Nonmonotonic Target Dependence of Cl K X-Ray-Production Cross Sections in Single Heavy-Ion-Atom Collisions

Chlorine K x-ray-production cross sections have been measured in single collisions of chlorine ions in low incident charge states with gas targets at MeV energies. The cross sections are nonmonotonic as a function of target atomic number, but they approach monotonicity with increasing projectile energy. To explain these results in terms of 2pσ-2pπ transitions in nearly symmetric collisions effectively requires $2p$ vacancy production simultaneous with the promotion of Cl $1s$ electrons.