Spectroscopy of Interstellar PAHs and Carbon Molecules and Ions: Bridging Astronomy and Laboratory Astrophysics.

Details Spectroscopy of Interstellar PAHs and Carbon Molecules and Ions: Bridging Astronomy and Laboratory Astrophysics. Spectroscopy of Interstellar PAHs and Carbon Molecules and Ions: Bridging Astronomy and Laboratory Astrophysics.

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.0320s&link_type=abstract

American Astronomical Society, AAS Meeting #212, #3.20; Bulletin of the American Astronomical Society, Vol. 40, p.187

Astronomy and Astrophysics

Astrophysics

1

Scientific paper

PAHs are a ubiquitous component of carbonaceous materials in space. PAHs are the best-known candidates to account for the IR bands. They are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). A major challenge is to reproduce in the laboratory the physical conditions that exist in the emission and absorption interstellar zones. We present spectra of neutral and ionized PAHs measured in the UV-NIR range in astrophysically relevant environments. The harsh physical conditions of the ISM -low temperature, collisionless, strong UV radiation fields- are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion.
The spectra are measured using high-sensitivity cavity ring down spectroscopy. The bands measured for ionized PAH are intrinsically broad (> 20 cm-1) while the bands associated with the neutral precursors are narrower (2-10 cm-1). The laboratory data are discussed and compared with astronomical spectra of DIBs and with the spectra of CS environments of selected carbon stars and the implications for the IS PAH population are derived. Carbon nanoparticles are also formed during the short residence time of the precursors in the plasma and are characterized with time-of-flight mass spectrometry. This finding holds great potential for understanding the formation process of interstellar grains. These experiments provide unique information on the spectra of free, large carbon molecules and ions in the gas phase. We are now in a position to directly compare laboratory spectra of free, cold, PAH ions and carbon particles with astronomical observations in the UV-NIR range (UV extinction, DIBs). This new phase offers tremendous opportunities for the data analysis of space missions geared toward the detection of large aromatic molecules (COS/HST, JWST).
Acknowledgements: This work is supported by NASA SMD (Planetary Science and APRA R&A Programs).

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