Helium-like ion

Schwartz has shown that for a helium-like ion, the contribution to the second-order MoUer-Plesset energy from the 1 angular momentum component can be approximated by the following expression ... 

Shull, H., and Lowdin, P.-O., J. Chem. Phys. 25, 1035, Correlation splitting in helium-like ions. ... 

In this way, accurate results for have been obtained for the helium atom and helium-like ions as well as for the hydrogen molecule [42-44], However, for a system with more electrons the problem is less easily solved. The first... 

Figure 18 Variation of the ground state energy of helium-like ions agai nst the Debye parameter. The lowermost curve is for He and the uppermost curve is for Ar16+ Reprinted with permission from [192] 2002, Springer Science + Business Media...

Figure 19 Plot of the lowest four S energies (au) of helium-like ions against different Debye parameters (au). The ionization limit is set to zero. Reprinted with permission from [193] 2002, Elsevier...

A. J. Thakkar and V. H. Smith Jr., Phys. Rev. A, 15,1 (1977). Compact and Accurate Integral-Transform Wavefunctions. I. The 11S State of the Helium-like Ions from H to through Mg10. ... 

Laser Spectroscopy of Hydrogen-Like and Helium-Like Ions... 

Abstract. Laser spectroscopy of hydrogen-like and helium-like ions is reviewed. Emphasis is on the fast-beam laser resonance technique, measurements in moderate-/ ions which provide tests of relativistic and quantum-electrodynamic atomic theory, and future experimental directions. 

Helium and helium-like ions are the prototypical many-electron system. All the bound-state QED physics of one-electron atoms is still present, of course, but with considerable added complication due to the electron-electron interaction. 

Fig. 2. Schematic of the n = 2 levels of helium-like ions showing the principal decay modes...

Obtaining experimental tests of the theory of hydrogen-like ions at moderate Z is challenging. Except for hydrogen there appear to be no measurements more precise than current theory. In the next decade, small but significant improvements in precision can be expected for Z = 2, 7 and 14. For moderate-.Z helium-like ions, laser techniques probe relativistic QED effects at higher precision than... 

In fig. 4 we plot the differences between the results of precision experiments and theory for the 23P(J - 23Pi and 23Pi - 23P2 intervals of helium-like ions for... 

The discrepancy between theories is indicated and the maximum discrepancy ranges from 23 ppm to 30 ppm for Z = 18-26 and differences are consistent. Our measurements are at this level of uncertainty. A further indication of the uncertainty or accuracy of theory can be gained by considering the two configuration interaction (Cl) calculations of Cheng et al [6,7]. The latest calculations for mid-Z helium-like ions [7] has resulted in new values which have shifted by up to 14 ppm from the earlier calculation [6]. The difference has been attributed to the exclusion of the Latter correction to the Dirac-Kohn-Sham potentials from which the QED corrections are evaluated. The new results are considered to be more reliable [7] and are in closer agreement to the unified calculation... 

A wide variety of plasma diagnostic applications is available from the measurement of the relatively simple X-ray spectra of He-like ions [1] and references therein. The n = 2 and n = 3 X-ray spectra from many mid- and high-Z He-like ions have been studied in tokamak plasmas [2-4] and in solar flares [5,6]. The high n Rydberg series of medium Z helium-like ions have been observed from Z-pinches [7,8], laser-produced plasmas [9], exploding wires [8], the solar corona [10], tokamaks [11-13] and ion traps [14]. Always associated with X-ray emission from these two electron systems are satellite lines from lithium-like ions. Comparison of observed X-ray spectra with calculated transitions can provide tests of atomic kinetics models and structure calculations for helium- and lithium-like ions. From wavelength measurements, a systematic study of the n and Z dependence of atomic potentials may be undertaken. From the satellite line intensities, the dynamics of level population by dielectronic recombination and inner-shell excitation may be addressed. 

Laser Spectroscopy of Hydrogen-Like and Helium-Like Ions Table 1. Lamb shift in mid- hydrogen-like ions... 

---