É. Biémont (1,2) ((1)IPNAS, University of Liège, B-4000 Liège, Belgium; (2)Astrophysics and Spectroscopy, University of Mons-UMONS, B-7000 Mons, Belgium)
Frequently, the investigation of the atomic structure of the lanthanide ions is prevented by the complexity of the configurations involved and by the high density of low-energy levels which render the spectra very intricate. Their knowledge however is vital in astrophysics where there is a real need for such data in relation with the investigation of stellar abundance, e.g. in the sun and in CP stars.
The knowledge of the heavy elements belonging to the sixth row of the periodic table is important in astrophysics (theories of stellar nucleosynthesis), and some of these atoms, like tungsten, play a considerable role in controlled thermonuclear fusion research.
A detailed investigation of the refractory elements of the fifth row also shows that many gaps subsist concerning our knowledge of the radiative parameters of these atoms or of their ions.
For these reasons, we have realized a systematic analysis of the radiative properties (oscillator strengths, A-values, lifetimes, BFs, Landé factors,…) of these three groups of
elements (more precisely, the first three ionization stages have been considered) combining the experimental determination of radiative lifetimes with theoretical calculations of branching fractions (BF).
A large number of lifetimes (about 700 values) have been measured by laser spectroscopy for the elements Rb to Xe, Cs to Rn and for the lanthanides and, in many
cases, the corresponding BFs have been calculated using a relativistic Hartree-Fock (HFR) approach modified for inclusion of core-polarization (CPOL) effects. This combination of lifetime measurements with HFR+CPOL BFs determination has led to transition probabilities for about 64 000 transitions (lanthanides) and these results are stored in the DREAM database: Database on Rare Earths At Mons University. Similarly data for about 13 000 transitions (fifth and sixth rows of the periodic table) are available in the DESIRE database: DatabasE for the SIxth Row Elements.
At the time of the meeting, we will discuss the most recent and exciting results obtained in the field as well as the difficulties encountered when investigating the atomic structures of such heavy and complex atomic systems.
Talk presented at 3d CDAMOP, 14-16 December 2011, Delhi University, Delhi, India.