Electronic Excitations and Stability of the Ground State of C60 Molecules

A model study of the singlet excitons in the C60 molecule with emphasis on the Coulomb interaction between excited electron and hole leads to a physical understanding of the interaction effects on the absorption spectra and to a new identification of the forbidden excitons in the third-harmonic generation spectra. These conclusions may be tested experimentally on the model predictions related to the optical Kerr effect. The model shows that, with sufficiently strong interatomic than onsite interaction, a T_{2G} exciton could have very low energy or become unstable against the closed-shell ground state. Properties of these interesting cases beyond the C60 are briefly examined.