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Sujet de stage / Master 2 Internship

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Spectroscopy and dynamics of molecules embedded in helium droplets

Contact: BRIANT Marc, , marc.briant@cea.fr, +33 1 69 08 81 21
Summary:
The objective of this internship is to identify and to understand the processes that are turned on when a molecule or a molecular assembly absorbs light within a helium droplet. These studies are motivated by fundamental physical chemistry considerations on the structure and dynamics of systems with many degrees of freedom.
Possibility of continuation in PhD: Oui
Deadline for application:16/03/2018

Full description:
This internship will focus on basic problems in molecular physical chemistry with the aim to identify and model the factors that influence a chemical reaction, in particular the structural factors.

This work is primarily experimental. It uses helium droplets as reaction medium after the molecule or the molecular assembly of interest was deposited on these droplets. In practice, helium droplets are generated by a supersonic expansion. By playing with the expansion conditions, we can adjust the size of the droplets. Then, the beam passes through several areas of collisional trapping which allows reagent molecules and solvent molecules to be deposited in the droplets. A technique, which was originally developed in our laboratory allows a strict determination of the number of deposited molecules which participated to the process under study, hence giving access to the stoichiometry of this processes which are studied in these droplets is well defined. The latter are induced by absorption of light of appropriate wavelength by the molecular system under study. This allows one to perform two types of experiments. One is a reaction dynamics experiment when the light absorption induced a reactive process whose dynamics informs on the set of forces responsible for this reaction.
The second is a spectroscopy experiment when the absorbed light simply evaporates the helium droplet. In the latter case, measuring the droplet evaporation as a function of the wavelength of the excitation laser is a direct measurement of the absorption spectrum of the molecules or the molecular assembly which is hosted by the droplet. Such spectra provide important structural information. These experiments are conducted on several existing experimental devices.

The intership will focus primarily on the second aspect and its extension as a PhD thesis will call the first type of experiences. Of course, continuation of the internship by a PhD thesis assumes that a scholarship is obtained. Candidates have to apply before the end of December of the current year.
Technics/methods used during the internship:
Molecular Physics

Laboratory
Tutor of the internship

 

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