We present inelastic neutron scattering (INS) and Raman results on Rb 1 C 7 0 powders. Well-structured INS intensities are observed in the gap region which separates internal from external vibrations in monomer fullerene compounds. These intensities constitute strong spectroscopic evidence for the formation of charged (C 7 0 ) 2 - 2 dimers in Rb 1 C 7 0 . Above 400 K the amount of dimers is found to decrease with temperature. However, no transition to a pure rotator phase is observed up to 500 K indicating a remarkably high stability of the C 7 0 dimers. The dimer formation is fully reversible.