Photodissociation Mechanisms of Major Mercury(II) Species in the Atmospheric Chemical Cycle of Mercury

Abstract

Mercury is ac ontaminant of global concern that is transported throughout the atmosphere as elemental mercury Hg 0 and its oxidized forms Hg I and Hg II .T he efficient gasphase photolysis of Hg II and Hg I has recently been reported. However,w hether the photolysis of Hg II leads to other stable Hg II species,toHg I ,ortoHg 0 and its competition with thermal reactivity remain unknown. Herein, we showt hat all oxidized forms of mercury rapidly revert directly and indirectly to Hg 0 by photolysis.R esults are based on non-adiabatic dynamics simulations,inwhich the photoproduct ratios were determined with maximum errors of 3%. We construct for the first time ac omplete quantitative mechanism of the photochemical and thermal conversion between atmospheric Hg II ,H g I ,a nd Hg 0 compounds.T hese results reveal new fundamental chemistry that has broad implications for the global atmospheric Hg cycle.T hus,p hotoreduction clearly competes with thermal oxidation, with Hg 0 being the main photoproduct of Hg II photolysis in the atmosphere,w hich significantly increases the lifetime of this metal in the environment.

Reconstruction of Nuclear Ensemble Approach Electronic Spectra Using Probabilistic Machine Learning

“…In addition, values for Δ E and f for the uracil nucleobase OH radical (U6OH radical) 29 and the HgBrOOH atmospheric compound, 58 both previously reported by our group, have been used to test the methodologies developed in the current work. For the U6OH radical, there are pairs {Δ E , f } for 9 different transitions and 100 geometries, whereas for HgBrOOH, there are data for 79 transitions and 200 geometries.…”

BrHgO• + CO: Analogue of OH + CO and Reduction Path for Hg(II) in the Atmosphere

“…Mercury is a neurotoxin which is transported globally by the atmosphere . Mercury deposits from the atmosphere to ecosystems most efficiently when it is in the form of Hg­(II) compounds. , Unfortunately, we are still uncovering major aspects of the redox chemistry of atmospheric mercury. − This complicates efforts to predict the impact of emissions reductions on the spatial distribution of mercury entry into ecosystems. , …”

“…Because NO 2 is the most abundant radical in the atmosphere, BrHg • mostly reacts with NO 2 , and the major product of this reaction is BrHgONO. , Calculations by Francés-Monerris et al and Lam et al indicate that BrHgONO can absorb light at λ > 300 nm. As the flux of such light is relatively intense in the lowermost atmosphere, these groups argued that BrHgONO undergoes fast photolysis.…”

“…As the flux of such light is relatively intense in the lowermost atmosphere, these groups argued that BrHgONO undergoes fast photolysis. Lam et al and Francés-Monerris et al presented evidence that BrHgONO photolysis will mostly produce BrHgO • via …”

Light‐Induced On/Off Switching of the Surfactant Character of the o‐Cobaltabis(dicarbollide) Anion with No Covalent Bond Alteration

“…The excited-state rotation and decay mechanism are confirmed through state-of-the-art [33][34][35] non-adiabatic molecular dynamics [36,37] performed in a model system, including only the first three singlet and four triplet states in the simulations, initially exciting the S 1 state. Full simulation details can be found in the SI.…”