Electronic states and stability of the insulatingRbC60dimer phase

Photoelectron spectra for the quenched, metastable dimer phase of ${\mathrm{RbC}}_{60}$ show states derived from the lowest unoccupied molecular orbital of ${\mathrm{C}}_{60}$ in an ∼0.5-eV-wide feature centered ∼1 eV below the Fermi level ${\mathit{E}}_{\mathit{F}}$. The onset of emission at ∼0.6 eV establishes a minimum gap for defect-free material. Identification of a signature for the dimer state has implications for the interpretation of previous photoemission experiments.