Samantha SENG
PhD in Chemistry
thesis defended on 16th november 2017
Laboratoire de Spectrochimie Infrarouge et Raman (LASIR)

Title and thesis summary
Publications
Oral & posters presentation

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Title and thesis summary

Phototransformation of compounds with atmospheric interest.
Spectroscopic study in gas phase, in cryogenic matrix and at the single particles scale.

Marine aerosols represent more than half of the global emission of particles into the atmosphere. Furthermore, sulfur organic compounds are generated by biological activities in the oceans and are emitted into the troposphere in the gaseous phase or are transported with sea-salt particles. These particles are subject to physicochemical changes due to atmospheric gases, sunlight and humidity exposure. The study of these transformation processes in the laboratory is essential for a better understanding of the mechanisms which are involved in these processes, and of the aerosols impact on the physical and chemical properties of the atmosphere.

In this work, the photochemical evolutions of inorganic and sulfur organic compounds, similar to compounds of marine origin, have been studied by spectroscopy in the gas phase, in cryogenic matrix and at the single particle scale. The acoustic levitation system coupled to micro-Raman spectrometry is a relevant tool for studying the photochemical mechanisms at the particle scale. The impact of the phototransformation of NaNO3 particles on their hygroscopic properties has been demonstrated. The experiments carried out in cryogenic matrix are especially interesting for the study of unimolecular processes involved in the photodegradation of the sulfur organic compounds and are complementary to studies in gas phase. The compounds produced by photolysis in gas phase and condensed phase are of atmospheric interest and have a potential impact on the atmospheric sulfur balance. The presence of oxygen and water modified the mechanisms and the nature of the photoproducts.

Thesis supervisor : Sophie Sobanska
Co-supervisor : Yeny Tobón
Referees : Stéphane Coussan et Eric Villenave
Examiners : Guilhem Simon et Céline Toubin

Financing: Université de Lille - Labex CaPPA

Publications

(i) L. Juncal, Y. Bava, L. Tamone, S. Seng, Y. Tobon, S. Sobanska, L. Picone, and R. Romano, “Experimental and theoretical investigation on conformational and spectroscopic properties of dimethyl dithiodiglycolate, [CH3OC(O)CH2S]2”, J. Mol. Struct., vol. 1137, pp. 524-529, Jun. 2017.
https://doi.org/10.1016/j.molstruc.2017.02.058

(ii) Y. Tobon, S. Seng, L. Picone, Y. Bava, L. Juncal, M. Moreau, R. Romano, J. Barbillat, S. Sobanska, “Photochemistry of single particles using acoustic levitation coupled with Raman microspectrometry”, J. Raman Spectrosc., vol. 48, pp. 1135-1137, Jun. 2017.
http://dx.doi.org/10.1002/jrs.5181

(iii) Y. Bava, L. Tamone, L. Juncal, S. Seng, Y. Tobon, S. Sobanska, L. Picone, and R. Romano, “Experimental and theoretical IR study of methyl thioglycolate, CH3OC(O)CH2SH, in different phases: Evidence of a dimer formation”, J. Mol. Struct., vol. 1139, pp. 160-165, Jul. 2017.
https://doi.org/10.1016/j.molstruc.2017.03.031

(iv) Y. Bava, L. Tamone, L. Juncal, S. Seng, Y. Tobon, S. Sobanska, L. Picone, and R. Romano, “Gas-phase and matrix-isolation photochemistry of methyl thioglycolate, CH3OC(O)CH2SH: Influence of the presence of molecular oxygen in the photochemical mechanisms”, J. Photochem. Photobiol. A Chem., vol. 344, pp. 101-107, Jul. 2017.
https://doi.org/10.1016/j.jphotochem.2017.05.003

 

Oral and posters presentation

Participation at more than 10 national and international conferences

Best poster award at the European Aerosol Conference 2016
EAC 2016
4-9 September 2016 – Tours
http://eac2016.fr/