Charge exchange (CX) x-ray spectroscopy is a vital diagnostic tool for astrophysical and fusion plasmas, yet its accuracy is limited by uncertainties in the orbital angular momentum ($l$) distribution of captured electrons. This study presents a systematic evaluation of prevalent $l$-distribution models through laboratory measurements of $L$-shell x-ray emission from ${\mathrm{Ar}}^{16+}$ colliding with He at energies of 1.2–10 keV/u. The measured x-ray spectra and relative line ratios are compared with theoretical results that are calculated with the use of $n$-resolved CX cross sections derived from the multichannel Landau-Zener method combined with various analytical $l$-distribution models and cascade deexcitation branching ratios. A systematic comparison reveals that the statistical $l$-distribution provides the best approximation to the measured spectra across the energy range considered. This work provides reliable atomic data for spectral models that can be used in astrophysical and fusion plasma diagnostics.

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• Atomic spectra
• Charge-exchange reactions
• Charge-transfer collisions
• Electronic transitions
• X-ray emission spectroscopy