Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session B5: Electron Collisions |
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Chair: Timothy Gay, University of Nebraska-Lincoln Room: Clark Hall 107 |
Wednesday, May 20, 2009 10:30AM - 10:42AM |
B5.00001: An Improved RMPS Approach to Ground and Metastable Ionization of Neutral Neon C.P. Ballance, M.S. Pindzola, D.C. Griffin The large ground state ionization potential of neutral neon has traditionally made it difficult for non-perturbative basis-set methods, such as the RMPS, to calculate the ground state ionization cross section from the ionization threshold to its peak value. Current developments in the parallel R-matrix suite of codes (see Ballance and Griffin, JPB {\bf 37}, 2943 (2004)) in conjunction with the ICFT method have allowed both electron-impact ground and metastable term and level-resolved ionization cross sections to be calculated in a very efficient manner. We shall present electron-impact ionization cross sections from the ground state and $1s^2 2s^2 2p^5 nl (n < 6)$ metastables, comparing with available experiments. We shall also investigate differences between initial term and level-resolved cross sections. [Preview Abstract] |
Wednesday, May 20, 2009 10:42AM - 10:54AM |
B5.00002: Electron-Impact Single Ionization of Mg and Al$^+$ J.A. Ludlow, C.P. Ballance, S.D. Loch, M.S. Pindzola, D.C. Griffin Electron-impact ionization of atoms and ions is a subject of continuing interest. The development of non-perturbative theoretical methods, such as TDCC, RMPS, and CCC, has enabled the benchmarking of experimental ionization data for many systems and has shown that perturbative distorted-wave methods are generally applicable when the ion is more than a few times ionized (see Griffin and Pindzola, Adv. At. Mol. Opt. Phys. {\bf 54}, 203 (2006)). For near neutrals, distorted-wave methods perform poorly. The good agreement with distorted-wave theory shown by the available experimental data for Mg and Al$^+$ is, therefore, surprising and has prompted new TDCC and RMPS calculations to be carried out for electron-impact ionization of ground state Mg and Al$^+$. We find that the available experimental single ionization cross sections for Mg and Al$^+$ lie substantially above the new theoretical cross sections. Furthermore, in the collisional ionization region near the ionization threshold, the Maxwellian-averaged ionization rates for the available experimental results are found to be as much as three times larger than the new theoretical results. [Preview Abstract] |
Wednesday, May 20, 2009 10:54AM - 11:06AM |
B5.00003: Fully relativistic B-spline R-matrix calculations for electron collisions with xenon Klaus Bartschat, Oleg Zatsarinny We have applied our recently developed fully relativistic Dirac $B$-spline $R$-matrix (DBSR) code~[1] to calculate electron scattering from xenon atoms. Results from a \hbox{31-state} close-coupling model for the excitation function of the metastable \hbox{${\rm (5p^5 6s)}~J=0,2$} states show excellent agreement with experiment~[2], thereby presenting a significant improvement over the most sophisticated previous Breit-Pauli calculations~[3,4]. This allows for a detailed and reliable analysis of the resonance structure. The same model is currently being used to calculate electron-impact excitation from the metastable $J=2$ state. The results will be compared with recent experimental data~[5] and predictions from other theoretical models~[6,7]. [1]~O.~Zatsarinny and K.~Bartschat, Phys. Rev. A {\bf 77} (2008) 062701. [2]~S.~J. Buckman {\it et al}., J. Phys. B {\bf 16} (1983) 4219. [3]~A.~N.~Grum-Grzhimailo and K.~Bartschat, J. Phys. B {\bf 35} (2002) 3479. [4]~M.~Allan {\it et al}., Phys. Rev. A {\bf 74} (2006) 030701(R). [5]~R.~O. Jung {\it et al}., Phys. Rev. A {\bf 72} (2005) 022723. [6]~R. Srivastava {\it et al}., Phys. Rev. A {\bf 74} (2006) 012715. [7]~J.~Jiang {\it et al}., J. Phys. B {\bf 41} (2008) 245204. [Preview Abstract] |
Wednesday, May 20, 2009 11:06AM - 11:18AM |
B5.00004: Inelastic Scattering of Electrons by Black Hole Atoms M.S. Pindzola, F. Robicheaux Electron-impact inelastic scattering processes involving black hole atoms are calculated by direct solution of the general relativistic Klein-Gordon equation. In Eddington-Finkelstein coordinates for the space-time metric, the Hamiltonian is non-singular, complex, and non-Hermitian. Bound states of electrons and black holes with masses ranging from 3.8 $\times$ 10$^{12}$ kg to 7.6 $\times$ 10$^{13}$ kg are found by matrix solution of the time-independent Klein-Gordon equation. Absorption effects on inelastic scattering of electrons by black hole atoms are investigated by comparing solutions of the time-dependent Klein-Gordon equation with and without general relativistic corrections to the Newtonian gravitational potential. [Preview Abstract] |
Wednesday, May 20, 2009 11:18AM - 11:30AM |
B5.00005: Electron-Atom Interaction and Optogalvanic Dynamics in a Hollow Cathode Discharge Plasma Around 659.9nm Kayode Ogungbemi, Prabhakar Misra Our study focuses on the rate of ionization of neon in a hollow cathode discharge lamp irradiated with a pulsed laser whose wavelength (659.9 nm) is in resonance with the neon transition. Changes in ionization rates were observed as a function of current variation across the lamp electrodes, thus enabling the atomic -- electron collisional processes within the plasma to be characterized. A mathematical model was developed to fit the optogalvanic waveforms for the 1s$_{5}$ -2p$_{2}$ neon transition at 659.9 nm and determine the instrumental time constant and exponential rate parameters in order to better understand the atom-electron interactions and the dynamics of the discharge plasma. [Preview Abstract] |
Wednesday, May 20, 2009 11:30AM - 11:42AM |
