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How Elementary Mercury Reacts in the Presence of Halogen Radicals and/or Halogen Anions: A DFT Investigation

Abstract : Reactions of elementary mercury in the gas phase (GEM) have been investigated at the DFT level in the presence of halogen radicals and/or halogen anions. In the presence of radicals, the formation of HgX3. and HgX42. is predicted to be favourable. Moreover, in the presence of anions, the free-radical liberation is enhanced from these two species allowing the presence of halogen free radicals even without the presence of light radiation. This enhancement is associated with the formation of HgX3-, which is predicted to be the most stable species. In solution, redox chemistry can occur and transform GEM in the presence of X2. The redox potentials of the couples HgX2/Hg for X=Cl, Br and I were calculated to be 0.52, 0.48 and 0.04 V, respectively. This study gives new opportunities to elucidate the environmental chemistry of Hg in the polar regions. In these areas GEM has a unique and fast reactivity due to a combination of factors such as the polar sunrise, the presence of halogenated radicals, snow and ice surfaces and cold temperatures. This reactivity, known as atmospheric mercury depletion events (AMDEs), leads to the deposition of significant amounts of Hg2+ in these regions. The reaction pathways of AMDEs are as yet unknown and the DFT approach may contribute to their elucidation and to the proposal of new mechanisms. Additionally, this study introduces hypotheses concerning the reactivity of GEM inside snowpacks.
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Submitted on : Wednesday, April 29, 2009 - 10:32:32 AM
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Laurent Maron, Aurélien Dommergue, Christophe Ferrari, Marlène Delacour-Larose, Xavier Faïn. How Elementary Mercury Reacts in the Presence of Halogen Radicals and/or Halogen Anions: A DFT Investigation. Chemistry - A European Journal, Wiley-VCH Verlag, 2008, 14 (27), pp.8322 à 8329. ⟨10.1002/chem.200800491⟩. ⟨insu-00379686⟩

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