Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session J1: Atomic Collisions |
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Sponsoring Units: GEC Chair: Don Madison, University of Missouri-Rolla Room: Burnham Yates Conference Center Ballroom I |
Friday, May 20, 2005 8:00AM - 8:36AM |
J1.00001: Direct Measurements of Electron Correlation in Atoms Invited Speaker: Electron impact double ionization can be used to measure the correlated motion of electrons in atoms provided that the ionization proceeds by discrete binary collisions over times that are short compared to orbital periods and that scattered and ejected electron interactions with the residual ion core are negligible. Furthermore, the precise mechanism of the ionizing collisions must be known. Two double ionization mechanisms (TS1 and TS2) involving the outer orbital electrons of magnesium have been experimentally identified that meet these criteria. These mechanisms have been characterized, and theoretically modeled. Through a proper choice of experimental geometry and kinematics the TS2 mechanism can be separated from TS1 and used for the direct measurement of correlated electron motion. [Preview Abstract] |
Friday, May 20, 2005 8:36AM - 9:12AM |
J1.00002: ``Reaction Microscopes": New Frontiers in Atomic and Molecular Collisions Invited Speaker: ``Reaction Microscopes'' -- the ``cloud chambers'' of atomic and molecular physics -- are based on novel many-particle imaging methods combined with cooling techniques for the preparation of the target. Determining in coincidence the complete vector momenta of several electrons and ions after the fragmentation of atoms, molecules or clusters, they allow to explore, for the first time, quantum dynamics at its very basic, thus fundamental and still unresolved level of a few interacting quantum particles on ultra-short time scales of atto- to femtoseconds (10$^{-18}$ s -- 10$^{-15} $ s). In a unique combination, large solid angles close to 4$\pi $ and superior momentum resolutions around a few percent of an atomic unit are reached corresponding to energy resolution of sub-$\mu $eV for ions and meV for electrons. Hence, so-far unreachable frontiers in atomic and molecular many-particle quantum dynamics have become accessible! In the talk the working principle as well as the performance of newest machines will be highlighted. Forefront-experiments will be presented which image the complete final-state many-particle momentum-state for electron, ion and ultra-short laser pulse impact. For charged-particle induced single ionisation, such measurements have revealed troubling discrepancies between experimental results and state-of-the-art predictions. For electron-impact double-ionization of He, the strongly correlated four-particle Coulomb continuum has been explored, just 24 eV above threshold. Simultaneous ionisation and excitation was investigated in a first kinematically complete experiment and laser-assisted electron collisions have become accessible. Laser-assisted collisions, laser driven wave packets recolliding with their parent ions along with ultra-short pump-probe techniques point into the future direction where one might envision controlling quantum motion on an attosecond time scale. [Preview Abstract] |
Friday, May 20, 2005 9:12AM - 9:48AM |
J1.00003: Convergent close-coupling calculations of atomic double ionization Invited Speaker: Convergent close-coupling (CCC) theory, originally developed to describe electron-atom collisions [1], was applied, with a great success, to atomic double photoionization (DPI). DPI from He and its isoelectronic sequence had been studied extensively and prediction of the theory in most cases had been confirmed experimentally [2]. Here we present latest applications of the CCC method to DPI which go beyond simple helium-like targets. The frozen-core approximation is used to describe DPI from the valence shell of Be and heavier alkaline-earth atoms as well as the outermost $np^6$ subshell of noble gases. A ``hybrid'' model combining a target-specific ground state and a He-like final state is employed to describe DPI from subvalent $2s^2$ shell of Ar and the H$_2$ molecule. Extension of the theory to describe DPI in strong laser fields is discussed. \begin{thebibliography}{1} \bibitem{BS95b} I. Bray and A.~T. Stelbovics, Adv.~Atom.~Mol.~Phys. {\bf 35}, 209 (1995). \bibitem{KB98d} A.~S. Kheifets and I. Bray, Phys.~Rev.~A {\bf 58}, 4501 (1998). \end{thebibliography} [Preview Abstract] |
Friday, May 20, 2005 9:48AM - 10:24AM |
J1.00004: Antihydrogen - Hydrogen Collisions Invited Speaker: Recently, both the ATRAP (G. Gabrielse et al., PRL 89 213404, (2002)) and ATHENA (M. Amoretti et al., Nature 419 (2002)) experiments at the CERN anti-proton decelerator have successfully created and detected low temperature antihydrogen atoms in the laboratory. Present efforts are directed toward the goal of trapping and cooling the antihydrogen into the ultra-cold regime in order to enable tests, of unprecedented accuracy, for some of the most fundamental symmetries of matter and anti-matter. Several methods for cooling have been proposed. Here we discuss the feasibility of cooling antihydrogen via its contact with ultra-cold matter, in particular hydrogen. The cooling efficiency is determined by the collision properties of this system. Annihilation of the leptons, the proton and antiproton, as well as re-arrangements into protonium and positronium during a collision conspire to limit the utility of sympathetic cooling. In this talk we will discuss the various collision processes and present calculated collision data in order to assess the viability of sympathetic cooling of antimatter in contact with matter. We will also discuss properties of the novel, unstable, exotic molecule (B. Zygelman et al., PRA 69, 042715 (2004)) that has been predicted as a possible by-product in a collision of antihydrogen with an hydrogen atom. Collaborators in this study include, A. Dalgarno, P. Froelich, S. Jonsell and A. Saenz. Partial support was provided by an NSF grant to the Harvard-MIT CUA where the author was a Visiting Scientist. [Preview Abstract] |
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