Anthropogenic mercury (Hg(0)) emissions oxidize to gaseous Hg(II) compounds, before deposition to Earth surface ecosystems. Atmospheric reduction of Hg(II) competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Global Hg models have postulated that Hg(II) reduction in the atmosphere occurs through aqueous-phase photoreduction that may take place in clouds. Here we report that experimental rainfall Hg(II) photoreduction rates are much slower than modelled rates. We compute absorption cross sections of Hg(II) compounds and show that fast gas-phase Hg(II) photolysis can dominate atmospheric mercury reduction and lead to a substantial increase in the modelled, global atmospheric Hg lifetime by a factor two. Models with Hg(II) photolysis show enhanced Hg(0) deposition to land, which may prolong recovery of aquatic ecosystems long after Hg emissions are lowered, due to the longer residence time of Hg in soils compared with the ocean. Fast Hg(II) photolysis substantially changes atmospheric Hg dynamics and requires further assessment at regional and local scales.
The electronic-structure properties of the low-lying electronic states and the absorption cross sections of mercury halides have been determined within the UV-vis spectrum range (170 nm ≤ λphoton ≤ 600 nm).
Frustrated Lewis pairs (FLPs) based on nitrogen heterocycles (pyridine, pyrazole,
and imidazole) with a silane or germane group in the α-position
of a nitrogen atom have been considered as potential molecules to
sequestrate carbon dioxide. Three stationary points have been characterized
in the reaction profile: a pre-reactive complex, an adduct minimum,
and the transition state connecting them. The effect of external (solvent)
or internal (hydroxyl group) electric fields in the reaction profile
has been considered. In both cases, it is possible to improve the
kinetics and thermodynamics of the complexation of CO
2
by
the FLP and favor the formation of adducts.
Diborane has long been realized to be analogous to ethylene in terms of its bonding MOs, both as to symmetries and splitting patterns. This naturally suggests an investigation to see whether other similar conjugated hydrocarbons manifest a similar boron‐substituted and H2 supplemented borane. That is, for a conjugated hydrocarbon structure with a neighbor‐paired resonance pattern, we propose to look at boranes where each carbon atom is replaced by a boron atom, and an H‐atom pair is added to each double bond of the resonance structure, with one H above the molecular plane and one below. This construction of concatenated diboranes is uniformly different than that for the previously known stable boranes of 4 or more B atoms. We find from quantum‐chemical computations that our so constructed polyboranes are stable. All this suggests a possible novel new chapter in borane chemistry – a chapter with some promise of understandings related to that for (alternant) conjugated hydrocarbons.
The weakly coordinating binary macropolyhedral anion closo,closo-
[B 21 H 18 ]À (B21; D 3h symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with b-and c-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, a-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical
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