Thesis of Jordan Claus

Defense of thesis  Jordan Claus - laboratory PhLAM

Abstract :

Volatile organic compounds (VOCs), in particular polycyclic aromatic compounds (PACs) and their derivatives, are molecules emitted into the atmosphere by various human activities, in particular during incomplete combustion processes and secondary reactions involving PACs. Some VOCs are known to be precursors of secondary organic aerosols (SOAs).
Aerosols have attracted growing interest in recent decades because of their impact on climate and human health. They can alter the physico-chemical properties of the atmosphere, have harmful effects on human health and contribute to climate change. In addition, factors such as humidity and the nature of the precursors influence SOAs production. The abundant presence of water in the atmosphere under various conditions, making it one of the major solvents, suggests that the process of microsolvatation, where water molecules associate with molecules of interest, is highly probable. To understand the formation of SOAs and the mechanisms associated with them, it is essential to explore the hydration of precursors. The molecular structure of compounds plays a crucial role in inter- and intra-molecular forces, which requires information on molecular structure in the gas phase to predict possible reactions and the formation of complexes and aggregates.
Fourier transform microwave spectroscopy (FTMW), combined with quantum chemical calculations, is an effective approach for studying molecular systems such as VOCs and exploring their intra- and inter-molecular interactions. This approach, which combines theory and experiment, makes it possible to characterize and model the conformational landscape, structure and internal dynamics of various molecules, including those of atmospheric interest and their complexes.
In this thesis, this approach has been used to characterize the hydrated complexes of a PAC, naphthaldehyde (C11H8O). The most stable conformations have been identified using quantum chemistry calculations, highlighting the structural preference and energies involved in the microsolvation process. The planarity of the structures was also an important point in this study, combining experiment and simulation.
The second part of this thesis concerns the development of a pulsed discharge injector for the laboratory study of open-layer species. A description of the current state of the device and the results obtained to date are provided.

Keywords : rotational spectroscopy,quantum chemistry calculations,microsolvation,secondary organic aerosol precursors,radicals,discharge