Theoretical studies on atmospheric chemistry of (CF3)2C(OH)CH3: Kinetics, mechanism and thermochemistry of gas phase reactions with OH radicals

Abstract

Abstract The mechanism, kinetics and thermochemistry of the reaction of (CF3)2C(OH)CH3 with OH radicals are theoretically investigated using DFT based M06-2X functional method. Three important H-abstraction channels have been identified for (CF3)2C(OH)CH3 + OH reaction and one transition state has been located for each reaction channel. Formation of pre-reactive complex at the entry of each reaction channel indicates an indirect mechanism for hydrogen-abstraction reaction. The rate coefficients for (CF3)2C(OH)CH3 are evaluated using canonical transition state theory along with Eckart's tunneling correction over a wide range of temperature (270–1000 K). At 298 K, our calculated total rate coefficient for (CF3)2C(OH)CH3 + OH reaction is in good agreement with the experimental result. The results show that H-abstraction from the CH3 group is the predominant channel and has more contribution to the total rate coefficient than that from the OH group of (CF3)2C(OH)CH3. The standard heats of formation for (CF3)2C(OH)CH3 molecule, (CF3)2C(OH)CH2 and (CF3)2C(O)CH3 radicals are estimated by using group-balanced isodesmic reactions and the values are −1599.6, −1369.8 and −1335.6 kJ mol−1, respectively at 298 K. The atmospheric lifetime of (CF3)2C(OH)CH3 is estimated to be around 5.0 years. The 100-year time horizon global warming potentials of (CF3)2C(OH)CH3 with respect to CO2 is 705. Potential atmospheric degradation routes for the resulting (CF3)2C(OH)CH2 radical is also discussed here.