Theoretical Investigation of the Hydrogen Abstraction Reaction of the OH Radical with CH₂FCH₂F (HFC-152):  A Dual-Level Direct Dynamics Study

Abstract

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.

Direct dynamics study on mechanism and kinetics of the biradical self‐reaction of HOO

“…This has already been observed in other hydrogen abstraction reactions [41][42][43][44][45][46][47][48][49]. Table I lists the harmonic vibrational frequencies and zero-point energies (ZPE) of reactants, postreactant complexes, transition states, and products at the CCSD/6-31þG(d,p) level of theory along with the available experimental data [37,50,51].…”

Theoretical study of a reaction mechanism of tropospheric interest: CH3CH2F + OH

“…After spin projection, the spin contamination is negligible. The spin-projected MP2 (PMP2) method is well known to reproduce barrier heights in close agreement with experimental values [9,39]. The PMP2 method estimates reaction barriers up to about 10 kcal mol -1 lower than the MP2 method due to the presence of large spin contamination, as displayed in Figure 2 Schematic potential energy surfaces for CH 3 CH 2 F + OH reaction: (a) H-abstraction channels; (b) non-H abstraction channels.…”

Mechanism and Kinetics of the Hydrogen Abstraction Reaction of C₂H₃ with CH₃F

“…Similar characteristics have been reported in the hydrogen abstraction reaction from fluorinated alkanes. 10,11,56 Fig.3, the ZPE curve is practically constant as s varies with only a gentle drop near the saddle point. This phenomenon is a usual characteristic for the hydrogen abstraction reaction.…”