Free Radical Reactions Involving Cl•, Cl2-•, and SO4-•in the 248 nm Photolysis of Aqueous Solutions Containing S2O82-and Cl-

Abstract

Rate constants and other properties are reported for photochemical reactions initiated by laser photolysis (248 nm) of S 2 O 8 2- (aq) in acidic solutions containing Cl - (aq) at 297 ± 2 K. The absorption spectra of SO 4 -• (aq) and Cl 2 -• (aq) are measured and compared to literature values. Equilibrium constants and rate constants involving Cl • (aq), Cl 2 -• (aq), H 2 O, SO 4 -• (aq), and S 2 O 8 2- (aq) are determined by analyzing the formation and decay of Cl 2 -• (aq) and SO 4 -• (aq) in a self-consistent chemical mechanism. For the first time, the anticipated pH dependence is observed unambiguously in the pseudo-first-order decay rate constant of Cl 2 -• . The rate constants for the reactions Cl • (aq) + Cl 2 -• (aq) → Cl 2 (aq) + Cl - (aq) and Cl 2 -• (aq) + Cl 2 -• (aq) → Cl 2 (aq) + 2Cl - (aq) are determined; rate constants for the latter are measured as a function of temperature and ionic strength. In addition, the ionic strength dependence of the reaction SO 4 -• (aq) + Cl - (aq) → SO 4 2- (aq) + Cl • (aq) is reported. Rate constants for the reactions of Cl • (aq) and Cl 2 -• (aq) with S 2 O 8 2- (aq) are reported for the first time. The present and previous (when available) experimental results are generally in good agreement within the context of the comprehensive chemical mechanism for this system.