Experimental band gap and core-hole electron interaction in epitaxial C-60films

This work employs a common experimental energy scale for photoemission, inv erse photoemission, and x-ray absorption data, which is essential for a rel iable experimental determination of energy separations (gaps) between occup ied and empty states of solids. For epitaxial layers of C-60 prepared on la yered VSe2 single crystals we demonstrate a good agreement between experime nt and previous quasiparticle calculations of the HOMO-LUMO distance and th e band gap. Comparison of inverse photoemission and x-ray absorption data f rom the same sample on a common energy scale shows that conduction-band sta tes cannot be derived from absorption data and enables us to determine the direct experimental value of the core-hole electron interaction U in solid C-60. [S0163-1829(98)08743-8].