  The carrier of the 2175 Angstrom interstellar extinction feature remains
unidentified since its first detection over 40 years ago. In recent years
carbon buckyonions have been proposed as a carrier of this feature, based on
the close similarity between the electronic transition spectra of buckyonions
and the 2175 Angstrom interstellar feature. We examine this hypothesis by
modeling the interstellar extinction with buckyonions as a dust component. It
is found that dust models containing buckyonions (in addition to amorphous
silicates, polycyclic aromatic hydrocarbon molecules, graphite) can closely
reproduce the observed interstellar extinction curve. To further test this
hypothesis, we call for experimental measurements and/or theoretical
calculations of the infrared vibrational spectra of hydrogenated buckyonions.
By comparing the infrared emission spectra predicted for buckyonions
vibrationally excited by the interstellar radiation with the observed emission
spectra of the diffuse interstellar medium, we will be able to derive (or place
an upper limit on) the abundance of interstellar buckyonions.
