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Motivated by possible atomic origins of the unidentified emission linedetected at 3.55 keV to 3.57 keV in a stacked spectrum of galaxy clusters(Bulbul et al. 2014), an electron beam ion trap (EBIT) was used to investigatethe resonant dielectronic recombination (DR) process in highly-charged argonions as a possible contributor to the emission feature. The He-like ArDR-induced transition 1s$^2$2l - 1s2l3l$^\prime$ was suggested to produce a3.62 keV photon (Bulbul et al. 2014) near the unidentified line at 3.57 keV andwas the starting point of our investigation. The collisional-radiative modelNOMAD was used to create synthetic spectra for comparison with both our EBITmeasurements and with spectra produced with the AtomDB database/AstrophysicalPlasma Emission Code (APEC) used in the Bulbul et al. (2014) work. Excellentagreement was found between the NOMAD and EBIT spectra, providing a high levelof confidence in the atomic data used. Comparison of the NOMAD and APEC spectrarevealed a number of missing features in the AtomDB database near theunidentified line. At an electron temperature of $T_e$ = 1.72 keV, theinclusion of the missing lines in AtomDB increases the total flux in the 3.5keV to 3.66 keV energy band by a factor of 2. While important, this extraemission is not enough to explain the unidentified line found in the galaxycluster spectra.

EBIT Observation of Ar Dielectronic Recombination Lines Near the Unknown Faint X-Ray Feature Found in the Stacked Spectrum of Galaxy Clusters