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+.

Long-distance charge−dipole attraction between atomic ion and randomly oriented polar molecule potentially makes the molecular orientation, which profoundly influences the products' kinetics of collisional reaction. Using the three-dimensional ion velocity map imaging technique, here we report a collision-energy dependent stereodynamics of dissociative charge exchange reaction Ar + + CO → Ar + O + C + in a range of 7.46−9.97 eV. At the lowest collision energy, the most C + products are forward-scattered and are along the collision axis and are attributed to three different dissociation channels including the predominant one experiencing the rotating intermediate ArC + . At the high collision energies, the remarkably diffusive distribution of C + arises from the prompt dissociation of the rebounded CO + . The different dynamic processes arising from the nearly collinear collision are elaborated explicitly on the basis of the data analyses using the Doppler kinetics models.

Dissociative electron attachments via the lowest shape resonant state 2 Π u of CO 2 − , e − + CO 2 → 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 CO 2 − ( 2 Π 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 CO 2 − ( 2 Π u ) are settled.