Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session N8: Electronic, Atomic, and Molecular Collisions |
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Chair: Leigh Hargreaves, Cal State Fullerton Room: 555AB |
Thursday, May 26, 2016 10:30AM - 10:42AM |
N8.00001: Positronium collisions with rare-gas atoms Ilya Fabrikant, Gleb Gribakin, Andrew Swann, Robyn Wilde We calculate elastic scattering of positronium (Ps) by the Xe atom using the recently developed pseudopotential method$^{\dagger}$ and review general features of Ps scattering from heavier rare-gas atoms: Ar, Kr and Xe. The total scattering cross section is dominated by two contributions: elastic scattering and Ps ionization (break-up). To calculate the Ps ionization cross sections we use the binary-encounter method for Ps collisions with an atomic target. Our results for the ionization cross section agree well with previous calculations carried out in the impulse approximation. Our total Ps-Xe cross section, when plotted as a function of the projectile velocity, exhibits similarity with the electron-Xe cross section for the collision velocities higher than 0.8~a.u., and agrees very well with the measurements at Ps velocities above 0.5~a.u. $^{\dagger}$Fabrikant I I and Gribakin G F 2014 \textit{Phys. Rev. A} {\bf 90} 052717 [Preview Abstract] |
Thursday, May 26, 2016 10:42AM - 10:54AM |
N8.00002: Perturbative, R-matrix, and MCHF treatments for near-threshold dielectronic recombination of Si-like ions Jagjit Kaur, Thomas Gorczyca, Nigel Badnell We present results from a variety of dielectronic recombination (DR) calculations for Si-like ions. A perturbative, multi-configurational Breit-Pauli method is used to calculate DR rate coefficients for the entire Si-like isoelectronic sequence. In addition, we have performed R-matrix and multi-configuration Hartree-Fock (MCHF) calculations to investigate the low-lying resonances that dominate the low-energy, near-threshold region in S$^{2+}$. This work is motivated by the astrophysical importance of DR of Si-like S$^{2+}$ in determining the sulfur ionization balance in the Orion nebula, a photoionized plasma corresponding to low-energy electrons. The computed DR rate coefficients comprise part of the assembly of the DR data base required in the modeling of dynamic finite density plasmas. [Preview Abstract] |
Thursday, May 26, 2016 10:54AM - 11:06AM |
N8.00003: Electron-ion Recombination and Photoionization of P~II Sultana Nahar Study of the inverse processes of photoionization and electron-ion recombination of P~II will be reported. It is a highly reactive ion and has been difficult to detect without detailed information of its interactions. Although a low charged ion, present study shows features in photoionization resulting from relativistic fine structure couplings at low energy region near the ionization threshold of many levels. Unified method under the framework of close coupling approximation and R-matrix method and an extension of Bell and Seaton theory has been used to study the inverse processes. The method gives the level-specific as well as the total recombination rate coefficients which include both the radiative recombination (RR) and dielectronic recombination (DR) in a precise manner. The present results include level specific rates and photoionization cross sections of 475 fine structure levels with $n\leq$10. Preliminary results on the total recombination rates show considerable interference of RR and DR around 4000 K and a DR peak around 10$^5$ K. [Preview Abstract] |
Thursday, May 26, 2016 11:06AM - 11:18AM |
N8.00004: Chaotic compound states in atomic processes: electron, photon and atom scattering, recombination, photoionization and radiation Victor Flambaum, Julian Berengut, Vladimir Dzuba, Gleb Gribakin, Celal Harabati, Michael Kozlov Level density of many-body states exponentially increases with the number of excited particles. When residual interaction exceeds the interval between these levels, the eigenstates (compound states) become chaotic superpositions of of thousands, or even millions of Slater determinant basis states.This situation takes place in highly excited nuclei, rare-earth and actinide atoms, open f-shell ions excited by the electron recombination and in ultracold collisions of open f-shell atoms. We derived formulas for the resonant