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Physical Review A

Relativistic many-body investigation of hyperfine interactions in excited S states of alkali metals: Francium and potassium

Alfred Owusu, R. W. Dougherty, G. Gowri, T. P. Das, Johannes Andriessen

Published Jul 1, 1997• 10 citations
Publisher

Abstract

To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited $5{}^{2}{S}_{1/2}--8{}^{2}{S}_{1/2}$ states of potassium and $8{}^{2}{S}_{1/2}--12{}^{2}{S}_{1/2}$ states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure. The net theoretical values of the hyperfine fields for the excited states studied are in excellent agreement with available experimental data for both atoms. There is a significant decrease in importance of the correlation contribution in going from the ground state to the excited states, the correlation contributions as ratios of the direct contribution decreasing rapidly as one moves to the higher excited states. However, the contribution from the exchange core polarization (ECP) effect is nearly a constant fraction of the direct effect for all the excited states considered. Physical explanations are offered for the observed trends in the contributions from the different mechanisms. A comparison is made of the different contributing effects to the hyperfine fields in potassium and francium to those in the related system, rubidium, studied earlier. Extrapolating from our results to the highly excited states of alkali-metal atoms, referred to as the Rydberg states, it is concluded that in addition to the direct contribution from the excited valence electron to the hyperfine fields, a significant contribution is expected from the ECP effect arising from the influence of exchange interactions between electrons in the valence and core states.

DOI
10.1103/physreva.56.305

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The one-electron contributions to the hyperfine constants for the excited SSS states of rubidium and cesium are calculated and compared with recent experimental results. From this comparison, the expected many-body contributions to the hyperfine constants are derived and shown to systematically decrease for higher excited states, in agreement with the situation found in earlier work on sodium. The physical origin of this behavior of the correlation effect is discussed.
Investigating Role of Electron Correlation Effects via Triple Excitations for Precise Evaluation of Energies and Hyperfine Structure Constants in 23^{23}23Na
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Abstract The hyperfine-structure constant A of the S , P , and D states in Cs atom with the principal quantum number n ≤ 12 are calculated using the Dirac–Fock approximation, the low-order many-body perturbation theory, and relativistic coupled-cluster method in single and double approximations with and without the inclusion of nonlinear terms. The importance of electron correlation effects, especially the nonlinear corrections of the cluster operators, is demonstrated by comparing the results of various approximations with available experimental values. Moreover, the correlation trends for individual electron correlation effects involving direct, core-polarization, and pair-correlation ones in members of Rydberg series are also investigated in the framework of the coupled-cluster theory. Some interesting features are observed.
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