Hydrogen peroxide photolysis in acidic aqueous solutions containing chloride ions. I. Chemical mechanism

Equilibrium constants and rate constants involving Cl^̇(aq), Cl₂^̇-(aq), H₂O, and H₂O₂(aq) are measured at 297 ± 2 K by analyzing the kinetics of formation and decay of Cl₂^̇-. The new results are in good agreement with previous studies, when available. The reaction between solvated chlorine atoms and hydrogen peroxide is reported for the first time: Cl^̇(aq) + H₂O₂(aq) → H⁺(aq) + Cl^-(aq) + HO₂^̇(aq), k₁₀ = (2.0 ± 0.3) × 10⁹ M^-1 s^-1 (±σ). The new results are used along with evaluations of literature data to arrive at recommendations for several key rate constants and equilibrium constants. Of particular interest, the recommended equilibrium constant for the reaction Cl^̇(aq) + Cl^-1(aq) ↔ Cl₂^̇-(aq) is K₅ = (1.4 ± 0.2) × 10⁵ M^-1(±σ).