The lifetime of the ferryl ion (minutes at pH below 1) is reduced by a fac-2ϩ

The oxidation of ferrous ions by ozone in acidic solutions of pH 0-2 was studied using a stopped-flow spectrophotometer. The reaction can be characterized as an oxygen atom transfer from O3 to Fe2+. An intermediate product assigned to be the ferryl ion, Fe02+, was found and its UV-vis spectrum measured. A reaction mechanism is proposed, which accounts for all our experimental results. Accordingly, the ferryl ion is formed by Fe2+ + 03 -» Fe02+ + 02 with a rate constant k = (8.2 ± 0.3) X 105 M"* 1 s-1. With an excess of Fe2+, the reaction Fe02+ 2H+ + Fe2+ -*• 2Fe3+ + H20, k = (1.4 ± 0.2) X 105 M_1 s-1, is dominant in the decay of FeO2"1", thus yielding the stoichiometric ratio [ 3]/ [ ß2+] = 0.5 for [Fe2+]o/[03]o 3. With an excess of O3, the decay is governed by H2O the following set of reactions:

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