The 217.5 nm band, infrared absorption and infrared emission features in hydrogenated amorphous carbon nanoparticles

Abstract

We report on the preparation of hydrogenated amorphous carbon nano-particles whose spectral characteristics include an absorption band at 217.5 nm with the profile and characteristics of the interstellar 217.5 nm feature. Vibrational spectra of these particles also contain the features commonly observed in absorption and emission from dust in the diffuse interstellar medium. These materials are produced under slow deposition conditions by minimizing the flux of incident carbon atoms and by reducing surface mobility. The initial chemistry leads to the formation of carbon chains, together with a limited range of small aromatic ring molecules, and eventually results in carbon nano-particles having an sp2/sp3 ratio = 0.4. Spectroscopic analysis of particle composition indicates that naphthalene and naphthalene derivatives are important constituents of this material. We suggest that carbon nano-particles with similar composition are responsible for the appearance of the interstellar 217.5 nm band and outline how these particles can form in situ under diffuse cloud conditions by deposition of carbon on the surface of silicate grains. Spectral data from carbon nano-particles formed under these conditions accurately reproduces IR emission spectra from a number of Galactic sources. We provide the first detailed fits to observational spectra of Type A and B emission sources based entirely on measured spectra of a carbonaceous material that can be produced in the laboratory.

69 pages, 11 figures, accepted for publication in ApJ

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Cited by in corpus (6)

• Observational Constraints on the Physical Properties of Interstellar Dust in the Post-Planck Era
• On the viability of the PAH model as an explanation of the unidentified infrared emission features
• Polyaromatic disordered carbon grains as carriers of the UV bump: FUV to mid-infrared spectroscopy of laboratory analogs
• Simulating the structural diversity of carbon clusters across the planar to fullerene transition
• The evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
• Hydrogenated amorphous carbon grains as an alternative carrier of the 9$-$13$\mu$m plateau feature in the fullerene planetary nebula Tc 1