Berlin 2001 – wissenschaftliches Programm
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A: Atomphysik
A 17: Posters Friday (Spectroscopy)
A 17.45: Poster
Freitag, 6. April 2001, 12:30–15:00, AT3
Theoretical investigations on the lifetime of the metastable 6s[3/2]2 level of Xe I — •C. Z. Dong, S. Fritzsche, B. Fricke, and W.–D. Sepp — Fachbereich Physik, Universität Kassel, D–34132 Kassel, Germany.
Recently, the metastable 6s[3/2]2 level of neutral xenon has been discussed in the context of new optical frequency standards for atomic clocks. For this lowest J = 2, odd–parity level, the lifetime is mainly governed by the 5p 5 6s[3/2]2 − 5p 6 1S0 magnetic–quadrupole (M2) transition to the ground state of xenon. In a high precision magnetic optical trap (MOT) experiment, Walhout and coworkers [1] determined a lifetime of about 42.9 ±3.9 s which, till today, is smaller by a factor of 2...3 when compared with the best theoretical calculations [2]. To investigate this striking discrepancy, here we report about an extensive multiconfiguration Dirac–Fock calculation for the 5p 5 6s[3/2]2 − 5p 6 1S0 M2 transition. Systematically enlarged wave function expansions were applied to incorporate all dominant effects of relativity, correlations, and relaxation of the electron density consistently. As found from these computations, a particular strong influence arise from the rearrangement of the electron density when the atom undergoes the transition. In a series of computational steps, we included all virtual single and double excitations from the { 5s, 5p } valance shells into different layers { ns, np, (n−1)d } of active shells (n=6−10) . These steps clearly show that large–scale computations are required in order to obtain an accurate result. At present, our best (largest) wave function expansion leads to a theoretical lifetime of 58.2 s which is in reasonable agreement with the experimental value of ∼ 43 s.
[1] M. Walhout, A. Witte and S. L. Rolston, Phys. Rev. Lett. 72 (1994) 2843.
[2] N. E. Small–Warren and L.–Y. C. Chiu, Phys. Rev. A11 (1975) 1777; P. Indelicato et al. (1994) unpublished.
[3] S. Fritzsche, C. Froese Fischer, C. Z. Dong, Comput. Phys. Commun. 124 (2000) 340; S. Fritzsche, J. Elec. Spec. Rel. Phen. (2001) in press.