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M/F Laboratory study of carbonaceous nanograins-water interactions in the era of the James Webb Space Telescope

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General information

Reference : UMR5589-JEALHE0-002
Workplace : TOULOUSE
Date of publication : Thursday, June 18, 2020
Scientific Responsible name : Sébastien Zamith
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Thanks to its unprecedented sensitivity, angular and spectral capabilities in the infrared, the James Webb Space Telescope (JWST, planned for launch in March 2021) will provide us with a new view of the physical and chemical structuration of photodissociation regions (PDRs) associated with star- and planet-forming regions [1]. In these PDRs, the matter, composed of gas and tiny dust particles, is coupled to the ultraviolet (UV) radiation from young stars. From previous infrared space missions such as the Spitzer telescope, we have observed the destruction of very small carbonaceous grains and the production of polycyclic aromatic hydrocarbons (PAHs) at the edge of these PDRs [2]. These carbonaceous nanograins come from the inner part of interstellar clouds where models predict a transition from gaseous to icy water [3].

This PhD project in the field of laboratory astrophysics aims at studying the evolution of analogs of carbonaceous nanograins in PDRs. These will be formed of mixed aromatics/aliphatics/water clusters controlled in size and temperature and isolated in physical conditions that approach those found in astrophysical environments. Their evolution under collisions with atoms/molecules and/or under UV photon irradiation will be investigated. The project takes advantage of the recent instrumental developments carried out at LCAR. On one hand, a versatile aggregation cluster source has been developed for collision induced dissociation experiments and measurements of the evaporation rate of size-selected clusters [4]. On the other hand, the PIRENEA 2 setup, built in the framework of the ERC Synergy Nanocosmos project [5], combines a cryogenic environment with a variety of ion trapping techniques in order to study molecular processes in conditions that approach those encountered in interstellar molecular clouds.

More specifically, the PhD project consists in studying the properties of small mixed clusters composed of PAHs (methylated PAHs) and water molecules, (PAH)n(H2O)m, m,n=1-10. The candidate will first optimize the source conditions to produce the species of interest and carry out collision induced dissociation experiments using the cluster group experimental setup. He/she will then produce the same species in PIRENEA 2 using a duplicate of the aggregation source. He/she will study the interaction of the mixed complexes with photon irradiation in the UV-visible range, exploring desorption processes and the possible formation of new molecular species by photochemistry. These processes will be studied as a function of the irradiation wavelengths as well as the size, stoichiometry and initial temperature of the clusters, which can be tuned between 10 and 300 K. To get further insights into these processes, the project will benefit from complementary theoretical studies that will be carried out by the MAD team at LCPQ [6]. The confrontation of the obtained data with astronomical data from the JWST ERS programme will be favored by the strong involvement of the MICMAC team in this program [1].

The PhD work will be carried out in an interdisciplinary context between experimental cluster physics, physical chemistry and astrophysics. It will involve a rich research team environment with members of the MICMAC Department at IRAP (laboratory astrophysics and astronomical observations), the Cluster Team at LCAR (experimental physics) and the MAD Team at LCPQ (simulations in quantum physics/chemistry).

The candidate must have a degree in molecular physics and willingness for experimental physics involving cryogenic ion traps and laser spectroscopy. The subject is part of an interdisciplinary context involving astrophysicists and theoreticians in molecular physics. Knowledge in astrochemistry and quantum chemistry will be necessary and could be completed, if necessary, during the PhD period.

[1] Programme “Early Release Science” (ERS) intitulé “Radiative feedback from massive stars”;
[2] P. Pilleri, J. Montillaud, O. Berné, and C. Joblin, Astron. & Astrophys 542, A69 (2012)
[3] D. Hollenbach, M. J. Kaufman, E. A. Bergin, G. J. Melnick, Astrophys. J. 690, 1497 (2009)
[4] I. Braud, S. Zamith, and J.-M. L'Hermite, Rev. Sci. Instrum. 88, 43102 (2017)
[5] A. Bonnamy et al., 2018,
[6] E. Michoulier, N. Ben Amor, Mathias Rapacioli, J. A. Noble, J. Mascetti, C. Toubin, A. Simon, Phys. Chem. Chem. Phys. 20, 11941-11953 (2018)

Work Context

The Laboratoire Collisions Agrégats Reactivité (LCAR) is a joint research laboratory of 41 people, with support from both CNRS Institute for Physics and University of Toulouse III. LCAR's activities take place on the Toulouse III University campus.

LCAR brings together six research teams, one theoretical and five experimental, whose work is dedicated to fundamental research. These research teams are divided into two main areas: "molecular physics" and "laser-matter interaction". Since 2015, two experiments carried out by a team from the Institute for Research in Astrophysics and Planetology (IRAP) have been hosted at LCAR and significant synergies have been formed between this team and the molecular physics teams of LCAR.

The thesis will take place in an interdisciplinary context combining cluster physics, chemical physics and astrophysics. It will benefit from a synergy between several research teams with complementary skills: the MICMAC department of IRAP (laboratory astrophysics and astronomical observations), the LCAR cluster team (experimental physics) and the LCPQ MAD team (simulations of quantum physics).

The doctoral work will take place at LCAR on joint experiments carried out by the cluster team from LCAR and MICMAC group from IRAP. The student will be co-supervised by Christine Joblin (DR CNRS IRAP) and Sébastien Zamith (CR CNRS LCAR) in a team of ½ dozen people.

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