scholarly journals Gas-Phase Photolysis of Hg(I) Radical Species: A New Atmospheric Mercury Reduction Process

2019 ◽  
Vol 141 (22) ◽  
pp. 8698-8702 ◽  
Author(s):  
Alfonso Saiz-Lopez ◽  
A. Ulises Acuña ◽  
Tarek Trabelsi ◽  
Javier Carmona-García ◽  
Juan Z. Dávalos ◽  
...  
Keyword(s):  
Gas Phase ◽  
Reduction Process ◽  
Atmospheric Mercury ◽  
Radical Species ◽  
Mercury Reduction

Gas-phase pyrolysis of trans 3-pentenenitrile: competition between direct and isomerization-mediated dissociation

2021 ◽  
Vol 23 (11) ◽  
pp. 6462-6471
Author(s):  
Piyush Mishra ◽  
Sean M. Fritz ◽  
Sven Herbers ◽  
Alexander M. Mebel ◽  
Timothy S. Zwier
Keyword(s):  
Gas Phase ◽  
Molecular Beam ◽  
Microwave Spectroscopy ◽  
Radical Species ◽  
Flash Pyrolysis

The flash pyrolysis of trans 3-pentenenitrile was studied by mass-correlated broadband microwave spectroscopy, where both molecular and radical species were observed within our jet-cooled molecular beam, including 2,4-pentadienenitrile.

scholarly journals Global atmospheric model for mercury including oxidation by bromine atoms

2010 ◽  
Vol 10 (24) ◽  
pp. 12037-12057 ◽  
Author(s):  
C. D. Holmes ◽  
D. J. Jacob ◽  
E. S. Corbitt ◽  
J. Mao ◽  
X. Yang ◽  
...  
Keyword(s):  
Gas Phase ◽  
Atmospheric Model ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Deposition Flux ◽  
Mercury Deposition ◽  
Photochemical Reduction ◽  
Global Atmospheric Model ◽  
Summer Maximum ◽  
Southeast Us

Abstract. Global models of atmospheric mercury generally assume that gas-phase OH and ozone are the main oxidants converting Hg0 to HgII and thus driving mercury deposition to ecosystems. However, thermodynamic considerations argue against the importance of these reactions. We demonstrate here the viability of atomic bromine (Br) as an alternative Hg0 oxidant. We conduct a global 3-D simulation with the GEOS-Chem model assuming gas-phase Br to be the sole Hg0 oxidant (Hg + Br model) and compare to the previous version of the model with OH and ozone as the sole oxidants (Hg + OH/O3 model). We specify global 3-D Br concentration fields based on our best understanding of tropospheric and stratospheric Br chemistry. In both the Hg + Br and Hg + OH/O3 models, we add an aqueous photochemical reduction of HgII in cloud to impose a tropospheric lifetime for mercury of 6.5 months against deposition, as needed to reconcile observed total gaseous mercury (TGM) concentrations with current estimates of anthropogenic emissions. This added reduction would not be necessary in the Hg + Br model if we adjusted the Br oxidation kinetics downward within their range of uncertainty. We find that the Hg + Br and Hg + OH/O3 models are equally capable of reproducing the spatial distribution of TGM and its seasonal cycle at northern mid-latitudes. The Hg + Br model shows a steeper decline of TGM concentrations from the tropics to southern mid-latitudes. Only the Hg + Br model can reproduce the springtime depletion and summer rebound of TGM observed at polar sites; the snowpack component of GEOS-Chem suggests that 40% of HgII deposited to snow in the Arctic is transferred to the ocean and land reservoirs, amounting to a net deposition flux to the Arctic of 60 Mg a−1. Summertime events of depleted Hg0 at Antarctic sites due to subsidence are much better simulated by the Hg + Br model. Model comparisons to observed wet deposition fluxes of mercury in the US and Europe show general consistency. However the Hg + Br model does not capture the summer maximum over the southeast US because of low subtropical Br concentrations while the Hg + OH/O3 model does. Vertical profiles measured from aircraft show a decline of Hg0 above the tropopause that can be captured by both the Hg + Br and Hg + OH/O3 models, except in Arctic spring where the observed decline is much steeper than simulated by either model; we speculate that oxidation by Cl species might be responsible. The Hg + Br and Hg + OH/O3 models yield similar global budgets for the cycling of mercury between the atmosphere and surface reservoirs, but the Hg + Br model results in a much larger fraction of mercury deposited to the Southern Hemisphere oceans.

