In molecular dissociative ionization by electron collisions and dissociative electron attachment to molecule, the respective positively and negatively charged fragments are the important products. A compact ion velocity mapping apparatus is developed for the angular distribution measurements of the positive or negative fragments produced in the electron-molecule reactions. This apparatus consists of a pulsed electron gun, a set of ion velocity mapping optic lenses, a two-dimensional position detector including two pieces of micro-channel plates, and a phosphor screen, and a charge-coupled-device camera for data acquisition. The positive and negative ion detections can be simply realized by changing the voltage polarity of ion optics and detector. Velocity sliced images can be directly recorded using a narrow voltage pulse applied on the rear micro-channel plate. The efficient performance of this system is evaluated by measuring the angular distribution of O(-) from the electron attachments to NO at 7.3 and 8.3 eV and O(+) from the electron collision with CO at 40.0 eV.

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We reported an imaging study of the dissociation dynamics of temporary negative ion N(2)O(-) formed in the low-energy electron attachment, e(-) + N(2)O → N(2)O(-) → N(2) + O(-). With the help of ab initio molecular dynamics calculations, the evolution of momentum distributions of the O(-) fragment in terms of the electron attachment energy is identified as the result of a competition between two distinctly different indirect pathways, namely, climbing over and bypassing the energy ridge after the molecular structure bending. These two pathways prefer leaving the N(2) fragment at the high vibrational and rotational states, respectively.

Stereo-dynamics of dissociative electron attachments to CO 2 is investigated by the O − anion velocity imaging experiments combined with the R-matrix calculations. 2 Π g as a Feshbach resonant state of CO 2 − is confirmed to play roles in the dissociations around 8.0 eV. We find that the dynamic evolutions of the Renner-Teller effect lead to the dramatically different anisotropic O − momentum distributions.