SPIN DENSITY OF TRIPLET BENZOPHENONE

Abstract

Spin distribution in the lowest triplet state of benzophenone has been an interesting problem foe $^research^{1,2}$ The debate centers on the extent of delocalization of the unpaired spin into the aromatic rings. Attempts to calculate spin densities have been hampered by the unavailability of excited state geometry. We have conducted an ENDOR investigation of benzophenone using both the proton and the carbonyl $^{13}C$. With this approach one can calculate the geometry and spin distribution simultaneously in a self-consistent manner. We have taken $4,4^{\prime}$ -dibromo-diphenylether as our host crystal. The $^{13} C$ experiment was difficult, but it distinguished between the choices of sign for the hyperfine tensor components. of Hochstrasser et. $al^{1}$ The proton ENDOR shifts are large in comparison with those in benzil, suggesting a substantially greater delocalization of the unpaired electrons. A quantitative model of spin distribution in benzophenone will be discussed.