SPIN DENSITIES IN TRIPLET BENZOPHENONE

The lowest photoexcited triplet state of benzophenone in single crystals of 4,4́-dibromodiphenyl ether has been studied by optically detected ENDOR. The hyperfine coupling tensors for eight protons and carbonyl-13C have been determined by analyzing the angular dependence of the ENDOR spectra. A point-dipole model is presented to account for the anisotropic hyperfine tensor elements based solely on spin densitites and molecular geometry. A set of spin densities and a ring-twist angle have been found which, together, best reproduce the observed dipole interaction tensors as calculated from our model. Data from zero-field ODMR experiments on 17O-benzophenone performed by S. Yamauchi and D. W. Pratt at the University of Pittsburgh enabled us to remove the correlation between n and π spin densities on oxygen. A final fit of all data shows the n electron to be localized on oxygen and the π electron to be delocalized onto the rings. © 1979 American Institute of Physics.