  A theory of optical excitations by using a tight binding model with
long-range Coulomb interactions is developed. The model is applied to a C60
molecule and a cluster, and is treated by the Hartree-Fock approximation
followed by a configuration interaction method. Lattice fluctuations are taken
into account by a bond disorder model. We first examine what strength of
Coulomb interaction is appropriate to describe the electronic structures
observed by photo-electron and optical absorption spectroscopy. Then, we
demonstrate that the photo-excited states are mainly intramolecular (i.e.
Frenkel) excitons with small charge-transfer components. We examine to what
extent the dipole forbidden transitions of a single C60 molecule become
dipole-allowed by lattice fluctuations or intermolecular interactions.
