Shock-wave processing of C60 in hydrogen
1 Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
2 Shock Induced Materials Chemistry Lab, Solid State and Structural Chemistry Unit, Indian Institute of Science, 560012 Bangalore, India
3 Inorganic and Physical Chemistry, Indian Institute of Science, 560012 Bangalore, India
4 UJF-Grenoble 1/UMR CNRS 5588, Laboratoire Interdisciplinaire de Physique, 38041 Grenoble, France
5 Institut d’Astrophysique Spatiale, UMR CNRS 8617, Université Paris-Sud, Bât. 121, 91405 Orsay, France
6 Department of Aerospace Engineering, Indian Institute of Science, 560012 Bangalore, India
Received: 6 June 2016
Accepted: 24 October 2016
Context. Interstellar carbonaceous particles and molecules are subject to intense shocks in astrophysical environments. Shocks induce a rapid raise in temperature and density which strongly affects the chemical and physical properties of both the gas and solid phases of the interstellar matter.
Aims. The shock-induced thermal processing of C60 particles in hydrogen has been investigated in the laboratory under controlled conditions up to 3900 K with the help of a material shock-tube.
Methods. The solid residues generated by the exposure of a C60/H2 mixture to a millisecond shock wave were collected and analyzed using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman micro-spectroscopy, and infrared micro-spectroscopy. The gaseous products were analyzed by Gas Chromatography and Cavity Ring Down Spectroscopy.
Results. Volatile end-products appear above reflected shock gas temperatures of ~2540 K and reveal the substantial presence of small molecules with one or two C atoms. These observations confirm the role played by the C2 radical as a major product of C60 fragmentation and less expectedly highlight the existence of a single C atom loss channel. Molecules with more than two carbon atoms are not observed in the post-shock gas. The analysis of the solid component shows that C60 particles are rapidly converted into amorphous carbon with a number of aliphatic bridges.
Conclusions. The absence of aromatic CH stretches on the IR spectra indicates that H atoms do not link directly to aromatic cycles. The fast thermal processing of C60 in H2 over the 800–3400 K temperature range leads to amorphous carbon. The analysis hints at a collapse of the cage with the formation of a few aliphatic connections. A low amount of hydrogen is incorporated into the carbon material. This work extends the range of applications of shock tubes to studies of astrophysical interest.
Key words: astrochemistry / shock waves / circumstellar matter / dust, extinction / methods: laboratory: solid state
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