MAGNETIC-FIELD EFFECTS ON THE PHOTOCHEMICAL HYDROGEN ABSTRACTION OF 2',3',4',5',6'-PENTAFLUOROACETOPHENONE IN A BRIJ-35 MICELLAR SOLUTION

Magnetic field effects (MFEs) on the photochemical hydrogen abstraction of 2',3',4',5',6'-pentafluoroacetophenone in a Brij 35 micellar solution were investigated by a nanosecond laser flash photolysis technique and compared with acetophenone. The decay rate of a radical pair generated in the reaction of acetophenone decreased with increasing magnetic field strength B from O T to 0.34 T, but was saturated by 0.34 T. On the other hand, the decay rate of the pair in the reaction of pentafluoroacetophenone decreased with increasing B from O T to 1.34 T. The difference in these MFEs is explained in terms of the electron spin relaxation of the radical pairs and the escape rate of the ketyl radicals from these pairs. The magnetic field dependence of these rate constants was obtained by an analysis of the time profiles of the transient absorbance of the ketyl radicals generated.