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

The method of laser flash photolysis with excitation at 308 nm was used to study the photochemistry of persulfate-ion in aqueous solutions with additi ons of N,N-dimethylformamide (DMF). The photolysis of S2O82- in water gives rise to SO4.- radical anions with a 0.55 quantum yield. The rate constant of SO4(.-) recombination was measured (2k=(2.7+/-0.2) x 10(9) M-1 s(-1) at ionic strength mu=0.9 M). In the presence of DMF the additional intermediat e absorption band appears with a maximum at 380 nm, belonging to radical (C H2)-C-. (CH3)NCHO. Its extinction coefficient was determined (epsilon(380), 1700 +/- 200 M-1 Cm-1). The rate constants of reactions S04(.-)S+MF((4.3 +/ - 0.2) x 10(8) M-1 s(-1)) and (CH2)-C-.(CH3)NCHO + O-2((1.3 +/- 0.1) X 10(9 ) M-1 S-1) Were measured. Thus, DMF is a good acceptor of active radicals ( e.g.,(OH)-O-. radical) which have absorption in the far UV region and which are impossible to detect directly in purse photochemical experiments. (C) 2000 Elsevier Science S.A. All rights reserved.