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. 2022 Dec 22;126(50):9408-9413.
doi: 10.1021/acs.jpca.2c06887. Epub 2022 Dec 13.

Imaging the Atomistic Dynamics of Single Proton Transfer and Combined Hydrogen/Proton Transfer in the O- + CH3I Reaction

Arnab Khan  1 , Atilay Ayasli  1 , Tim Michaelsen  1 , Thomas Gstir  1 , Milan Ončák  1 , Roland Wester  1
Affiliations

Imaging the Atomistic Dynamics of Single Proton Transfer and Combined Hydrogen/Proton Transfer in the O- + CH3I Reaction

Arnab Khan et al. J Phys Chem A. .

Abstract

We report on reactive scattering studies of the proton transfer and combined hydrogen/proton transfer in the O- + CH3I reaction. We combine state-of-the-art crossed-beam velocity map imaging and quantum chemistry calculations to understand the dynamics for the formations of the CH2I- + OH and CHI- + H2O products. The experimental velocity- and angle-differential cross section show for both products and at all collision energies (between 0.3 and 2.0 eV) that the product ions are predominantly forward scattered. For the CHI- + H2O channel, the data show lower product velocities, indicative of higher internal excitation, than in the case of single proton transfer. Furthermore, our results suggest that the combined hydrogen/proton transfer proceeds via a two-step process: In the first step, O- abstracts one H atom to form OH-, and then the transient OH- removes an additional proton from CH2I to form the energetically stable H2O coproduct.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(A–E) O– + CH3I → CH2I– + OH channel (proton transfer) product center-of-mass frame velocity distributions of the CH2I– product at different collision energies. At the top of the images, the Newton diagram illustrates the relative orientation of the velocity vectors of the reactants and the charged product ions. The white dotted circle in each velocity image gives the kinematic cutoff for proton transfer reaction. (F–J) Velocity integrated angular distributions for CH2I– ions.
Figure 2
Figure 2
(A–D) Center-of-mass frame velocity distributions of the CHI– ions from the O– + CH3I → CHI– + H2O (combined hydrogen/proton transfer) channel at different relative collision energies. The Newton diagram shown at the top of the experimental data represents the relative orientations of all the velocity vectors of the reactants and the CHI– product ions. The white dotted circle shows the kinematic cutoff values for the combined hydrogen/proton transfer pathway. (E–H) Velocity integrated angular distributions for CHI– products.
Figure 3
Figure 3
Collision-energy-dependent relative branching ratio of the CH2I– and CHI– ions. The relative branching ratio is obtained by dividing the branching ratio of the CH2I– and CHI– ions. The error on the collision energy stems from the uncertainty in measuring the velocity vectors of the O– and CH3I reactant beams. The error on the branching ratio represents the statistical accuracy.
Figure 4
Figure 4
Energy levels and minimum-energy pathways of different reaction channels calculated at the CCSD(T)/aug-cc-pVTZ(-PP)//MP2/aug-cc-pVTZ(-PP) level. The abbreviation “TS” represents the transition state. All energies are given in the units of eV.
See this image and copyright information in PMC

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