Experimental study of the x-ray transitions in the heliumlike isoelectronic sequence: Updated results

We revisit the discrepancy between experiments and theory for the x-ray transitions of heliumlike ions and report on a measurement of the $n=2\to n=1$ x-ray transitions of heliumlike ${\mathrm{Cu}}^{27+}$. These measurements were carried at the Livermore electron beam ion trap facility and achieved an accuracy of 18 ppm. The measured values show reasonable agreement with theory, but they do not follow the trend established by other measurements with similar uncertainties.

Figure 1

Comparison of the experimental and calculated values of the $1s2p{}^1{P}_1\to 1s^2{}^1{S}_0$ wavelength in different heliumlike ions. The theoretical wavelengths ${\lambda }_{theor}$ are given by (a) Indelicato [12], (b) Drake [11], and (c) Vainshtein and Safronova [13]. The solid points are from measurements on heavy-ion accelerators [6, 7, 8, 9, 10]; the open points are from measurements on a tokamak [5]. A value of 12 398.54 eV Å was used to convert between energy and wavelength at the time the experimental and theoretical data were produced. (Figure adapted from [5].)

Figure 2

Comparison of selected experimental and calculated values of the $1s2p{}^1{P}_1\to 1s^2{}^1{S}_0$ transition energy in different heliumlike ions. All values are normalized to those calculated by Drake [11]. The calculated values from Cheng et al. [24] are given as a solid green line. Experimental values shown as black solid circles are from heavy-ion accelerators [6, 7, 8, 9, 10]; open circles denote tokamak results [5], open squares are results from the Livermore electron beam ion traps [19, 20], and the blue diamond is from the NIST electron beam ion trap [21]. A value of 12 398.42 eV Å was used to convert between energy and wavelength.

Figure 3

Typical spectrum of heliumlike ${\mathrm{Cu}}^{27+}$ showing the transitions from levels $1s2p{}^1{P}_1,1s2p{}^3{P}_2,1s2p{}^3{P}_1$, and $1s2s{}^3{S}_1$ to the $1s^2{}^1{S}_0$ ground state, labeled $w,x,y$, and $z$, respectively, in the notation of Gabriel [50].

Figure 4

Comparison of selected experimental and calculated values of the $1s2p{}^1{P}_1\to 1s^2{}^1{S}_0$ transition energy in different heliumlike ions. All values are normalized to those calculated by Drake [11]. The calculated values from Cheng et al. [24] are given as a solid green line; those from Artemyev et al. [1] are given as a dashed blue line. Experimental values are shown as black solid squares and are from the following sources: ${\mathrm{C}}^{4+},{\mathrm{N}}^{5+}$, and ${\mathrm{O}}^{6+}$, Ref. [31]; ${\mathrm{S}}^{14+}$, Refs. [6, 59]; ${\mathrm{Ar}}^{16+}$, Refs. [9, 27, 30]; ${\mathrm{K}}^{17+}$ and ${\mathrm{Sc}}^{19+}$, Ref. [5]; ${\mathrm{Ti}}^{20+}$, Refs. [5, 32]; ${\mathrm{V}}^{21+}$, Refs. [5, 21]; ${\mathrm{Cr}}^{22+}$, Ref. [5]; ${\mathrm{Fe}}^{24+}$, Refs. [5, 7, 26]; ${\mathrm{Ge}}^{30+}$, Ref. [19]; ${\mathrm{Kr}}^{34+}$, Refs. [10, 20]. The present value for ${\mathrm{Cu}}^{27+}$ is shown as a solid red circle. A value of 12398.42 eV Å was used to convert between energy and wavelength. The polynomial fit of the experimental data put forth by Chantler et al. [32] is shown as a green area. This fit does not include the experimental values for $Z=6$, 7, and 8, as well as the newest values for $Z=18$, 26, and 29.