Issue |
EAS Publications Series
Volume 46, 2011
PAHs and the Universe: A Symposium to Celebrate the 25th Anniversary of the PAH Hypothesis
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Page(s) | 109 - 115 | |
DOI | https://doi.org/10.1051/eas/1146011 | |
Published online | 30 March 2011 |
C. Joblin and A.G.G.M. Tielens (eds)
EAS Publications Series, 46 (2011) 109-115
The NASA Ames PAH IR Spectroscopic Database and the far-IR
1
NASA Ames Research Center, MS 245-6, Moffett Field, CA
94035,
USA
e-mail: Christiaan.Boersma@nasa.gov
2
NASA Ames Research Center, MS 230-3, Moffett Field, CA
94035,
USA
3
Department of Physics and Astronomy, PAB 213, The University of
Western Ontario, London, ON
N6A 3K7,
Canada
4
SETI Institute, 515 N. Whisman Road, Mountain View, CA
94043,
USA
5
NASA Headquarters, MS 3Y28, 300 E St. SW, Washington, DC
20546,
USA
Polycyclic Aromatic Hydrocarbons (PAHs) are widespread across the Universe and influence many stages of the Galactic lifecycle. The presence of PAHs has been well established and the rich mid-IR PAH spectrum is now commonly used as a probe into (inter)stellar environments. The NASA Ames PAH IR Spectroscopic Database has been key to test and refine the “PAH hypothesis”. This database is a large coherent set (>600 spectra) of laboratory measured and DFT computed infrared spectra of PAHs from C10H8 to C130H28 and has been made available on the web at (http://www.astrochem.org/pahdb). With a new spectral window opening up; the far-IR, the study of PAH far-IR spectra and the quest for identifying a unique member of the interstellar PAH family has begun. To guide this research, the far-IR (>20 μm) spectra of different sets of PAHs are investigated using the NASA Ames PAH IR Spectroscopic Database. These sets explore the influence of size, shape, charge and composition on the far-IR PAH spectrum. The far-IR is also the domain of the so-called “drumhead” modes and other molecular vibrations involving low order bending vibrations of the carbon skeleton as a whole. As with drums, these are molecule and shape specific and promise to be a key diagnostic for specific PAHs. Here, the sensitivity of these “drumhead” modes to size and shape is assessed by comparing the frequencies of the lowest drumhead modes of a family of circular shaped (the coronene “family”) and rhombus shaped (the pyrene “family”) PAH molecules. From this study, some consequences for an observing strategy are drawn.
© EAS, EDP Sciences 2011