Kinetic isotope effects in the gas phase reactions of OH and Cl with CH<sub>3</sub>Cl, CD<sub>3</sub>Cl, and <sup>13</sup>CH<sub>3</sub>Cl

Abstract

Abstract. The kinetic isotope effects in the reactions of CH3Cl, 13CH3Cl and CD3Cl with OH radicals and Cl atoms were studied in relative rate experiments at 298±2 K and 1013±10 mbar. The reactions were carried out in a smog chamber using long path FTIR detection and the spectroscopic data analyzed employing a non-linear least squares spectral fitting method using measured high-resolution infrared spectra as well as absorption cross sections from the HITRAN database. The reaction rates of 13CH3Cl and CD3Cl with OH and Cl were determined relative to CH3Cl as: kOH+CH3ClkOH+CH3Cl/kOH+13CH3Cl}kOH+13CH3Cl=1.059±0.008, kOH+CH3ClkOH+CH3Cl/kOH+CD3ClkOH+CD3Cl=3.9±0.4, kCl+CH3ClkCl+CH3Cl/kCl+13CH3ClkCl+13CH3Cl =1.070±0.010 and kCl+CH3ClkCl+CH3Cl/kCl+CD3ClkCl+CD3Cl=4.91±0.07. The uncertainties given are 2σ from the statistical analyses and do not include possible systematic errors. The unexpectedly large 13C kinetic isotope effect in the OH reaction of CH3Cl has important implications for the global emission inventory of CH3Cl.

Stable bromine isotopic composition of atmospheric CH₃Br

“…The reasons for o app value for d 81 Br-CH 3 Br of  (5 being substantially lower than the previously noted o for d 13 C-CH 3 Cl of (5993.7 (Gola et al, 2005), is likely to reflect dilution of the CH 3 Br concentration by nonfractionating sink processes, the mass dependency (smaller shifts for heavier atoms) and the characteristics of the primary tropospheric isotope fractionating atmospheric sink (e.g. the reaction with the hydroxyl radical).…”

“…Yvon-Lewis et al, 2009), the rate-limiting step in those processes is the net partitioning between air Á soil air and airÁseawater; such phase partitioning is unlikely to induce a substantial KIE (Huang et al, 1999). Laboratory experiments have demonstrated vapour-phase reactions of CH 3 Cl with Cl and OH radicals inducing a strong KIE for stable carbon isotopes in the remaining methyl halide substrate pool (Gola et al, 2005). We derived an apparent isotope enrichment factor (o app ) for the Stockholm free air d 81 Br-CH 3 Br dataset (i.e.…”

Stable carbon isotope ratio of methyl chloride emitted from glasshouse‐grown tropical plants and its implication for the global methyl chloride budget

“…The development of a technique for measuring the stable carbon isotopic composition of CH 3 Cl [ Rudolph et al , 1997] allowed Thompson et al [2002] to calculate for the first time the isotopic mass balance of atmospheric CH 3 Cl, although their isotopic database was very limited. Recent findings on important isotopic information for the removal of CH 3 Cl by reaction with OH radicals [ Gola et al , 2005] and CH 3 Cl emission from senescent or dead leaves [ Keppler et al , 2004] led Keppler et al [2005] to reanalyze the CH 3 Cl mass balance, and they have proposed that senescent plants and leaf litter in tropical and subtropical regions are likely the largest global sources of CH 3 Cl (1800 to 2500 Gg yr −1 ) to the atmosphere. However, isotopic data to reliably constrain the atmospheric budget are still lacking for some important sources.…”

Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

“…Isotopic ratio fluxes in combination with net mass fluxes can place greater constraints on methyl halide budgets and several groups have attempted to use stable isotopes to constrain the methyl chloride budget in this fashion (Gola et al, 2005;Keppler et al, 2005). A limited number of isotopic signatures have been measured for production and loss mechanisms involving methyl chloride (Keppler et al, 2005 and references therein).…”