State-selective Charge Exchange in 19.5–100 keV amu−1 O6+ Collision with He and H2

Abstract

The cross sections of state-selective charge exchange (CX) between highly charged ions and neutrals are important for modeling extreme ultraviolet and soft X-ray emissions in many astrophysical objects with hot plasma impacting cold media. By using cold-target recoil-ion momentum spectroscopy, we measure O ^6+ CX collisions with He and H _2 in the collision energy range of 19.5 to 100 keV amu ^−1 . The relative cross sections of state-selective single CX are reported for electron capture into O ^5+ (1 s ^2 nl ) n = 2, 3, 4, 5, ≥6 and n = 3, 4, 5, ≥6 for He and H _2 , respectively. With the collision energy increasing to 100 keV amu ^−1 , the main capture channel shifts to higher n for both target species as compared to available theoretical results. We also report state-selective cross sections for double CX with He, where doubly excited states of ${{\rm{O}}}^{4+}(1{s}^{2}{nln}^{\prime} l^{\prime} )$ with ${nln}^{\prime} l^{\prime} $ being 2 s ^2 ( ^1 S), 2 s 2 p ( ^1 P), 2 p ^2 ( ^1 D), and 2 p ^2 ( ^1 S) [symmetric configurations] and 2 s 3 l , 2 p 3 l −2 s 4 l , and 2 s 5 l −2 p 5 l [asymmetric configurations] are distinguished. It is found that the contributions of doubly excited states with asymmetric configurations are dominant and symmetric configurations increasingly come into play with the increase of collision energy. The present results provide experimental benchmarks available for theoretical calculations.

Keywords

• Atomic spectroscopy
• Atomic physics
• Collision physics
• Atomic data benchmarking
• Charge exchange recombination