Fourier transform incoherent broadband cavity enhanced absorption spectroscopy developed for the study of cold astrophysical anions in a planar laval nozzle expansion
Bejjani, Raghed
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https://hdl.handle.net/2142/107333
Description
Title
Fourier transform incoherent broadband cavity enhanced absorption spectroscopy developed for the study of cold astrophysical anions in a planar laval nozzle expansion
Author(s)
Bejjani, Raghed
Contributor(s)
Benidar, Abdessamad
Georges, Robert
Issue Date
2020-06-22
Keyword(s)
Instrument/Technique Demonstration
Abstract
The molecular diversity of cold interstellar medium has been recently enriched with the detection of molecular anions: $C_4H^-$, $C_6H^-$, $C_8H^-$, $C_3N^-$, $C_5N^-$ and $CN^-$. Although by far less abundant than neutrals, anions could play a significant role in the chemistry of molecular clouds\footnote{A. Van Orden, R.J. Saykally, Chem. Rev. 98 (1998) 2313-2358}$^,$\footnote{W. Weltner Jr, R.J. Van Zee, Chem. Rev. 89 (1989) 1713-1747}. With the exception of $C_5N^-$, whose identification in space was based on high-level ab initio calculations\footnote{J. Cernicharo et al. The Astrophysical Journal 688, no 22008: L83 86}, the astronomical detection of these anions was made possible thanks to the laboratory characterization of their rotational spectra. Our ultimate goal is to characterize the anionic carbon chains $C_x^-$ (x = 3, 4, 5,…) through their electronic spectra in order to explain the absorption features already observed one century ago in some diffuse interstellar clouds illuminated by reddened stars.
We will represent our new instrument based on a planar de Laval supersonic plasma source coupled to Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (IBB-CEAS) in conjunction with a high-resolution Fourier transform spectrometer for the detection. Preliminary results obtained on neutral species ($O_2$, $CH_4$, $C_2H_2$) will be presented.
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