How elementary mercury reacts in the presence of halogen radicals and/or halogen anions: a DFT investigation.
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 HgX(3)* and HgX(4)* 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 HgX(3)(-), which is predicted to be the most stable species. In solution, redox chemistry can occur and transform GEM in the presence of X(2). The redox potentials of the couples HgX(2)/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 Hg(2+) 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.
Maron
Laurent
L
Laboratoire de Physique et Chimie des Nanoobjets (UMR 5215), INSA, Université Paul Sabatier, 135, avenue de Rangueil, 31077 Toulouse Cedex, France. laurent.maron@irsamc.ups-tlse.fr
Dommergue
Aurélien
A
Ferrari
Christophe
C
Delacour-Larose
Marlène
M
Faïn
Xavier
X