Selenium (Se) is an essential element for fauna, flora, and human health. Up to a third of Se can cycle through the atmosphere. The volatile organic Se species include dimethyl selenide (CH3SeCH3), dimethyl diselenide (CH3SeSeCH3), and methaneselenol (CH3SeH), and will undergo rapid atmospheric oxidation. To better constrain the fate of atmospheric Se compounds, high-level ab initio electronic structure calculations were performed to estimate the thermodynamic properties of 11 gaseous Se species (HSe•, H2Se, CH2Se, CH3SeH, •CH2SeH, CH3Se•, CH3SeSe•, CH3SeCH3, CH3Se•CH2, CH3SeSeCH3, and CH3SeSe•CH2) using their atomization reactions. Several corrections were applied to provide highly accurate calculated standard enthalpies of formation at 298 K, ΔfH°298 K. Standard molar entropy at 298 K, S°298 K, and heat capacity, Cp(T) over the temperature range 300–1500 K, from vibrational, translational, and external rotation contributions were computed using statistical thermodynamics based on the vibrational frequencies and structures obtained at the CCSD(T)/aVTZ level of theory. Hindered rotational contributions to S°298 K and Cp(T) were calculated from the energy levels, where the internal rotation potential was calculated at the MP2/aVTZ level of theory. The bond dissociation energies at 298 K for H–Se, Se–Se, and C–Se bonds in the Se molecules were derived from their calculated ΔfH°298 K values. The same protocol was applied to O and S species for comparison with Se. Their ΔfH°298 K, S°298 K, and Cp(T) values were in good agreement with the corresponding available literature data. This work provided the first thermodynamic properties for the organic Se species. The data obtained in this work could be used in chemical-transport models to assess the fate of atmospheric Se and its speciation unravelling the Se biogeochemical cycles.

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De 2021 à 2024, les scientifiques de l’Ifremer et du laboratoire EPOC, rattaché entre autres au CNRS, ont recherché dans l’eau de mer et dans des mollusques la présence d’une centaine de contaminants.

Ab initio MRD-CI calculations have been performed for the SH radical in its low-lying valence states as well as vertically for the first Rydberg terms (2π24s, 2π24p and 2π23d). The lowest 1 4,2Σ-...

A high-level quartic ab initio potential energy surface of methanol has been used to calculate spectroscopic constants of the 12CH3OH molecule. These include coefficients of quartic anharmonic reso...

The reactivity of hydroxyl radicals (HO·) towards three neonicotonoid insecticides, namely imidacloprid, thiacloprid and acetamiprid was investigated. These radicals were generated by photolysis of H2O2 solutions. Flash photolysis experiments were used to determine the rate constants of 5.5 × 1010 M−1s−1, 6 × 1010 M−1s−1, and 7.5 × 1010 M−1s−1, for the reactions of HO· with acetamiprid, imidacloprid, and thiacloprid, respectively. Continuous irradiation experiments in the absence and presence of H2O2 allowed the identification and toxicity evaluation of the primary photo- and oxidation products of the insecticides. In all cases, the less toxic 6-chloronicotinic acid was found to be the major product at higher degrees of oxidation. The results reported here indicate that the half life of the insecticides due to their reaction with HO· radicals in natural aquatic reservoirs may vary between 5 h and 19 days, and therefore the hydroxyl radical-mediated oxidation may be a significant abiotic elimination route. However, elimination of the insecticide under such conditions might not improve the quality of the contaminated water, as the primary products of degradation still show considerable toxicity to Vibrio fischeri assays.

🎖️Florent Louis, élu Fellow de la Royal society of chemistry Ce titre prestigieux récompense Florent Louis, chercheur au Laboratoire PhysicoChimie des Processus de Combustion et de l'Atmosphère (PC2...

The sulfate radical anion (SO4●–)-initiated oxidation of the herbicide metazachlor (MTZ) was investigated in aqueous and gaseous phases using the density functional theory at the M06-2X/6-311++G(3df,3...