Mechanism of Decomposition of Peroxynitric Ion (O₂NOO^-): Evidence for the Formation of O₂^.- and ^.NO₂ Radicals

The rate constant of the self-decomposition of O₂NOO^- was determined to be 1.35 ± 0.03 s^-1 at 25°C. The decomposition rate constant of O₂NOO^- in the presence of C(NO₂)₄, CuSO₄, SOD, and Fe(CN)₆^4- was found to be 2.4 ± 0.2 s^-1, independent of the concentration of these substrates. The oxidation yields of C(NO₂)₃^- and ferricyanide were measured to be 47 ± 5 and 83 ± 9% of added peroxynitrate, respectively, where the latter decreased to 54 ± 6% in the presence of SOD. We therefore suggest that ca. 50% of O₂NOO^- homolyses into O₂^.- and ^.NO₂ (k = 1.05 ± 0.23 s^-1). The equilibrium constant of the homolysis of O₂NOO^- into ^.NO₂ and O₂^.- and the reduction potential of the couple O₂NOOH,H⁺/NO₃^/ were calculated to be 2.3 × 10^-10 M and 1.83 V, respectively.