Excitation of resonance lines of doubly charged ions of alkali-earth elements in electron--atom collisions

Excitation of resonance lines of doubly charged ions of calcium, strontium, and barium is studied for collisions of slow electrons (E< or =300 eV) with Ca, Sr, and Ba atoms. Consideration of the results obtained allowed us to draw the conclusion that formation of doubly charged ions of these elements in resonance states is determined mainly by the interaction of an incident electron with the electrons of the outer np6 subshell of the atoms, i.e., a single-electron process