Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session J3: Heavy Particle Collisions |
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Chair: Francis Robicheaux, Auburn University Room: A703 |
Wednesday, June 15, 2011 10:30AM - 10:42AM |
J3.00001: Target Ionization in Collisions with Few-keV Molecular Ions Kevin Carnes, Nora G. Johnson, Wania Wolff, Ben Berry, A. Max Sayler, Itzik Ben-Itzhak The dominant channel in slow (few keV) collisions between a molecular ion and a target atom is dissociative capture, $e.g.$ H$_{2}^{+}$ + Ar $\to $ H + H + Ar$^{+}$. Our coincidence imaging method allows us to collect all three collision products and therefore determine the efficiency of detecting the recoil ion. Using that efficiency, we measure the probability of target ionization ($e.g.$ H$_{2}^{+}$ + Ar $\to $ H + H$^{+}$ + Ar$^{+ }$+ e$^{- })$ relative to all collision induced dissociation ($e.g.$ H$_{2}^{+}$ + Ar $\to $ H + H$^{+}$ + Ar$^{ }$+ e$^{-}$, H + H$^{+}$ + Ar$^{+ }$+ e$^{-})$. We find that the probability for target ionization, and by implication target excitation, is greater than 10{\%} and therefore should not be neglected in theory calculations. [Preview Abstract] |
Wednesday, June 15, 2011 10:42AM - 10:54AM |
J3.00002: Ultracold atom-ion collisions with Beryllium Diego Valente, Robin C\^ot\'e We investigate charge transfer in collisions of Be-Be$^{+}$ at ultralow temperatures. Using the best available $^{2}\Sigma_{g}^{+}$ and $^{2}\Sigma_{u}^{+}$ potential curves, we calculate the elastic, charge-transfer, and total cross sections. Results found for several Be isotopes are presented and discussed. In the low temperature limit, we analyze the structure presented by the cross sections as functions of energy. For higher temperatures beyond this limit, we compare the quantum calculations with those obtained by a semiclassical Langevin formula. We find charge-transfer cross sections to be large even at a higher temperature range, indicating this scheme is a candidate for producing cold ions efficiently by sympathetically cooling them with ultracold atoms. [Preview Abstract] |
Wednesday, June 15, 2011 10:54AM - 11:06AM |
J3.00003: Radiative association of H$_2$ and H$^-$ at low temperature: can we observe H$_3^-$ in the interstellar medium? Mehdi Ayouz, Olivier Dulieu, Maurice Raoult, Viatcheslav Kokoouline We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of H$_3^-$ after the low energy collision (below 0.5~eV) of H$_2$ with H$^-$. Using recently obtained potential energy and permanent dipole moment surfaces of H$_3^-$, we calculate the lowest rovibrational levels of the H$_3^-$ electronic ground state, and the cross section for the formation of H$_3^-$ by radiative association between H$^-$ and ortho- and para-H$_2$. We discuss the possibility for the H$_3^-$ ion to be formed and observed in the cold and dense interstellar medium in an environment with a high ionization rate and thus suggest a way to detect the H$_3^-$ ion in the interstellar medium. Such an observation would be a probe for the presence of H$^-$ in the interstellar medium. [Preview Abstract] |
Wednesday, June 15, 2011 11:06AM - 11:18AM |
J3.00004: Capture of highly charged ions in a rare-earth permanent-magnet Penning trap Nicholas D. Guise, Samuel M. Brewer, Joseph N. Tan Highly charged ions extracted from the NIST electron beam ion trap (EBIT) are captured and stored in a rare-earth Penning trap built around a cylindrical NdFeB permanent magnet. Ions of charge $qe$, emerging from the EBIT with typical energy $4.0 q$ keV, are slowed electrostatically while entering the Penning trap, then captured by pulsing closed the Penning trap front endcap voltage at the time of arrival. Stored ions are later detected by pulsing open the back endcap to dump to a microchannel plate. In this first prototype trap,\footnote{S.M. Brewer and J.N. Tan, BAPS.2009.DAMOP.T1.107} species including Ne$^{10+}$ and N$^{7+}$ are confined with storage times of order 1 second, showing the potential of this setup for manipulation and spectroscopy of highly charged ions in a controlled environment. Such experiments will use a more elaborate apparatus that incorporates a two-magnet Penning trap for improved B-field homogeneity, a field-emission electron gun for in-trap loading of low-$Z$ ions, and optical access for spectroscopy experiments on trapped ions. Possible applications include spectroscopic studies of one-electron ions in Rydberg states,\footnote{U.D. Jentschura, \textit{et al.}, Phys. Rev. Lett. \textbf{100}, 160404 (2008)} as well as highly charged ions of interest in atomic physics, metrology, and plasma diagnostics. [Preview Abstract] |
Wednesday, June 15, 2011 11:18AM - 11:30AM |
J3.00005: Spatially Modulated Interaction Induced Bound States and Scattering Resonances Ran Qi, Hui Zhai We study the two-body problem with a spatially modulated interaction potential using a two-channel model, in which the inter-channel coupling is provided by an optical standing wave and its strength modulates periodically in space. As the modulation amplitudes increases, there will appear a sequence of bound states. Part of them will cause divergence of the effective scattering length, defined through the phase shift in the asymptotic behavior of scattering states. We also discuss how the local scattering length, defined through short-range behavior of scattering states, modulates spatially in different regimes. These results provide a theoretical guideline for new control technique in cold atom toolbox, in particularly, for alkali-earth-(like) atoms where the inelastic loss is small. [Preview Abstract] |
Wednesday, June 15, 2011 11:30AM - 11:42AM |
