Ion Momentum Imaging Study of the Ion–Molecule Charge Exchange Reaction of Ar+ + CO2

Ion velocity map imaging study of the charge transfers from N2+/N+ to H2O

Considering important roles of ion-molecule collision in planetary atmospheres, here we investigate the charge transfer dynamics of N2+/N+ + H2O → N2/N + H2O+ in the collision energy range of 0.42-2.09 eV. In the collisions with N2+, the H2O+ yield is populated in the bending-motion vibrational states of the A 2A1 state and its production efficiency is enhanced monotonously with the decrease in collision energy. The H2O+ velocity images recorded with the three-dimensional ion velocity map imaging technique exhibit two categories of spatial distributions: at relatively high energies, the narrow and forward-scattered distribution corresponds to the resonant or prompt charge transfer in large-impact-parameter collisions; small-impact-parameter or intimate collisions are preferred at the lower energies, leading to the H2O+ distribution closer to the center of masses. The charge transfers from N+ exhibit similar dynamics; by contrast, an intermediate complex (N⋯H2O)+ is more likely to be experienced in the low-energy intimate collision.

Inverse Isotope Kinetic Effect of the Charge Transfer Reactions of Ar+ with H2O and D2O

Hydrogen isotopic effect, as the key to revealing the origin of Earth's water, arises from the H/D mass difference and quantum dynamics at the transition state of reaction. The ion-molecule charge-exchange reaction between water (H2O/D2O) and argon ion (Ar+) proceeds spontaneously and promptly, where there is no transition-state or intermediate complex. In this energetically resonant process, we find an inverse kinetic isotope effect (KIE) leading to the higher charge transfer rate for D2O, by the velocity map imaging measurements of H2O+/D2O+ products. Using the average dipole orientation capture model, we estimate the orientation angles of C2v axis of H2O/D2O relative to the Ar+ approaching direction and attribute to the difference of stereodynamics. According to the long-distance Landau-Zener charge transfer model, this inverse KIE could be also attributed to the density-of-state difference of molecular bending motion between H2O+ and D2O+ around the resonant charge transfer.

Ion Velocity Map Imaging Study of the Reactive Collisions between Carbon Dioxide and Helium Ion

The reactive collision between He+ and CO2 plays an important role in substance evolutions of the planetary CO2-rich atmosphere. Using a three-dimensional ion velocity map imaging technique, we investigate the low-energy ion-molecule reactions He+ + CO2 → He + CO2+/He + CO+ + O/He + CO + O+. The velocity images of the products CO+ and O+ of dissociative charge-exchange reactions are distinctly different from those of charge-exchange product CO2+. The remarkable features of stereodynamics are observed in the dissociative charge-exchange reaction and are attributed to the spatial alignment of the initially random target CO2 during the He+ approach. Branching ratios of different channels of dissociative charge exchange are further obtained with the Doppler kinematics model, indicating a high preference for the energy-resonant channel.

Dissociation Dynamics of Anionic Carbon Dioxide in the Shape Resonant State 2Πu

Dissociative electron attachments via the lowest shape resonant state ²Π_u of CO₂^-, e^- + CO₂ → O^- + CO, are investigated with our high-resolution anion velocity map imaging apparatus. The production efficiency curve of O^- obtained in this work is consistent with those reported previously. The forward-backward asymmetric distribution superimposed on the isotopic background is observed in the time-sliced velocity image of O^- yield, implying that the dissociation of CO₂^-(²Π_u) proceeds through a combinational motion of bond stretching and bending. Thereby, the coproduct CO is proposed to be in the rovibrational states. The long-standing arguments about the dissociation dynamics of CO₂^-(²Π_u) are settled.

Ion-Molecule Charge Exchange Reactions between Ar+ and trans-/cis-Dichloroethylene

We report an ion velocity imaging study of the charge exchange reactions between Ar⁺ ion and trans-/cis-dichloroethylene in the collision energy range of 2.1-9.5 eV, and we find that the energy-resonant charge transfer plays a dominant role in the large impact-parameter reaction. The parent yields C₂H₂Cl₂⁺ in the high-lying excited states are directly produced in the charge exchange reactions, while they prefer spontaneous fragmentations in photoionization. This significant difference indicates that the present charge exchange reactions are much slower than the photoelectron detachment. The structural relaxations of the target molecule are allowed in multiple dimensions of freedom during the charge transfer, which should be frequently observed for the charge exchange reactions with large molecules.

Stereodynamics Observed in the Reactive Collisions of Low-Energy Ar+ with Randomly Oriented O2

Stereodynamics of the collisional reaction between mutually aligned or oriented reactants has been a striking topic of chemical dynamics for decades. However, the stereodynamic aspects are scarcely revealed for the low-energy collision with a randomly oriented target. Here in the dissociative charge-exchange reaction between randomly oriented O₂ and low-energy Ar⁺, we, using the three-dimensional ion velocity map imaging technique, clearly observe a linear alignment and a nearly isotropic distribution of the O⁺ yields along the collision axis. These observations are rationalized with the Doppler kinetic models in which the O₂ bond is assumed to be parallel or unparallel to the collision axis of the large impact parameter collision. The linearly aligned O⁺, as the predominant yield, is produced in the parallel collision, while a rotating O₂⁺, as the intermediate in the unparallel collision, leads to the isotropic distribution of O⁺.

Ion momentum imaging study of the ion–molecule reaction Ar+ + O2 → Ar + O2+

O₂⁺ products of the charge exchange reactions between Ar⁺ and O₂ are distributed in the wider range of scattering angle at higher collision energy.