Shake-up effects and intermolecular tunneling in C60 ions.

The multiplet structure induced by the Coulomb interactions in ${\mathrm{C}}_{60}$${\mathrm{}}^{\mathit{n}\mathrm{\ensuremath{-}}}$ (n=1\char21{}12) is analyzed. The lowest partially occupied molecular orbital gives rise to a set of levels that fill a relatively wide band (\ensuremath{\approxeq}2\char21{}3 eV). A large (\ensuremath{\sim}1 eV) intramolecular effective repulsion is found. The anions are also shown to be highly polarizable. The optical-absorption and photoemission spectra are calculated. The probability of exciting the molecule upon the addition or removal of one electron is shown to be significant, and this effect may give rise to the insulating behavior of ${\mathrm{K}}_{4}$${\mathrm{C}}_{60}$. The role of intermolecular interactions in suppressing the net repulsion within the ${\mathrm{C}}_{60}$ molecules is discussed.