Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermal Activation of Methane by MgO$^+$: Temperature Dependent
  Kinetics, Reactive Molecular Dynamics Simulations and Statistical Modeling   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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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: supr-con
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The categories of this paper are: hep-lat
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The categories of this paper are: comp-gas
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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: ao-sci