Positive/negative ion velocity mapping apparatus for electron-molecule reactions

Abstract

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.

Communication: State mixing by spin-orbit coupling in the anionic chloroiodine dissociations

“…12,13,17 The sliced images of I − are depicted in Figs 10 and the polarized molecular local bond 16 would indeed introduce a forward-backward asymmetry of the angular distribution, but they cannot be responsible for the present imagepattern evolution with the electron energy. Since the angular distributions are primarily relevant to the symmetries of the resonant states in the Franck-Condon region, 8,10,[12][13][14][15][16] all of these images should presumably show the typical up-anddown ( 2 state) or backward-forward ( 2 state) distributions.…”

“…The state-of-the-art VMI technique enables us to identify different anionic fragments of the DEA process and record the angular distribution of a specific fragment in the full range θ = 0 = 2π . [12][13][14][15][16] In the Franck-Condon region of the vertical electron attachment, various resonant states of ICl − are accessible. The potential energy curves of both the neutral ICl at the ground state and the anion ICl − at the low-lying resonances were recalculated with the internally contracted multi-reference CI method including the SO coupling.…”

Dissociative electron attachments to ethanol and acetaldehyde: A combined experimental and simulation study

“…17,18 A brief introduction is given here. An effusive molecular beam of the sample was perpendicular to the pulsed electron beam (with a thermal energy spread of 0.5 eV) which was emitted from a homemade electron gun and collimated with the homogenous magnetic field (∼20 Gauss) produced by a pair of Helmholtz coils.…”

“…Molecular dynamics simulations based on quantum chemistry methods are applicable and provide for some insights into the dissociation dynamics of the complicated polyatomic molecules. 15,16 In this work, the DEAs to ethanol and acetaldehyde are investigated by both the state-of-the-art anion velocity map imaging (VMI) 17,18 experiments and ab initio molecular dynamics simulations. …”

Ion-momentum imaging of dissociative attachment of electrons to molecules

“…In the velocity slice imaging methods of Krishnakumar [21], Nandi [54] and Tian et al [22], a time-gated subset of a mass-specific 3-dimensional anion fragment momentum distribution is measured on a 2-dimensional detector. Depending on the type of detector, these experiments allow the ion hit data to be stored either event-by-event or frame-by-frame, where one frame is an integration of many events.…”