Physicochemical characterisation of biogenic volatil organic compounds and of their hydrates.
Our study deal on the physicochemical properties of molecules of atmospheric interest in the gas phase, in particular the microsolvation process, which could be useful to better understand what leads to the formation of secondary organic aerosols. We studied the mechanism of hydration of several oxidation products of monoterpenes, which include myrtenal and perillaldehyde, which are two unsaturated aldehydes of close structures, with the verbenone and the fenchone, which are two ketones. The structures of many conformers (up to 3 molecules of water bound to molecules) have been optimized by quantum chemistry calculations at MP2 / 6-311++G(d,p) and B3LYP-D3BJ / def2- TZVP levels of theory. The hydrates cohesion is done thanks to hydrogen bonds and Van der Waals interactions. We were able to evidence of the existence of many of them by supersonic jet mircowave spectroscopy in the range of frequencies 2 - 20GHz and determine their experimental structure. For the myrtenal, we recorded and analyzed the pure rotation spectra, as well as those of isotopologists in natural abundance (13C and 18O). With the support of quantum chemistry calculations, we have determined its molecular structure in the gas phase. Regarding the hydrates of myrtenal, we analyzed the spectraof 2 mono-, 2 di- and a trihydrate, while for perillaldehyde 4 mono- and 2 dihydrates are characterized. Withketones, weanalyzedthespectraof2mono-, 2di-and1trihydrateof verbenone, while for the microhydration of fenchone, we characterized 2 mono-, 2-di- and 3-trihydrates. In order to confirm the structure of the complexes, we used water enriched with oxygen 18, which allowed us through the constants of rotation of the isotopomers to calculate the structure of the detected hydrates by determining the position of the oxygen atoms by calculating their substitution coordinates, as well an effective structure limited to the arrangement of water molecules around the substrate.
Thesis supervisor :
Thérèse Huet (Université de Lille)
Thesis co-supervisor :
Pascal Dréan (Université de Lille)
Mme Maria Eugenia SANZ (King's College London)
M. Pierre ASSELIN (Université P. et M. Curie)
M. Philippe DUBUISSON (Université de Lille)
M. Alberto LESARRI (Universidad de Valladolid)
Mme Marie-Renée DEBACKER (Université de Reims)
Financing: Lille 1 University / Labex CaPPA