Three-dimensional electron momentum densities of graphite and fullerene: acomparison

We report on the three-dimensional electron momentum densities (EMD) of gra phite and fullerene obtained by a so-called (gamma, e gamma) experiment, i. e. the coincident detection of an inelastically scattered hard x-ray photon with its recoil electron. A monochromatized flux of 10(12) photons s(-1) a t 150 keV from the high-energy x-ray wiggler beamline of the ESRF was direc ted onto thin graphite or fullerene targets. Comparison with a pseudopotent ial and a full-potential linear muffin-tin orbital calculation in the case of graphite is made. Inclusion of electron correlation via the Lam-Platzman correction is discussed. The experimental EMD of C-60 shows stronger elect ron delocalization in the 'buckyball' compared to graphite, which is suppor ted by theory.