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Accueil > EN > Recruitment > PhD project

High Resolution Laser spectroscopy of NH3 and its deuterated isotopologues in the infrared (1.95-2.05μm).

par Johanna Leclercq - publié le

Title of the PhD project :
High Resolution Laser spectroscopy of NH3 and its deuterated isotopologues in the infrared (1.95-2.05μm).

Name of the PhD Director : Patrice CACCIANI
Name of the co-director or collaborator : Jean COSLEOU

Laboratory : PhLAM

Financial supports : Governemental grant

Identified Research Programmes : CPER CLIMIBIO

Summary of the PhD project :
Our research focus is the study of internal modification mechanisms ("conversion") of nuclear spin in molecules with identical nuclei (spin isomers). In this frame, spectroscopy of ammonia molecule is needed to determine the ortho/para character of transitions. This molecule acts as a precursor in the formation of so-called secondary fine particles (aerosols). A new high resolution laser source has been acquired granted by the CPER CLIMIBIO, whose spectral range covers an energy range where NH3 molecule as well as its isotopologues ND2H, NHD2 ND3 have absorption bands.

The analysis of these complex bands requires a comparison with ab initio calculations. Their accuracy is constantly improving by the adjustment of the potential surface supported by the feedback from precise experimental data. In fact, ammonia, a light molecule, has many interacting combination bands in this energy range, which make analysis difficult but remain a challenge for theoreticians, in particular because of the possibility of internal large amplitude motion, the nitrogen atom passing through the plane of the three hydrogens (also called inversion).
The project has both theoretical and experimental parts, since it will start recording the absorption spectra of these molecules at different temperatures, analyzing them, then establishing a correspondence between the transitions observed and calculated using different informations and methods : position, oscillator strength, temperature variation, observation of transitions with a common upper state, selection rules (observation of branches within the band absorption).