Ab Initio Molecular Dynamics Simulation Study on the Stereo Reactions between Atomic Oxygen Anion and Methane

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Dynamics

Background:

• The ion-molecule reaction between atomic oxygen anion (O⁻) and methane (CH₄) is crucial in various chemical environments.
• Previous studies primarily focused on the exothermic H-abstraction pathway.

Purpose of the Study:

• To systematically investigate the ion-molecule reaction between O⁻ and CH₄ using advanced computational methods.
• To explore both exothermic and endothermic reaction pathways and their mechanisms.

Main Methods:

• On-the-fly ab initio molecular dynamics simulations were employed.
• Three distinct O⁻ attack modes on the methane molecule were considered.
• The influence of thermal vibrations of CH₄ on reaction dynamics was analyzed.

Main Results:

• An endothermic pathway producing methoxide anion (OCH₃⁻) and a hydrogen atom (H) was identified, in addition to the dominant exothermic H-abstraction yielding hydroxide anion (OH⁻) and methyl radical (CH₃).
• The internal motions of radical products were found to be significantly dependent on the O⁻ attack orientation.
• The minor endothermic pathway proceeds via a roaming mechanism involving a transient negative ion intermediate [HO-CH₃]⁻.

Conclusions:

• The O⁻ + CH₄ reaction exhibits complex dynamics with multiple competing pathways.
• Understanding these pathways is essential for accurately modeling chemical processes involving these species.
• The study highlights the importance of considering less common reaction channels and their mechanisms.