RAMAN-SCATTERING IN C-60 AND ALKALI-METAL-DOPED C-60 FILMS

The Raman-active modes of solid films of C60 and MxC60 (x-6; M = K, Rb, Cs) have been studied experimentally. The mode activity is dominated by intraball interactions, and the effect of the M+ ions on the C60 spectrum is observed to be almost insensitive to the radius or mass of the alkali metal. The tangential modes of solid C60 are observed to soften in M6C60 by -60 cm-1, which can be attributed to a charge-transfer-induced elongation of the intraball bond lengths, similar to that observed in graphite intercalation compounds. Conversely, the radial modes are found to upshift slightly, indicating that a competing mechanism counteracts the effect of the bond elongation.