Pulse-radiolysis study of some unstable complexes of iron

Pulse radiolysis of oxygen-containing solutions of ferrous perchlorate in perchloric acid (l M) enables the formation and disappearances of a ferric hydroperoxide complex, Fe3+HO–2, to be observed. The rate constant for its formation by reaction of HO2 radicals with free ferrous ions is 2.1 ± 0.4 × 106 M–1s–1 in the pH range 0–2.1. The complex disappears in a first-order reaction with a rate constant independent of pH in the range 0–2.1. It exhibits a broad absorption in the region 280–600 nm, with Iµ430 nm= 280 ± 30 M–1 cm–1. In the absence of oxygen, a different absorbing species can be seen, attributed to a ferric hydride complex, Fe3+H–. This is formed by the reaction of hydrogen atoms with free ferrous ions with k= 7.5 ± 2 × 106 M–1 s–1. It disappears by reaction with hydrogen ions, with k= 1.06 ± 0.1 × 104 M–1 s–1. Its absorption spectrum exhibits a maximum at 325 nm, Iµ325= 650 ± 65 M–1 cm–1.