EXCITATION OF COLLECTIVE PLASMON STATES IN FULLERENES

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