Photochemistry of Methyl thioglycolate, CH3OC(O)CH2SH, in condensed phase

YENY A. TOBÓN; A. LORENA PICONE; LUCIANA C. JUNCAL; RALUCA CIURARU; CHRISTIAN GEORGE; ROSANA M. ROMANO; SAMANTHA SENG; YANINA B. BAVA; MYRIAM MOREAU; SOPHIE SOBANSKA

Nancy

Conferencia; Conférence de Physique Chimie - Physical Chemistry, CPC16; 2016

Sulphur-rich compounds are important species found in marine environments which contribute to the global sulfur cycle. The sulfur-containing species evolves to different oxidation states. The most studied cases are the oxidation of SO2 and dimethylsulfide (DMS) to SO42-to form secondary sulfated aerosols [1-2].Considering that thiol compounds, such as methyl thioglycolate (MTG), are well known to be precursor in free-radical photoinitiated polymerization processes [3], photoreactivity of S-rich species in the atmosphere can be also suspected. Moreover, most of studies have reported oxidation processes in gaseous phase as the main way when the photolysis of condensed phase has been poorly explored. So, in order to better comprehend the atmospheric sulfur cycle we investigated in this work the photolysis of a thiol species (MTG) in condensed phase.Liquid methyl thioglycolate (MTG) pure or in aqueous solution were irradiated with UV-Vis light and the processes taking place in the condense phase were followed by Raman spectroscopy and HR-PTR-ToF-MS. We have studied these systems by three different approaches: study in bulk conditions, study of individual micrometric particles through an acoustic levitation system, and study at the gas-liquid interfaces. Results of the three experimental conditions showed various products. Pure MTG in levitation is first oxidized, without irradiation, to its disulfide derivative, (CH3OC(O)CH2S)2 and then, S8 and SO42- are formed under irradiation on the surface of microdroplets with a particle size reduction. When MTG is in water solution photoreactivity is slower than in levitation. Bulk experiments showed the formation in condensed phase of methyl acetate, CH3OC(O)CH3, and S8. Finally irradiation at the gas-liquid interface showed the formation in gas phase of a series of organosulfur compounds, like dimethyl sulfide, thiols (e.g. methanethiol, butenethiol) or oxygen and sulfur containing compounds. Both gaseous and condensed characterizations match with an additional way for the formation of secondary sulfated compounds which are of atmospheric interest.