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 4d104fm–4d94fm+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 4d104fm–4d94fm+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 4p64dk (k=8–10) and 4d104fm (m=1–2) ground configuration ions predominantly excited in hotter laser-produced plasma. The most intense lines of the 4d104f2–4d104f5d transitions in the Gd XVII and Tb XVIII spectra were classified for the first time.

The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented.

Spectra of hafnium, tantalum, tungsten, and rhenium in the range of 145–350Å, excited in a low-inductive vacuum spark, have been recorded on a grazing-incidence vacuum spectrograph using a grating with 3600 lines/mm and a radius of 3 m. The wavelengths and intensities of more than 3800 lines in the tungsten spectrum have been measured. Comparison with the Hartree-Fock calculations showed that most spectral lines should be due to transitions in the W VIII spectrum. Short-wavelength lines due to the 4f ¹³5s ²5p ⁶-4f ¹³5s ²5p ⁵6s transitions have been identified in the W VIII spectrum and the Re IX, Ta VII, and Hf VI isoelectronic spectra.

Aims. Our goal is to accurately determine bound-to-bound transition wavelengths and energy levels of the low-lying open-shell configurations 4f⁴, 4f³ 5d, 4f³6s, and 4f³ 6p of doubly ionised neodymium (Nd III) through high-resolution spectroscopy and semi-empirical calculations. Methods. The emission spectra of neodymium (Nd, Z = 60) were recorded using Penning and hollow cathode discharge lamps in the region 11 500-54000 cm⁻¹ (8695–1852 Å) by Fourier transform spectroscopy at resolving powers up to 10⁶. Wavenumber measurements were accurate to a few 10⁻³ cm⁻¹. Grating spectroscopy of Nd vacuum sliding sparks and stellar spectra were used to aid line and energy level identification. For the analysis, new Nd III atomic structure and transition probability calculations were carried out using the Cowan code parameterised by newly established levels. Results. The classification of 432 transitions of Nd III from the Penning lamp spectra resulted in the determination of 144 energy levels of the 4f⁴, 4f³ 5d, 4f³ 6s, and 4f³ 6p configurations of Nd III, 105 of which were experimentally established for the first time. Of the 40 previously published Nd III levels, one was revised and 39 were confirmed. Conclusions. The results will not only benchmark and improve future semi-empirical atomic structure calculations of Nd III, but also enable more reliable astrophysical applications of Nd III, such as abundance analyses of kilonovae and chemically peculiar stars, and studies of pulsational wave propagation in these stars.

New spectrograms of multiply ionized iron have been recorded and analyzed, targeting the Fe vii spectrum. As a result, several previously unknown spectral lines and energy levels have been identified in this spectrum. These new data have been analyzed together with all previously published laboratory and astrophysical data on this spectrum. The energy levels have been interpreted using parametric calculations with Cowan codes. Radiative transition rates calculated in this work supplemented other previously published calculations in constructing a complete set of recommended transition probabilities. The ionization energy of Fe vii has been redetermined with a fivefold improvement in accuracy. Its new value is 1,007,928(20) cm⁻¹, corresponding to 124.9671(25) eV.

The spectrum of eight-times ionized iron, Fe ix, was studied in the 110–200 Å region. A low inductance vacuum spark and a 3 m grazing incidence spectrograph were used for the excitation and recording of the spectrum. Previous analyses of Fe ix have been greatly extended and partly revised. The number of known lines in the 3p ⁵3d–3p ⁵4f and 3p ⁵3d–3p ⁴3d ² transition arrays is extended to 25 and 81, respectively. Most of the identifications of the Fe ix lines from the 3p ⁵3d–3p ⁴3d ² transition array in the solar spectrum have been confirmed and several new identifications are suggested.