A FLASH PHOTOLYSIS STUDY OF 1‐METHYLINDOLE

Abstract

Abstract— The conventional flash photolysis of 1‐methylindole in aqueous media was studied at Λ excitation ≥290 nm. The transients observed 20 μs after excitation consisted mainly of the radical cation (R + ). the hydrated electron (e ‐ aq ) and the triplet state (T). Electron counting experiments indicate that photoionization is the only source of R + with e ‐ aq /R + = 1.07±0.09 in neutral media. Quenching of the R + yield with H + indicates that the fluorescent state is the precursor to 80% of the photoionization events with the remainder probably arising from a prefluorescent state. The triplet decays with a lifetime of 29 μs in deaerated neutral media. This decay is unchanged by N 2 O saturation, but T reacts with acrylamide with k ≥2.8 × 10 9 M ‐1 . In 2 M Br ‐ , R + and T yields are increased by factors of 2–3. Consideration of fluorescence quenching and T enhancement by Br‐permits an estimate of φ Isc between 0.33 and 0.49. The increased R + yield at high Br‐concentrations cannot be accounted for by induced photoionization or triplet state reactions.