Multiple Ionization of Ca, Sr and Ba by Electron Impact

Abstract

Ionization efficiency curves (IE curves) of Ca, Sr and Ba by electron impact in the energy range from the ionization potentials to 1000 eV are obtained with a mass spectrometer which has a crossed beam ion source. The ions having up to three fold positive charges are studied. The IE curves of Ca + , Sr + and Ba + have some structures which correspond to autoionization processes. They are observed at 25.5 eV and 28.5 eV for Ca + , 19 eV, 21.5 eV and 24 eV for Sr + , and 15 eV and 19 eV for Ba + . The IE curves of Ca 2+ , Sr 2+ and Ba 2+ have remarkable breaks at 30 eV, 27.5 eV and 20 eV respectively, which are attributed to Auger processes, and many humps are observed below the breaks in the IE curves of Ca 2+ and Sr 2+ . The IE curve of Ba 3+ has a break at about 86 eV, which is also attributed to Auger cascade. The relative abundance ratios of the multiply charged ions to the singly charged ions obtained at 500 eV are compared with those by other works.