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

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.

Stability of C59 Knockout Fragments from Femtoseconds to Infinity

“…In all such formation pathways, and likewise, for the further evolution of existing fullerenes in interstellar and circumstellar environments, energetic processing plays an important role. This processing can take many forms, such as the radiation fields from stars, both in the UV range and at longer wavelengths (Greenberg et al 2000;Moore & Hudson 2009); energetic electrons and ions in shock-heated gases and plasmas (Slavin et al 2004;Micelotta et al 2010a;Chakraborty 2024); or energetic atoms or ions in stellar winds and supernova shockwaves (Micelotta et al 2010a(Micelotta et al , 2010b. Each of these is capable of breaking down molecular material and they constitute the driving forces behind the rich chemical makeup of the ISM (Tielens 2013;Herbst 2017).…”