Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session S4: Electron and Positron Scattering-Theory |
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Chair: Don Madison, University of Missouri-Rolla Room: Knoxville Convention Center 301E |
Friday, May 19, 2006 8:00AM - 8:12AM |
S4.00001: Importance of Different Interactions for Simultaneous Excitation-Ionization of Helium by Electron Impact A.L. Harris, M. Foster, J.L. Peacher, D.H. Madison, K. Bartschat Fully differential cross sections (FDCS) for simultaneous excitation-ionization of helium by 500 eV electron-impact are examined using various theoretical models. In the first Born approximation-Hartree Fock (FBA-HF), the projectile electron is treated as a plane wave, and the ejected electron is treated as a static-exchange Hartree-Fock distorted wave. In the first Born approximation-R-Matrix (FBA-RM), the ejected electron is represented as a closed-coupling R-Matrix wavefunction which has an improved treatment of exchange between the ejected electrons and bound state electrons. In the six distorted wave (6DW) model, all two particle interactions are included on an equal footing. The unique feature of all of these calculations is the use of fully-correlated initial state wavefunctions, such as the Hylleraas or Pluvinage. The different theories are compared with experimental data, and agreement is best for higher ejected- electron energies and smaller scattering angles. [Preview Abstract] |
Friday, May 19, 2006 8:12AM - 8:24AM |
S4.00002: A simple method for obtaining accurate electron scattering phase shifts from ab initio MBPT energies of an atom in a cavity I. M. Savukov We present a simple method for obtaining elastic scattering phase shifts and cross sections from precise ab initio many-body perturbation theory (MBPT) energies of atoms in variable cavities. This method does not require calculations of wavefunctions of continuum states, can be generalized to many atoms and ions, and is extremely convenient because existing codes developed for energy calculations can be used without modifications. High precision of the method and close agreement with experiment are illustrated on examples of e-Ar and e-Kr scattering. Correlations as well as relativistic corrections are systematically considered. [Preview Abstract] |
Friday, May 19, 2006 8:24AM - 8:36AM |
S4.00003: R-MATRIX II Calculations for Electron Collisions with Ni~II Anil Pradhan, Justin Oelgoetz, Sultana Nahar, V. Burke, P. Burke, C. Noble The R-matrix II approach is especially designed to generate configuration-interaction expansions in a systematic manner, taking account of correlations due to one- two-, and three-electron excitations. The program package, PRMAT, is used to carry out heretofore the most elaborate electron scattering calculations for the astrophysically important ions Ni II and Fe II. Over 100 LS terms are included in the eigenfunction expansions, which yield good agreement with spectroscopically observed term energies. Large CI expansions are particularly important for accurate treatment of resonances that dominate the near-threshold behavior of collision strengths. Results are presented for a number transitions and compared with earlier works. [Preview Abstract] |
Friday, May 19, 2006 8:36AM - 8:48AM |
S4.00004: Electron-Impact Double Ionization of H$^-$ M.S. Pindzola, F. Robicheaux, J. Colgan The time-dependent close-coupling method for three electron systems is used to calculate the electron-impact double ionization of H$^-$. The total 9d wavefunction is represented by a coupled channels expansion involving simple products of 3d radial lattices and 6d coupled spherical harmonics. Following time evolution of the total 9d wavefunction according to the Schrodinger equation, collision probabilities are found by projection of the total 9d wavefunction onto fully antisymmetric products of spatial and spin functions representing three outgoing Coulomb waves. The non-perturbative double ionization cross section results for H$^-$ are found to be more than a factor of 5 below the experimental measurements of Peart et al., J.Phys.B{\bf 4}, 88 (1971) and in excellent agreement with the experimental measurements of Yu et al., J.Phys.B{\bf 25}, 4593 (1992). [Preview Abstract] |
Friday, May 19, 2006 8:48AM - 9:00AM |
S4.00005: Effect of Exchange Distortion on Spin Polarized Electron-Xenon Scattering Z. Stegen, D.H. Madison, H. Saha, K. Bartschat, R. Panajotovic, S. Bellm, J. Lower, Erich Weigold It has been know for some time that the possibility for exchange between continuum electrons and bound electrons (normally called exchange distortion) can have an important effect on the outcome of electron-atom collisions particularly if the continuum electron is spin polarized. The proper way to treat this exchange would be through a Hartree-Fock or R-matrix calculation for the continuum electron wavefunction. Such calculations are sufficiently difficult that it has been common practice to use the Furness-McCarthy (FM) local potential approximation. Although the FM approximation normally gives improved agreement between experiment and theory, there is good evidence which indicates that the FM approximation should not work. We will examine the accuracy of the FM approximation for ionization of xenon by spin polarized electron-scattering via comparing individual partial waves obtained from the Hartree-Fock method, the R-Matrix method and the FM approximation. The theoretical results will be compared with some new measurements of the spin asymmetry for electron-impact ionization of xenon from ANU. [Preview Abstract] |
Friday, May 19, 2006 9:00AM - 9:12AM |
S4.00006: The ionization dynamics of electron impact H$_{2}$ and H$_{2}$O molecules Junfang Gao, Don Madison, Jerry Peacher, Martyn Hussey, Andrew Murray In the last couple of decades, (e,2e) spectroscopy has been used to investigate molecular structure. More recently, low to intermediate energy (e.g. below 500 eV) (e,2e) results have been reported for ionization of molecules. These low energy results are more sensitive to the collision dynamics of ionization, 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 the H$_{2}$ and H$_{2}$O molecules. The importance of the exchange distortion potential and exchange amplitude will be examined. Our theoretical results will be compared with recent experimental measurements. [Preview Abstract] |
Friday, May 19, 2006 9:12AM - 9:24AM |
S4.00007: State-selected predissociation of H$_3$ V. Ngassam, A.E. Orel Experimental studies of the predissociation of well-defined Rydberg states of H$_3$ have produced a complex three-body fragmentation pattern that is highly dependent on the initial state and show dramatic isotope effects. We present results of theoretical investigations for the fragmentation of selected Rydberg states of H$_3$ into three ground state hydrogen atoms as well as two-body predissociation into H + H$_2^+$(v,j). The non-adiabatic couplings and the surfaces are taken from previous studies. The dynamics are carried out using a wave packet propagation method in full-dimensionality including the effects of the Jahn-Teller interaction. Work supported by the NSF PHY-02-44911 [Preview Abstract] |
Friday, May 19, 2006 9:24AM - 9:36AM |
S4.00008: Dissociative Electron Attachment to ClCN and BrCN J. Royal, A.E. Orel ClCN and BrCN are pseudobihalogens. They have the interesting property that since both fragments, CN and Cl/Br, have positive electron affinities, two fragment channels are open. This means that dissociative electron attachment is possible into both CN$^{-}$ and Cl$^{-}$/Br$^{-}$ channels. The resonance parameters for these systems are obtained from electron scattering calculations using the Complex Kohn variational method. These resonance parameters are used as input into a full three dimensional wave packet calculation using the multi-configuration time-dependent Hartree (MCTDH) method. The resonances leading to dissociation into the product channels will be discussed and the calculated cross sections will be reported and compared to available experiment. Work supported by the NSF PHY-02-44911 and from The Center for Biophotonics, an NSF Science and Technology Center PHY 0120999. [Preview Abstract] |
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