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The hyperfine constants of the levels 2p 2 ( 3P)3s 4P J, 2p 2 ( 3P)3p 4P o J and 2p 2 ( 3P)3p 4D o J, deduced by Jennerich et al. [Eur. Phys. J. D 40, 81 (2006)] from the observed hyperfine structures of the transitions 2p 2 ( 3P)3s 4P J→ 2p 2 ( 3P)3p 4P o J and 2p 2 ( 3P)3s 4P J→ 2p 2 ( 3P)3p 4D o J recorded by saturation spectroscopy in the near-infrared, strongly disagree with the ab initio values of Jönsson et al. [J. Phys. B: At. Mol. Opt. Phys. 43, 115006 (2010)]. We propose a new interpretation of the recorded weak spectral lines. If the latter are indeed reinterpreted as crossover signals, a new set of experimental hyperfine constants is deduced, in very good agreement with the ab initio predictions. © 2010 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg., SCOPUS: ar.j, info:eu-repo/semantics/published

The hyperfine structure constants for the 1s 22s 22p 3 -4 S o ground state in nitrogen and the 1s 22s 22p 33s 5 S o excited state in oxygen are calculated using the MCHF Atomic Structure Package. The single excitation picture is explored through the use of compact wave functions allowing radial non-orthogonalities. Electron correlation is described through numerical multiconfiguration Hartree-Fock calculations for configuration expansions obtained by allowing all single and double excitations from the reference configuration to an active set of orbitals. The latter is increased in a systematic way allowing the convergence of the hyperfine parameters to be studied. Three- and four-particle effects are shown to be important and are taken into account in a sequence of large configuration interaction calculations. The final results are in good agreement with experiment.

The Dirac kinetic energy (DKE) form of the normal mass shift operator $$\left( {\tfrac{{m_e }} {M}\sum\nolimits_{i = 1}^N {T_i } } \right)$$ , which is an approximation of the $$\left( {\tfrac{1} {{2M}}\sum\nolimits_{i = 1}^N {P_i^2 } } \right)$$ operator built on the relativistic electron momenta, is widely used in relativistic atomic structure calculations. In the present paper, we illustrate the progressive breakdown of the Dirac kinetic energy form relatively to the momentum form when increasing the nuclear charge along the lithium isoelectronic sequence. Both forms are incorrect in the relativistic case but the DKE operator provides expectation values that are closer to the results obtained with the more complete relativistic recoil operator.

We present a summary of the research activities of the "Quantum Chemistry and Atomic Physics" theoretical group of the "Chimie Quantique et Photophysique" Laboratory at Université Libre de Bruxelles. We emphasize the links between the three orientations of the group: theoretical atomic spectroscopy, structure, and molecular dynamics and list the perspectives of our collaboration. © Springer-Verlag 2012., SCOPUS: ar.j, info:eu-repo/semantics/published