THE METALLOFULLERENE TM-AT-C-82 - ISOMER-SELECTIVE ELECTRONIC-STRUCTURE

We present studies of the electronic structure and the optical propert ies of the endohedral monometallo-fullerene Tm@C-82 using photoemissio n and electron energy-loss spectroscopy in transmission. In particular , the impact of the isomer symmetry of the C-82 cage (C-s or C-3v) On the electronic structure and on the optical properties is analysed in detail. For both isomers, combined XPS and XAS measurements of the Tm 4f and 4d states offer conclusive proof of a divalent encaged Tm ion. No significant change of the valence of the ran earth ion upon changes in the cage symmetry is observed. From the C 1s excitation spectra we find a more pronounced LUMO for the C-3v(8) isomer, as is expected fo r the higher symmetry of the cage. Additional information about the op tical properties was obtained from the low-energy loss function. With use of a Kramers-Kronig analysis, the dielectric function, epsilon, an d the optical conductivity, sigma, have been derived. epsilon(0) and t he onset of the spectral weight are found to be 7.7 [12.8] and 0.6 eV [0.8 eV] for the C-s(6) (C-3v(8)} isomer, respectively.