Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session GT1: Ionization of Atoms and Molecules |
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Chair: T.N. Rescigno, Lawrence Berkeley National Laboratory Room: Doubletree Hotel Pine |
Tuesday, October 18, 2005 8:00AM - 8:30AM |
GT1.00001: Low-Energy Electron Impact Ionization of Helium Invited Speaker: Following the completion of the measurements of the doubly-differential cross sections (DDCSs) for the electron-impact ionization of atomic hydrogen, the simplest three-body Coulomb system, we applied the experimental techniques developed to the simplest four-body system, electron scattering from helium. Recently completed measurements of the absolute DDCSs for the electron impact ionization of helium at low incident energies will be presented. The measurements were taken using the moveable nozzle technique developed in our laboratory.\footnote{M.\ Hughes, K.\ E.\ James, Jr., J.G.Childers, and M.A.\ Khakoo, {\it Meas. Sci. Technol.} {\bf 14}, 841 (2003)} Data were taken at incident energies of 26~eV, 28~eV, 30~eV, 32~eV, 34~eV, 36~eV, and 40~eV. The results are compared to the theoretical convergent close-coupling (CCC) calculations of Bray {\it et al.}\footnote{Igor Bray, Dmitry V.Fursa, and Andris T.\ Stelbovics {\it J.\ Phys.\ B} {\bf 36}, 2211 (2003), and private communication.} and good agreement is observed. This work is funded by the National Science Foundation under grant \# NSF-RUI-PHY-0096808. In collaboration with Murtadha A. Khakoo, California State University, Fullerton. [Preview Abstract] |
Tuesday, October 18, 2005 8:30AM - 9:00AM |
GT1.00002: Time-dependent studies of ionization of atoms and molecules Invited Speaker: The time-dependent close-coupling method has been a successful and efficient method of calculating cross sections for many fundamental atomic processes including electron-impact excitation and ionization, multiple photon ionization and heavy-ion impact collisions. In the past decade this method has been applied to the electron-impact ionization of many atoms and ions. Beginning with studies of the electron-impact ionization of hydrogen, the time-dependent method has also been applied to multi-electron systems such as He, Li, Be, C, and O, as well as many of their ions. Also, electron-impact excitation cross sections have been calculated for many of these systems. Recently a program of work was initiated to apply these time-dependent techniques to the electron-impact ionization of small diatomic molecules. This work was motivated by the need for accurate cross sections for these molecules, as well as complementary work on photoionization of light molecules. In this talk an overview will be given of our time-dependent method, especially as applied to molecular systems. Recent results will be presented for electron-impact ionization cross sections of various atomic ions, and very recent results will be presented for the electron-impact ionization of H$_2^+$. Comparison will be made, where available, with previous theoretical and experimental results. This work is supported in part by grants to Auburn University from the U.S. Department of Energy. Work at Los Alamos National Laboratory is performed under the auspices of the U.S. Department of Energy. In collaboration with Michael Pindzola, Auburn University. [Preview Abstract] |
Tuesday, October 18, 2005 9:00AM - 9:15AM |
GT1.00003: An Elementary Method for Averaging over Molecular orientations in the Calculation of Electron-Impact Ionization of Molecules Junfang Gao, Don H. Madison, Jerry L. Peacher One of the difficulties associated with the calculation of fully differential cross sections (FDCS) for electron-impact ionization of molecules is that the experimental data typically do not resolve the orientation of the molecules which means that the theoretical approaches have to average over all orientations. This is not a problem for elementary approaches but it becomes an important constraint for more sophisticated approaches which require extensive computer time for a single orientation. A new method is proposed for averaging over molecular orientations which can be shown to be valid for gerade states if the S-basis function is dominate in the formation of the Molecular Orbital (MO). This method for averaging the orientations will be used to calculate FDCS in the DWIAOA (Distorted Wave Impulse Approximation Orientation Average) and 3DWOA (3- body Distorted Wave Orientation Average). Results will be presented for electron impact ionization of Hydrogen, Nitrogen and Water molecules over a wide range of incident-electron energies. The agreement with experimental data is good. [Preview Abstract] |
Tuesday, October 18, 2005 9:15AM - 9:30AM |
GT1.00004: First-Principles treatment of molecular double photoionization Daniel A. Horner, T.N. Rescigno, C.W. McCurdy We have developed a new computational approach to solving molecular double photoionization problems. The approach combines both Gaussian functions and the grid-based, exterior complex scaling discrete-variable representation (ECS-DVR) in a hybrid basis. Gaussian functions are well established and ideal for expanding molecular electronic states and the ECS-DVR on a finite-element grid has had much success solving atomic electron-impact ionization and double photoionization problems. The hybrid Gaussian ECS-DVR method allows us to extend our treatment of problems with two active electrons in the continuum to molecular targets. We have performed calculations of absolute fully-differential cross sections for the double photoionization of molecular hydrogen. Unlike other model calculations, this is a true {\em ab initio} approach. [Preview Abstract] |
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