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Autre Publication Scientifique Année : 2019

Gas phase THz spectroscopy of atmospheric precursor of secondary organic aerosols

Arnaud Cuisset

Résumé

Aromatic oxygenated compounds present in our atmosphere have a high emission rate from biomass burning [1] and mainly exist in the gas phase. They contribute to the secondary organic aerosols (SOA) formation via OH-oxidation processes [2]. The capability to monitor them in the atmosphere is required to fully understand the impact of SOA on the climate. Compared to lighter volatile organic compounds, it is for the moment not possible to detect and quantify them in the atmosphere by measuring their high resolution rovibrational signatures using on board instruments. Even in laboratory environment, the rovibrational structure of MP has up to present not been resolved at room temperature due to the huge density of states. Only millimeter-wave spectroscopy has the capacity to fully resolve Doppler limited rotational transitions at room temperature, as recently demonstrated by our group [3-4]. This study provides a full conformational analysis in the ground and in the lowest energy vibrational states of the MethoxyPhenol (MP) isomers by absorption and emission spectroscopies using a frequency multiplication chain [5] and a mm-wave Fourier transform chirped-pulse spectrometer [6], respectively. Such studies highlight the huge density of lines in MP spectra explained by rather small rotational constants and the presence of hot bands and several conformers. Guided by quantum chemistry calculations, the conformational landscape of the three MP has been characterized. The resolution of MP rovibrational structures requires to perform measurements at a very low temperature in molecular jets [7]. We took advantage of two complementary experimental configurations : (i) the JET-AILES apparatus, coupled to the AILES THz beamline of the SOLEIL synchrotron, which was used for middle resolution broadband scans of the 3 MP isomers in the fingerprint region (900-1700 cm-1) ; (ii) the SPIRALES set-up, with mid-IR quantum cascade laser (QCL) sources coupled to a pulsed molecular jet. This last set-up allowed to fully resolve the 18 mid-IR vibrational band of 3-MP centered at 950 cm-1. Finally, microwave, THz and IR spectrometers coupled to free jet supersonic beams suggest the possibility to study hydrated MP complexes in order to bridge the gap between gas-phase and SOA in the atmosphere towards the study of micro-solvation processes.
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hal-04512897 , version 1 (20-03-2024)

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  • HAL Id : hal-04512897 , version 1

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Arnaud Cuisset. Gas phase THz spectroscopy of atmospheric precursor of secondary organic aerosols. 2019. ⟨hal-04512897⟩

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