DOUBLE-IONIZATION OF NEUTRAL ATOMS, POSITIVE AND NEGATIVE-IONS BY ELECTRON-IMPACT

New experimental data on double-ionization cross sections of neutral a toms, positive and negative ions by electron impact are reported. Thes e and other relevant data are compared with recent multiple-ionization semiempirical formulae extended for the case of two-electron ionizati on. Theory gives analytical dependence of the double-ionization cross sections on the main parameters of the collision system in a wide ener gy range. Far the He atom, He-like ions and H- ion high-energy asympto tic behaviour of the double-ionization cross sections are considered o n the basis of a quantum mechanical treatment. Suggested cross section scaling for fast collisions, employing a target-effective nuclear cha rge, is in good agreement with experimental data.