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A: Fachverband Atomphysik
A 13: Posters: Photoionization and atomic systems in external fields
A 13.2: Poster
Tuesday, March 11, 2008, 16:30–18:30, Poster C3
An approximate quantum number in doubly excited helium — •Ralph Püttner1, Jiang Yuhai1,2, Dominique Delande3, Michael Martins4, and Günter Kaindl1 — 1Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14,14195 Berlin, Germany — 2Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany — 3Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany — 4Laboratoire Kastler-Brossel, Université Pierre et Marie Curie-Paris 6, ENS, CNRS; 4 Place Jussieu, F-75005 Paris, France
Helium close to the double ionization threshold is a prototypical system for studying quantum chaos. In this contribution experimental and theoretical total photoionization cross sections of doubly excited He up to the single ionization threshold I15 of He+ are presented, revealing excellent agreement. All spectra are dominated by principal Rydberg series, what is explained by the observation that the quantity F = N − K is approximately a good quantum number for a large fraction of states. The statistical distributions of nearest-neighbor energy spacings between resonances of Rydberg series with small F approach a Wigner distribution. The results show no indication for a transition to full chaos – i.e. a loss of all approximate quantum numbers – in He. From these results we derive a lower limit for the appearance of Eriscon fluctuations, which are also expected directly below the double ionization threshold.