Theoretical study on the reaction path and rate constants of the hydrogen atom abstraction reaction of CH2O with CH3/OH

Abstract

Abstract The direct dynamics of the hydrogen abstraction reactions of CH 2 O with CH 3 /OH are studied using ab initio molecular orbital theory. Both the geometry optimizations of all the stationary points and the vibrational frequency calculations are carried out at the UQCISD/6-311G(d, p) level. The single-point energy is obtained by the multicoefficient Gaussian 3-version 3s (MCG3/3) method. The analysis to the changes of the interatomic distances on the minimum energy paths show that, the breaking of C–H bonds of CH 2 O and (i) the forming of C–H bond of CH 4 in the reaction of CH 2 O with CH 3 , (ii) the forming of O–H bond of H 2 O in the reaction of CH 2 O with OH, are both concerted. For each reaction, there exists a reactive vibrational normal-mode, and its frequencies change is relevant to the forming and breaking of the above covalent bond. Furthermore, the theoretical forward reaction rate constants in the temperature range 300–3000 K are computed by canonical variational transition state theory with small-curvature tunneling correction (CVT/SCT) method. The computed values of the rate constants are in good agreement with the available experimental data in the measured temperature range. Moreover, the tunneling effects are found to contribute significantly to the rate constants at low temperatures.