ELECTRON-IMPACT DOUBLE-IONIZATION OF MAGNESIUM

Electron-impact double-ionization cross sections differential in the a ngles of the two ejected electrons have been measured at impact energi es of 422 and 1052 eV. The energies of the ejected electrons were fixe d at 100 eV each. The cross sections are very different at the two inc ident energies. At 1052 eV the ejected electrons are preferentially fo und in the forward direction with respect to the incident beam. At 422 eV they are found in the forward and backward directions with approxi mately equal probability. The 422-eV cross sections are largest when t he incident-electron and ejected-electron momentum vectors lie in a co mmon plane. The observations are discussed in the context of several m odels for double ionization. [S1050-2947(98)08301-2].