The triplet wave function of C60 from W-band electron nuclear double resonance spectroscopy

Electron-nuclear double resonance spectra at 95 GHz and electron-spin-echo envelope-modulation spectra at 9.5 GHz are reported for a frozen solution of fully C-13 enriched C-60 molecules in their photoexcited triplet state. Analysis of these data reveals that the triplet wave function is largely localized on a part of the molecule. Upon excitation, the C-60 molecule adopts a structure of D-5d symmetry with four symmetry inequivalent carbon atoms. The equator atoms each carry 3.8% of the spin density and the atoms next to the equator 1.1%, together accounting for 98% of the total spin density. These pi-spin densities make the hyperfine interaction mainly anisotropic. A slight s-spin density on the equator atoms adds a sizable isotropic hyperfine coupling. The triplet wave function is calculated quantum-chemically and compared with the observed spin-density distribution. (C) 2000 American Institute of Physics. [S0021-9606(00)00716-9].