Theoretical studies on mechanism and kinetics of the hydrogen-abstraction reaction of CF3CH2CH2OH with OH radical

The hydrogen abstraction reaction of CF3CH2CH2OH + OH has been studied theoretically by dual-level direct dynamics method. The required potential energy surface information for the kinetic calculation was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. Five stable conformers of CF3CH2CH2OH have been located. For each conformer, there are three potential H-abstraction sites (Cα, Cβ and -OH), and some of the H atoms can be abstracted by more than one abstraction channel due to the different attack orientations of the incoming OH radical. As a result, 31 distinct Habstraction channels have been identified for the reaction. The individual rate constants for each Habstraction channel were calculated by the improved canonical transition-state theory with smallcurvature tunneling correction (ICVT/SCT), and the overall rate constant was evaluated by the Boltzmann distribution function. It is shown that the calculated rate constant is in good agreement with the available experimental data at 298 K, and exhibits negative temperature dependence with 200-350 K. H-abstraction from the α site dominates the reaction at low temperatures, while the contributions from the β and OH abstractions should be taken into account as temperature increases. The fitted four-parameter expressions within 200-1000 K for the overall rate constants as well as the rate constants from the α, β and OH abstractions were given to provide good estimation for future laboratory investigations. In addition, because of the lack of available experimental data for the product radicals involved in the reactions, their enthalpies of the formation (ΔHf,298°) were predicted via isodesmic reaction at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level.

Highlights► The PES for the reaction of CF3CH2CH2OH + OH was explored. ► Five conformers of CF3CH2CH2OH were considered in the kinetic calculation. ► The individual ICVT/SCT rate constants for each H-abstraction channel were evaluated. ► The selectivity of reaction sites was determined.