Electron-energy-loss studies of ${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{C}}_{70}$ (x=0, 3, and 6)

The electronic structure of undoped and Rb-doped ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ has been studied by high-energy electron-energy-loss spectroscopy in transmission. Excitations of valence and core electrons reveal the occupation of bands derived from the lowest unoccupied molecular orbitals upon n-type doping of the solid fullerenes. Detailed information on the electronic structure of π and σ electrons is provided.