The pulse radiolysis of deaerated aqueous carbonate solutions. I. Transient optical spectrum and mechanism. II. pK for OH radicals

The pulse radiolysis of deaerated aqueous carbonate solutions in the neutral and alkaline pH was studied. A mechanism is presented, and several rate constants have been determined (all are in units of M^-1 sec^-1). k(OH + CO₃^2-) = 4.2 × 10⁸, k(O^- + CO₃^2-) < 10⁷, 2k(CO₃^- + CO₃^-) = 1.2₅ × 10⁷ (zero ionic strength), and k(OH + HCO₃^-) = 1.5 × 10⁷. In the pulse radiolysis of carbonate solutions a transient optical absorption appears which is identified as the carbonate radical ion (CO₃^-). Its spectrum is reported and has a maximum extinction coefficient of 1860 ± 160 M^-1 cm^-1 at 6000 A. There is a pH dependency of the rate of CO₃^- formation, from which the pK for the ionic dissociation of OH radicals has been determined as 11.8 ± 0.2, where pK is defined as -log {[H⁺][O^-]/ [OH]}. The results are compared with earlier work.