Kinetics, mechanism and thermochemistry of the gas phase reactions of CF3CH2OCH2CF3 with OH radicals: A theoretical study

Abstract

Theoretical investigations have been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CF3CH2OCH2CF3 and OH radical using a newly developed DFT based M06-2X functional method. Two important H abstraction channels have been identified according to different orientations of the two H atoms bonded to same carbon atom in CH2 group, and one transition state has been located for each reaction channel. At the entry of each reaction channel, formation of pre-reactive complex indicates an indirect hydrogen-abstraction reaction. The rate coefficients were calculated for the first time over a wide range of temperature (250–1000K) and can be expressed as a model equation: kOH=2.55×10−11exp(−(2883.7−387626/T)/T)cm3molecule−1s−1. At 298K, our calculated rate coefficient for CF3CH2OCH2CF3 with OH radical 1.32×10−13cm3molecule−1s−1 is in very good agreement with the experimental result of kOH=1.30×10−13cm3molecule−1s−1. Using a group-balanced isodesmic reaction, the standard heats of formation for CF3CH2OCH2CF3 and CF3CHOCH2CF3 radical are estimated to be −365.64 and −316.84kcalmol−1, respectively. The calculated bond dissociation energy for the CH bond in CF3CH(H)OCH2CF3 is found to be 95.82kcalmol−1 at 298K. The atmospheric lifetime of CF3CH2OCH2CF3 was estimated to be around 0.272 years. The global warming potential and the main degradation process of alkoxy radical CF3CH(O)OCH2CF3 are also discussed.