The Sn IX-Sn XII spectra excited in a vacuum spark have been analysed in the 130-160 Å wavelength region. The analysis was based on the energy parameter extrapolation in the isonuclear Sn VI-VIII and Sn XIII-XIV sequence. 266 spectral lines belonging to the 4d m -(4d m−1 4f + 4p 5 4d m+1 ) (m = 6-3) transition arrays were classified in the Sn IX-Sn XII spectra for the first time. All 18 level energies of the 4d 3 configuration and 39 level energies of the strongly interacting 4d 2 4f and 4p 5 4d 4 configurations were established in the Sn XII spectrum. The energy differences between the majority of the 4d m levels and about 40 levels of the 4d m−1 4f + 4p 5 4d m+1 configurations were determined in each of the Sn IX, Sn X and Sn XI spectra (m = 6-4). As a result, all intense lines were classified in the 130-140 Å region relevant to the extreme ultraviolet (EUV) lithography. It was shown that the most of the intense lines in the 2% bandwidth at 135 Å belong to the transitions in the Sn XI-Sn XIII spectra.
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.
Spectra of multicharged ions have been analyzed for all stable elements in the period from Z = 37 (Rb) to Z = 50 (Sn), in the region of n = 4, Δn = 0 transitions. The transition arrays (4s2 + 4p2 + 4s4d)-4s4p, 4s4f and 3d94s, 3d94d-3d94p have been identified in zinc-like and nickel-like ions respectively, with the help of the ab initio relativistic parametric potential method and of the Slater-Condon method with generalized least-squares fits of energy parameters.
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