scholarly journals Theoretical Study about the Effect of Halogen Substitution on the Reactivity of Antitumor 3-Formylchromones and Their Free Radicals

2017 ◽  
Vol 2017 ◽  
pp. 1-5
Author(s):  
Maximiliano Martínez-Cifuentes ◽  
Boris Weiss-López ◽  
Ramiro Araya-Maturana
Keyword(s):  
Free Radicals ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Theoretical Study ◽  
Computational Study ◽  
Bond Dissociation Enthalpy ◽  
Radical Species ◽  
Anticancer Compounds ◽  
Dissociation Enthalpy ◽  
Polarizable Continuum

The mandatory presence of a chlorine atom on the aromatic ring of 6-hydroxy-3-formyl angular chromones, on the respiration inhibition of mammary carcinoma mouse, is explained through a computational study of these compounds. This study analyzes the reactivity of the neutral molecules and their free radicals, in gas phase and with water solvation, incorporated by the polarizable continuum medium (PCM) approach. Electrophilic reactivities were evaluated using Fukui (f+) and Parr (P+) functions. The stabilities of radical species formed by the abstraction of a hydrogen atom from the O-H bond were evaluated by bond dissociation enthalpy (BDE) and spin density (SD) calculations. This study has potential implications for the design of chromone analogues as anticancer compounds.

scholarly journals Quantum Chemical and Kinetic Study on Radical/Molecule Formation Mechanism of Pre-Intermediates for PCTA/PT/DT/DFs from 2-Chlorothiophenol and 2-Chlorophenol Precursors

2019 ◽  
Vol 20 (7) ◽  
pp. 1542
Author(s):  
Chenpeng Zuo ◽  
Hetong Wang ◽  
Wenxiao Pan ◽  
Siyuan Zheng ◽  
Fei Xu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Intermediate Formation ◽  
Polychlorinated Dibenzofurans ◽  
Formation Mechanisms ◽  
Coupling Mechanism ◽  
Phenoxy Radical ◽  
Radical Species ◽  
Molecule Formation ◽  
Kinetic Calculations

Polychlorinated phenoxathiins (PCPTs), polychlorinated dibenzothiophenes (PCDTs), and polychlorinated thianthrenes (PCTAs) are sulfur analogues of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/DFs). Chlorothiophenols (CTPs) and chlorophenols (CPs) are key precursors for the formation of PCTA/PT/DTs, which can react with H or OH to form chloro(thio)phenoxy radical, sulfydryl/hydroxyl-substituted phenyl radicals, and (thio)phenoxyl diradicals. However, previous radical/radical PCTA/DT formation mechanisms in the literature failed to explain the higher concentration of PCDTs than that of PCTAs under the pyrolysis or combustion conditions. In this work, a detailed thermodynamics and kinetic calculations were carried out to investigate the pre-intermediate formation for PCTA/PT/DTs from radical/molecule coupling of the 2-C(T)P with their key radical species. Our study showed that the radical/molecule coupling mechanism explains the gas-phase formation of PCTA/PT/DTs in both thermodynamic and kinetic perspectives. The S/C coupling modes to form thioether-(thio)enol intermediates are preferable over the O/C coupling modes to form ether-(thio)enol intermediates. Thus, although the radical/molecule coupling of chlorophenoxy radical with 2-C(T)P has no effect on the PCDD/PT formation, the radical/molecule coupling of chlorothiophenoxy radical with 2-C(T)P plays an important role in the PCTA/PT formation. Most importantly, the pre-PCDT intermediates formation pathways from the couplings of sulfydryl/hydroxyl-substituted phenyl radical with 2-C(T)P and (thio)phenoxyl diradicals with 2-C(T)P are more favorable than pre-PCTA/PT intermediates formation pathways from the coupling of chlorothiophenoxy radical with 2-C(T)P, which provides reasonable explanation for the high PCDT-to-PCTA ratio in the environment.

