  For field-effect-doped fullerenes it was reported that the superconducting
transition temperature Tc is markedly larger for C60.2CHX_3 (X=Cl, Br)
crystals, than for pure C60. Initially this was explained by the expansion of
the volume per C60-molecule and the corresponding increase in the density of
states at the Fermi level in the intercalated crystals. On closer examination
it has, however, turned out to be unlikely that this is the mechanism behind
the increase in Tc. An alternative explanation of the enhanced transition
temperatures assumes that the conduction electrons not only couple to the
vibrational modes of the C60-molecule, but also to the modes of the
intercalated molecules. We investigate the possibility of such a coupling. We
find that, assuming the ideal bulk structure of the intercalated crystal, both
a coupling due to hybridization of the molecular levels, and a coupling via
dipole moments should be very small. This suggests that the presence of the
gate-oxide in the field-effect-devices strongly affects the structure of the
fullerene crystal at the interface.
