2) Environmental Sciences

The physical properties, chemical reactions, evolution, and characterisation of either particles or molecules involved in atmospheric processes are tackled from a physicochemical perspective using commercial or home-built instrumentation. Our research activities with respect to this theme are described below.

The structural properties of volatile organic compounds (VOCs) are investigated. These studies are supported by the LabEx CaPPA and the CPER CLIMIBIO and ECRIN. Three objectives are considered:

1. Identify the position of micro-solvation sites with water. We aim to show how water could interact with the oxidation products of volatile organic compounds, minority compounds of the atmosphere, in the gas phase, especially with monoterpenoids (alhedydes and bicyclic ketones comprising 10 carbon atoms). For example, mono-, di- and tri-hydrates were characterized for verbenone and nopinone, using quantum chemical calculations and Fourier-transform microwave spectroscopy in a pulsed supersonic jet.
2. Study the structural changes of the parent species associated to micro-hydration. For example, we have shown how a hydration process changes (case of fenchol), or does not change (case of myrtenol), the conformational landscape of the host molecule, at the level of a functional group, in terms of relative energy. We have emphasized the importance of hydrogen bonding in stabilizing the lowest energy species.
3. The study of solvent species is extended from water to hydrogen sulphide (H2S), the latter being ubiquitous in the atmosphere. They are emitted by human activities (combustion processes), but natural sources provide the largest amounts of sulphur compounds. They play a crucial role in the formation of secondary organic aerosols (SOAs), by transforming organic volatile compounds (VOCs) mainly emitted by terrestrial vegetation into the condensed phase, in particular through weak interactions (hydrogen bond, London dispersion forces). Note that hydrogen bond involving an atom of sulphur is expected to be weaker than that involving an oxygen atom. We performed the first quantitative characterisation of the hydrogen bond of H2S with biogenic volatile organic compounds. Our work on fenchol and fenchone indicated that sulphur behaves differently from oxygen during the micro-solvation process.