Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session QR2: Electron Impact Ionization of Atoms and Molecules |
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Chair: Klaus Bartschat, Drake University Room: Salon A-D |
Thursday, October 16, 2008 10:00AM - 10:30AM |
QR2.00001: Out of plane ($e,2e$) experiments on helium autoionizing levels Invited Speaker: Out-of-plane $(e,2e)$ measurements and calculations are reported for the helium auto\-ionizing levels $(2s^2)^1\negthinspace S$, $(2p^2)^1\negthinspace D$, $(2s2p)^1\negthinspace P$, and for direct ionization.\footnote{B. A. deHarak, K.~Bartschat and N. L. S. Martin, Phys. Rev. Lett. 100, 063201 (2008)} We present the data as both angular distributions and energy spectra over the resonances. While the recoil peak almost vanishes in the angular distribution for direct ionization, it remains significant for the auto\-ionizing levels and exhibits a characteristic shape for each orbital angular momentum $L=0,1,2$. These findings can qualitatively be explained by an $L$-dependent addition to the ionization amplitude. A first order distorted-wave calculation underestimates the recoil peaks, but a second-order model in the projectile$-$target interaction can quantitatively reproduce their observed magnitudes. As for the angular distributions a second order theory is necessary to reproduce the experimental energy spectra. [Preview Abstract] |
Thursday, October 16, 2008 10:30AM - 11:00AM |
QR2.00002: Electron Impact Ionization of the Rare Gases Invited Speaker: Detailed information about the electron impact ionization process can be obtained from fully differential cross section measurements, in which the ionized electron is detected in coincidence with the outgoing scattered projectile electron. Incident and outgoing electron momenta are completely determined in these measurements. A considerable body of experimental and theoretical data exists for H and He targets, and the level of agreement between theory and experiment for these simple atoms is exceptional. However, there are still significant discrepancies between theory and experiment in the case of ionization of more complex atomic targets such as the heavier rare gas atoms. In this talk I will present recent measurements and theoretical predictions of fully differential cross sections for ionization of a range of rare gas targets: He, Ne, Ar and Xe. The talk will concentrate primarily on experiments which have been performed by two experimental groups, our group in Australia [1-3] and that of Lahmam-Bennani [3-5] in France. The experimental conditions span two different kinematic regimes, one with intermediate incident electron energy and low ejected electron energy, and the other with higher incident electron energy, and ejected electron energies which correspond to large energy transfer in the collision process. All experiments have been performed in a coplanar asymmetric configuration in which the scattered electron is detected at a small forward scattering angle. The experimental apparatus used in Australia is of quite different design to that in France, and I will present the results of an experiment in which the two groups have collaborated to produce data under identical kinematic conditions and for the same targets, using these two very different experimental approaches. This comprehensive set of experimental data has provided an interesting challenge to theory, and I will discuss the state of play with regard to the alignment between curent state-of–the-art theoretical models and the experimental results. \\[3pt] [1] Stevenson and Lohmann, Phys. Rev. A 73, 020701R (2006) \\[0pt] [2] Stevenson and Lohmann, Phys. Rev. A 77, 032708 (2008) \\[0pt] [3] Naja et al, J. Phys. B: At Mol. Opt. Phys. 41, 085205 (2008) \\[0pt] [4] Catoire et al, J. Phys. B 39, 2827 (2006) \\[0pt] [5] Kheifets et al, J. Phys. B 41, 145201 (2008). [Preview Abstract] |
Thursday, October 16, 2008 11:00AM - 11:15AM |
QR2.00003: GEC Student Award for Excellence Finalist: Atomic and Molecular Signatures for charged particle ionization Ola Al-Hagan, Don Madison, Christian Kaiser, Andrew Murray Charged particle ionization of atoms and molecules has been studied over several years and two prominent features are observed for both atoms and molecules -- one where the bound electron is ejected in a direction which conserves momentum for a classical projectile-electron collision (the binary peak) and a smaller feature where this electron is ejected in the opposite direction (recoil peak). These conventional studies are all performed in the projectile scattering plane. Here we report results for a plane perpendicular to the conventional plane, and we find two new features -- one the same for both atoms and molecules and one completely opposite. Quantum calculations are used to ascribe simple classical descriptions to these features. [Preview Abstract] |
Thursday, October 16, 2008 11:15AM - 11:30AM |
QR2.00004: Accuracy of the Gamow Factor for Approximating the PCI (Post Collision Interaction) in Electron-Impact Ionization of Atoms D.H. Madison, H.P. Saha, B. Lohmann, M.A. Stevenson, L.R. Hargreaves Recently Kheifets et al. (J. Phys. B, 41, 145201,2008) reported a distorted wave Born (DWBA) calculation for ionization of helium, neon and argon where the post collision interaction (PCI) between the two final state electrons was approximated using the Gamow-factor (which they called the G-factor). For cases where there was a large difference between experiment and theory at the recoil peak, the G-factor significantly improved agreement between experiment and theory. The G-factor is an approximation for including the final state Coulomb interaction between the two continuum electrons in the final state wavefunction which is attractive due to its simplicity. The 3DW (three-body-distorted-wave) method properly includes the Coulomb interaction in the final state wavefunction without approximation. We will examine the accuracy of the G-factor approximation by comparing 3DW results with G-factor results for ionization of neon, argon and xenon. [Preview Abstract] |
Thursday, October 16, 2008 11:30AM - 11:45AM |
QR2.00005: ABSTRACT WITHDRAWN |
Thursday, October 16, 2008 11:45AM - 12:00PM |
QR2.00006: ABSTRACT WITHDRAWN |
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