Direct ab initio dynamics studies of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical

Abstract

The kinetics of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical were studied using the direct ab initio dynamics approach. BHandHLYP/cc-pVDZ method was employed to optimize the geometries of stationary points as well as the points on the minimum energy path (MEP). The energies of all the points for the two reactions were further refined at the QCISD(T)/cc-pVTZ level of theory. No barrier was found at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory for both reactions. The forward and reverse rate constants were evaluated with both canonical variational transition state theory (CVT) and microcanonical variational transition state theory (μ VT) in the temperature range of 300–2,500 K. The fitted three-parameter Arrhenius expression of the calculated CVT rate constants at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory are k^CVT (n – C₃H₇)=1.68×10⁻¹⁴ T^0.84 e^(319.5/T) cm³ molecule⁻¹ s⁻¹ and k^CVT (iso-C₃H₇)=4.99×10⁻¹⁴ T^0.90 e^(159.5/T) cm³ molecule⁻¹ s⁻¹ for reactions of n-C₃H₇ + H and iso-C₃H₇ + H, respectively, which are in good agreement with available literature data. The variational effects were analysed.

Figure Comparison of the calculated forward rate constants at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory and the available experimental and theoretical data of the reaction vs 1,000/T for the two reactions.