Revisiting chemical kinetics for H + CH₄ → H₂ + CH₃ using variational transition state theory: comparison with global dynamics calculations.

Authors

Edson F V de Carvalho, Marcelo A P Pontes, Luiz F A Ferrão, Francisco B C Machado, Orlando Roberto-Neto

Published in

Journal of molecular modeling. Volume 32. Issue 10. Sep 09, 2026. Epub Sep 09, 2026.

Abstract

For both the forward and reverse reaction, there are no accurate rate constants at the VTST/MT level using potential energy surfaces built with the density functional theory (DFT) approach. Calculations of rate constants in function of temperature are carried out for the elementary reaction H + CH₄ → H₂ + CH₃ using variational transition state theory with multidimensional tunneling corrections (VTST/MT) with density functional theory (DFT) and are compared with previous global dynamics calculations reported in the literature. Calculations show that the dual-level method based on an M06-2X PES is capable of providing an accurate framework to compute thermal rate constants in comparison with global dynamics methods.
The CCSD(T) method with the aug-cc-pVnZ (n = 3-5) basis set is employed to characterize the stationary states for the forward and reverse reactions and the M06-2X and ωB97X-D DFTs are used to generate potential energy surfaces (PESs) in the VTST/MT calculations. At the CVT/μOMT level and using the M06-2X PES, the rate constants at 300 and 600 K are 2.54 × 10^-19 and 2.92 × 10^-15 cm³ molecule^-1 s^-1, which are in excellent agreement with the multi-configurational time-dependent Hartree (MCTDH) calculations (1.9 × 10^-19 and 2.9 × 10^-15 cm³ molecule^-1 s^-1). For the reverse H₂ + CH₃ reaction, CVT/μOMT shows good agreement with results using CCSD(T) and analytical PESs. The kinetic isotope effect (KIE) (k^CH4+H/k^CH4+D) at 500, 600, and 700 K are 0.65, 0.71, and 0.77 in good agreement with experimental data, respectively equal to 0.8 ± 0.2, 0.9 ± 0.2, and 1.0 ± 0.2.

PMID:
42714651
Bibliographic data and abstract were imported from PubMed on 10 Sep 2026.

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