Poster

On Graphene in Space

¹Xiuhui Chen, ²Aigen Li, ¹Joanxin Zhong (¹Xiangtan University, ²University of Missouri)

The 217.5 nm interstellar extinction bump, the most prominent spectroscopic absorption feature in the interstellar extinction curve, remains unidentified sicne its first detection in 1965 (Stecher 1965, ApJ, 142, 1681). It was originally attributed to graphite (Stecher & Donn, 1965, 142, 1683). But graphite fails to simultaniously account for both the stability of the central wavelength of the bump and the variation of the bump width. More recently, polycyclic aromatic hydrocarbon (PAH) molecules have been suggested as a candidate (Joblin et al. 1992, ApJ, 393, L89, Li & Draine 2001, ApJ, 554, 778, Steglich et al. 2011, ApJ, 712, L16). Although PAHs do have a strong absorption band around 200nm due to the pi-pi* electronic transition, individual PAHs also show other sharp absorption features which are not observed in the interstellar space.

In this work we examine graphene as a potential candidate for the mysterious 217.5nm extinction bump. Graphene could arise from PAHs through a complete loss of their H atoms (Berne & Tielens, 2012, PNAS, 109, 401) or from graphite through fragmentation (grain-grain shattering). Both quantum-chemical computations and laboratory experiments have shown that the pi-pi* electronic transitions cause a strong absorption band near 217.5nm (trevisanutto et al. 2010, Phys. Rev. B, 81, 121405; Nelson, et al. 2010, Appl. Phys. Lett., 97, 253110).

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