Laser flash photolysis of sodium persulfate in aqueous solution with additions of dimethylformamide

Abstract

The method of laser flash photolysis with excitation at 308 nm was used to study the photochemistry of persulfate-ion in aqueous solutions with additions of N, N-dimethylformamide (DMF). The photolysis of S 2O 8 2− in water gives rise to SO 4 − radical anions with a 0.55 quantum yield. The rate constant of SO 4 − recombination was measured (2 k=(2.7±0.2)×10 9 M −1 s −1 at ionic strength μ=0.9 M). In the presence of DMF the additional intermediate absorption band appears with a maximum at 380 nm, belonging to radical CH 2(CH 3)NCHO. Its extinction coefficient was determined ( ε 380=1700±200 M −1 cm −1). The rate constants of reactions SO 4 − +DMF((4.3±0.2)× 10 8 M −1 s −1 ) and CH 2 (CH 3 )NCHO+O 2 ((1.3±0.1)× 10 9 M −1 s − 1 ) were measured. Thus, DMF is a good acceptor of active radicals (e.g., OH radical) which have absorption in the far UV region and which are impossible to detect directly in pulse photochemical experiments.