Laboratory investigation of shock-induced dissociation of buckminsterfullerene and astrophysical insights

¹ Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) – UMR 6251, 35000 Rennes, France
e-mail: ludovic.biennier@univ-rennes.fr
² Department of Chemistry, GITAM School of Science, GITAM Deemed-to-be-University, Bengaluru, India
³ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁴ Laboratoire de Chimie et Physique Quantiques, IRSAMC, Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex 4, France
⁵ Quantum Solid-State Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁶ Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore, India
⁷ Shock Induced Materials Chemistry Lab, Solid State and Structural Chemistry Unit, Indian Institute of Science, 560012 Bangalore, India
⁸ Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d’Orsay, ISMO, 91405 Orsay, France
⁹ Université Grenoble Alpes/UMR CNRS 5588, Laboratoire Interdisciplinaire de Physique, 38041 Grenoble, France
¹⁰ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 75005 Paris, France
¹¹ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France
¹² Department of Aerospace Engineering, Indian Institute of Science, Bangalore, India
¹³ Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India

Received: 29 May 2023
Accepted: 6 October 2023

Abstract

Fullerene C₆₀ is one of the most iconic forms of carbon found in the interstellar medium (ISM). The interstellar chemistry of carbon-rich components, including fullerenes, is driven by a variety of energetic processes including UV and X-ray irradiation, cosmic-ray (CR) bombardment, electron impact, and shock waves. These violent events strongly alter the particle phase and lead to the release of new molecular species in the gas phase. Only a few experimental studies on the shock processing of cosmic analogs have been conducted so far. We explored in the laboratory the destruction of buckminsterfullerene C₆₀ using a pressure-driven shock tube coupled with optical diagnostics. Our efforts were first devoted to probing in situ the shock-induced processing of C₆₀ at high temperatures (≤ 4500 K) by optical emission spectroscopy. The analysis of the spectra points to the massive production of C₂ units. A broad underlying continuum was observed as well and was attributed to the collective visible emission of carbon clusters, generated similarly in large amounts. This proposed assignment was performed with the help of calculated emission spectra of various carbon clusters. The competition between dissociation and radiative relaxation, determined by statistical analysis, alludes to a predominance of clusters with less than 40 carbon atoms. Our laboratory experiments, supported by molecular dynamics simulations performed in the canonical ensemble, suggest that C₆₀ is very stable, and that high-energy input is required to process it under interstellar low-density conditions and to produce C₂ units and an abundance of intermediate-sized carbon clusters. These results provide some insights into the life cycle of carbon in space. Our findings hint that only J-type shocks with velocities above ~100 km s⁻¹ or C-type shocks with velocities above 9 km s⁻¹ can lead to the destruction of fullerenes. Observational tracers of this process remain elusive, however. Our work confirms the potential of shock tubes for laboratory astrophysics.