# Thermal Activation of Methane by MgO$^+$: Temperature Dependent Kinetics, Reactive Molecular Dynamics Simulations and Statistical Modeling

Source: [Thermal Activation of Methane by MgO$^+$: Temperature Dependent Kinetics, Reactive Molecular Dynamics Simulations and Statistical Modeling](<https://www.sota2.com/research/paper/68fa3c3c1e209131ce8d8f09>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-25T01:01:56.391Z

Authors: Brendan C. Sweeny, Hanqing Pan, Asmaa Kassem, Jordan C Sawyer, Shaun G. Ard, Nicholas S. Shuman, Albert A. Viggiano, Sebastian Brickel, Oliver T. Unke, Meenu Upadhyay, Markus Meuwly

Published: 2020-02-06T08:19:54.000Z

## Abstract

The kinetics of MgO$^+$ + CH$\_4$ was studied experimentally using the variable ion source, temperature adjustable selected ion flow tube (VISTA-SIFT) apparatus from 300 $-$ 600 K and computationally by running and analyzing reactive atomistic simulations. Rates and product branching fractions were determined as a function of temperature. The reaction proceeded with a rate of $k = 5.9 \\pm 1.5 10^{-10}(T/300 $ K$)^{-0.5 \\pm 0.2}$ cm$^3$ s$^{-1}$. MgOH$^+$ was the dominant product at all temperatures, but Mg$^+$, the co-product of oxygen-atom transfer to form methanol, was observed with a product branching fraction of $0.08 \\pm 0.03 (T / 300 $ K$)^{-0.8 \\pm 0.7}$. Reactive molecular dynamics simulations using a reactive force field, as well as a neural network yield rate coefficients about one order of magnitude lower. This underestimation of the rates is traced back to the multireference character of the transition state \[MgOCH$\_4$\]$^+$. Statistical modeling of the temperature-dependent kinetics provides further insight into the reactive potential surface. The rate limiting step was found to be consistent with a four-centered activation of the C-H bond, consistent with previous calculations. The product branching was modeled as a competition between dissociation of an insertion intermediate directly after the rate-limiting transition state, and traversing a transition state corresponding to a methyl migration leading to a Mg-CH$\_3$OH$^+$ complex, though only if this transition state is stabilized significantly relative to the dissociated MgOH$^+$ + CH$\_3$ product channel. An alternative non-statistical mechanism is discussed, whereby a post-transition state bifurcation in the potential surface could allow the reaction to proceed directly from the four-centered TS to the Mg-CH$\_3$OH$^+$ complex thereby allowing a more robust competition between the product channels.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/2002.02151>)

[PDF](<https://arxiv.org/pdf/2002.02151.pdf>)