Single and Double Ionization of Ca by Electron Impact

Abstract

In order to examine the validity of the power law for multiple ionization by electron impact, the probability curves of single and double ionization of Ca are studied in succession to the previous study on Na, K and Mg.
The formation of Ca⁺⁺ is not a simple square function of electron energy, but it increases gradually above the threshold and has two or three maxima between 25 eV and 30 eV, then increasing again steeply. The steep increase at 31 eV agrees well with the curve obtained by Fayard et al..
It is suggested that three different kinds of processes contribute to the formation of Ca⁺⁺. That is, process (I) which follows the square law corresponds to the direct ionization process, and process (II) which has some maxima is attributed to some autoionization processes, and process (III) which is linear to the energy is attributed to Auger ionization process caused from ionization of 3p electron.
Also brief discussion on formation of Ca⁺ is given.