On the photochemistry of aqueous solutions of chloride, bromide, and iodide ions

The photochemistry of aqueous solutions of Cl^-, Br^-, I^- and OH^- was investigated at 2537, 2288, and 1849 Å., in the temperature range 5-37°. The excited halide ions dissociate into a halogen atom and a solvated electron. Scavengers for solvated electrons, such as H₃O⁺, N₂O, or acetone compete with the secondary diffusive recombination of these but do not interact with the spectroscopic excited state. Cl atoms dehydrogenate ethanol and methanol, while I atoms appear to be unable to do so at all wave lengths. For Br atoms, however, the results indicate that at 2288 Å., formed in their lower energy ²P_3/2, state, they do not dehydrogenate the scavengers but may be able to do so when formed in the higher energy ²P_1/2 state at 1849 Å. The effects of temperature, wave length, added salt, and type of halide ion indicate that the atom-electron pair is formed from the excited ion in a distinct step. This process, essentially one of charge asymmetrization, competes with the deactivation of the excited ion. The value of the limiting constant quantum yield, T, obtained at high scavenger concentrations depends on this competition.