multi-electron recombination via di-electron doorway states leading to the many-electron compound resonances and performed numerical calculations for the electron recombination with gold (Au+25) and tungsten ions (W+1724). A recent experiment showed that the electron recombination of tungsten ion W20+exceeds the direct recombination by three order of magnitude. Our calculations agree with the experimental results for Au+25 and W20+. Other manifestation of chaos are enhancement of weak interactions and Raman photon scattering, and suppression of the photoionization. Our publications: PRL 70, 4051 (1993); PRA 50, 267 (1994); 66, 012713 (2002); 86, 022714 (2012); 88,062713 (2013); 91, 052704 (2014); 92, 062717 (2015). [Preview Abstract] |
Thursday, May 26, 2016 11:18AM - 11:30AM |
N8.00005: Monte Carlo simulations of multiple scattering effects in laser assisted free-free scattering experiments B.A. deHarak, J.L. Savich, H.M. Roberts, E.G. Brown, M.R. McGill, B.N. Kim, C.M. Weaver, N.L.S. Martin We have conducted a series of Monte Carlo simulations of laser assisted free-free scattering experiments. The simulations make use of Kroll-Watson approximation\footnote{N. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973)} to account for the effects of the laser field on the scattering process. The parameters for these simulations are believed to mimic the experimental conditions of the work reported by Wallbank and Holmes\footnote{B. Wallbank and J. K. Holmes, Can. J. Phys. 79, 1237 (2001)}, particularly the target number density. The simulations account for the effects multiple scattering (i.e., the scattering of a single incident electron from multiple target atoms). We present a comparison of the results of these simulations to the experimental results of Wallbank and Holmes\footnote{Ibid.}\footnote{B. Wallbank and J. K. Holmes, Phys. Rev. A 48, R2515 (1993)}. [Preview Abstract] |
Thursday, May 26, 2016 11:30AM - 11:42AM |
N8.00006: Electron attachment to the interhalogens ClF, ICl, and IBr. T. M. Miller, J. P. Wiens, J. C. Sawyer, N. S. Shuman, A. A. Viggiano, M. Khamesian, V. Kokoouline, I. I. Fabrikant Electron attachment rate coefficients have been measured for the interhalogens ClF, ICl, and IBr over the range 300-900 K using a flowing-afterglow Langmuir-probe apparatus. The ClF case was also studied theoretically. ClF was found to attach electrons somewhat inefficiently with a rate coefficient of 7.5x10$^{\mathrm{-9}}$ cm$^{\mathrm{3}}$/s at 300 K, doubling by 700 K. Even so, attachment to ClF is more efficient than seen earlier for F$_{\mathrm{2}}$ and Cl$_{\mathrm{2}}$, which brings up the interesting distinction that attachment to F$_{\mathrm{2}}$ and Cl$_{\mathrm{2}}$ is known to have $p$-wave threshold behavior, while in ClF the inversion symmetry is broken, allowing an $s$-wave component. The increase in the rate coefficient for attachment to ClF with temperature was found to be less pronounced than with F$_{\mathrm{2}}$ and Cl$_{\mathrm{2}}$. \textit{Ab initio} potential energy curves were calculated for ClF and ClF$^{\mathrm{-}}$, and R-matrix theory was used to obtain the resonance widths and energies for the ground state curve crossing, which takes place near the equilibrium internuclear separation in ClF. A local complex potential model was used to calculate attachment cross sections and thermal rate coefficients. There is reasonable agreement between theory and experiment within the estimated 25{\%} uncertainties in the data. Cl$^{\mathrm{-}}$ is the only product ion from thermal electron attachment to ClF. Attachment to ICl is even less efficient by almost an order of magnitude than to ClF, namely, 9.5x10$^{\mathrm{-10}}$ cm$^{\mathrm{3}}$/s at 300 K. Attachment to IBr is small enough that we place an upper limit of \textless 10$^{\mathrm{-10}}$ cm$^{\mathrm{3}}$/s at 300 K. [Preview Abstract] |
Thursday, May 26, 2016 11:42AM - 11:54AM |
