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Physical Sciences and Mathematics *Commons*^{™}

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## Full-Text Articles in Physical Sciences and Mathematics

Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich

#### Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich

*Physics Faculty Research & Creative Works*

We studied mutual ionization in 200-keV H-^{+}He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.

Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin

#### Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin

*Physics Faculty Research & Creative Works*

We examined nearest-neighbor spacing (NNS) statistics in doubly excited states of helium near the double ionization threshold. Using the Brody parameter q to measure the NNS distribution between the regular Poisson distribution (q=0) and the chaotic Wigner distribution (q=1), we showed that for levels near the N=20 threshold of He⁺, or at about 0.13eV below the double ionization threshold, the NNS distribution has q=0.66. The result shows the slow approach of the NNS of helium energy levels towards the Wigner distribution vs the excitation energy. Using an s-wave model where the angular momentum of ...