Speaker
Description
Synopsis
We have performed experimental and theoretical studies of knockout processes with carbonaceous molecules, and draw conclusions about the lifetimes of their decay products and their possible survival in astro- physical environments.
Abstract
The presence of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium was proposed in the 1980’s [1][2] and later confirmed in 2021 [3][4][5][6]. Fullerenes, another family of carbon-based molecules, were experimentally observed [7] and later also discovered in space [8]. To gain better understanding of the formation and survival of these molecules in astrophysical environments, we have studied their collisions with single energetic atoms, leading to different knockout processes.
Spontaneous loss of a single carbon atom is an energetically unfavoured decay channel for PAHs and fullerenes. In contrast, when bombarded with atoms or ions, single atom knockout occurs at a significant rate for center of mass collision energies in the 100 eV range [9]. We have studied such knockout events on short (picosecond) timescales theoretically using the LAMMPS molecular dynamics software, and experimentally on timescales of up to minutes using an ion storage ring. The experimentally determined stability of the decay products of these carbon-based structures had previously been limited to studies on microsecond timescales [9][10][11][12]. In experiments at the DESIREE (Double Electro- Static Ion Ring ExpEriment) facility, however, we have now been able to monitor their survival on extended timescales, through colliding PAHs and fullerenes of various energies with stationary He atoms and then store the knockout fragments in a cryogenic environment mimicking interstellar conditions. We find that a portion of the knockout fragments dissociate spontaneously on timescales of tens of milliseconds, but that a significant fraction are cold enough to remain intact for the entire duration of the measurements (minute timescales). This leads us to conclude that they will survive indefinitely [13].
References
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[3] Cernicharo J et al. 2021 Astron. Astrophys. 649 L15.
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[5] Burkhardt A M et al. 2021 ApJL 913 L18
[6] Sita M L et al. 2022 ApJL 938 L12
[7] Kroto H W et al. 1985 Nature 318 162
[8] Cami J et al. 2010 Science 329 5996
[9] Gatchell M and Zettergren H 2016 Journal of Physics B 49 162001
[10] Stockett M H et al. 2018 Carbon 139 906
[11] Stockett M H et al. 2014 Phys. Rev. A 89 03271
[12] Stockett M H et al. 2015 J. Phys. Chem. Lett. 22 4504
[13] Gatchell M et al. 2021 Nature Communications 12 6646
