title: Mass-Dependent and -Independent Fractionation of Mercury Isotope during Gas-Phase Oxidation of Elemental Mercury Vapor by Atomic Cl and Br.
abstract: This study presents the first measurement of Hg stable isotope fractionation during gas-phase oxidation of Hg(0) vapor by halogen atoms (Cl(•), Br(•)) in the laboratory at 750 ± 1 Torr and 298 ± 3 K. Using a relative rate technique, the rate coefficients for Hg(0)+Cl(•) and Hg(0)+Br(•) reactions are determined to be (1.8 ± 0.5) × 10(-11) and (1.6 ± 0.8) × 10(-12) cm(3) molecule(-1) s(-1), respectively. Results show that heavier isotopes are preferentially enriched in the remaining Hg(0) during Cl(•) initiated oxidation, whereas being enriched in the product during oxidation by Br(•). The fractionation factors for (202)Hg/(198)Hg during the Cl(•) and Br(•) initiated oxidations are α(202/198) = 0.99941 ± 0.00006 (2σ) and 1.00074 ± 0.00014 (2σ), respectively. A Δ(199)Hg/Δ(201)Hg ratio of 1.64 ± 0.30 (2σ) during oxidation of Hg(0) by Br atoms suggests that Hg-MIF is introduced by the nuclear volume effect (NVE). In contrast, the Hg(0) + Cl(•) reaction produces a Δ(199)Hg/Δ(201)Hg-slope of 1.89 ± 0.18 (2σ), which in addition to a high degree of odd-mass-number isotope MIF suggests impacts from MIF effects other than NVE. This reaction also exhibits significant MIF of (200)Hg (Δ(200)Hg, up to -0.17‰ in the reactant) and is the first physicochemical process identified to trigger (200)Hg anomalies that are frequently detected in atmospheric samples.
authors: University of Chinese Academy of Sciences, Beijing 100190, China.
authors: Guangyi
authors: G
authors: Sun
authors: Jonas
authors: J
authors: Sommar
authors: Xinbin
authors: X
authors: Feng
authors: Center for Advances in Water and Air Quality, Lamar University , Beaumont, Texas 77710, United States.
authors: Che-Jen
authors: CJ
authors: Lin
authors: Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors: Maofa
authors: M
authors: Ge
authors: Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors: Weigang
authors: W
authors: Wang
authors: Environmental Chemistry and Technology Program, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
authors: Runsheng
authors: R
authors: Yin
authors: Xuewu
authors: X
authors: Fu
authors: Lihai
authors: L
authors: Shang
mesh_terms: D005591:Chemical Fractionation; D007554:Isotopes; D008628:Mercury; D008629:Mercury Isotopes; D010084:Oxidation-Reduction
chemical_list: D007554:Isotopes; D008629:Mercury Isotopes; D008628:Mercury