Molecular- and atomic-like photoionization of C₆₀ in the extreme ultraviolet

Photoion yield spectra of C₆₀ in the gas phase were measured from 23 to 180 eV by synchrotron radiation. Two peaks at 26 and 34 eV and a flat area ranging 40-50 eV are newly observed in the high-energy side of the giant resonance at ∼20 eV. These features are assigned to the shape resonance on photoionization of the valence electrons of C₆₀; the ionized electron is temporarily trapped inside a centrifugal barrier. Above ∼50 eV the yield curve shows a steady decrease with increasing photon energy like the photoabsorption cross section of atomic carbon. Thus, the spectrum is interpreted as essentially determined by photoionization of the 2s orbitals of carbon atoms.