Processes involving electron capture and multiple ionization in collisionsof fast H+ and He2+ ions with lead atoms

A crossed-beam technique incorporating time-of-flight analysis and coincide nce counting of the collision products has been used to study Pbq+ formatio n with q up to 8 in collisions between ground-state Pb atoms and H+ and He2 + ions within the range 50-600 keV amu(-1). The separate cross sections for simple charge transfer, transfer ionization, and pure ionization leading t o the formation of Pbq+ ions have been obtained and the relative importance of these processes has been established. Accurate measurements and rigorou s theoretical descriptions of these multielectron processes in such heavy a toms are difficult and data are still very limited. The present measurement s have been designed to extend our previous studies of multiple ionization of a few selected heavy metal atoms and to provide a further check on the e xtent to which the main collision processes can be described quantitatively in terms of simple models based on an independent electron description. In our previous work with Fe, Cu, and Ga atoms using the same experimental ap proach, we were able to describe the formation of multiply charged ions thr ough both transfer ionization and pure ionization with a high degree of suc cess using an independent electron model. However, the present results for Pb show that the success of this simple approach is much more Limited for t hese much heavier atoms. [S1050-2947(99)00412-6].