Application of ion imaging to the electron impact ionization of oxygen using crossed beams and a custom designed fast multichannel pulse generator

In this article we introduce the application of ion imaging to the detection of product ions produced in electron-molecule collisions. Unlike photoinitiation experiments in which a short duration laser pulse is used to excite a reagent molecule or to prepare an exotic species for subsequent reaction, collisions involving electrons (or ions) involve field-sensitive charged beam pulses of longer duration than laser pulses. Such experiments require the fast switching of electric fields with particular attention to the elimination of stray fields, contact potentials, and noise pickup on cables and electrical feedthroughs. We have recorded preliminary O-2(+) and O+ ion images from 100 eV electron impact ionization of O-2 supersonic molecular beams. The triggering of the nozzle, field plates, electron gun, and repeller/extractor elements was achieved using a low cost, versatile, fast multichannel pulse generator with fiber-optic coupling that was designed to produce low noise trigger pulses for commercial and custom made pulsed high voltage power supplies. (C) 2002 American Institute of Physics.