B5.00006: Experimental and Theoretical Studies of Low Energy Electron Impact Ionization for Molecular Hydrogen Ola Al-Hagan, Don Madison, James Colgan, Christian Kaiser, Andrew Murray, Mitch Pindzola Experimental and theoretical fully differential cross sections will be presented for 35.5 eV electron-impact ionization of molecular hydrogen. Experimental measurement performed for several different planes ranging from the scattering plane to a plane perpendicular to the beam direction will be compared with both non-perturbative close-coupling and perturbative three-body distorted wave (3DW) theoretical calculations. Surprisingly, the largest experimental cross sections are found not in the scattering plane but rather in a plane tilted at 45 degrees to the beam direction. Perturbative calculations suggest that this is due to polarization of the molecule. Both the close-coupling and the 3DW results are in better agreement with experiment in the perpendicular plane than they are in the scattering plane. [Preview Abstract] |
Wednesday, May 20, 2009 11:42AM - 11:54AM |
B5.00007: H$^{-}$ and D$^{-}$ channels of Dissociative Electron Attachment to water molecules Hidehito Adaniya, Benedikt Rudek, Timur Osipov, Sun Lee, Thorsten Weber, Marcus Hertlein, Markus Schoeffler, Mike Prior, Ali Belkacem A COLTRIM technique is modified to measure the kinetic energy and angular distribution of H$^{-}$ and D$^{-}$ ions arising from dissociative electron attachment to water and heavy water molecules. A low energy pulsed electron, an effusive water target, a pulsed extraction plate are used in combination with the COLTRIMS spectrometer. The spectrometer carries an electrostatic lens system to compensate the effusiveness of the target. This technique is applied to study the H$^{-}$ and D$^{-}$ channels in the three Feshbach resonances of water and heavy water anion. The measured kinetic energy release will give the energy partitioning among the fragments, and the means to identify the two-body and three-body breakup channels. The angular distribution of the H$^{-}$(D$^{-}$) ions with respect to the electron beam is found to reflect well the breakup dynamics of the H$_{2}$O$^{-}$ at the dissociation. The experimental results are compared with the theoretical predictions. [Preview Abstract] |
Wednesday, May 20, 2009 11:54AM - 12:06PM |
B5.00008: Dissociative Electron Attachment to HCCCN Slim Chourou, Ann Orel Experiments on dissociative electron attachment (DEA) to HCCCN below 12 eV have led predominantly to formation of CCCN$^-$, CN$^-$, HCC$^-$ and CC$^-$ negative ions. It has been concluded that these fragments result mainly from the decay of $\pi$*-shape resonant state upon electron attachment that involves distortion of the symmetry of the linear neutral molecule. In order to study the dynamics of dissociation in these channels, we subdivided the molecule into three fragments (H), (CC) and (CN); therefore, four internal coordinates consisting in the distances between the center of masses of (H) and (CC) fragments, (CC) and (CN) fragments, the (H)-(CC) angle and the (CC)-(CN) angle are included in the calculation. We have performed electron scattering calculations using Complex Kohn Variational method to determine the resonance energies and autoionization width for various geometries of the system and construct the complex potential energy surfaces relevant to the metastable HCCCN$^{-*}$ ion. The nuclear dynamics is treated using the Multiconfiguration Time-Dependent Hartree (MCTDH) formalism and the flux of the propagating wavepacket is used to compute the DEA cross section relevant to 4 channels in question. The results are then compared to the available findings. [Preview Abstract] |
Wednesday, May 20, 2009 12:06PM - 12:18PM |
B5.00009: Spin Torque on Molecular Rotation Induced by Polarized Electrons T.J. Gay, J.W. Maseberg We have measured the linear and circular polarization of $391.4$ nm N$_{2}^{\:+}$ $B\:^{2}\Sigma_{u}^{+}(v'=0)$~$\rightarrow$~$X\:^{2}\Sigma_{g}^{+}(v''=0)$ $P$-branch fluorescence produced by spin-polarized electron impact excitation of N$_{2}$ $X\:^{1}\Sigma_{g}^{+}(v=0)$ ground states. We find the linear polarization to be ${\sim}0.03$ for an energy range of $20$ eV above threshold. Of particular note, however, is that the resulting non-zero values of the spin-normalized circular polarization (energy-averaged value of P$_3$/P$_e=0.0133(8)$) indicate that spin-rotation coupling, in the absence of well defined electron orbital angular momentum $(\Lambda=0)$, acts to produce oriented rotational angular momenta in the excited molecular state prior to decay. [Preview Abstract] |
Wednesday, May 20, 2009 12:18PM - 12:30PM |
B5.00010: Dissociative recombination of N$_2$H$^+$ Valery Ngassam, Ann E. Orel Dissociative recombination of N$_2$H$^+$ plays an important role in astrochemistry since it is thought to be the main route for N$_2$ formation. A one-dimensional study of DR of N$_2$H$^+$ has failed to explain experimental results. Studies of dissociative recombination and attachment in other polyatomic systems have shown that simple one-dimensional models can fail to capture the correct dissociation dynamics. We have carried out an investigation of this multidimensional effect on N$_2$H$^+$. We study the system in limited dimensionality (\textit{i.e.} as a diatomic N$_2$-H$^+$) and then contrast this with multidimensional studies. We perform electron scattering calculations using the complex Kohn variational method to determine the resonance parameters of this system. The time dependent wave packet method is used to solve the one dimension problem and the Multi-Configuration Time-Dependent Hartree method is used for the wave packet propagation on the multi-dimensional resonant potential energy surfaces. We report the computed DR cross sections compared to available experiments and we discuss the mechanisms leading to dissociation into the various product channels. [Preview Abstract] |
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