Energetic ion processing of polycyclic aromatic hydrocarbons in the solid phase

    First Stage Researcher (R1)
    Recognised Researcher (R2)
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    Leading Researcher (R4)
    15/06/2021 00:00 - Europe/Brussels
    France › Caen


Carbonaceous materials play an important role in space. Polycyclic Aromatic Hydrocarbons (PAHs) are a ubiquitous component of organic matter in space or in terrestrial atmosphere. This class of molecules typically contains planar hexagonal carbon structures, which are fused like small pieces of graphene and decorated by hydrogen atoms around their exterior perimeters. Their contributions invoked in a broad spectrum of astronomical observations that range from the ultra-violet to the far-infrared and cover a wide variety of objects and environments from meteorites and interplanetary dust particles to outer Solar System bodies to the interstellar medium in the local Milky Way and in other galaxies [e.g. A. G. G. M. Tielens, Rev. Mod. Phys. 85 (2013) 1021 ; A.G.G. M Tielens, Annu. Rev. Astron. Astrophys. 46 (2008) 289 ; E. Peeters et, A&A 390 (2002) ]. PAH molecules can represent up to 20% of the interstellar carbon mass [C. Joblin and G. Mulas EAS Publications Series 2009 p. 133], therefore, they have profound implications for the complex chemistry in space. Despite the lack of specific PAH molecule identification, the relation between the spectral IR features and PAH systems is now commonly accepted as they all display similar IR-signatures. This has been shown, to survive in such harsh environments, typically PAH molecules contain 50-100 carbon atoms, and can be represented as clusters containing tens of PAH molecules (representing very small grains, VSGs). In dense clouds, the VSGs can, subsequently, freeze out on grains or serve as nucleation sites for small molecules forming ice covered VSGs. Individual PAHs can also efficiently condense onto dust grains as “guest molecules” in icy grain mantles, much as is the case for most other smaller interstellar molecules [S. A. Sandford & L. J. Allamandola 1993 ApJ 417 815. These examples highlight the importance of understanding how energetic processing affects the formation, survival, and destruction of PAHs. Another key question concerns the role of a surrounding environment (e.g. covering with icy mantels) in these processes and formation of new species in PAH/ice interface (e.g. complex organic molecules -prebiotic molecules like nucleobases). Several laboratory studies were carried out to investigate the effects of vacuum ultraviolet (VUV) photolysis on several PAH:H2O ice mixtures (e.g. A. L. F. de Barros et al, Astrophys. J. 848 (2017) 112; J. Bouwman et al Astron. Astrophys. 525 (2011) A93; Bernstein, M. P. Astrophys. J. 664 (2007) 1264 and citation therein). T. Pino et al (Astron. Astrophys. 623 (2019) A134) have investigated relies of large carbonaceous molecules by swift heavy ion irradiation. However, there are no data about interaction highly energetic ions with pure PAH and PAH-water mixed ices. Therefore, in the present thesis, we present to investigate ion irradiation of ices in energy range from keV to MeV to probe PAH molecules evolution (fragmentation, sputtering) and formation of new species in different water ice proportions. The obtained results will be compared with available data for photo-processing. Thesis objectives are: (i) to mimic energetic ion processing of polycyclic aromatic hydrocarbon (PAH) ices due to interaction with cosmic rays/solar wind; (ii) to obtain destruction cross section (and if possible sputtering yields) of PAH molecules as a function of ion energies and ice composition (pure PAH and PAH-water mixed ices). The ultimate goal is to determine their dependence on the electronic/nuclear stopping power. (iii) to identify a new species formed by ion irradiation in PAH /PAH-water ices and to determine their formation cross sections. As a particular case, we plan to study reactivity in interface between PAH and water sandwich ice to look for CO/CO2 molecules formation. (iv) to compare obtained data for ion irradiation with literature data for photoprocessing of PAH ices.

Funding category: Contrat doctoral

PHD title: Doctorat de Physique

PHD Country: France

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Specific Requirements

A M.Sc. degree or equivalent in Physics, Chemistry or related fields, with a background in experimental physics  (e.g. vacuum techniques, FTIR, mass spectrometry, …)

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EURAXESS offer ID: 630138
Posting organisation offer ID: 97611


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