On buckyonions as a carrier of the 2175 Å interstellar extinction feature

In recent years buckyonions have been suggested as a carrier of the 2175 Å interstellar extinction feature, based on the close similarity between the electronic transition spectra of buckyonions and the 2175 Å interstellar extinction feature. We examine this hypothesis by calculating the interstellar extinction with buckyonions as a dust component. It is found that dust models containing buckyonions (in addition to amorphous silicates, PAHs, graphite or amorphous carbon) can closely reproduce the observed interstellar extinction curve. However, a more severe challenge to the buckyonion hypothesis is provided by the non-detection of the ~7-8 μm C-H stretching bands expected from buckyonions in the diffuse interstellar medium. This will allow us to place an upper limit on the abundance of buckyonions.