Dipole Polarizabilities of Fluorinated Hydrocarbons

Dipole polarizabilities of fluorinated C2 and C3 hydrocarbons have been studied using Coupled Cluster theory including single, double and non-iterative triple substitutions (CCSD(T)) – in conjunction with three basis sets: Pol, Z3Pol and HyPol. All molecular geometries were optimized at the MP2/aug-ccpVTZ level. We have found only small effects of electron correlation on electric properties in fluorinated species. The dipole polarizabilities increase slightly with the increasing fluorination of ethene and propene. For fluorinated ethenes Pol and Z3Pol basis sets give polarizabilities in very good agreement with the literature data

The Kinetics of the Reaction C2H5• + HI → C2H6 + I• over an Extended Temperature Range (213-623 K): Experiment and Modeling

The present study reports temperature dependent rate constants k1 for the title reaction across the temperature range 213 to 293 K obtained in a Knudsen flow reactor equipped with an external free radical source based on the reaction C2H5I + H• → C2H5• + HI and single VUV-photon ionization mass spectrometry using Lyman-α radiation of 10.2 eV. Combined with previously obtained high-temperature data of k1 in the range 298-623 K using the identical experimental equipment and based on the kinetics of C2H5• disappearance with increasing HI concentration we arrive at the following temperature dependence best described by a three-parameter fit to the combined data set: k1 = (1.89 ± 1.19)10−13(T/298)2.92±0.51 exp ((3570 ± 1500)/RT), R = 8.314 J mol-1 K-1 in the range 213-623 K. The present results confirm the general properties of kinetic data obtained either in static or Knudsen flow reactors and do nothing to reconcile the significant body of data obtained in laminar flow reactors using photolytic free radical generation and suitable free radical precursors. The resulting rate constant for wall-catalyzed disappearance of ethyl radical across the full temperature range is discussed. Highly correlated ab initio quantum chemistry methods and canonical transition state theory were applied for the reaction energy profiles and rate constants. Geometry optimizations of reactants, products, molecular complexes, and transition states are determined at the CCSD/cc-pVDZ level of theory. Subsequent single-point energy calculations employed the DK-CCSD(T)/ANO-RCC level. Further improvement of electronic energies has been achieved by applying spin-orbit coupling corrections towards full configuration interaction and hindered rotation analysis of vibrational contributions. The resulting theoretical rate constants in the temperature range 213-623 K lie in the range E-11-E-12 cm3 molecule-1 s-1, however experiments and theoretical modelling seem at great odds with each other

Improved mechanistic model of the atmospheric redox chemistry of mercury

12 pags, 4 figs, 3 tabs. -- The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.1c03160.We present a new chemical mechanism for Hg0/HgI/HgII atmospheric cycling, including recent laboratory and computational data, and implement it in the GEOS-Chem global atmospheric chemistry model for comparison to observations. Our mechanism includes the oxidation of Hg0 by Br and OH, subsequent oxidation of HgI by ozone and radicals, respeciation of HgII in aerosols and cloud droplets, and speciated HgII photolysis in the gas and aqueous phases. The tropospheric Hg lifetime against deposition in the model is 5.5 months, consistent with observational constraints. The model reproduces the observed global surface Hg0 concentrations and HgII wet deposition fluxes. Br and OH make comparable contributions to global net oxidation of Hg0 to HgII. Ozone is the principal HgI oxidant, enabling the efficient oxidation of Hg0 to HgII by OH. BrHgIIOH and HgII(OH)2, the initial HgII products of Hg0 oxidation, respeciate in aerosols and clouds to organic and inorganic complexes, and volatilize to photostable forms. Reduction of HgII to Hg0 takes place largely through photolysis of aqueous HgII-organic complexes. 71% of model HgII deposition is to the oceans. Major uncertainties for atmospheric Hg chemistry modeling include Br concentrations, stability and reactions of HgI, and speciation and photoreduction of HgII in aerosols and clouds.This work was funded by the USEPA Science to Achieve Results (STAR) Program. This work was also supported by the Slovak Grant Agency VEGA (grant 1/0777/19), the highperformance computing facility of the Centre for Information Technology (https://uniba.sk/en/HPC-Clara) at Comenius University, and the U.S. National Science Foundation under awards 1609848 and 2004100. We thank Helene Angot (CU Boulder) for the Hg measurement data.Peer reviewe

Reactivity of CHI3 with OH Radicals: X-Abstraction Reaction Pathways (X = H, I), Atmospheric Chemistry, and Nuclear Safety

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Theoretical Study of the Reactions of H Atoms with CH3I and CH2I2

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Modelling of the behaviour of iodine oxides

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Theoretical study of the reaction of BrHgO + CO: An analogue of OH + CO

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Modelling of the behaviour of iodine oxides

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Thermochemistry of HIO2 species and reactivity of iodous acid with chlorine atom

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