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An Excursion in Laboratory Astrophysics: Large Carbonaceous Compounds

Thursday, February 27, 2020 - 11:00
Dr. Shubhadip Chakraborty
Institut de Recherche en Astrophysique et Planetologie, France
The interstellar medium (ISM) contains a plethora of various small and large organic molecules. Among the large organic molecules (PAHs) and fullerenes such as C60 and C70 are the main candidates. The presence of PAHs is revealed by the mid-infrared spectra of various astronomical objects, which comprise several broad emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 microns, called the aromatic infrared bands (AIBs). After 35 years of extensive research it has now been generally accepted that these bands arise from the infrared fluorescence of thermally excited PAHs of large size (50-100 C atoms) pumped by single FUV photon (Allamandola et al. 1985; Leger et al.1989). A similar process can be invoked for C60, which carries bands at 7.0, 8.5, 17.4 and 18.9 microns. Very recently, the diffuse interstellar bands (DIBs) at 9632 and 9577 Angstrom have been ascribed to the C60+ Campbell et al. (2015). It is interesting to mention that there are hundreds DIBs observed in the ISM and their carriers remain an enigma since 100 years. In the ISM, the processing of PAHs is driven by the interaction with stellar radiation, shock waves and cosmic rays. Berne & Tielens (2012) proposed that the formation of C60 is driven by the photolysis of large PAHs. On the other hand, Garcia-Hernandez et al. (2011) proposed that C60 could be formed from amorphous carbon due to shocks driven by fast stellar winds. In my talk I will demonstrate the use of laboratory astrophysics to solve some of the above questions. Experimental and theoretical IR spectroscopy of hot PAHs was performed Chakraborty et al. (2019) for an in-depth understanding of the carriers of AIBs and the physical state of cosmic C60 Joblin & hakraborty (2020). We also recorded the NIR spectrum of C60 at low temperature in the context of the identification of DIBs Chakraborty et al. (2020). Finally, I will show some experimental simulations of the evolution of interstellar dust analogues upon low velocity shocks.
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