Theoretical investigation on gas-phase reaction of CF3CH2OCH3 with OH radicals and fate of alkoxy radicals (CF3CH(O)OCH3/CF3CH2OCH2O)

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF₃CH₂OCH₃ (HFE-263fb2) with OH radicals using ab-initio and DFT methods. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels, respectively. Our calculations reveal that hydrogen abstraction from the CH₂ group is thermodynamically and kinetically more facile than that from the CH₃ group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CF₃CH₂OCH₃ and radicals (CF₃CHOCH₃ and CF₃CH₂OCH₂) are also reported for the first time. The calculated bond dissociation energies for the CH bonds are in good agreement with experimental results. At 298 K, the calculated total rate coefficient for CF₃CH₂OCH₃ + OH reactions is found to be in good agreement with the experimental results. The atmospheric fate of the alkoxy radicals, CF₃CH(O)OCH₃ and CF₃CH₂OCH₂O are also investigated for the first time using the same level of theory. Out of three plausible decomposition channels, our results clearly point out that reaction with O₂ is not the dominant path leading to the formation of CF₃C(O)OCH₃ for the decomposition of CF₃CH(O)OCH₃ radical in the atmosphere. This is in accord with the recent report of Osterstrom et al. [CPL 524 (2012) 32] but found to be in contradiction with experimental finding of Oyaro et al. [JPCA 109 (2005) 337].