Infrared spectroscopy of carbonaceous nanograins isolated in extreme conditions

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].