Jan Olof Ekberg

Spectra of Rb ii, Sr iii, Y iv, Zr v, Nb vi, and Mo vii in the Vacuum Ultraviolet

The characteristic resonance-line spectrum in the Kr i isoelectronic sequence, consisting of the five transitions to the 4p6 1S0 ground state from levels with J = 1 in the 4p54d and 5s configurations has been observed from Rb ii to Mo vii. The observations were made with sliding sparks, on the 10.6-m normal-incidence spectrograph at NBS and the 5-m grazing-incidence spectrograph in Lund. A number of transitions from higher levels of the type 4p5nd, 4p5ns, and 4s4p65p were also observed. Isoelectronic comparisons are given for all observed levels. The ionization energies in electron volts are Rb ii 27.285Y iv 60.60Nb vi 102.06Sr iii 42.87Zr v 80.36Mo vii 125.66.Anomalous relative intensities observed for the 4p54d transitions are found to be caused by excitation conditions within the light source.

Analyses of the XUV Spectra of K, Ca, Sc and Ti Isoelectronic with P I, Si I and Al I

An isoelectronic comparison of spectra in the P I, Si I and Al I sequences has been made for the elements K, Ca, Sc and Ti. In the course of this study we have also identified some lines in the spectra of adjacent elements in the same sequences, for example S IV, Ar IV, Ar V and Ar VI. In the P I and Si I sequences the study is restricted to transitions to the ground configurations 3s23p2 and 3s23p3. In the Al I like spectra we have identified transitions between the configurations 3s23p, 3s3p2, 3p3, 3s2nd, 3s2nf, 3s3p3d and 3s3p4s, where the nd and nf series have been traced to n = 6, and for nf in Ca VIII to n = 7.

Analyses of the Mg I-like Spectra K VIII, Ca IX, Sc X and Ti XI

The Mg I-like spectrum Ti XI has been analysed by using the line list of the titanium vacuum-spark spectrum in the region 50 to 425 A published by Svensson and Ekberg. At the same time the iso-electronic spectra of potassium, calcium and scandium have been checked and extended. The main new results concern the singlets, but the triplet systems have also been improved. Intersystem combinations have been found for Ca IX, and the singlet-triplet connection for the other element has been established by interpolation. The np- and nd-series are now extended to n=7 and the nf-series to n=6. However, series perturbations affect the determination of the ionization energies, which causes an uncertainty of 0.08% to 0.05%.

Term Analysis of Fe VII

The spectrum of six times ionized iron, Fe VII, has been observed by using low- and high-voltage sliding sparks. The spectrograms were recorded on the 10.7 m normal incidence and 10.7 m grazing incidence spectrographs at the National Bureau of Standards, Washington, and on the 3 m normal incidence spectrograph at our institute. More than 400 lines have been classified in the region 104-270 A as transitions to the ground configuration, 3p63d2, and 20 lines from 1010 A to 1362 A as 3d4s-3d4p combinations. All 13 levels of 3d2 and 3d4s have been observed as well as 141 levels of the 3d4p, 3dnf (n = 4-10), 3p53d3 and 3p53d24s configurations. The level structure of 3d2, 3d4s, 3d4f, 3d5f, 3d6f and 3p53d24s has been theoretically interpreted and the energy parameters, determined from least-squares fits to the observed level values, are compared with Hartree-Fock calculations. The ionization energy is found from the 3dnf series to 1 008 000 ± 100 cm-1 (124.98 ± 0.1 eV). Predicted wavelengths and intensities of the forbidden transitions within 3d2 are collected in a list containing 17 entries from 1490 to 8729 A. A comparison with Thackerays line list for RR Telescopii shows an excellent agreement as regards both wavelengths and intensities.

