Cross Sections for Ionization by Electrons. I. Absolute Ionization Cross Sections of Zn, Cd, and Te2. II. Comparison of Theoretical with Experimental Values for Atoms and Molecules

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Abstract
Ionization cross sections for Zn, Cd, and Te2 vapors have been measured by collection of the total positive ion currents produced from electron impact by 50‐eV electrons in the specially designed ion source of a mass spectrometer. The results: σi(Zn) = 5.03±0.45×10−16 cm2, σi(Cd) = 8.54±0.33×10−16 cm2, σi(Te2) = 17.46±0.48×10−16 cm2. These results are combined with available data to set up a compilation of absolute ionization cross sections for 27 atoms. Very limited agreement is found with theoretical ionization cross sections: It is shown that ionization cross sections of molecules cannot be calculated reliably by summation of the ionization cross sections of the constituent atoms.