Stage de niveau M2, L3 dans l’équipe SYSTEMAE
Polycyclic aromatic hydrocarbons (PAHs) are thought to represent a significant fraction of the carbon budget in the interstellar medium (ISM). Recent detections of cyano-substituted PAHs – including species as large as cyanocoronene – as well as pure aromatic hydrocarbons such as indene, raise important questions about their formation pathways in the ISM. In a bottom-up perspective, the mechanisms leading to the first aromatic ring species, namely c-C₆H₆ and c-C₅H₆, from small hydrocarbon precursors are still debated. These species are considered cornerstone molecules in interstellar chemistry, acting as essential building blocks for larger aromatic structures.
We have initiated preliminary work,1 currently under review at Nature Astronomy, that explores the role of phenylium in interstellar aromatic chemistry. A measurement campaign on ion–molecule reactions at the SOLEIL synchrotron is planned within the timeframe of this internship. In parallel, we are developing a new experimental setup to address the fundamental question of how the first aromatic rings are formed in space.
A major challenge lies in the fact that small hydrocarbons can exist in multiple isomeric forms, each exhibiting distinct reactivities. Our setup is designed to overcome this complexity by enabling the selection of ions based on both mass and shape, using a combination of mass spectrometry and ion mobility techniques. Reaction rates will be measured in an ion trap. However, knowing the structures of the resulting products is equally critical, as different isomers can channel the chemical network along divergent pathways. To this end, isomer-specific characterization of the products will be carried out using ultraviolet action spectroscopy.
The reaction rates obtained in this project will be implemented into astrochemical models, in collaboration with J.-C. Loison, to directly assess the impact of these processes on the chemical evolution of interstellar environments. In addition, the ISMO team currently includes two postdoctoral fellows, one PhD student, and two CNRS researchers (including myself), providing a stimulating and collaborative environment for carrying out this research.
[1] J.-C. Loison, et al., arXiv:2506.13290 2025.
Techniques/methods in use:
The selected applicant will gain expertise in a range of fields, including astrochemistry, kinetics, mass spectrometry, and spectroscopic techniques.
This internship has the potential to evolve into a funded Ph.D. thesis project by Agence Spatiale d’Ile de France.
Location: Institut des Sciences Moléculaires d’Orsay (ISMO), Bât. 520, Université Paris-Saclay, Orsay
Contact: Ugo Jacovella