State-selective electron capture in Ar 16++H (1s) collisions for charge-exchange recombination spectroscopy

Abstract

State-selective electron capture in collisions of Ar¹⁶⁺ ions with ground-state hydrogen atoms has been modeled using the two-center wave-packet convergent close-coupling approach. The partially stripped He-like projectile ion is represented using a model potential. Experimental measurements are not available for this collision system and to date, only the classical trajectory Monte Carlo (CTMC) method has been applied to calculate cross sections. The calculated total electron-capture cross section (TECS) is in good agreement with the previous CTMC results at the low energies but slightly larger at higher energies. This is likely because, in this work, we account for capture into highly excited states, which contribute significantly to the TECS at the intermediate energies. The n-resolved electron-capture cross sections have also been presented for capture into states with n=6−19, where n is the final-state principal quantum number. The most important of these are the cross sections for capture into the n=14−17 states, which are used in charge-exchange recombination spectroscopy techniques. For these cross sections, a significant difference is observed between the present and previously published data. The cross sections differ by an order of magnitude in the 10−60 keV u⁻¹ energy range. The agreement between the calculations is observed at the energies above 70 keV u⁻¹. The nℓ-resolved electron-capture cross sections have also been presented at 15, 60, 100 and 200 keV u⁻¹ projectile energies, where ℓ is the final-state angular momentum quantum number.