EXTERNAL MAGNETIC-FIELD AND MAGNETIC ISOTOPE EFFECTS UPON THE LIFETIMES OF BIRADICALS DERIVED FROM BENZOPHENONE DERIVATIVES

The decay profile of several isotope-labelled biradicals containing a benzophenone ketyl and a hydrogen-donor radical has been examined by m eans of nanosecond laser flash photolysis in the presence of an extern al magnetic field. Noticeable magnetic isotope effects are observed on the decay kinetics: deuteration of the particular C-H bond in the hyd rogen donor results in retardation of the biradical recombination, whe reas C-13 substitution of the benzylic carbon in the hydrogen donor sh ortens the biradical decay time. The observed results can be interpret ed in terms of the relaxation mechanism and molecular motion.