X-ray signature of charge exchange in the spectra of L-shell iron ions

The X-ray signature of charge exchange between highly charged L-shell iron ions and neutral gas atoms was studied in the laboratory in order to assess its diagnostic utility. Significant differences with spectra formed by electron-impact excitation were observed. In particular, a strong enhancement was found of the emission corresponding to n >= 4 -> n = 2 transitions relative to the n = 3 -> n = 2 emission. This enhancement was detectable even with relatively low-resolution X-ray instrumentation (E/Delta E approximate to 10) and may enable future identification of charge exchange as a line-formation mechanism in astrophysical spectra.