| Photolysis of H2O2 or S2O8 2− in aqueous solutions containing Cl− has been investigated by the laser flash photolysis - long path absorption technique. The corresponding unified chemical mechanisms are proposed based upon previous research and the analyses of the present work. The absorption spectra of the transient species Cl2− and SO4− are individually determined. The kinetics of the formation and decay of Cl2− is investigated in both systems. The kinetics of SO4− decay is studied in the SO4− + Cl− system.; Both Cl2− and SO4− follow mixed-first-and-second-order mechanisms in their decay. The dependence of the pseudo-first-order decay rate constant of Cl2 − on pH is observed. The pseudo-first-order decay rate constant of SO4− is proposed also to depend on pH. The reaction Cl2− + Cl → Cl2 + Cl− is identified as an important pathway for Cl 2− decay, when [Cl−] < 1 × 10−3 M. The aqueous reactions H 2O2 + Cl → HO2 + Cl− + H+, S2O82− + Cl → products, and S2O82− + Cl 2− → products are reported. Several equilibrium constants and rate constants involving Cl, Cl−, Cl 2−, H2O, H2O2, SO4−, and S2O8 2− are determined at 297 ± 2 K.; The primary quantum yields of hydroxyl radicals (ΦOH) in the 248nm and 308nm photolysis of H2O2 are determined using Cl− as a scavenger of OH. The value of Φ OH is close to unity and exhibits no wavelength dependence. The competition kinetics on the formation of Cl2− is investigated as a function of pH and reactant concentrations. Some important reaction rate constants and equilibrium constants involving Cl, Cl−, Cl2−, H2O, and H2O 2 in aqueous solution are evaluated critically. The implications of the present results are discussed in relation to atmospheric chemistry. |
