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Infrared spectroscopy of carbonaceous nanograins isolated in extreme conditions




Duration: 5 months full-time internship
6 months full-time internship

Latest starting date: 15/05/2024

Localisation: Laboratoire Collisions Agrégats Réactivité - UMR5589
Université Paul Sabatier - Bat. 3R4
118 route de Narbonne
31062 Toulouse Cedex 09, France

Alexandre MARCINIAK, PhD

This research master's degree project could be followed by a PhD

Work package:
In the interstellar medium (ISM), cosmic grains are crucial for its chemistry. Indeed, these catalytic platforms interacts with molecules of the gas phase and produces new species which chemically enrich star and planet forming regions. In some regions of the ISM, it exists an abundant population of grains which have a (sub-)nanometer size, also called nanograins. Since they have a huge surface over volume ratio, nanograins are at play in the physical and chemical evolution of these regions. Microscopically, they correspond to atomic or molecular clusters down to single molecules of polycyclic aromatic hydrocarbon (PAH) [1]. The nanograin morphology especially drives the fundamental interactions (adsorption, desorption, molecular diffusion) between them and small molecules of the gas phase (e.g. H2O, CO, etc.). Therefore, the understanding of nanograin structures is a crucial step which remains very little explored up to now [2]. The PIRENEA 2 setup (see Figure 1) has been developed in the framework of the ERC-Synergy NANOCOSMOS [3,4] in order to study gas-nanograin-photon interaction in astrophysical conditions. PIRENEA 2 is equipped with a molecular cluster source to produce the nanograins and a cryogenic ion trap (ICR cell in Figure 1) to store them in extreme isolation conditions (~10 K, ~10-11 mbar). PIRENEA 2 has recently been coupled with a tunable IR laser source (IR OPO). In this context, the internship project aims to systematically characterize the structures of cationic carbonaceous nanograins (e.g. PAHn+ or [PAHn(H2O)m]+, [5]). The student will perform the measurements of the IR (2.5 – 4.5 μm range) action spectra of different nanograins and study the modification of these spectra as a function of the nanograin composition. Moreover, these results will be compared to quantum chemistry calculations, performed by our collaborators at LCPQ, in order to evaluate the nanograin structures [6]. These new data will notably help to interpret astrophysical observations which are currently performed by the James Webb Space Telescope [7].

Working principle of PIRENEA 2 (developed by IRAP and LCAR). Nanograins are (i) produced by the molecular cluster source, then (ii) they are mass selected and (iii) transferred and stored in an ICR (ion cyclotron resonance) cell in extreme conditions (~10 K, ~10-11 mbar). This cell allows to measure by non-destructive mass spectrometry at high resolution, the (photo-)product ions as a function of the IR wavelength of an IR OPO (optical parametric oscillator). From this measurement, we obtain (iv) the IR action spectra of the nanograins as a function of the experimental conditions: number of monomers (N), number of additional water molecules (NW), etc.

[1] Pilleri, P. et al. A&A 542, A69 (2012). [2] Chatterjee, K. et al. Chem. Sci. 9, 2301 (2018). [3] Bonnamy, A. et al., Nanocosmos - PIRENEA 2 setup, [4] Marciniak, A. et al. hal-03752080, [5] Zamith, S. et al. J. Phys. Chem. A 126, 3696-3707 (2022). [6] Dontot, L. et al. J. Phys. Chem. A 123, 9531-9543 (2019). [7] Berné, O. et al. PASP 134 (1035), 054301 (2022).

Areas of expertise:
molecular physics, spectroscopy, cluster physics, mass spectrometry, optics

Required skills for the internship:
Good education background in physics (quantum physics, molecular physics, electromagnetism, optics, electronics) and strong interest in experimental physics and data analysis. Knowledge in (astro-)chemistry are a not mandatory but will be appreciated.