The photolysis of Na 2 S 2 O8 aqueous solutions containing Cl -ions is a clean method for kinetic studies of the species Cl • / Cl 2 •-in the absence and presence of added aromatic substrates. Laser and conventional flashphotolysis techniques were employed to investigate the aqueous phase reactions of chlorine atoms and Cl 2 •-(340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl 2 •-in aqueous solutions containing chloride ion concentrations in the range 1 × 10 -4 to 0.6 M, total radical (Cl • + Cl 2 •-) concentrations in the range (0.1-1.5) × 10 -5 M, and pH in the range 2.5-3.0. Interpretation of the experimental data is supported by kinetic computer simulations. The rate constants 6 × 10 9 M -1 s -1 e k e 1.2 × 10 10 M -1 s -1 and < 1 × 10 5 M -1 s -1 were determined for the reactions of Cl • and Cl 2 •-with benzene, respectively, in the aqueous phase. The organic radicals produced from these reactions exhibit an absorption band with maximum at 300 nm, which was assigned to a Cl-cyclohexadienyl radical (Cl-CHD). The kinetic analysis of the traces supports a reversible reaction between O 2 and Cl-CHD. A reaction mechanism leading to the formation of chlorobenzene is proposed.

The photophysics and photochemical behavior of the phenoxazin‐3‐one dyes, resazurin and resorufin, have been studied in aqueous solutions. The irradiation of resazurin in the presence of amines leads to deoxygenation of the N‐oxide group, giving resorufin. This photoreaction is highly dependent on the amine structure and is efficient only in the presence of tertiary aliphatic amines. The absorption and fluorescence properties of these dyes are dependent on pH. At pH above 7.5 both dyes are in their anionic form. For resorufin this form is highly fluorescent (ΦF= 0.75). At lower pH the fluorescence is strongly reduced. The N‐oxide dye presents a very weak fluorescence quantum yield (0.11), which also is reduced at low pH. Flash photolysis experiments allowed characterization of the triplet state and the transients formed after irradiation of these dyes in the absence and presence of amines. The triplet quantum yields are 0.08 for resazurin and 0.04 for resorufin. The photodeoxygenation of N‐oxide in the presence of amines occurs from the triplet state.

Laser and conventional flash photolysis of Na 2 S 2 O 8 aqueous solutions containing Clions were employed to investigate the reactions of chlorine atoms and Cl 2 •radical ions with toluene, benzoic acid, and chlorobenzene. A mechanism is proposed which accounts for the faster decay of Cl 2 •in aqueous solutions containing increasing concentrations of the organic substrates. Interpretation of the experimental data is supported by kinetic computer simulations. Chlorine atoms react with the three substituted aromatics studied here almost with diffusioncontrolled rate constants, k ) (1.8 ( 0.3) × 10 10 M -1 s -1 . The high reactivity observed for Cl atoms contrasts with that of the Cl 2 •radical ions, for which the rate constant for its reactions with the substituted benzenes is e 1 × 10 6 M -1 s -1 . The organic radicals produced from these reactions, as well as the nature of the reaction products are discussed. The observed results seem to support an addition mechanism yielding chlorocyclohexadienyl radicals (Cl-CHD) as the most significant reaction channel following reaction of Cl atoms and the organic compounds. In air-saturated solutions, subsequent thermal reactions of Cl-CHD radicals lead both to chlorination and oxidation of the aromatics.