Ground State Energy Of Heliumlike Ions Research Articles

Two-electron self-energy contribution to the ground-state energy of helium-like ions

The two-electron self-energy contribution to the ground-state energy of helium-like ions is calculated both for a point nucleus and an extended nucleus in a wide interval of Z. All the two-electron contributions are compiled to obtain most accurate values for the two-electron part of the ground-state energy of helium-like ions in the range Z = 20–100. The theoretical value of the ground-state energy of 238U 90+, based on currently available theory, is evaluated to be −261382.9(8) eV, without higher-order one-electron QED corrections.

Two-electron Lamb-shift calculations on heliumlike ions.

Complete second-order calculations of the two-electron contribution to the ground-state energy of heliumlike ions are presented and compared with recent experimental results. Calculations involve relativistic many-body effects and two-electron Lamb-shift (vacuum-polarization and self-energy) contributions as well as the recently presented nonradiative QED corrections. Agreement between experimental and theoretical results verifies the many-body part of the calculation. The accuracy of the results is not high enough to test the QED part of the calculations, but an improvement by half an order of magnitude would provide an experimental test of the QED effect for heavy ions beyond the first-order Lamb shift. {copyright} {ital 1996 The American Physical Society.}

Measurement of two-electron contributions to the ground-state energy of heliumlike ions.

We report direct measurements of two-electron contributions to the ground-state energy of high-{ital Z} heliumlike ions. The difference in radiative-recombination x-ray energy (i.e., ionization potential of the recombined ion) was measured for bare and hydrogenlike target ions trapped in an electron-beam ion trap for six elements ranging from {ital Z}=32 to {ital Z}=83. The achieved uncertainties (as small as 1.6 eV) test the second-order many-body contributions to the energy and approach the size of the two-electron (screened) Lamb shift. We also report a measurement of the ground-state ionization potential of heliumlike bismuth relative to heliumlike xenon. All results are in agreement with available theories.

Screened QED effects in many-electron ions

We review recent progress in calculations of the structure of high- Z many-electron ions. Relativistic many-body perturbation; theory calculations of correlation and Breit effects are augmented by screened self-energy and vacuum polarization calculations. Screening by the direct part of the Dirac-Fock potential is included to all orders, while a subset of exchange effects is included to first order. This approach gives excellent agreement with experiment for the Li and Na isoelectronic sequences. The calculation of omitted two-photon QED effects is discussed, with particular emphasis on recent calculations of the ladder and crossed-ladder diagram for the 1s 2 ground-state energy of helium-like ions.

Evaluation of two-photon exchange graphs for highly charged heliumlike ions.

Contributions of one-loop ladder and crossed-ladder graphs to the ground-state energy of heliumlike ions are calculated in Furry representation QED. With the aid of a contour rotation, the graphs are evaluated to all orders in Z\ensuremath{\alpha} in the range Z=10--110. Particular attention is given to the relation of this work to recent many-body perturbation theory and configuration-interaction calculations.