ELECTRON-ENERGY-LOSS SPECTRA OF FULLERENE C-60 IN THE GAS-PHASE

Electron energy-loss spectra Of gaseous fullerene C60 were measured in the energy-loss range 1-10 eV and with residual energies E(r) from 0.08 to 20 eV. The spectrum recorded with E(r)=20 eV, with distinct bands at 2.24, 3.77, 4.88 and 6.1 eV, resembles the UV absorption spectrum except for a higher relative intensity of the lowest band at 2.2 eV. The 6.1 eV band correlates with a 6.4 eV band observed in solid state EELS and confirms the single molecule nature of this excitation (collective excitation of the pi electrons) in the solid. In spectra recorded at lower E(r), where forbidden transitions are further enhanced, the relative intensity of the 2.2 eV band increases further, and a sharp peak emerges at 2.98 eV. Additional signals are recorded around 3.4 and 4.4 eV, without forming new distinct bands. The lowest triplet state, reported at 1.6 +/- 0.1 eV, is missing in the present spectra. Possible transition assignments of the EEL spectra are discussed. Comparison of gas phase and solid state spectra permits identification of solid state specific features.