Ultraviolet photoelectron spectra of metallofullerenes, two Ca@C-82 isomers

Ultraviolet photoelectron spectra (UPS) of two Ca@C-82 isomers (III and IV) were measured with a synchrotron radiation light source. The photoelectron onset energies of isomers III and IV were 0.7 and 0.8 eV below the Fermi l evel, respectively, which indicates their semiconductive nature. When the e xcitation energy is tuned, spectral intensity changes as other fullerenes h ave shown. Their upper valence band (0-5 eV) spectra are different from tho se of other metallofullerenes such as La@C-82,Sc@C-82 and Gd@C-82 as well a s those of empty C-82 but their lower valence band spectra (below 5 eV) are almost identical. Comparison between the UPS and ab initio calculation ass uming transfer of two electrons from encapsulated calcium atom to the cage (i.e. Ca+2@C-82(-2)) suggests C-2(c) geometry for isomer III and C-s for is omer IV. (C) 2001 Elsevier Science B.V. All rights reserved.