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

Rubén Meana-Pañeda, Donald G. Truhlar, Antonio Fernández-Ramos

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Abstract

We 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 (OMT) transmission coefficient (CVT/OMT) 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 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.

Original languageEnglish (US)
Article number094302
JournalJournal of Chemical Physics
Volume134
Issue number9
DOIs
StatePublished - Mar 7 2011

Bibliographical note

Funding Information:
A. F.-R. and R. M.-P. thank Xunta de Galicia for financial support through “Axuda para a Consolidación e Estructuración de unidades de investigación competitivas do Sistema Universitario de Galicia, 2007/50, cofinanciada polo FEDER 2007–2013.” This work was supported in part by the U.S. Department of Energy (DOE), office of Basic Energy Sciences, through Grant No. DE-FG02-86ER13579 (2009) and as part of the Combustion Energy Frontier Research Center (2010).

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