Ab initio transition state theory calculation of the rate constant for the hydrogen abstraction reaction H2O2+H→H2+HO2

Large basis set and two levels of ab initio calculation (ROHF and MCSCF) are used to determine the electronic structure of reactants, products, and saddle point involved in the hydrogen abstraction reaction H2O2+H→H2+HO2. The calculated ROHF and MCSCF imaginary frequency ω≠ corresponds to the motion of an hydrogen atom between H2O2 and H and has respectively, a magnitude of 6826.5 and 2909.9 cm−1. Calculated (MP2//ROHF and MP2//MCSCF) values of 8.92 and 7.92 Kcal/mol are, respectively, found for the barrier height of the title reaction. The ab initio results are used with the transition state theory (TST) to evaluate the rate constant kTST(T) over the range of temperature 200⩽T⩽2000 K. Tunneling corrections to kTST(T) are considered through the evaluation of the transmission coefficient by Wigner (W) and zero curvature tunneling (ZCT) methods. Our results show that the calculated rate constants based on the ROHF electronic structure results do not agree with the experimental values. The best agreement with the preferred experimental values measured by Baulch et al. for 300⩽T⩽800 K and with the values measured by Stang and Hampson for 850⩽T⩽2000 K is found for the calculation based on the MCSCF electronic structure results and using the ZCT method to account for tunneling correction to kTST.