STSM by Elisabetta Micelotta, University of Helsinki (FI) with Henning Zettergren, Stockholm University (SE)
On February 12, 2017 (7 days)

The stability of interstellar fullerenes

Fullerenes C60 and C70 are the largest molecules detected in space so far. Because of their highly symmetric structures, they are two of the most resistant molecules known on Earth. However, their actual stability under the harsh conditions of the interstellar medium has not been investigated yet. Retrieving such information is important to establish the role of fullerenes in the evolutionary scheme of cosmic dust, in terms of possible building blocks of larger grains and also in terms of possible implications for astrobiology.

The goal of this STSM has been to start investigating the interactions between C60 and a gas of H, He and C ions for collision energies below few tens of keV, typically arising from supernova shocks. The shocks propagate into the interstellar medium, heating and accelerating the gas. We have determined the energy ranges of our projectiles and evaluated the collision rate expected under astrophysical conditions. This information is necessary to properly model the fragmentation of C60 molecules via classical Molecular Dynamics (MD) simulations.

The theoretical work started during this STSM will result in at least two separate publications and will be complemented by experiments at the DESIREE facility, which we planned during my stay. The aim is to measure the absolute destruction cross sections and threshold energies for C60 following ionic bombardment in the sub-keV energy regime. This project also represents the beginning of a long-term collaboration to investigate
the stability of more carbonaceous structures of astrophysical relevance, like e. g. hydrocarbon nanoparticles.

Figure: Kinetic energy distribution of the considered ionic projectiles for the minimum and maximum gas temperature relevant for this study. The specific energy ranges resulting from non-thermal acceleration are reported in the top panel.

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