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Reference : UMR8214-BERGAN-001
Workplace : ORSAY
Date of publication : Wednesday, July 22, 2020
Scientific Responsible name : Séverine Boyé-Péronne
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
The evolution of diluted matter in astrophysical media, such as the interstellar space medium, planetary atmospheres or cometary coma, results from a complex photochemistry involving many stable or radical species in the gas phase. This photochemistry can be induced by the galactic flux or the solar radiation in the spectral domain of the Vacuum-UltraViolet (VUV, wavelength below 200 nm). A good understanding of this evolution requires a precise modeling of the photochemistry in these media taking into account both the photoinduced processes and the full chemical reaction network. The models need detailed description of the processes as well as quantitative data with their carefully evaluated error bars. Such qualitative and quantitative information can be gained from laboratory experimental studies.
Among the various processes occurring in the VUV photochemistry of the astrophysical media, photoionisation is a crucial step which generate reactive ionic species playing key roles in ion-molecule reaction networks. The main objective of the PhD project is to acquire new and high-quality experimental laboratory data on the VUV photoionisation of radical molecules. Very little information is known about these species, especially their cations. The thesis work will provide unprecedented data (molecular constants) to the astrophysical and planetary communities to help the improvement of models. The studies will be focused on the most abundant radical species in astrophysical media (CN, CH, C2H, NH, NH2, N3,...). From a fundamental point of view, the results will enable to refine the theoretical models used to describe the rovibronic structure of open-shell systems affected by (ro)vibronic couplings.
During the PhD, the student will develop a radical source based on H-abstraction from a selected precursor, induced by atomic fluorine. This source will be implemented in a new experimental setup, VULCAIM (Vacuum-Ultraviolet Laser for Considering Astrophysical and Isolated Molecules), available in our group at ISMO. VULCAIM couples a PFI-ZEKE (pulsed field ionization zero-kinetic energy) photoelectron spectrometer to a high-resolution VUV laser radiation generated by four-wave mixing in rare gases. He will have the opportunity to work with the high-resolution VUV laser, unique to France (only three in the world),
Prior to the laser experiments, complementary studies will be performed on the DESIRS beamline of SOLEIL french synchrotron facility to record photoionisation spectrum with vibrational resolution over a large spectral range. These surveys will help to identify the pertinent regions to be explored at much higher resolution at ISMO.
In the framework of collaborations, the PhD student will perform ab initio calculations to assign the recorded spectra.
PhD position financed by "Région Ile de France" (DIM ACAV+ 2020)
The candidate will perform experiments mainly at ISMO and at the synchrotron SOLEIL.
Constraints and risks
Experimental works with lasers, vacuum devices, high voltages, and liquid and gaseous species (possibly toxic and explosive)
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