EXCITATION OF COLLECTIVE PLASMON STATES IN FULLERENES

We present theoretical and experimental electron-energy-loss spectroscopy results concerning the excitation of collective plasmon states in isolated fullerenes (gas targets). The large number of active electrons in a carbon cluster and the strong Coulomb interaction among them lead to a rich spectrum of collective states. States with total angular momentum up to L = 8HBAR have a strong collective character. The equivalents of both pi and sigma plasmons in graphite are predicted for a whole range of carbon clusters C20, C60, C70, and C100. The theoretical results compare very well with experimental photoexcitation results in C60 and C70 and EELS data on gas targets C60 and C70.