J3.00006: Excitation processes in proton collisions with Li atoms Teck-Ghee Lee, M.S. Pindzola Excitation processes in proton collisions with Li are studied by direct solution of the time-dependent Schr\"{o}dinger equation in cylindrical coordinates. Within a straight-line trajectory approximation, a time-dependent close-coupling method based on an expansion of a one-electron 3D wavefunction in rotational functions is used to calculate excitation cross sections at incident energies ranging from 10 keV to 200 keV. A peudopotential method is used to treat the 1s$^2$ core. The time-evolved wavefunction which includes all the inelastic processes, including charge transfer, excitation and ionization, is projected onto the lattice states to obtain excitation cross sections for the Li(2s) to Li(2p,3l,4l) transitions. Results are compared with the existing data. This work was supported in part by grants from US DOE. Computational work was carried out at NERSC in Oakland, California. [Preview Abstract] |
Wednesday, June 15, 2011 11:42AM - 11:54AM |
J3.00007: Charge transfer between O$^{6+}$ and atomic hydrogen Y. Wu, P.C. Stancil, H.P. Liebermann, R.J. Buenker, D.R. Schultz, Y. Hui The charge exchange process has been found to play a dominant role in the production of X-rays and/or EUV photons observed in cometary and planetary atmospheres and from the heliosphere. Charge transfer cross sections, especially state-selective cross sections, are necessary parameters in simulations of X-ray emission. In the present work, charge transfer due to collisions of ground state O$^{6+}$($1s^2~^1S$) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling method (QMOCC). The multi-reference single- and double-excitation configuration interaction approach (MRDCI) has been applied to compute the adiabatic potential and nonadiabatic couplings, and the atomic basis sets used have been optimized with the method proposed previously to obtain precise potential data. Total and state-selective cross sections are calculated for energies between 10 meV/u and 10 keV/u. The QMOCC results are compared to available experimental and theoretical data as well as to new atomic-orbital close-coupling (AOCC) and classical trajectory Monte Carlo (CTMC) calculations. A recommended set of cross sections, based on the MOCC, AOCC, and CTMC calculations, is deduced which should aid in X-ray modeling studies. [Preview Abstract] |
Wednesday, June 15, 2011 11:54AM - 12:06PM |
J3.00008: Four-Body Charge Transfer Processes in Proton-Helium Collisions Uttam Chowdhury, Allison Harris, Jerry Peacher, Don Madison Recent advancements in experimental techniques now allow for the study of fully differential cross sections for four body collisions. The simplest four-body problem is a charged particle collision with a helium atom in which both atomic electrons change state. This type of collision can result in many different outcomes, such as double excitation, excitation-ionization, double ionization, transfer-excitation, transfer-ionization, and double charge transfer. Theoretically fully differential cross sections will be presented and compared with absolute experimental data for transfer-excitation in proton helium collisions. The model used is a fully quantum mechanical, first order perturbative method that includes all relevant two particle interactions. Numerically, this requires a full nine-dimensional integral, and is quite computationally expensive. The role of different scattering mechanism will be discussed. [Preview Abstract] |
Wednesday, June 15, 2011 12:06PM - 12:18PM |
J3.00009: Isotope effect on charge transfer in collisions of H with He$^+$ and He$^{2+}$ Jerome Loreau, Sergey Ryabchenko, Nathalie Vaeck In magnetically confined plasmas, the presence of impurities can be used as a diagnostic tool through the observation of their emission lines. In the edge region, where particle energies are lower than 100 eV, charge transfer with the hydrogen from the plasma can significantly modify the abundance of the impurities. In this work, we study the charge transfer process in collisions of H with He$^+$ or He$^{2+}$ ions at energies between 0.1 and 200 eV/amu. To calculate the cross section for these reactions, we use a quantal method which consists in a combination of ab initio and wave packet propagation methods, and compare our results with the use of the semi-classical eikonal method. We consider in particular the isotope effect that arises when hydrogen is replaced by deuterium or tritium. Indeed, it was demonstrated using semi-classical methods that the isotope effect could be significant at energies as high as 200 eV/amu. [Preview Abstract] |
Wednesday, June 15, 2011 12:18PM - 12:30PM |
J3.00010: Charge exchange cross sections in slow collisions of Si$^{3+}$ with Hydrogen atom Dwayne C. Joseph, Edwin Quashie, Bidhan C. Saha In recent years both the experimental and theoretical studies of electron transfer in ion-atom collisions have progressed considerably. Accurate determination of the cross sections and an understanding of the dynamics of the electron-capture process by multiply charged ions from atomic hydrogen over a wide range of projectile velocities are important in various field ranging from fusion plasma to astrophysics. The soft X-ray emission from comets has been explained by charge transfer of solar wind ions, among them S$^{\mbox{i3}}$+, with neutrals in the cometary gas vapor. The cross sections are evaluated using the (a) full quantum [1] and (b) semi-classical molecular orbital close coupling (MOCC) [2] methods. Adiabatic potentials and wave functions for relavent singlet and triplet states are generated using the MRDCI [3] structure codes. Details will be presented at the conference. \\[4pt] [1] L. B. Zhao, D. C. Joseph, B. C. Saha, H. P. Liebermann, P. Funke and R.J. Buenker, Phys. Rev A, 79, 034701 (1009). [2] M. Kimura and N.F. Lane, At. Mol. Opt. Phys 26, 79 (1990). [3] R. J. Buenker,``Current Aspects of Quantum Chemistry 1981, Vol 21, edited by R. Carbo (Elsevier, Amsterdam) p 17. [Preview Abstract] |
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