Analysis of the Spectrum of Seven-Times-Ionized Molybdenum (Mo viii) and Isoelectronic Comparison of the Spectra Y v—Mo viii

The spectrum of Mo viii has been observed in a sliding-spark discharge with a 5-m grazing-incidence spectrograph. The analysis has yielded nearly all levels of the 4p44d configuration that can combine with the 4p5 2P ground term. Six of the eight levels of the 4p45s configuration given previously by Charles and by Chaghtai were confirmed. New values were found for the remaining two. The 4s24p44d+4s24p45s+4s4p6 level structure has been theoretically interpreted, with configuration-interaction effects included. The 4s4p6²S12 level was found to have a 21% 4s24p4(1D)4d2S character and the 4s24p4(¹D)4d²S12 level a 19% 4s4p6 2S character. The energy parameters determined by a least-squares fit to the observed level values are compared with Hartree–Fock (HF) calculations. The ionization energy is estimated to be 144.0 ± 1.0 eV. Isoelectronic comparisons for the level positions in Y v, Zr vi, Nb vii, and Mo v are given graphically. The ratios of the fitted energy parameters to the HF values are compared for these ions.

J-Dependent 3s4p 3PJ Lifetimes in Mg-Like Sulphur and Chlorine

An experimental and theoretical study of the lifetimes of the 3s4p 3P levels in S V and Cl VI is reported. Using the beam-foil technique and extensive cascade corrections with the ANDC method we obtain the following lifetimes in ns: 0.72 ± 0.07 (3P2) and 0.37 ± 0.04 (3P1) in S V, whereas both levels have the same lifetime, 0.24 ± 0.03 ns, in Cl VI. The theoretical analysis shows that the large lifetime difference in S V results from a mixing of the 3s4p 1P1 and 3P1 levels, which is enhanced by interactions between the 3s4p and 3p3d configurations. Calculated transition probabilities for the individual decay channels from the 3s4p 3P levels are also given. In addition, the theoretical analysis indicates an erroneous identification of the 3p3d 1P and 1F levels in S V.

Analysis of the Spectrum of Five-Times-Ionized Zirconium (Zr vi)

The spectrum of Zr vi has been observed in a sliding-spark discharge with a 5-m grazing-incidence spectrograph. The analysis has yielded nearly all levels of the 4p44d configuration that can combine with the 4p52P ground term. All of the 4p45s levels as given by Chaghtai were confirmed. The 4s24p44d+4s24p45s+4s4p6 level structure has been theoretically interpreted, with configuration-interaction effects included. The 4s4p6²S12 level was found to have a 24% 4s24p4(1D)4d2S character and the 4s24p4(¹D)4d²S12 level a 21% 4s4p6 2S character. The energy parameters determined from a least-squares fit to the observed level values are compared with Hartree–Fock (HF) calculations. The ionization energy is estimated to be 95.8±0.6 eV.

The Spectrum of Six-Times-Ionized Chromium, Cr VII

The spectrum of six-times-ionized chromium, Cr VII, has been observed from 90 A to 2 000 A by using a 5-m grazing-incidence spectrograph and a 3-m normal-incidence spectrograph. The light source was either an open vacuum spark or a vacuum sliding spark. About 135 lines have been identified as combinations between 60 levels in the configurations 3s23p6, 3s23p53d, 4s, 4p, 4d, 4f, 5s, 5d and 6s as well as 3s3p63d and 3s3p64p. The energy parameters determined from least-squares fits of the observed level values are compared with Hartree-Fock calculations. The ionization energy, 3s23p5 2P3/2-3s23p6 1S0, is determined to 1 291 900 ± 600 cm-1 (160.17 ± 0.07 eV).

Additions to the spectrum and energy levels and a critical compilation of singly-ionized boron, B II

We have undertaken the study of the Li-like spectrum of doubly ionized boron, B III. The spectroscopic data have been obtained with beam-foil spectroscopy and high-resolution spark spectroscopy. The experimental work was combined with theoretical calculations using ab initio and semi-empirical techniques. About 50 new transitions have been observed, and most of the previously known lines have been measured with improved accuracy. We have also critically evaluated all previous and recent data for this spectrum. Complete data on wavelengths and energy levels based on this analysis are tabulated.

The Spectrum of Five-times-ionized Chromium, Cr VI

The spectrum of five-times-ionized chromium has been observed by using a 5-m grazing-incidence spectrograph and a 3-m normal-incidence spectrograph. The light sources have been a vacuum sliding spark and an open vacuum spark. 95 lines have been classified in the region 144 to 2 496 A. These transitions have fixed the terms of the series built on the 3p61S0 limit up to 6s, 6p, 5d, 10f, 6g, and 7h as well as 10 levels of 3p53d12 and 15 levels of 3p53d4s. The ionization energy is 731 020±6cm-1 (69.633 eV).