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Interpretation and critical compilation of atomic spectra
Permanent : Jean-François Wyart
Thésitif : Ali Meftah
The interpretation of the spectral lines of free atoms and ions is more than a century old and should continue providing other branches of physics (laboratory and astrophysical plasmas, nuclear physics through hyperfine effects) with unique diagnostics and informations. It will stay active in the vicinity of ever larger plasma and controlled fusion devices (tokamak ITER and LMJ laser). After being pioneer in infrared Fourier Transform spectrometry which led to classify the last unknown spectra of lanthanide and actinide neutral atoms in the 70’s, our laboratory established collaborations with experimentalists producing multicharged ion spectra by beam-foil excitation, in tokamaks, sparks and by laser impact. For all those spectra, the accurate calculation of the free ion level energies and radiative transition probabilities is the crucial step for comparison with experimental wavelengths and intensities. The theoretical methods used here are mainly perturbative. In multicharged high-Z ions, the relativistic parametric method deriving from the Breit-Dirac equation leads to ab initio levels of relativistic configurations ; in the case of neutral atoms and weakly charged ions, the Racah-Slater method is the unique way to understand complex spectra with open shells ndN and nfN. Those calculations are performed by means of codes written in our laboratory, codes by R.D. Cowan or by the code RELAC. The reliability of predictions can be improved by means of global studies of a long sequence of configurations, radial parameters being constrained to obey regularities. Such studies have been applied to the isoelectronic sequences of Ni I [1] and Pd I with subsequent predictions of wavelengths for lasing lines in the X-UV region. Atomic spectroscopy remains of high interest for astronomers. The unprecedented quality of stellar spectra provided by Hubble Space Telescope revealed errors and lacks in early laboratory spectra. This has stimulated new studies, such as those of Dy III and Ta III [2], two of the very last unknown doubly charged ion spectra, as well as revisions in spectra of several neutral atoms of the platinum group [3]. The classification of actinide spectra which was never abandoned by our team and is now active on 99Es I and 99Es II [4], led to a critical compilation of all actinide experimental levels and prominent lines. This database is now accessible on-line on our website.
Figure. Spectrum (black) of a laser irradiated xenon gas jet from LULI (intensity 1014 W/cm2, pulse duration 600 ps) as compared with transitions 3d8-3d76f et 3d8-3d77f of Xe28+ (blue) 3d7-3d66f de Xe 29+ (red) calculated by means of the code RELAC. Those ions are dominant, but transitions of Xe 30+ , Xe 27+ and Xe 26+ have also been identified [5].
For further reading:
[1] Classification of the Nickel-like Silver Spectrum (Ag XX) from a fast capillary discharge Plasma
A. Rahman, J.J. Rocca, J.-F. Wyart,
Physica Scripta, 70, 21-25 (2004)
[2] The Third Spectrum of Tantalum (Ta III): Fine and Hyperfine Structure
V.I. Azarov, W-Ü L. Tchang-Brillet, J.-F. Wyart and F.G. Meijer,
Physica Scripta, 67 190 (2003)
[3] Improved Oscillator Strengths and Wavelengths for Os I and Ir I, and new results on early r-process nucleosynthesis
S. Ivarsson, J. Andersen, B. Nordstrom, X. Dai, S. Johansson, H. Lundberg, H. Nilsson, V. Hill, M. Lundqvist, J.-F. Wyart,
Astron. & Astroph., 4091141-1149 (2003)
[4]Studies of electronic configurations in the emission spectra of lanthanides and actinides: applications to Es I and Es II, predictions for Fm I
J.-F. Wyart, J. Blaise, E.F. Worden,
J. Sol. State Chem. 178, 589-602 (2005)
[5]Spectra of Laser Irradiated Xenon and Krypton in the Wavelength Range 0.5-1.0nm V.Nagels, C. Chenais-Popovics, V. Malka, J.C. Gauthier, A. Bachelier, J.-F. Wyart,
Physica Scripta 68, 233-43 (2003)
Actinides Tables
Selected constants energy levels and atomic spectra of Actinides
J. Blaise, J.F. Wyart
