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11 g 1238 1384 J 1481

11 g 1238 1384 J 1481

800 1000 1200 1400 1600 Raman Shift (cm' )

Fig. 11.22. Unpolarized Raman spectra (T = 300 K) for solid C«,, K3CHI, RbjC«,, NasCffl, K^Cso, Rb6CM and CsjC^ [11.3,15]. The tangential and radial modes of Ag symmetry are identified, as are the features associated with the Si substrate. From these spectra it is con-

the interactions between the CM molecules and the alkali metal ions.

As a result of alkali metal doping, electrons are transferred to the tt electron orbitals on the surface of the C60 molecules, elongating the C-C bonds and downshifting the intramolecular tangential modes. A similar effect was noted in alkali metal-intercalated graphite, where electrons are transferred from the alkali metal M layers to the graphene layers [11.116]. The magnitude of the mode softening in alkali metal-doped C60 is comparable (~60% of that for alkali metal-doped graphite intercalation compounds) and can be explained semiquantitatively by a charge transfer model [11.117]. Referring to Fig. 11.24, the dependence of the Raman frequencies on alkali

Fig. 11.23. Breit-Wigner-

the Raman-active Hg( 1) mode for KjQo for both polarizations

HH(||, II) and HV(||,_L). Also shown are two components for

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