Electron collision studies with trapped positive ions

Abstract

Positive ions have been trapped for periods of ca. 100 /zs within the space charge of a magnetically confined electron beam, ionized by this beam and detected mass-spectrometrically. The theory of the trap is developed and compared at many points with experiment. Cross section functions are given for the ionization of Ne +, Ar + , Kr + , Xe + , and the dissociation of CO + by electrons; the ionization of Ne 2 + and CO + by electrons is also investigated. From measurements of fragment ion currents CH 2 + , CH + from methane, it is shown that the dissociation of CH 4 + by electrons can contribute unwanted effects interfering with the appearance potential of the fragment ion. Effects due to excitation of ions by electrons are observed in the noble gases.