CH2Cl and CHCl2 Radical Chemistry: The Formation by the Reactions CH3Cl + F and CH2Cl2 + F and The Destruction by the Reactions CH2Cl + O and CHCl2 + O

Abstract

Abstract The primary product formation of the reactions CH2Cl + O and CHCl2 + O in the gas phase has been studied around room temperature. The coupling of a conventional discharge flow reactor via a molecular sampling system to a mass spectrometer with electron impact ionization allowed the determination of labile and stable species (set-up A). The radicals are formed by H atom abstraction in the reactions CH3Cl + F and CH2Cl2 + F. The product analysis leads to the following branching fractions relative to precursor consumption: For CH2Cl + O, the channel HCHO + Cl yields 19 % and CO + HCl + H yields 43 %, the contributions of the labile species HCO is found but not quantified. For CHCl2 + O the channel CO + HCl + Cl yields 70 %, ClCHO and the labile ClCO are detected but not quantified. The comparison to CH3 + O shows the stepwise increase of channel fractions for the CO forming routes by chlorination of the methyl radical. The rates of the reactions have been studied relative to CH3 + O and CH3OCH2 + O. Laser-induced multiphoton ionization combined with TOF mass spectrometry and molecular beam sampling from a flow reactor (set-up B) was used for the specific and sensitive detection of the CH2Cl, CHCl2, CH3, and CH3OCH2 radicals. The rate coefficient of the reactions CH2Cl + O was derived with reference to the reaction CH3OCH2 leading to k = (8.1±1.8)×1013 cm3/(mol·s) and for CHCl2 + O with reference to CH3 + O leading to k = (3.8±1.9)×1013 cm3/(mol·s). For CH3Cl + F and CH2Cl2 + F the rate coefficients have been determined with set-up A leading to k = (4.3±0.9)×1013 cm3/(mol·s) for CH3Cl + F and k = (8.4±3.8)×1013 cm3/(mol·s) for CH2Cl2 + F. Only a negligible temperature dependence in the temperature range from 250–360 K was observed for all reactions studied.