Study of gas-phase reactions within the modified Marcus model. II. CH3OH + CH3 → CH2OH + CH4

Publication date: Available online 23 May 2018 Source:Computational and Theoretical Chemistry Author(s): I.A. Romanskii In the framework of the Marcus theoretical model, using the intramolecular reorganization (IMR) method, the kinetics of the CH3OH + CH3 → CH2OH + CH4 reaction was studied over the temperature range of 10-550 K. The electronic activation energy (Ea ) was calculated at the UCCSD(T)/6-31+G**//B3LYP/6-31+G** level. The calculation of the reaction rate constant, k, defined as the integral over the distance Q(C ...C), was carried out on the assumption that for a hydrogen atom in the activated complex (AC) two extreme types of vibrations are possible: isolated vibration in the reagent well (oscillatory model 1, in which all frequencies are identified as real) and vibration in the C..H..C structure (oscillatory model 2 corresponding to TST). In both cases, the temperature dependence of the rate constant includes nonlinear (80 - 550 K) and linear (10 - 80 K) sections. It is shown that the change in the dependence character is due to the presence of a minimum in the Q - Ea plot. Kinetic data were used to analyse the “temperature plateau” phenomenon, observed for the CH3OH + CH3 reaction in the solid phase. The course of the temperature dependence of this reaction at 10-150 K can be reproduced assuming that the energy of the reagents in the solid phase is close to the average for the effective interval Q of the enthalpy of activation of the gas-phase reaction,...

Source: Computational and Theoretical Chemistry - May 24, 2018 Category: Chemistry Source Type: research