Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Abstract

Abstract. The interactions between benzophenone triplet state and halide anion species (Cl−, Br− and I−) have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements provided rate constants, kq (M−1 s−1), close to diffusion controlled limit for iodide (~8×109 M−1 s−1), somewhat less for bromide (~3×108 M−1 s−1) and much lower for chloride (>106 M−1 s−1). The halide (X−) quenches the triplet state, and a product, having a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X2−). We therefore suggest that such reactive quenching can be a photosensitized source of halogen in the atmosphere and represents a driving force for the chemical oxidation of the oceanic surface.