Astrophysical charge-exchange modeling depends on an accurate database of state-resolved and velocity-dependent cross sections. The cross sections, resolved by the quantum state with principal n and orbital angular momentum ℓ, are pivotal in determining X-ray and extreme ultraviolet (EUV) emissions following charge exchange between highly charged ions and neutrals. However, the current cross-sectional data are primarily theoretically derived and have undergone limited experimental validation. Using high-resolution cold-target recoil-ion momentum spectroscopy, we conduct an experimental study on state-selective cross sections of charge exchange between 5.36 and 75 keV u‑1 N5+ ions and He. Evidently, at low collision energies electrons are mainly captured in the n = 3 state of N4+ ions, and higher n capture competitively comes into play as the increase of collision energy. The relative cross sections are reported for state-selective electron capture into 2s, 2p, 3s, 3p, 3d, 4ℓ, 5ℓ, and n ≥ 6 Rydberg series of N4+(1s2nl) ions. The ℓ distributions commonly used in astrophysical literature are evaluated by comparing them to the measured ℓ-resolved state-selective cross sections for the dominant n = 3 capture, which allows us to experimentally derive the collision-energy-dependent EUV line ratios.
