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Spectroscopy of Jet-Cooled Neutral and Ionized PAHs: Implications for Interstellar DustWe present the gas-phase spectroscopy of neutral and ionized polycyclic aromatic hydrocarbons (PAHs) measured in the W-Visible-NIR range in an astrophysically relevant environment. These measurements provide data on PAHs and nanometer sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laborat'ory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature ($\sim lOO$-K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS) and multiplex integrated cavity output spectroscopy (MICOS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. The electronic bands measured for ionized PAH are found to be intrinsically broad ($\geq$20 cm$^{-l}$) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10 cm$^{-l}$). The laboratory data are discussed and compared with recent astronomical spectra of large and narrow DIBs and with the spectra of circumstellar environments of selected carbon stars (see contribution of Cami et al.) and the implications for the interstellar PAH population are derived. Preliminary results also show that carbon nanoparticles are formed during the short residence time of the precursors in the plasma. This finding holds great potential for understanding the formation process of interstellar grains.
Document ID
20050184201
Acquisition Source
Headquarters
Document Type
Conference Paper
Authors
Salama, F.
(NASA Ames Research Center Moffett Field, CA, United States)
Tan, X.
(National Academy of Sciences - National Research Council Moffett Field, CA, United States)
Biennier, L.
(National Academy of Sciences - National Research Council Moffett Field, CA, United States)
Cami, J.
(National Academy of Sciences - National Research Council Moffett Field, CA, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2005
Subject Category
Astronomy
Meeting Information
Meeting: AAS 206th Meeting
Location: Minneapolis, MN
Country: United States
Start Date: May 29, 2005
End Date: June 2, 2005
Sponsors: American Astronomical Society
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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