Charge transfer in alkali-metal-doped polymeric fullerenes

We present room-temperature Raman measurements of pressure-polymerized ${\mathrm{C}}_{60}$ and compare them with the spectra of Rb${\mathrm{C}}_{60}$ in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized ${\mathrm{C}}_{60}$ and the rubidium-doped orthorhombic compound, have the same overall structure and the $A{\mathrm{C}}_{60}$ compounds can be considered as the doped species of the ${\mathrm{C}}_{60}$, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency $H_g\mathrm{}\left(7\right)\mathrm{}$ and $H_g\mathrm{}\left(8\right)\mathrm{}$ modes. The low values for the coupling constants compared to the ones in the ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ can explain the lack of superconductivity in the $A{\mathrm{C}}_{60}$ compounds.