  We theoretically investigate optical absorption spectra of $\soc^{6-}$ and
$\rug^{6-}$, and discuss relations with the optical properties of alkali metal
doped fullerides $A_6\soc$ and $A_6\rug$. This is a valid approach for systems
where Frenkel exciton effects are dominant. We use a tight binding model with
long ranged Coulomb interactions and bond disorder. Optical spectra are
obtained by the Hartree-Fock approximation and the configuration interaction
method. We find that the Coulomb interaction parameters, which are relevant to
the optical spectra of $A_6\soc$ ($A_6\rug$) in order to explain the excitation
energies and relative oscillator strengths of absorption peaks, are almost the
half of those of the neutral $\soc$ ($\rug$). The reduction of the effective
Coulomb interactions is concluded for the heavily doped case of $\soc$ and
$\rug$. This finding is closely related with the experimental fact that
dielectric constants of fullerides which are maximumly doped with alkali metals
become about twice as large as those of the neutral systems.
