Carbonate radical in flash photolysis and pulse radiolysis of aqueous carbonate solutions

The carbonate radical, CO₃^-, may be generated by the reaction of carbonate or bicarbonate ions with hydroxyl radicals. The flash photolysis of hydrogen peroxide solutions and the pulse radiolysis of water are utilized as sources of hydroxyl radicals from which it is found that the basic form of the hydroxyl radical, O^-, contributes little to the production of CO₃^-, even up to pH 14. Reactions of CO₃^- with hydrogen peroxide (k = 8 × 10⁵ M^-1 sec^-1) and with HO₂^- (k = 5.6 × 10⁷ M^-1 sec^-1) are observed. The carbonate radical and the perhydroxyl radical ion, O₂^-, are formed in equimolar concentrations in the flash photolysis of oxygen-saturated carbonate solutions, and from this, the extinction coefficient of O₂^- is found to be 1850 ± 200 M^-1 cm^-1 by comparison with the better known extinction coefficient of CO₃^-. The product of the reaction CO₃^- + O₂^- is assumed to be CO₅^- having a half-life time of several seconds and ε_CO52-2600 = 410 M^-1 cm^-1.