An Electron Spin Resonance Study of the Spin Adducts of OH and HO₂ Radicals with Nitrones in the Ultraviolet Photolysis of Aqueous Hydrogen Peroxide Solutions

The photolysis of H₂O₂ in aqueous solution has been used to study and characterize electron spin resonance (e.s.r.) spectra of the •OH and •HO₂ radical spin adducts with the spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and phenyl-t-butyl nitrone (PBN). At high concentrations of spin trap and low concentrations of H₂O₂ an e.s.r. spectrum is obtained which we assign to the •OH radical adduct (for DMPO, a^N = 15.3 G, a_β^H = 15.3 G, [Formula: see text] and g = 2.0060; for PBN, a^N = 15.3 G, a_β^H = 2.75 G, and g = 2.0057). At low concentrations of spin trap and high concentrations of H₂O₂• a second spin adduct spectrum is obtained which we assign to the spin adduct of the HO₂ radical (for DMPO, a^N = 14.3 G, a_β^H = 11.7 G, a_γ^H = 1.25 G, g = 2.0061; for PBN, a^N = 14.8 G, a_β^H = 2.75 G, and g = 2.0057).