OPTICAL PHONON MODES IN SOLID AND DOPED C-60

A review of our experimental studies on Raman- and infrared-active vibrational modes in solid and doped C60 films is presented and compared to group theoretical predictions. Results of Raman scattering and infrared transmission studies on pristine fcc films indicate that C60 should be viewed as a molecular solid with weak intermolecular coupling. Laser flux-dependent Raman scattering results for pristine C60 are presented which indicate that it is relatively easy to promote a photo-transformation of solid C60. Finally, Raman scattering studies on oxygen- and alkali metal (M)-doped C60, M(x)C60 (x = 3,6; M = K,Rb,Cs) are also presented. For the insulating M6C60 compounds, additional mode splitting due to the electric field of the cation sublattice is observed. The effect of the alkali metal doping on the Raman-active C60 modes is found to depend only weakly on the radius of the alkali metal ion. Thus, the principal role of the alkali metal dopant appears to be one of charge transfer and no evidence for significant M-C60 interactions is observed in the vibrational spectra. In the case of the metallic K3C60 compound, H(g)-derived C60 modes are observed to broaden relative to those in pristine C60 or M6C60. This observation is discussed in terms of the implications for superconductivity.