ELECTRONIC-STRUCTURE OF BARIUM-DOPED C-60

We have investigated the electronic structure of Ba-doped C-60 films w ith Pa concentrations of up to x approximate to 12 (BaxC60) by applyin g valence-band photoemission and x-ray-absorption spectroscopy. A crys tal orbital (CO) formalism based on a semiempirical Hamiltonian of the intermediate-neglect-of-differential-overlap type has been employed t o derive solid-state results for the Ba-doped C-60 fullerides. Using x -ray diffraction, we show three distinct phases for the bulk BaxC60 sy stem with Ba concentrations of up to x=6. In all cases, the experiment al observations strongly indicate that fulleride formation leads to th e occupation of hybrid bands on both sides of the Fermi level. The the oretical data indicate that the alkaline-earth atoms are essentially m onovalent and hybridize strongly with the pi-type functions of the C-6 0 network. The Ba atoms in the BaxC60 fullerides deviate from the limi t of complete charge transfer as a consequence of the competition betw een covalent Ba-C-60 bonding and ionic contributions. Furthermore, it is shown that the calculated density-of-state profiles reproduce the p hotoemission data in the extreme outer valence-band region.