Electron spin resonance studies of inorganic radicals in irradiated aqueous solutions. I. Direct observation

A search has been carried out for the esr spectra of radical intermediates present during steady-state, in situ radiolysis of aqueous solutions of inorganic salts. The technique used is capable of detecting radicals which react by diffusion-controlled recombination if the esr line widths are small (<1 G). In fact out of 15 systems studied, only four gave detectable esr signals. One is forced to conclude that the esr lines of the radicals formed in the other systems are broad. The radicals successfully studied are ·SO₃^- (from OH + SO₃^2-, g = 2.00306), ·PO₃^2- (from OH + HPO₃^2-, a^P = 567.6 G, g = 2.00154), ·HPO₂^- (from OH + H₂PO₂^-, a^P = 480.4, a^H = 89.7 G, g = 2.00293), and -·CS₂^- (from e_aq^- + CS₂, g = 2.00804). No esr lines were detected from solutions of HCO₂^-, CO₃^2-, S^2-, Se^2-, SeO₃^2-, Br^-, I^-, SCN^-, OCN^-, N₃^-, HO₃^-, NO₂^-, NH₂OH, or AsO₂^-. Steady-state measurements of radical concentrations have been used to determine rates of radical recombination for the species ·SO₃^-, ·PO₃^2-, and ·HPO₂^-.