A search for spectral signatures of aromatic cations in diffuse interstellar absorption: confrontation laboratory spectroscopy astronomical observations

Details A search for spectral signatures of aromatic cations in diffuse interstellar absorption: confrontation laboratory spectroscopy astronomical observations A search for spectral signatures of aromatic cations in diffuse interstellar absorption: confrontation laboratory spectroscopy astronomical observations

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....6804b&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #6804

Computer Science

Scientific paper

Polycyclic Aromatic Hydrocarbons (PAHs) are now recognized as an important constituent of the interstellar medium gaseous phase. This family of molecules and in particular their ionic derivatives seems to be one of the most promising candidates for identification of the Diffuse Interstellar Bands (DIBs). These absorption bands are observed in the visible spectral range in the spectra of stars partially masked by gas cloud. The possible identification of PAHs as molecules responsible for these bands must be done through direct comparison with PAHs spectra recorded in conditions as close as possible to those of the interstellar medium. These low temperature and collision-free conditions can be recreated in the laboratory with supersonic beams. A van der Waals complex PAH-Ar is then ionized by resonant two-photon ionization. The ion absorption of a tunable visible laser photon causes the argon departure, and the detection of this dissociation by a mass spectrometer allows the recording of the PAH cation spectrum. Using this technique, the spectra of phenylacetylene+-Ar and of acenaphthene+-Ar could be obtained. The spectral profile is wide and lorentzian, showing an intramolecular dynamics dominated by ultrafast internal conversion. Two observation campaigns with the Télescope Bernard Lyot at the Pic du Midi allowed us to perform a systematic search for these broad bands, thanks to specific observational protocole and data processing. Upper-limits of abundance were determined for five PAH cations. Interstellar absorption zones identified in our spectra are of variable width and some of them are very likely the result of a combination due to several species. According to our measurements between 525 and 840 nm, the diffuse interstellar absorption represents 87 % of the interstellar absorption in front of the BD +40 4220 star.

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