Cross-sections for ionization of positive ions by electron impact

Abstract

Simple methods of evaluating ionization rate coefficients which have been used in various ionization-balance calculations are compared with values measured in the laboratory. Laboratory measurements are by the crossed-beams method and by plasma spectroscopy, and it is shown that on average both kinds of experiments favour the Exchange Classical Impact Parameter (ECIP) method of calculating ionization rate coefficients although it is not clear why this should be so. This evidence supports Summers' (1974) ionization balance calculations which are based on ECIP ionization crosssections. It is also shown that on average the Coulomb – Born calculations, for the small sample considered, are in no better agreement with laboratory measurements near threshold than those by the simpler methods.