High-level direct-dynamics variational transition state theory calculations including multidimensional tunneling of the thermal rate constants, branching ratios, and kinetic isotope effects of the hydrogen abstraction reactions from methanol by atomic hydrogen
2011; American Institute of Physics; Volume: 134; Issue: 9 Linguagem: Inglês
10.1063/1.3555763
ISSN1520-9032
AutoresRubén Meana‐Pañeda, Donald G. Truhlar, Antonio Fernández‐Ramos,
Tópico(s)Spectroscopy and Quantum Chemical Studies
ResumoWe report a detailed theoretical study of the hydrogen abstraction reaction from methanol by atomic hydrogen. The study includes the analysis of thermal rate constants, branching ratios, and kinetic isotope effects. Specifically, we have performed high-level computations at the MC3BB level together with direct dynamics calculations by canonical variational transition state theory (CVT) with the microcanonically optimized multidimensional tunneling (μOMT) transmission coefficient (CVT/μOMT) to study both the CH3OH + H → CH2OH + H2 (R1) reaction and the CH3OH + H → CH3O + H2 (R2) reaction. The CVT/μOMT calculations show that reaction R1 dominates in the whole range \documentclass[12pt]{minimal}\begin{document}$298\le T(\rm K)\le 2500$\end{document}298≤T(K)≤2500 and that anharmonic effects on the torsional mode about the C–O bond are important, mainly at high temperatures. The activation energy for the total reaction sum of R1 and R2 reactions changes substantially with temperature and, therefore, the use of straight-line Arrhenius plots is not valid. We recommend the use of new expressions for the total R1 + R2 reaction and for the R1 and R2 individual reactions.
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