We present a theoretical result on the ultraviolet absorption of nanoscale graphite onions with a central void. The polarizability and the excitation cross section of particles in this geometry are obtained in the electrostatic (nonretarded) approximation and using a 'spherically uniaxial' dielectric tensor transported from planar graphite. We study the influence of the ratio r/R of the inner and outer radii on the extinction efficiency. It appears that the onion particles for r/R about 0.6 well reproduce the observed UV absorption bump of interstellar dust around 5.7 eV. We also investigate the effects of the hollow structure of the carbon particles on a second absorption peak around 18 eV.
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Henrard et al. (1993) studied this question.