Hamburg 2009 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 29: Photoionization II

A 29.2: Hauptvortrag

Donnerstag, 5. März 2009, 14:30–15:00, VMP 8 R208

Threshold Fragmentation of Simple Atoms by Electron Impact and FLASH VUV Light — •Alexander Dorn — Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany

Double ionization (DI) of an atom by electron impact (e,3e) or by absorption of one photon (γ,2e) is a process purely mediated by electron correlation and, therefore, is a very fundamental and intriguing problem in physics. Using many-particle imaging spectrometers (reaction microscopes) we have measured the momentum vectors of all final state continuum particles close to the DI threshold. Here, due to the vanishing kinetic energy the Coulomb-interaction among all particles should lead to highly symmetric electron emission patterns. For the three-electron final continuum state resulting from the (e,3e) reaction on helium at 5 eV excess energy the symmetric emission of the ejected electrons with 120^∘ relative angles was observed settling a long standing issue between various theories and rising new questions on whether the emission configuration depends on the target structure.

In order to enable kinematically complete (γ,3e) studies on the fundamental three-electron atom lithium we have implemented a magneto-optical trap into a reaction microscope. Due to the small cross section in the order of 1 barn this process can be studied only at high flux photon sources as the Free Electron Laser at Hamburg (FLASH). In a recent pilot experiment at FLASH we studied DI of optically pumped Li(2p). It turns out that the dynamic correlation between a photoionized 1s-electron and the ejected 2p-electron strongly depends on the spatial alignment of the 2p-orbital.