N8.00007: Two-dimensional model of resonant electron collisions with diatomic molecules and molecular cations. Martin Vana, David Hvizdos, Karel Houfek, Roman Curik, Chris H Greene, Thomas N Rescigno, C William McCurdy A simple model for resonant collisions of electrons with diatomic molecules with one electronic and one nuclear degree of freedom (2D model) which was solved numerically exactly within the time-independent approach [1] was used to probe the local complex potential approximation and nonlocal approximation to nuclear dynamics of these collisions [2]. This model was reformulated in the time-dependent picture and extended to model also electron collisions with molecular cations, especially with H$_{\mathrm{2}}^{\mathrm{+}}$. This model enables an assessment of approximate methods, such as the boomerang model or the frame transformation theory. We will present both time-dependent and time-independent results and show how we can use the model to extract deeper insight into the dynamics of the resonant collisions. [1] K. Houfek, T.N. Rescigno, C.W. McCurdy, Phys. Rev. A 73 (2006) 032721 [2] K. Houfek, T.N. Rescigno, C.W. McCurdy, Phys. Rev. A 77 (2008) 012710 [Preview Abstract] |
Thursday, May 26, 2016 11:54AM - 12:06PM |
N8.00008: The role of dipole resonances in the photodetachment of AgF$^-$ N. Douguet, O. Dulieu, S. Fonseca dos Santos, V. Kokoouline, M. Raoult Dipole electronic resonances could play a significant role in the formation and photodetachment of negative molecular ions by providing a doorway for attachment of a low-energy electron incident on the neutral molecule. In this study, we consider photodetachment of the AgF- anion. Vibrational and rotational degrees of freedom are included in the theoretical approach. Close-coupling equations for the electron motion are solved using the renormalized Numerov method. The photodetachment cross section is computed. It demonstrates a significant effect of the dipole resonances on the photodetachment spectrum. Anisotropy in the photoelectron spectrum near the dipole resonances is studied. Our results are compared with recent experimental data [1]. [1] D. B. Dao and R. Mabbs, J. Chem. Phys. 141, 154304 (2014) [Preview Abstract] |
(Author Not Attending)
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N8.00009: Ultracold Rotational Quenching Study of CO with H$^{+}$ Rajwant Kaur, T. J. Dhilip Kumar Cooling and trapping of polar molecules have stimulated research in precise monitoring and controlling dynamics in ultracold regime. There has been considerable interest in the study of molecular inelastic collision processes at cold and ultracold temperatures. Collisional study of polar interstellar species CO, adds an additional astrophysical importance to model interstellar medium. Present work focuses on rotational quenching of abundant interstellar species, CO with H$^{+}$ using quantum-mechanical scattering calculation. Rate coefficients for molecular rotational transitions of CO due to collision with H$^{+}$ are obtained in the range of 10$^{-5}$ K to 200 K from cross sections which are computed using close coupling calculations as implemented in MOLSCAT. The data generated from ultracold to higher temperatures assist in investigating the chemistry of interstellar clouds. Calculations are performed on ground state \textit{ab initio} potential energy surface using MRCI/cc-pVTZ method. Rotational transitions are studied in the rigid-rotor approximation with CO bond length fixed at an equilibrium value of 2.138 a.u. Asymptotic potentials are computed using the dipole and quadrupole moments, and the dipole polarizability components. [Preview Abstract] |
Thursday, May 26, 2016 12:18PM - 12:30PM |
N8.00010: Stopping of Protons in Copper at low velocities$^{\mathrm{\ast )}}$ Edwin E. Quashie, Bidhan C. Saha, Alfredo A. Correa An \textit{ab initio} study including non-linear effects is reported of the electronic stopping power~ of protons in copper over a wide range of proton velocities (v $=$ 0.01-10 a.u.).~Time-dependent density functional theory coupled with molecular dynamics [1] is used to study~electronic excitations produced by energetic protons. A plane-wave pseudo-potential scheme~ is employed to solve the time-dependent Kohn-Sham equations for a moving proton in a periodic~copper crystal. These electronic excitations and the band structure determine the stopping power~of the material and alter the interatomic forces for both channeling and off-channeling trajectories.~Our off-channeling results are in quantitative agreement with experiments. Details will be presented at the conference [1] E. Runge and E. R. U. Gross, Phys. Rev. Lett. \textbf{52,} 997 (1984). $^{\mathrm{\ast )}}$ Supported by NNSA [Preview Abstract] |
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