Single and Double Ionization of Na, K and Mg by Electron Impact

The ionization efficiency curves for Na + , Na ++ , K + , K ++ , Mg + and Mg ++ are studied with essentially monoenergetic electrons. It is proved that Na + , K + and Mg + follow the linear law up to 1.5 eV, 0.8 eV and 2 eV above the thresholds, respectively, and that Na ++ and K ++ follow the square law up to about 20 eV and 15 eV above the thresholds, respectively. These results agree with the theoretical prediction that n-fold multiple ionization would be proportional to a n-th power of excess electron energy. Two remarkable humps are found in the I. E. curve for Mg + , which are attributed to autoionization processes, These processes occur at 2.3±0.1 eV and 5.0±0.2 eV above the ionizotion potential, the first one may correspond to the excited states of Mg atom, 1 F° and 3 D°, but any excited states to be correlated to the second one is not known. Contrary to expectation, the I. E. curve for Mg ++ is not a square curve of excess energy but has a complex shape. In order to explain the shape, possibility of autoionization due to excitation of inner shell electron is suggested.