Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session LW2: Electron Impact Ionization and Excitation II |
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Chair: Klaus Bartschat, Drake University Room: Holiday Inn Salon B |
Wednesday, October 11, 2006 1:30PM - 2:00PM |
LW2.00001: Kinematically Complete Experiments on Single Ionization in Simple Atomic Systems Invited Speaker: Fully differential studies on atomic reaction dynamics are crucially important to advance our understanding of the few-body problem. In the case of electron impact, fully differential cross sections for single ionization have been measured for several decades. The vast majority of these studies were restricted to electrons ejected into specific planes. More importantly, for ion impact such experiments are much more challenging and fully differential cross sections (FDCS) became only available a few years ago. However, at the same time these measurements for ion impact also yielded the first complete three-dimensional images of the FDCS. The sobering conclusion of these studies was that our understanding of ionization processes in atomic collisions is much less complete than assumed previously. In this talk new unexpected results on three-dimensional FDCS will be presented for kinematic regimes for which so far no experimental FDCS have been obtained yet. These include collisions involving highly relativistic and highly charged ions as well as relatively slow p projectiles. \newline \newline In collaboration with Ahmad Hasan, Natasha Maydanyuk, Matt Foster, Brian Tooke and Don Madison, University of Missouri-Rolla. [Preview Abstract] |
Wednesday, October 11, 2006 2:00PM - 2:15PM |
LW2.00002: Multiparameter Ionization and Excitation Measurements Invited Speaker: Over recent years there has been a sustained and impressive development of technologies to aid the measurement of atomic and molecular collision processes. In particular, the application of multi-parameter coincidence techniques to atomic and molecular fragmentation processes has uncovered interesting new phenomena e.g. [1,2]. The underlying idea is to map measured arrival coordinate of particles (spatial and temporal) on to parameters of physical relevance through the action of time independent or dependent electric and/or magnetic fields [3,4]. The main challenge is in fashioning such fields to obtain greatest sensitivity for the parameters of greatest interest. In my talk I will review recent spectrometer developments discuss the potential for further improvements. The power of modern measurement techniques will be illustrated by selected examples of recent measurements by our group and others. Strengths and weaknesses of various experimental approaches will be discussed. \newline \newline In collaboration with: S. Bellm, AMPL, RSPHYSSE, Australian National University; D.H. Madison, Z. Stegen, University of Missouri - Rolla; K. Bartschat, Drake University; Colm T. Whelan, Old Dominion University. \newline \newline [1] T. Weber \textit{et al}, Nature \textbf{431}, 437 (2004). \newline [2] M. Schulz \textit{et al}., Nature \textbf{422}, 48 (2003). \newline [3] J. Ullrich \textit{et al}, Rep. Prog. Phys. \textbf{66}, 1463 (2003). \newline [4] C. Miron \textit{et al}, Rev. Sci. Instrum. \textbf{68}, 3729 (1997). [Preview Abstract] |
Wednesday, October 11, 2006 2:15PM - 2:30PM |
LW2.00003: Charge Dependent Effects in Double-Photo-Ionization of Helium-Like Ions Matt Foster, James Colgan A study is made of triple differential cross sections (TDCS) for double-photo-ionization (DPI) of helium-like ions. The angular distribution between the equal energy outgoing electrons is examined as a function of the nuclear target charge. Time-dependent close-coupling theory (TDCC) will be used to solve the time-dependent Schr\"{o}dinger equation for both outgoing electrons. The TDCC method treats the correlation between the electrons without approximation. Previous theoretical models that have calculated the TDCS for helium-like ions have only included the electron-electron interaction through approximate perturbative methods. We will analyze the effects of the electron correlation and its dependence relative to the nuclear charge. We will compare our calculations with previous experimental and theoretical work, where available. [Preview Abstract] |
Wednesday, October 11, 2006 2:30PM - 2:45PM |
LW2.00004: Coincidence studies of electron impact ionization over the full in-plane angular range. Birgit Lohmann, Mark Stevenson, Anthony Keehn Electron impact ionization is a fundamental collision process which plays a significant role in plasma physics, discharge physics and radiobiology. For example, modelling the interaction of electrons with matter in biological systems requires reliable data on electron impact ionization cross sections. Detailed information on the energy and angular distributions of the emitted electrons produced in electron impact ionization processes is obtained from coincidence measurements of the outgoing species [1]. However, experiments using conventional electron coincidence spectrometers usually are unable to measure the full angular distribution of ejected electrons, due to mechanical constraints. We present fully differential cross sections for electron impact ionization of argon which have been obtained using a magnetic-angle-changer [2] in a conventional coincidence spectrometer, which has enabled us to measure the full 360 degree ejected electron distribution in the scattering plane. [1] D. S. Milne-Brownlie, S. J. Cavanagh, Birgit Lohmann, C. Champion, P.-A. Hervieux and J. Hanssen, Phys. Rev. A, \textbf{69} (2004) 032701. [2] F. H. Read and J. M. Channing, Rev. Sci. Instrum. \textbf{67} (1996) 2372 [Preview Abstract] |
Wednesday, October 11, 2006 2:45PM - 3:00PM |
LW2.00005: Ionization dynamics for electron impact ionization of H$_{2}$O Junfang Gao, Don Madison, Martyn Hussey, Andrew Murray Water is arguably the most important substance in the universe. Recently (e, 2e) spectroscopy has been used to study low to intermediate incident energy (e.g. below 107.6eV) fully differential cross sections for electron impact ionization of water. These low energy results are very sensitive to the collision dynamics, so accurate theories are in the needed to interpret the experimental data. The distorted wave impulse approximation (DWIA) and molecular three-body distorted wave (M3DW) approximation were recently introduced by our group. These approximations will be used to study the fully differential cross sections for low energy electron-impact ionization of H$_{2}$O molecules. The importance of the polarization potential will be examined. Our theoretical results will be compared with recent experimental measurements. [Preview Abstract] |
Wednesday, October 11, 2006 3:00PM - 3:15PM |
LW2.00006: Near-Threshold Electron Impact Excitation of the Electronic states of N2 D.S. Newman, M. Lange, J. Matsumoto, J.C. Lower, S.J. Buckman Using a new position-sensitive, time-of-flight technique we have measured differential scattering cross sections for a number of electronically excited levels of N2 at energies between 8.5 and 15 eV. This technique has the advantage of providing a uniform transmission for the scattered particles as a function of energy, and thus removes substantial uncertainty from the inelastic cross sections that are derived through a comparison with the elastic scattering intensity. The present results are compared with a number of recent measurements. [Preview Abstract] |
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