Dresden 2011 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 9: Interaction with VUV and X-ray light (FEL) II
A 9.3: Hauptvortrag
Dienstag, 15. März 2011, 11:30–12:00, BAR 205
Coupling dependence regarding the Cooper minima positions in two-photon ionization of rare gases — •Markus Braune1, Toralf Lischke1, Ande Meissner1, Markus Ilchen2, Sascha Deinert2, Jens Viefhaus2, Andre Knie3, and Uwe Becker1 — 1Fritz-Haber-Institut, Berlin — 2DESY, Hamburg — 3Uni Kassel
Cooper-Minima in partial cross sections in single photoionization are known to arise from the decrease of the overlap integral of the two possible wave functions with different angular momentum of the outgoing electron. Reflections of these intensity variations along photon energy are also exhibit in the angular distribution of photoelectron emission. Such radial effects should actually not show severe deviations for different angular momentum coupling multiplets of the same electron configuration. This is in fact the case for the single-photon ionization of all rare gases. However, open-shell atoms show larger deviations due to so called anisotropic interactions of the outgoing electron and the ionic core in the final state. Very little is known on the strength and behaviour of these anisotropic final state interactions. The second step of sequential two-photon ionization can be regarded as the ionization of an open shell system, namely the singly charged ion of the first ionization step. Hence such interactions are expected to occur. Indeed some recent calculations predict large effects with respect to the higher order anisotropy parameter β4 showing completely different behaviour in the region of the Cooper minima for the different multiplets. Results of our very recent angle resolved photoelectron spectroscopy measurements are presented.