ELECTRONIC AND GEOMETRIC STRUCTURE OF LA-AT-C-82 AND C-82 - THEORY AND EXPERIMENT

Core-level and valence-band photoemission studies of films of La@C82 a nd C82 demonstrate charge transfer from La to the fullerene cage and t he formation of a nonmetallic solid with the uppermost band centered 0 .64 eV below the Fermi level. Comparison to results for C82 demonstrat es that there are modifications to the electronic-state distribution t hroughout the valence band. Bonding of the molecular radicals in the p ure solid is found to be significantly stronger than in empty fulleren e solids which sublime at much lower temperatures. Detailed calculatio ns for isolated La@C82 molecules allow comparison with the experimenta l results. They show the tendency of the La ions to move from the cent er of the molecule toward the cage. Comparisons of calculations for La @C82 based on C3, and C2 structures show that much of the energy diffe rence between the two structures is lost upon La incorporation. Bond-l ength analyses allow comparison with extended x-ray-absorption fine-st ructure data for the metal-carbon coordination which has been measured for Y@C82. They show sizable La-induced effects on the structure of t he carbon cage in the proximity of the La ion.