavenge the H atoms at high dose rates. Excellent agreement is obtained between experiment and theory except at high dose rates, where the calculated $\mathrm{G[}\mathrm{Fe}\mathrm{(III)]\text{'}s}$ are slightly too high in both dosimeters.