Ultraviolet photoelectron spectra of C82 and KxC82

Photoelectron spectra of C82, one of the newly isolated fullerene compounds, are measured with a synchrotron-radiation light source. The spectra resemble those of C84, and their spectral onset is at 1.15 eV below the Fermi level (EF). The first band is a broadband and consists of two peaks located at 2.2 and 3.3 eV. A slight structure is observed at the low-binding-energy side of the first band. The intensity of the two peaks of the band oscillates with the incident photon energy change, as is observed in C60, C70, and C84. The second band is located between 4 and 6.2 eV with a peak at 5.3 eV and an accompanying shoulder at the low-binding-energy side. The third band is located between 6.2 and 9 eV and consists of a peak at 7.8 eV and a distinct shoulder at 6.5 eV. Potassium dosing brings a new band between EF and the first band and its intensity grows as the potassium dosage increases. The spectral onset approaches EF in accordance with an increase of potassium dosage but it does not cross EF, which indicates the semiconductive nature of the potassium-dosed C82 complex. The spectra of low or high potassium dosage can be understood by the rigid-band model, but the spectral change at medium potassium dosage seems to support a nonrigid-band filling of the electrons from the potassium atoms.