Ups of buckminsterfullerene and other large clusters of carbon

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: C50(0.3–0.6 eV), C60 (1.5–2.0 eV), and C70 (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 (C60) 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 C60.