EGAS41 - Swansea University

41 st EGAS CP 64 Gdańsk 2009
Radiative lifetimes and transition probabilities in Hf I
and Hf III
G. Malcheva 1 , S. Enzonga Yoca 2,3 , R. Mayo 4,5 , M. Ortiz 5 , L. Engström 6 , H. Lundberg 6 ,
H. Nilsson 7 , É. Biémont2,8 and K. Blagoev 1
1 Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee,
BG - 1784 Sofia, Bulgaria
2 IPNAS (Bât. B15), University of Liége, Sart Tilman, B-4000 Liége, Belgium
3 CEPAMOQ, Faculty of Sciences, University of Douala, PO Box 8580, Douala, Cameroon
4 CIEMAT, Avda. Complutense, 22, 28040 Madrid, Spain
5 Faculty of Physics, Univ. Complutense de Madrid, E-28040 Madrid, Spain
6 Department of Physics, Lund University, P.O. Box 118, S-221 00 Lund, Sweden
7 Lund Observatory P.O. Box 43, S-221 00 Lund, Sweden
8 Astrophysics and Spectroscopy, University of Mons-Hainaut, B-7000 Mons, Belgium
∗ Corresponding author: bobcheva@issp.bas.bg,
Hafnium has been observed in the spectra of some stars, in particular in mild barium star
HD 202109 (ζ Cyg), Sirius A and in the photosphere of δ Scuti (the prototype of the class
of pulsating variables). Hf is also of astrophysical interest as a chronometer for stellar
and galaxy evolution. This stimulated the present investigation of radiative lifetimes and
transition probabilities in Hf I and Hf III.
In the present work radiative lifetimes of 9 odd excited levels in Hf III (5d6p 3 P 0,1 ,
1 D 2 , 3 D 1,2,3 , 3 F 2,3,4 ) and of 2 odd levels in Hf I (5d 2 6s6p z 3 D 2,3 ) are reported. They
were measured using a time-resolved laser-induced fluorescence (TR-LIF) technique [1].
The investigated levels in Hf I were excited in a single-step process from the ground term
(5d 2 6s 2 a 3 F), whereas in Hf III, we started from the low-lying 5d6s 3 D and ground 5d 2
3 F terms.
Free hafnium atoms and ions were generated by laser ablation in a vacuum chamber
with 10 −6 -10 −5 mbar background pressure. For the ablation, an Nd:YAG laser with 10 ns
pulse duration was used. The laser system for the excitation of the Hf I and Hf III levels
consisted of a dye laser which had a pulse duration of about 1-2 ns.
For all of the investigated levels the lifetimes have been measured for the first time.
The error bars are in the interval 10-25%. A multiconfigurational relativistic Hartree-Fock
method (HFR) (as described by Cowan [2]), including core-polarization effects, has been
used to compute radiative lifetimes and branching fractions of 15 Hf III levels, including
those measured in this work. A first set of transition probabilities is also proposed for 55
transitions of Hf III. The results are compared with the experimental data.
Acknowledgment
This work was financially supported by the Integrated Initiative of Infrastructure Project
LASERLAB- EUROPE (contract RII3-CT-2003-506350), the Swedish Research Council through
the Linnaeus grant and by the Spanish Ministry of Education and Research (project FIS2006-
10117). É. Biémont is Research Director of the Belgian FRS-FNRS. Financial support from
this organization is acknowledged. NSF of Bulgaria is acknowledged for financial support (grant
1516/05).
References
[1] Z.G. Zhang, S. Svanberg, P. Quinet, P. Palmeri, É. Biémont, Phys. Rev. Lett. 87,
273001 (2001)
[2] R.D. Cowan, The Theory of atomic Structure and Spectra (University of California
Press, Berkley, California, USA, 1981)
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