Electron-momentum spectroscopy of fullerene

The energy-resolved electron-momentum density of fullerene has been measured. Clear differences are found from the energy-momentum densities of either diamond or graphite. The energy-momentum density of fullerene can be described as being composed of a $\sigma$ band and a split $\pi$ band. The observed spectral momentum densities are compared to the calculated orbitals of a C${}_{60}$ molecule in momentum space. Good agreement is found. A simple classification of the orbitals is proposed that explains elegantly the calculated and observed structures. The splitting of the $\pi$ band can be interpreted as a consequence of the curvature of the carbon network forming the fullerene molecule.