J O Ekberg

Transitions in Multiply Excited FVI and FVII

The transitions 1s2s2p2 5P-1s2p3 5S0 in F VI and 1s2s2p 4P0-1s2p2 4P in F VII have been investigated using the method of beam-foil spectroscopy. The fine-structure separations have been determined for the 1s2s2p2 5P term in F VI and for both 4P terms in F VII. The results are compared with recent theoretical calculations of fine structure, based on relativistic wavefunctions, and with previous experimental data. Lifetime measurements are reported for the 1s2p2 4P5/2 level and the 1s2p3 5S20 level.

Lifetimes of the 2s2p1P Level in Be-Like NIV and OV Obtained from Beam-Foil Experiments and Extensive Cascade Analyses

Lifetime measurements using the beam-foil method are reported for the 2s2p 1P level in Be-like N IV and O V. The results, 0.425 ± 0.015 ns in N IV and 0.338 ± 0.015 ns in O V, are in excellent agreement with the majority of recent theoretical results. The existing systematic discrepancy between theory and experiments in this sequence is thereby removed for these two ions. It is shown that this agreement is possible only when the most prominent cascades that repopulate the 2s2p 1P level, are explicitly included in the analysis through the application of the ANDC method. Lifetimes of these cascading levels are also reported and are found to be in good agreement with previous experimental and theoretical results.

Transitions and energy levels in Mg-like Ge XXI-Zr XXIX observed in laser-produced linear plasmas

Transitions in Ge XXI, Se XXIII, Sr XXVII, Y XXVIII, and Zr XXIX were identified in the extreme-ultraviolet spectra emitted from linear plasmas that were produced using line-focused laser beams. A grazing-incidence spectrograph viewed the plasma in the axial direction. The spectral lines were quite narrow owing to the reduced ion motion along the line of sight. Transitions of the type 3s2-3s3p, 3s3p-3p2, 3s3p-3s3d, 3p2-3p3d, 3s3d-3p3d, and 3p3d-3d2 were identified, and the wavelengths in the range 100-230 A were measured with an uncertainty of ± 0.010 A. The energy levels were determined from a large number of combinations. Fitted energy levels are presented for all of the elements from Ga XX to Zr XXIX with an uncertainty smaller than 50 cm−1.

Accurate Experimental Lifetimes of Excited Levels in Sodiumlike Sulfur, S VI

The lifetimes of the terms 3p 2P, 3d 2D, 4s 2S, 4p 2P, 4d 2D, 4f 2F, 5g 2G, 6g 2G, 6h 2H, 7h 2H, 7i 2I and 8k 2K in sodiumlike sulfur, S VI, have been determined using the beam-foil excitation technique. Most of the decay curves were analyzed by means of the ANDC method which corrects for cascading in a very detailed way. Accurate results were thereby obtained which show that an excellent agreement exists between experimental and theoretical values. Some previously noted disagreements between the results of beam-foil experiments and theoretical investigations are explained as being due to less accurate analyses of the experimental data.

A renewed study of singly ionized boron

Some energy levels and lifetimes in B II have been studied using classical emission spectroscopy and beam-foil spectroscopy. Revisions are suggested for the excitation energies of the 2s3s 1S and 2s5p 1P0 levels. The 2p3s 1P0 and 2s6p 1P0 terms have also been located. Lifetimes have measured for the 2s2p 1P0, 2p21S, 2s3d 1D and 2p23P levels. The results are compared with theoretical data.

Additions to the spectrum and energy levels and a critical compilation of helium-like and hydrogen-like boron, B IV and B V

Using beam-foil spectroscopy, we have observed several new lines in the B IV and B V spectra. This experimental work was combined with theoretical calculations using ab initio and semi-empirical techniques. We have also critically evaluated all previous and recent experimental and theoretical data for these spectra. Complete data on wavelengths and energy levels based on this analysis are tabulated.

Transitions and energy levels in Al-like Ge XX, Se XXII, Sr XXVI, Y XXVII and Zr XXVIII

Transitions in Ge XX, Se XXII, Sr XXVI, Y XXVII and Zr XXVIII were identified in the extreme-ultraviolet spectra emitted from linear plasmas that were produced using line-focused laser beams. A grazing-incidence spectrograph viewed the plasma in the axial direction. Transitions between levels of the three odd configurations 3s2 3p, 3p3 and 3s3p3d and the even 3s3p2 and 3s23d were identified and the wavelengths in the range 90-220 A were measured with an uncertainty of about 0.010 A. Energy values, determined from the observed combinations were compared with values obtained from multiconfiguration Dirac-Fock calculations. Fitted energy levels of 3p3 and 3s3p3d are also presented for elements between Cu and Rb.

Lifetimes and Oscillator Strengths for the Resonance Transitions in Cu-Like Iodine, I XXV

Using the beam-foil time-of-flight technique we have measured decay curves for 4s 2S1/2 -4p 2P1/2, 3/2 and 4p 2P1/2, 3/2 -4d 2D3/2, 5/2 transitions in Cu-like iodine, I XXV. Accurate experimental lifetimes of the 4p levels have been obtained after careful cascade corrections using the ANDC technique. The results are 46.7 ± 2 ps (2P1/2) and 23.1 ± 1 ps (2P3/2). These values are in good agreement with relativistic Hartree-Fock calculations. An up-to-date comparison between experimental and theoretical oscillator strengths is given for the whole copper sequence.

Extended analysis of doubly ionized chromium, Cr III

The third spectrum of chromium has been analyzed by using a low voltage sliding spark discharge and the 10.7 m normal incidence spectrograph at the National Institute of Standards and Technology, Washington, DC. In the analysis 143 new levels of the 3d3 4d and 3d3 5s configurations have been found giving a total of 352 known levels in Cr III. Almost 1900 lines, half of which are new classifications, have been observed in the wavelength region 763 A to 2675 A as transitions between levels of 3d4, 3d3 4s, 3d3 5s, 3d3 4d, 3d3 4p and 3d2 4s4p. From the obtained level energies wavelengths have been predicted with an uncertainty smaller than 0.005 A. A theoretical interpretation of the observed levels has been performed using the Cowan code. Theoretical transition probabilities have been calculated for the observed combinations.

Lifetimes of the 3p 2P1/2, 2P3/2 and 3d 2D3/2, 2D5/2 Levels in Cl VII

The beam-foil excitation technique has been applied to determine lifetimes of the 3p 2P1/2, 2P3/2 and 3d 2D3/2, 2D5/2 levels in Na-like Cl VII. Using the ANDC method accurate values have been obtained which confirm recent theoretical values and explain some previously noted differences between theoretical and experimental oscillator strengths for transitions in multiply ionized Na-like ions.