EUV spectra of Gd and Tb ions excited in laser-produced and vacuum spark plasmas

Extreme UV spectra of the gadolinium and terbium ions excited in the laser-produced plasma and vacuum spark sources were recorded in the 40–120 Å region and investigated on the basis of the Hartree–Fock calculations using Cowan code. The intense peaks in the 65–75 Å region of the vacuum spark spectra were interpreted as a manifold of the 4d 10 4f m –4d 9 4f m +1 transitions in the ions with a partially filled 4f shell. The drastic narrowing of these peaks was observed in the spectra of the laser-produced plasma. It was explained by a change of the 4d 10 4f m –4d 9 4f m +1 ( m >2) transition arrays mostly contributing to the intensity of the peaks in the vacuum spark spectra for the 4–4 transitions in the simplest spectra of the 4p 6 4d k ( k =8–10) and 4d 10 4f m ( m =1–2) ground configuration ions predominantly excited in hotter laser-produced plasma. The most intense lines of the 4d 10 4f 2 –4d 10 4f5d transitions in the Gd XVII and Tb XVIII spectra were classified for the first time.