IONIZATION OF POSITIVE IONS

The classical binary-encounter model for ionization by charged-particle impact is modified to permit evaluation of the cross section for ionization of positive ions by electron impact. General scalable expressions are obtained and compared with available experimental data and quantum-theoretical approximations. The dependence on ionic charge is discussed, and a simple physical interpretation emerges. Our results indicate that this model is nearly as reliable as the Born approximation for this process; i.e., they agree well with existing experimental data for energies much larger than threshold and are everywhere within a factor of two. © 1969 The American Physical Society.