An insight into mercury reduction process by humic substances in aqueous medium under dark condition

2017 ◽  
Vol 24 (16) ◽  
pp. 14499-14507 ◽  
Author(s):  
Krushna Vudamala ◽  
Parthasarathi Chakraborty ◽  
Budati Bala Venkata Sailaja
Keyword(s):  
Aqueous Medium ◽  
Humic Substances ◽  
Reduction Process ◽  
Dark Condition ◽  
Mercury Reduction ◽  
Insight Into

Identification and gas phase kinetics of radical species in Cat-CVD processes of SiH4

2001 ◽  
Vol 395 (1-2) ◽  
pp. 47-50 ◽  
Author(s):  
Yoshitaka Nozaki ◽  
Makiko Kitazoe ◽  
Katsuhiko Horii ◽  
Hironobu Umemoto ◽  
Atsushi Masuda ◽  
...  
Keyword(s):  
Gas Phase ◽  
Radical Species ◽  
Gas Phase Kinetics ◽  
Kinetics Of

Vacuum-ultraviolet (147.0 nm and 123.6 nm) photolysis of 1,1-dimethylcyclopropane

1981 ◽  
Vol 59 (3) ◽  
pp. 537-542
Author(s):  
Joseph B. Binkewicz ◽  
Michael Kaplan ◽  
Richard D. Doepker
Keyword(s):  
Gas Phase ◽  
Vacuum Ultraviolet ◽  
Molecular Processes ◽  
Radical Scavengers ◽  
Primary Reaction ◽  
Radical Species ◽  
Molecule Reaction ◽  
Reaction Channels ◽  
A Charge ◽  
Photo Decomposition

The gas-phase photolysis of 1,1-dimethylcyclopropane has been investigated using xenon (147.0 nm) and krypton (123.6 nm) resonance radiation. Major products observed in order of decreasing importance were isobutene, ethylene, hydrogen, 1,3-butadiene 2-methyl-1,3-butadiene, propylene, allene, methylacetylene, and acetylene. Radical scavengers, NO and O2, and radical interceptors, H2S/D2S and HI, were used to determine the relative importance of radical and molecular processes. CH3, C2H3, C3H5, and C4H7 radical species were identified and quantified. Ten primary reaction channels were postulated, of which the elimination of methylene was the most predominant, accounting for 34% of the photo-decomposition at 147.0 nm and 39% at 123.6 nm. Although ionization was established at 123.6 nm (η = 0.10) the nature of a charge transfer or other ion-molecule reaction channel leading to the formation of 2-methyl-1-butene and 2-methyl-2-butene could not be determined.

Electrochemical reduction of dodecylpyridinium bromide in aprotic solvents: Mechanistic studies

2011 ◽  
Vol 76 (12) ◽  
pp. 1895-1908 ◽  
Author(s):  
Magdaléna Hromadová ◽  
Lubomír Pospíšil ◽  
Romana Sokolová ◽  
Viliam Kolivoška
Keyword(s):  
Pyrolytic Graphite ◽  
Mercury Electrode ◽  
Reduction Process ◽  
Ex Situ ◽  
Aprotic Solvents ◽  
Mechanistic Studies ◽  
Radical Species ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy ◽  
Adsorption Phenomena

Reduction mechanism of 1-dodecylpyridin-1-ium bromide (DPBr) in dimethylsulfoxide has been studied on mercury electrode. Based on the classical polarographic methods as well as on the use of AC techniques it was shown that DPBr is reduced in a reversible one electron transfer step followed by dimerization of the corresponding radical species. Reduction process is accompanied by the adsorption phenomena even in the non-aqueous solvents. Possible modes of DPBr adsorption have been studied by the ex situ scanning tunnelling microscopy (STM) imaging of these molecules on highly oriented pyrolytic graphite.

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