Theoretical investigation of the hydrogen abstraction reaction of the OH radical with CH2FCH2F (HFC-152): a dual-level direct dynamics study.

The hydrogen abstraction reaction of the OH radical with CH(2)FCH(2)F (HFC-152) is studied theoretically over the 150-3000 K temperature range. In this study, the two most recently developed hybrid density functional theories, namely, BB1K and MPWB1K, are applied, and their efficiency in reaction dynamics calculation is discussed. The BB1K/6-31+G(d,p) method gives the best result for the potential energy surface (PES) calculations, including barrier heights, reaction path information (the first and second derivatives of PES), geometry of transition state structures, and even weak hydrogen bond orientations. The rate constants were obtained by the dual-level direct dynamics with the interpolated single-point energy method (VTST-ISPE) using the BB1K/MG3S//BB1K/6-31+G(d,p) quantum model. The canonical variational transition state theory (CVT) with the small-curvature tunneling correction methods are used to calculate the rate constants in comparison to the experimental data. The total rate constant and its temperature dependency in the form of a fitted three-parameter Arrhenius expression is k(T) = 5.4 x 10(-13)(T/298)3.13 exp{-322/T} cm3 molecule(-1) s(-1). A significant variational effect, which is not common generally for hydrogen-transfer reactions, is reported and analyzed.