Positive-ion production by electron bombardment of alkali halides

We present an experimental investigation of positive-ion production by electron bombardment of alkali halides. Measurements of the mass distributions and yields of both positive ions and neutral species indicate that the positive ions are formed by gas-phase ionization of ground-state neutral atoms and molecules. The gas-phase mechanism is shown to account for the ion mass distributions, the magnitude of the ion yields, and the dependence of ion yield on incident electron current.