LOW-ENERGY EXCITATIONS OF NEUTRAL C60

Low-energy excited states of a neutral C60 molecule are studied in detail. The system is described by a Su-Schrieffer-Heeger Hubbard-type Hamiltonian which is solved perturbatively in the electron-electron interactions. The optical-absorption spectrum is computed including both the direct and one-phonon-induced processes. Electronic-correlation effects are qualitatively important and, if and only if the electron-electron interaction is taken to be large enough, good agreement with experiments is achieved. Furthermore, it is shown that, in this model, the lowest-energy spin-triplet state is stable against decay due to a large Coulomb binding. Also, the theory predicts a triplet-triplet band about at 0.45 eV which, to my knowledge, has not yet been observed experimentally.