Electron detachment processes in keV H-, Li-, Na-, K--rare-gas collisions

Abstract
Electron detachment processes have been measured for the (quasi-) two-electron negative ions with ns2 structures (n=1, 2, 3, 4), namely H-, Li-, Na- and K- in collisions with He, Ne and Ar at energies of 0.5-100 keV amu-1. Total detachment cross sections have been determined for n=1-4. Detachment with simultaneous ns-np excitation has been measured for n=2 and 3. Finally, cross sections for target excitation and/or ionisation have been estimated for 50 keV. For energies above 1 keV amu-1, the total detachment cross sections are found to scale with the cross section for H- at the same velocity as the inverse square of the detachment energies. Simultaneous ns-nsp excitation is found to be important ( approximately 30%) and exhibits a considerable alignment. Target excitation at these energies is relatively small in all cases except for Na--Ne, due to strong quasi-molecular effects in this system.