Electron transfer from Gd ions to the C cage in endohedral Gd@C82 probed by resonant photoemission spectroscopy

The charge transfer from Gd ions to C cage in endohedral Gd@C82 is probed by resonant photoemission spectroscopy. A careful data analysis shows that only one feature, ascribed to the 4f electron emission resonates across the Gd 4d?4f edge. The lack of the resonating spectral weight from the Gd 6s2 or 5d6s states, which in turn are detected in the resonant photoemission spectrum of metallic Gd and the binding energy of the 4f-1 resonating structure in valence band are the proof of an ionic picture (Gd3+) of the Gd-C bond. By fitting the integrated intensity of the 4f-1 structure with a Fano line shape, the time scale of the resonance process resulted to be of the order of 1.26×10-16 s.