UPS of Buckminsterfullerene and other large clusters of carbon

Abstract Ultraviolet photoelectron spectra (UPS) are reported for mass-selected negative carbon clusters extracted from a pulsed supersonic beam. In the size range from 48 to 84 atoms, three clusters were found to be closed-shell species with appreciable HOMO-LUMO gaps: C 50 (0.3–0.6 eV), C 60 (1.5–2.0 eV), and C 70 (0.7–1.2 eV). UPS data for all other clusters revealed no appreciable HOMO-LUMO gap, indicating they are either open-shell species, or closed-shell species with small HOMO-LUMO gaps. Buckminsterfullerene (C 60 ) was found to have the lowest electron affinity (2.6–2.8 eV) of any cluster. Agreement between these UPS data and electronic structure calculations strongly support the spheroidal shell model for C 60 .