The analysis of the n=2-2 transitions in the XUV spectra of Cr to Ni

Over 400 new identifications of emission lines in the grazing-incidence spectra of the elements from chromium to nickel are reported. The great majority of these lines belong to the 2sⁿ2p^k-2s^n-12p^k+1 transition arrays in the O I to Be I isoelectronic sequences. Some of the spectra belonging to the N I, C I, B I and Be I sequences are identified as intercombination lines. The new data, taken together with other published results in the F I to Li I isoelectronic sequences, allow a complete listing of 2sⁿ2p^k-2s^n-12p^k+1 transitions in the elements from chromium to nickel, with their appropriate term schemes. The term schemes lead to wavelength predictions for various forbidden transitions. The use of these allowed and forbidden transitions has been proposed by other authors for diagnostic purposes in solar-flare and laboratory plasmas. In addition to the n=2-2 transitions the wavelengths of some Na I-like ions of the elements Cr to Ni are presented. The plasma source used to obtain the spectra and to differentiate between the emission from separate ionisation stages was created by focusing the output of a 40 GW neodymium glass laser system onto plane metallic targets.