Mechanistic study of the reaction of CH2F2 with Cl atoms in the absence and presence of CH4 or C2H6: decomposition of CHF2OH and fate of the CHF2O radical. Issue 18 (17th April 2019)

• Record Type: Journal Article
• Authors: Østerstrøm, Freja F.; Andersen, Christina; da Silva, Gabriel
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 18(2019)
• Page Start: 9376
• Page End: 9383
• Publication Date: 2019-04-17
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c8cp06425c
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : First experimental and theoretical study determining the atmospheric fates of CHF2 OH and CHF2 O; products from degradation of a chlorofluorocarbon replacement. Abstract : To assess the atmospheric fate of fluorinated compounds, chamber experiments were performed with Fourier transform infrared spectroscopy investigating the products of difluoromethane, CH2 F2, at 296 ± 2 K. The reactions were initiated by reaction of CH2 F2 with Cl atoms in the absence and presence of CH4 or C2 H6 in air or O2 . No evidence of formation of the fluorinated alcohol, CHF2 OH, from the reactions of the CHF2 O2 radical with either CH3 O2 or CH3 CH2 O2 was observed. However, evidence of an alkoxy radical pathway was observed to form CHF2 OH. The alkoxy radical, CHF2 O, abstracts a hydrogen atom from CH2 F2 (with reaction mixtures of high initial CH2 F2 concentrations) to give the alcohol CHF2 OH that in turn decomposes with a rate coefficient of k (CHF2 OH) = (1.68 × 10 −3 ± 0.19 × 10 −3 ) s −1, giving a half-life of the alcohol of (412 ± 48) s. Theoretical calculations indicate that the CHF2 OH decomposition is unlikely to be a unimolecular process, and we instead propose that it is catalyzed by –OH groups present in molecules, or on particles or surfaces. HC(O)F is formed in a yield indistinguishable from 100% from the decomposition of CHF2 OH. The competition between the reaction of CHF2 O radicals with O2 and with CH2 F2 was investigated and an experimental rate coefficient ratio of 0.57 ± 0.08 of reaction with O2 over reaction with CH2 F2 was determined. Ab initio calculations support a larger reaction barrier for the O2 reaction by 0.5 kcal mol −1, with transition state theory predicting a rate coefficient ratio of 0.35, in reasonable agreement with experiment. The primary product of the atmospheric degradation of CH2 F2 is expected to be C(O)F2 formed by the reaction of CHF2 O with O2 .