Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session PR2: Ion Atom Collisions I |
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Chair: M. Schulz, Missouri University of Science and Technology Room: Salon A-D |
Thursday, October 16, 2008 8:00AM - 8:30AM |
PR2.00001: Contemporary theoretical methods to treat atomic processes in gaseous and plasma environments: Heavy particle collisions studied using supercomputers Invited Speaker: Interactions among photons, electrons, ions, atoms, molecules, and surfaces are ubiquitous within gaseous and plasma environments and their detailed description is fundamental to understanding and controlling these scientifically and technologically important states of matter. Reaching a more accurate and comprehensive knowledge of such atomic processes has been greatly aided by use of contemporary computational resources and through a close interplay with advancing experimental techniques. Following an introduction to atomic processes in gaseous and plasma environments and of methods used to solve the heavy particle collision problem, recent studies will be described which have been enabled by massively parallel computer solutions. [Preview Abstract] |
Thursday, October 16, 2008 8:30AM - 9:00AM |
PR2.00002: Electronic Correlation in Ion-Atom Collisions Invited Speaker: In this talk, I will examine the correlated electronic dynamics that occur during single and double ionization of helium by ion impact. A non-perturbative time-dependent close-coupling method (TDCC) is applied to fully describe the interaction between the outgoing ionized electrons. Also, the projectile-atom interaction is constructed as a multipole expansion that includes monopole, dipole, quadrupole, and octopole terms. Excellent agreement is obtained between our TDCC calculations and experimental measurements for single and double ionization cross sections for antiproton impact of helium. At an impact energy of 1 MeV we find that the double-to-single ionization ratio is twice as large for antiproton impact as for proton impact, confirming a long-standing unexpected experimental measurement. I will also report on our progress towards fully differential cross sections for 6 MeV proton impact double ionization of helium. [Preview Abstract] |
Thursday, October 16, 2008 9:00AM - 9:15AM |
PR2.00003: Theoretical study on one- and two-electron processes involving capture in ion-Helium collisions Tom Kirchner, Myroslav Zapukhlyak Motivated by recent efforts to disentangle the effects of heavy-particle-electron couplings and electron-electron interactions on differential cross sections in ion-atom collisions [1,2] we have carried out a rather comprehensive theoretical study on various one- and two-electron processes that include capture over a broad range of impact energies. The calculations are based on the independent electron model, the two-center basis generator method for orbital propagation, and the eikonal approximation to extract angular-differential cross sections from impact-parameter-dependent transition amplitudes. Selected results for proton, He$^{2+}$, and Ar$^{15+ ... 18+ }$impact on helium atoms will be presented and compared with experimental and previous theoretical data where available. In general, good agreement with measurements is found, even for shell-specific capture in highly-charged argon impact collisions, for which close-coupling calculations are very demanding. The status of theory will be assessed and future directions will be pointed out. [1] A. Hasan et al., Phys. Rev. A \textbf{74}, 032703 (2006) [2] M. Zapukhlyak, et al., Phys. Rev. A \textbf{77}, 012720 (2007) [Preview Abstract] |
Thursday, October 16, 2008 9:15AM - 9:30AM |
PR2.00004: Isotope Effects in Ion-Atom Collisions Charles Havener The ion-atom merged-beams apparatus at Oak Ridge National Laboratory is used to measure charge transfer for low energy collisions of multi-charged ions with H and D. The apparatus has been relocated and upgraded to accept high velocity beams from the 250 kV High Voltage Platform at the Multi-Charged Ion Research Facility. Isotope effects for charge transfer processes have recently received increased attention. (Stolterfoht et al , PRL 99, 103201 (2007)). The higher velocity beams allow, for the first time, measurements with both H and D from keV/u down to meV/u collision energies. When charge transfer occurs at relatively large distances (via radial couplings) the ion-induced dipole attraction leads to trajectory effects (Havener et al., ICPEAC XVII Proceedings, Brisbane, 1991) causing differences in the charge transfer cross section for H and D. Such a strong isotope effect has now been directly observed for Si$^{4+}$ + H(D), but not for N$^{2+}$ + H(D). Strong effects have been predicted in the charge transfer cross section for the fundamental system He$^{2+}$ + H(D, T) ( Stolterfoht et al.) at collision energies where charge transfer occurs primarily through united-atom rotational coupling. Currently we are exploring systems where isotope effects in rotational coupling can be measured. [Preview Abstract] |
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