A laser flash photolysis study of the decay of SO4− and Cl2− radical anions in the presence of Cl− in aqueous solutions

The rate constant for the reaction of sulphate radical (SO4−) with Cl− has been determined using laser photolysis, at 248 nm, of peroxodisulphate anions to produce the radicals and time resolved optical absorption of the transient species (at 450 or 480 nm for SO4− and 350 nm for Cl2−) for the kinetic determinations. The experiments were performed, in the absence of added sulphate, as a function of temperature and ionic strength and yielded (at an ionic strength of 0.0157 M): kIV=(9.90±0.16)×109exp((−7.12±2.0) kJ mol−1/RT) M−1 s−1, where the errors reflect the 2σ statistical error. This reaction produces Cl2−, the formation and decay of which were also monitored allowing a determination of the rate constant of its second-order self-recombination reaction which gave k=(6.50±1.40)×108 M−1 s−1 at 293 K and zero ionic strength.