The Allure of High Total Angular Momentum Levels in Multiply-Excited Ions

Abstract

In the interaction of fast ions with dense matter, the collision frequency is high enough to facilitate the simultaneous excitation of several electrons. Such multiply-excited few-electron systems have been exploited variously for plasma diagnostics. Beam-foil spectroscopic techniques, benefiting from the inherent time-resolution offered by the geometry of typical experiments, have proven particularly fruitful for the study of emission patterns and level lifetimes of specific multiply-excited levels, especially those of maximum spin and total angular momentum. Typical cases are recalled to illustrate some general principles. Among many others, earlier beam-foil measurements have targeted the core-excited 2p53s3p 4D7/2 – 2p5 3s3d 4F9/2 transition in several Na-like spectra ranging from S VI to Cu XIX. Data on the six intermediate elements missing at that time are now added. The interest in such atomic systems with multiple excitations and high total angular momentum values is discussed with a variety of examples.

EUV Beam-Foil Spectra of Scandium, Vanadium, Chromium, Manganese, Cobalt, and Zinc

“…Another prompt spectrum has been recorded at 23 MeV, at which ion beam energy the most prominent charge state should be q = 12+ [51] (V XIII, Na-like spectrum). That spectrum has been shown elsewhere [34]. Figure 9 shows spectra of the short-wavelength part of the range investigated.…”

“…There also should be the corresponding transition array Cr XV 4f-5g (wavelength estimate near 18.0 nm) which may be part of the unidentified line group near 17.92 nm (Figure 13b). A section of the same spectrum has been presented in [34] to highlight a transition (with a wavelength near 28.2 nm) in a core-excited Na-like ion (spectrum Cr XIV*). The survey spectrum has been recorded using relatively narrow spectrometer slits (50 µm), because a high ion beam current facilitated this mode of operation.…”

“…For examples of such work on elements of present emphasis see in [29][30][31][32][33][34][35][36][37]. From this field of activity evolved a quest for finding spin-changing intercombination lines in iron group ions with an open n = 3 valence shell, and for measuring their transition rates (see, for example, in [38][39][40][41][42][43]).…”

EUV Beam-Foil Spectra of Titanium, Iron, Nickel, and Copper

“…(Numerous data sets have been lost due to the mishaps of data storage media and computer system changes over several decades.) The recordings were made at the Bochum tandem accelerator laboratory about 30 years ago starting out with observations of electric dipole (E1) transitions, decay curves of regular and displaced terms, and various isoelectronic studies of specific configurations (for examples of such work on elements of present emphasis, see [45][46][47][48][49][50][51][52][53][54]). From this work, a quest evolved for finding spin-changing intercombination lines in iron group ions with an open n = 3 valence shell, and for measuring their transition rates (see, for example, [55][56][57][58][59][60]).…”

Calcium and Potassium Spectra in the EUV

“…Rather weak features of the proper line width (typically about 3 channels FWHM) can be discriminated from the background. Figure 5 shows the beam-foil spectrum of Ca near the most prominent line of the doubly excited spectrum Ca X* [50,51]. There are several lines that are almost as narrow as single transitions should appear, but nevertheless they are known [1] to represent blends of Ca IX lines.…”