Far-ir Pah Spectroscopy And The Identification Of An Individual Astronomical Pah Molecule
Abstract
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. With a new spectral window opening up in the far-IR, the quest for identifying a unique member of the interstellar PAH family has begun. To guide this search, the far-IR (> 20 μm) spectra of different sets of PAHs are investigated using the NASA Ames PAH IR Spectroscopic Database - a large coherent set (> 600 spectra) of laboratory measured and DFT computed infrared spectra of PAHs from C10H8 to C130H28. These sets explore the influence of size, shape, charge and composition on the far-IR PAH spectrum.
The far-IR is 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 for drums, these modes are considered to be very 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 the study of the far-IR PAH spectra of different sets as well as from the analysis of the `drumhead’ modes, some suggestions for an observing strategy are made.- Publication:
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American Astronomical Society Meeting Abstracts #216
- Pub Date:
- May 2010
- Bibcode:
- 2010AAS...21641101B