Binary encounter models for electron ionization of atoms: A one parameter expression for electron energy dependent (E < 200 eV) single ionization cross section

A one parameter expression for the single ionization cross-section of atoms by electrons is presented. This is done following analysis of current binary encounter based approaches and models. Using this expression, the agreement obtained with available experimental data for 45 elements (from ionization threshold up to 200 eV ionizing electron energy) is shown to be comparable with (or better than) that achieved using other multi-parameter approaches. We associate the single parameter used here with the effective reduction in the number of equivalent electrons within a given shell accessible for electron ionization. We attribute this reduction effect to intra-shell shadowing of part of the shell electrons by other electrons of the same shell. For atoms with 2s2pi (i = 3, 4, 5, 6) outer shell configurations we suggest also an intershell shadowing effect. Finally, we discuss the possibility of a meaningful contribution of deep inner shell ionization (50–100 eV binding energy) to the single ionization cross-section due to various post-collision interactions. These interactions may be responsible for decreasing the formation probability of doubly charged ions.

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► A single parameter expression for the electron ionization cross section of atoms.
► Agreement with experiments is comparable with other multi-parameter expressions.
► Contribution of deep inner shells due to post-collision interactions is discussed.