Imaging the Ion-Molecule Reaction Dynamics of O- + CD4

While neutral reactions involved in methane oxidation have been intensively studied, much less information is known about the reaction dynamics of the oxygen radical anion with methane. Here, we study the scattering dynamics of this anion-molecule reaction using crossed-beam velocity map imaging with deuterated methane. Differential scattering cross sections for the deuterium abstraction channel have been determined at relative collision energies between 0.2 and 1.5 eV and ab initio calculations of the important stationary points along the reaction pathway have been performed. At lower collision energies, direct backscattering and indirect complex-mediated reaction dynamics are observed, whereas at higher energies, sideways deuterium stripping dominates the reaction. Above 0.7 eV collision energy, a suppressed cross section is observed at low product ion velocities, which is likely caused by the endoergic pathway of combined deuteron/deuterium transfer, forming heavy water. The measured product internal energy is attributed mainly to the low-lying deformation and out-of-plane bending vibrations of the methyl radical product. The results are compared with a previous crossed-beam result for the reaction of oxygen anions with nondeuterated ̧methane and with the related neutral-neutral reactions, showing similar dynamics and qualitative agreement.

A global full-dimensional potential energy surface and quasiclassical trajectory study of the O(1D) + CH4 multichannel reaction

The QCT calculations based on an accurate global full-dimensional PES are capable of reproducing the experimental dynamic features for O(¹D) + CH₄.

Trapped Abstraction in the O((1)D) + CHD3 → OH + CD3 Reaction

Despite significant progress made in past decades, it is still challenging to elucidate dynamics mechanisms for polyatomic reactions, in particular, involving complex formation. The reaction of O((1)D) with methane has long been regarded as a prototypical polyatomic system of direct insertion reaction in which the O((1)D) atom can insert into the C-H bond of methane to form a "hot" methanol intermediate before decomposition. Here, we report a combined theoretical and experimental study on the O((1)D) + CHD3 reaction, on which good agreement between theory and experiment is achieved. Our study revealed that this complex-forming reaction actually proceeds via a trapped abstraction mechanism, rather than an insertion mechanism as has long been thought. We anticipate that this reaction mechanism should also be responsible for the reaction of O((1)D) with ethane and propane, as well as many other chemical reactions with deep wells in the interaction region.