RAMAN-SCATTERING AND LATTICE-DYNAMICS OF FULLERIDES MXC60

A review of our investigations of Raman spectra of intramolecular and external modes in pristine and doped fullerene C60 is given. Experimental results are compared with group-theoretical predictions. In low-frequency spectra of M6C60 new bands are found that we have assigned to external modes. An intepretation of M6C60 external modes and lattice dynamics calculations are carried out. From an analysis of the excitation profile of resonant Raman spectra it is found that expected changes of internuclear distances in the excited state of C60 should be close to the form of the A(g) mode at 1468 cm-1. Moreover, a destructive interference of A(g) modes in M3C60 and M6C60 is observed. The essential broadening, a shift and the Fano lineshape of low-frequency intramolecular H(g) bands in metallic M3C60 are found. A narrowing of these bands in insulating C60 and M6C60 indicates the strong electron-phonon interaction of H(g) Jabn-Teller modes. An estimation of the electron-phonon coupling constants for some modes is given. A possible origin of low-energy electronic excitations appearing in M3C60 resonant Raman spectra at lambda(i) = 1064 nm excitation is discussed.