Photophysique de systèmes carbonés dans les conditions du milieu interstellaire // Photophysics of few nm-size carbonaceous particles in conditions relevant to those of the interstellar medium

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Interpretation of interstellar medium observations, in extinction (absorption and scattering) and in emission, relies on a complex modelling of the photophysical properties (i.e. competition between all radiative and non-radiative relaxation channels of the isolated systems) of the interstellar molecules and dust components using laboratory data on analogues. Up to now, analogues of the interstellar species from a few tens to few hundreds carbon atoms have been scarcely explored in the laboratory although they may contain up to several tens of % of the available interstellar carbon and they are suspected to play a crucial role in the physics and chemistry of the interstellar medium. Their properties have been extrapolated from smaller species or nanoparticle analogues. The main reason, above all, is the lack of sources of large molecular systems in the gas phase. In the recent years, albeit the soot nucleation process in sooting flames remains largely unexplained and has challenged researchers for at least the last 40 years, it has been shown that the soot nucleation process efficiently generates species of sizes in between the soot molecular precursors (up to about the C24H12 molecular size) and the smallest particles of the soot nuclei distribution (containing about a hundred carbon atoms). The goal of the project is to tune original flames and efficiently produce such systems of similar size and structures as those suspected in space, and study their photophysics in conditions mimicking those of the interstellar medium. Structural characterisation, electronic absorption and the peculiar recurrent fluorescence (although called Poincaré fluorescence) will then be probed performing online and ex situ experiments completed by theoretical modelling.
In more details, the project will combine several online laser diagnostics of laboratory flames laser induced fluorescence, laser induced incandescence and resonant multiphoton ionization. These online experiments will be performed on cooled sampled species to drastically reduce the spectral congestion and clean up the flame background (target T=50K, a unique setup), completed by highly sensitive time-of-flight mass spectrometry (TOFMS) using various photoionization (PI) schemes from resonant 2 colour to direct VUV processes. Precise identification of the large molecular structures involved in the soot nucleation will thus be accessible, as well as their radiative properties. This project should thus allow to progress on the identification of carriers of interstellar spectral features observed in absorption and in emission, with a focus on the UV range.
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Début de la thèse : 01/10/2026
WEB : https://www.ismo.universite-paris-saclay.fr/spectroscopie-electronique-des-pahs-et-derives/

Contrats ED : Programme blanc GS-Physique

Université Paris-Saclay GS Physique

572 Ondes et Matière

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Education on physics or chemical -physics at the master level, skills in experimental work and lasers are required, as well as skills on programming for analysis and physical modeling of the data.