Generation of superoxide radicals by photolysis of oxygenated ethanol solutions

Vacuum-UV photolysis of oxygenated aqueous ethanol solutions with a Xe-plasma lamp yields relatively high concentrations of superoxide radical in short time periods. The superoxide radical in this system is identified by its absorption spectrum (λ_max = 240 nm, ε = 2350 M^-1 cm^-1), ESR spectrum in a glass at low temperatures with the characteristic low-field g_∥ = 2.072 and high-field g_⊥ = 2.006, second-order decay kinetics (k_obsd = 22 M^-1 s^-1 in 12 M ethanol containing 0.01 M KOH; k_obsd = 8.7 × 10⁵ M^-1 s^-1 in 12 M ethanol containing 0.085 M H₂SO₄), and reactivity with cytochrome c. Two mechanisms for O₂^- formation, consistent with experimental results, are proposed for the photolysis of dilute and concentrated ethanol solutions.