Theoretical studies on the mechanism and kinetics of the hydrogen abstraction reactions of threo-CF3CHFCHFC2F5 and erythro-CF3CHFCHFC2F5 (HFC-43-10mee) by OH radicals

Abstract

In this research, some well-tested density functional theory (DFT) methods are used to investigate the potential energy surfaces for the hydrogen abstraction reactions of threo-CF3CHFCHFC2F5 and erythro-CF3CHFCHFC2F5 (HFC-43-10mee) by OH radicals. M06-2X density functional method along with the standard 6-31+G(d,p) basis set is employed to optimize the geometries for the reactants, van der Waals complexes, saddle-points and products. The vibrational frequencies are also computed at the M06-2X/6-31+G(d,p) level. In order to obtain more accurate energies, single-point calculations are performed at the M05-2X/MG3S, M06-2X/MG3S, MPWB1K/MG3S, BB1K/MG3S and KMLYP/6-311++G(2d,2p) levels of theory. Consistent results are obtained for the computed energies by different DFT methods. Transition state theory is employed to compute the thermal rate coefficients in the temperature range from 200 to 2000K. Quantum tunneling effects are computed for an unsymmetrical Eckart potential barrier. The computed rate coefficients employing M05-2X/MG3S and MPWB1K/MG3S are in more agreement with the available experimental data. On the basis of this theoretical study, the atmospheric lifetime of the HFC-43-10mee is estimated to be about 18years.