Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session BT2: Electron Impact Ionization |
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Chair: Klaus Bartschat, Drake University Room: Doubletree Crystal City Crystal Ballroom B |
Tuesday, October 2, 2007 8:00AM - 8:30AM |
BT2.00001: Electron-Atom Ionization Calculations using Propagating Exterior Complex Scaling Invited Speaker: The exterior complex scaling method (\textit{Science} \textbf{286} (1999) 2474), pioneered by Rescigno, McCurdy and coworkers, provided highly accurate \textit{ab initio} solutions for electron-hydrogen collisions by directly solving the time-independent Schr\"{o}dinger equation in coordinate space. An extension of this method, propagating exterior complex scaling (PECS), was developed by Bartlett and Stelbovics (\textit{J. Phys. B} \textbf{37} (2004) L69, \textit{J. Phys. B} \textbf{39} (2006) R379) and has been demonstrated to provide computationally efficient and accurate calculations of ionization and scattering cross sections over a large range of energies below, above and near the ionization threshold. An overview of the PECS method for three-body collisions and the computational advantages of its propagation and iterative coupling techniques will be presented along with results of: (1) near-threshold ionization of electron-hydrogen collisions and the Wannier threshold laws, (2) scattering cross section resonances below the ionization threshold, and (3) total and differential cross sections for electron collisions with excited targets and hydrogenic ions from low through to high energies. Recently, the PECS method has been extended to solve four-body collisions using time-independent methods in coordinate space and has initially been applied to the $s$-wave model for electron-helium collisions. A description of the extensions made to the PECS method to facilitate these significantly more computationally demanding calculations will be given, and results will be presented for elastic, single-excitation, double-excitation, single-ionization and double-ionization collisions. [Preview Abstract] |
Tuesday, October 2, 2007 8:30AM - 9:00AM |
BT2.00002: Electron-Impact Excitation Out of the Metastable Levels of Argon and Other Rare Gas Atoms Invited Speaker: In a typical low-temperature plasma, the primary mechanism for populating excited levels is electron-atom collisions. While the vast majority of atoms are typically in their ground state, the few atoms in long-lived metastable levels can also serve as targets of the incident electrons. Indeed, in a typical plasma the excitation rate out of the metastable levels into select upper levels can surpass the excitation rate from the ground state. I will review our group's measurements of the excitation cross sections out of the metastable levels of neon, argon, krypton, and xenon. In addition to their applications in plasma modeling, the study of these cross sections has also been interesting from a fundamental collision-physics perspective. [Preview Abstract] |
Tuesday, October 2, 2007 9:00AM - 9:15AM |
BT2.00003: Single Ionization of He and H by 75 keV Proton Impact Jason Alexander, Aaron LaForge, Michael Schulz Recoil-ion momentum spectroscopy and projectile momentum spectroscopy have been applied to the study of single ionization of He and H by 75keV proton impact. Doubly differential cross sections as a function of the projectile energy loss (or equivalently electron energy) and the scattering angle will be discussed. The results will be compared to earlier doubly differential data for ionization of helium [1]. There, qualitative discrepancies to various theories were observed. Here, we will discuss to what extent these discrepancies can be attributed to an insufficient description of the initial target state. Analyzing the recoil-ion momenta will eventually enable us to obtain fully differential cross sections. [1] Vajnai, T. et al. Phys. Rev. Lett. 74 3588 (1995) [Preview Abstract] |
Tuesday, October 2, 2007 9:15AM - 9:30AM |
BT2.00004: Out-of-Plane Cross Sections for Electron Impact Ionization of He and H$_{2}$ Ola Al-Hagan, Don Madison, Christian Kaiser, Andrew Murray We have seen in recent years a sharp disagreement between the theory and experiment for heavy particle ionization of He for electrons ejected out of the scattering plan while good agreement was found in the scattering plane. The lack of agreement between experiment and theory for out-of-plane has been attributed to a double scattering mechanism where the projectile first `hits' the electron and then scatters off the nucleus. If these effects are important for a He nucleus, they should be even more important for a H$_{2}$ ion. We will report theoretical and experimental cross sections for in and out of the scattering plane for electron impact ionization for both He and H$_{2}$. We will show that the orientation of the molecular axis can produce very different results outside the scattering plane for molecules as compared to atoms. [Preview Abstract] |
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