Raman scattering and electron-phonon coupling in ${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{C}}_{60}$

In situ, interference-enhanced Raman scattering of ultrathin, solid solution films of ${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{C}}_{60}$ (0≤x≤3) prepared in UHV are reported. Variations of phonon linewidths of both selected low-frequency, radial and high-frequency, tangential intramolecular modes indicate strong electron-phonon coupling. The results directly support a recent theory for phonon-mediated superconductivity in alkali-${\mathrm{C}}_{60}$ systems.