<i>Ab initio</i> quantum-chemical computations of the absorption cross sections of HgX<sub>2</sub> and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

Sitkiewicz, Sebastian P.; Rivero, Daniel; Oliva‐Enrich, Josep M.; Saiz‐Lopez, Alfonso; Roca‐Sanjuán, Daniel

doi:10.1039/c8cp06160b

Cited by 30 publications

(45 citation statements)

References 71 publications

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“…Ab initio non‐adiabatic molecular dynamics (AINAMD) calculations with multiconfigurational quantum chemistry were used to determine these important properties. AINAMD is a well‐established state‐of‐the‐art tool, which in this work accounts for the multiconfigurational nature and the strong spin mixing previously detected in mercury molecules, enabling an accurate determination of the distinct photodissociation yields. The photolysis rates of the mercury compounds listed above were subsequently calculated and incorporated into a kinetic model for the transformations among Hg II , Hg I , and Hg 0 .…”

Section: Introductionsupporting

confidence: 89%

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

et al. 2020

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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.

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Section: Introductionsupporting

confidence: 89%

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

et al. 2020

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“…Concentrations of OH, HO 2 , NO 2 , and particulate matter (PM 2.5 ) are imported from MOZART (42). We have also included the gas-phase photoreduction of HgBr, HOHg, HgBr 2 , HgBrOH, HgBrOOH, HgBrONO, HOHgOOH, and HOHgONO using the photolysis rates calculated by CAM-Chem (20,21,43) (see SI Appendix, Supplementary Note 4 for HgBr 2 ), including the photolysis yields determined theoretically by multiconfigurational quantum chemistry (24), and an aqueous-phase photoreduction in cloud droplets with a photolysis rate constant 0.153 h −1 . We perform simulations for the period 2007-2013 using anthropogenic Hg emissions for 2010 (1) of 1,875 Mg/y.…”

Section: Methodsmentioning

confidence: 99%

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere

Saiz‐Lopez

Travnikov

Sonke

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg0 to the atmosphere where it is oxidized to reactive HgII compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized HgI and HgII species postulate their photodissociation back to Hg0 as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg0, HgI, and HgII species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of HgI and HgII leads to insufficient Hg oxidation globally. The combined efficient photoreduction of HgI and HgII to Hg0 competes with thermal oxidation of Hg0, resulting in a large model overestimation of 99% of measured Hg0 and underestimation of 51% of oxidized Hg and ∼66% of HgII wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the HgI and HgII photoreduction processes largely offset the efficiency of bromine-initiated Hg0 oxidation and reveal missing Hg oxidation processes in the troposphere.

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“…Within the harmonic approximation, the Wigner sampling is also a suitable choice to represent the nuclear quantum distribution. 5,[18][19][20][21][22][23][24] This method, however, fails for highly flexible molecules because the harmonic approximation cannot be applied. González et al proposed two new sampling protocols to simulate absorption spectra called "local temperature adjustment" and "individual QM/MM-based relaxation."…”

Section: Introductionmentioning

confidence: 99%

Multiscale Modeling of Electronic Spectra Including Nuclear Quantum Effects

Fehér¹,

Madarász

Stirling³

2021

Preprint

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<div>Theoretical prediction of electronic absorption spectra without input from experiment is no easy feat as it requires addressing all the factors that affect line shapes. In practice, however, the methodologies are limited to treat these ingredients only to a certain extent. Here we present a multiscale protocol that addresses the temperature, solvent and nuclear quantum effects, anharmonicity and reconstruction of the final spectra from the individual transitions. First, QM/MM molecular dynamics is conducted to obtain trajectories of solute-solvent configurations, from which the corresponding quantum corrected ensembles are generated through the Generalized Smoothed Trajectory Analysis (GSTA). The optical spectra of the ensembles are then produced by calculating vertical transitions using TDDFT with implicit solvation. To obtain the final spectral shapes, the stick spectra from TDDFT are convoluted with Gaussian kernels where the half-widths are determined by a statistically motivated strategy. We have tested our method by calculating the UV-vis spectra of a recently discovered acridine photocatalyst in two redox states and evaluated the impact of each step. Nuclear quantization affects the relative peak intensities and widths, which is necessary to reproduce the experimental spectrum. We have also found that using only the optimized geometry of each molecule works surprisingly well if a proper empirical broadening factor is applied. This is explained by the rigidity of the conjugated chromophore moieties of the selected molecules which are mainly responsible for the excitations in the spectra. In contrast, we have also shown that the molecules are flexible enough to feature anharmonicities that impair the Wigner sampling. </div>

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Ab initio quantum-chemical computations of the absorption cross sections of HgX₂ and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

Abstract: 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).

Cited by 30 publications

References 71 publications

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

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

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere

Multiscale Modeling of Electronic Spectra Including Nuclear Quantum Effects

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Ab initio quantum-chemical computations of the absorption cross sections of HgX2 and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

Abstract: 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).

Cited by 30 publications

References 71 publications

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

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

Photochemistry of oxidized Hg(I) and Hg(II) species suggests missing mercury oxidation in the troposphere

Multiscale Modeling of Electronic Spectra Including Nuclear Quantum Effects

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Product

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Ab initio quantum-chemical computations of the absorption cross sections of HgX₂ and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere