Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session P5: Ion-Atom and Ion-Ion Collisions |
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Chair: John Tanis, Western Michigan University Room: Fairfield |
Thursday, June 11, 2015 2:00PM - 2:12PM |
P5.00001: Controlled charge exchange between alkaline earth metals and their ions Marko Gacesa, Robin C\^ot\'e We theoretically investigate the prospects of realizing controlled charge exchange via magnetic Feshbach resonances in cold and ultracold collisions of atoms and ions. In particular, we focus on near-resonant charge exchange in heteroisotopic combinations of alkaline earth metals, such as $^9\mathrm{Be}^{+} + ^{10}\mathrm{Be}\leftrightarrow^{9}\mathrm{Be} + ^{10}\mathrm{Be}^{+}$, which exhibit favorable electronic and hyperfine structure. The quantum scattering calculations are performed for a range of initial states and experimentally attainable magnetic fields in standard coupled-channel Feshbach projection formalism, where higher-order corrections such as the mass-polarization term are explicitely included. In addition, we predict a number of magnetic Feshbach resonances for different heteronuclear isotopic combinations of the listed and related alkaline earth elements. Our results imply that near-resonant charge-exchange could be used to realize atom-ion quantum gates, as well as controlled charge transfer in optically trapped cold quantum gases. [Preview Abstract] |
Thursday, June 11, 2015 2:12PM - 2:24PM |
P5.00002: Inelastic processes in collisions of Na$^{+}$, K$^{+}$, Rb$^{+}$ ions with He and Ar atoms R. Ya. Kezerashvili, R.A. Lomsadze, M.R. Gochitashvili, N.O. Mosulishvili Absolute cross sections for charge-exchange, ionization, stripping and excitation for Na$^{+}$ - Ar, K$^{+}$ - He and Rb$^{+}$ - Ar collisions were measured in the energy range 0.7- 7.0 keV. The experimental techniques include a condenser-plate method, angle-and-energy -- dependent collision of product ions, energy loss and optical spectroscopy were used for an accurate determination of the structure of inelastic cross sections for these collisions. The experimental data are used to draw certain conclusions related to mechanisms of the corresponding processes. A correlation diagram of the adiabatic quasimolecular terms of these systems has been employed to discuss the mechanisms for these processes. It is shown that charge exchange in K$^{+}$- He as well as in Rb$^{+}$ - Ar collisions mostly occur through the channel resulting from the capture of the electron to the ground state of the atoms in regions of pseudo-crossing of the potential curves of $^{1}\Sigma $ symmetry. The primary ionization mechanism for all colliding pairs is investigated. Stripping in K$^{+\, }$- He collisions (stripping in case of Na$^{+}$, Rb$^{+}$ - Ar were not observed) occurs via a mechanism involving a transition of adiabatic term into the continuum in the region of nonadiabatic interaction of molecular orbits with orbital angular moments which are identical in the limit of the united atom. The excitation mechanisms of collision partners are established. [Preview Abstract] |
Thursday, June 11, 2015 2:24PM - 2:36PM |
P5.00003: Search for radiative double electron capture (RDEC) by fully-stripped ions in gas targets Nuwan Kumara, Anna Simon, David La Mantia, Asghar Kayani, John Tanis Radiative double electron capture (RDEC) by fully-stripped ions in collisions is a fundamental atomic process that can be used to study the electron-electron interaction. This is a one step process in which a single x-ray is emitted in association with the capture of two electrons to a bare projectile from the target. Only five attempts have been made since 1995 to observe RDEC and only one experiment (2.38 MeV/u O$^{8+}$ collision on a C foil) successfully reported positive results for the observation of the process.\footnote{A. Simon et al., PRL \textbf{104}, 123001 (2010).} We have started new measurements at WMU for gas targets (He, Ne and N$_{2})$ as well as a thin-foil C target with fully-stripped fluorine to compare the results with previous experiments and theoretical calculations. Gas targets are contaminant free compared to solid targets and the measurements have been started for gaseous N$_{2}$. This experiment is difficult and requires long counting times due to the relatively small RDEC cross compared to that for the single electron process of radiative electron capture. [Preview Abstract] |
Thursday, June 11, 2015 2:36PM - 2:48PM |
P5.00004: Heavy particle collisions using on the fly electronic structure J.F. Babb On-the-fly calculations for molecular processes involve determination of electronic structure as needed simultaneously with nuclear dynamics; rather than in advance. The application of the methodology to heavy particle collisions is explored. Suitable methods for electronic structure evaluation are investigated with applications to prototypical collisional problems. [Preview Abstract] |
Thursday, June 11, 2015 2:48PM - 3:00PM |
P5.00005: Collisions induced dissociation and Ab initio study of azobenzene derivatives bond structure and electronic configuration Mohammadreza Rezaee, Robert Compton Collision induced dissociation (CID) and ab initio calculations were utilized to study a few derivatives of azobenzene molecule and their product ions. High level computational methods along with large basis set size yield values in close agreement with the experimental results. M\"{o}ller-Plesset and coupled-cluster theory including perturbative triple excitations, CCSD(T), method were performed to obtain a high accuracy estimation of the bond dissociation energy value. The electron affinities have been studied experimentally using the photoelectron spectroscopy method as well as theoretically using ab inito calculations. For the trans-2,2',6,6' tetra-fluoro azobenzene the bond dissociation has been experimentally determined to be 1.88 eV and the vertical detachment energy is 1.78 eV. [Preview Abstract] |
Thursday, June 11, 2015 3:00PM - 3:12PM |
P5.00006: Cold chemistry in high density atom-ion environments Jesus Perez-Rios, Artjom Krukow, Amir Mohamadi, Joschka Wolf, Tobias Schenetzer, Johannes Hecker Denschlag, Chris H. Greene A single laser cooled $^{138}$Ba$^+$ is brought in contact with a high density atomic cloud of ultracold $^{87}$Rb atoms, as a result, different chemical reactions leads to the formation of atomic an molecular products that are detected. We show by first principles, as well as it is confirmed in the experiment, that three-body recombination is the main physical process behind the cold chemical reactions in high density atom-ion environments. In particular, it is found that the observed final products are a consequence of the three-body process followed by subsequent chemical processes, which are also studied. This work elucidates the role of the density in the chemical reactivity in ion-neutral systems. [Preview Abstract] |
Thursday, June 11, 2015 3:12PM - 3:24PM |
P5.00007: Ultracold collisions between Rb atoms and a Sr$^{+}$ ion Tomas Sikorsky, Ziv Meir, Ruti Ben-shlomi, Yehonatan Dallal, Roee Ozeri In last decade, a novel field emerged, in which ultracold atoms and ions in overlapping traps are brought into interaction. In contrast to the short ranged atom-atom interaction which scales as r$^{-6}$, atom-ion potential persists for hundreds of $\mu$m's due to its lower power-law scaling - r$^{-4}$. Inelastic collisions between the consistuents lead to spin and charge transfer and also to molecule formation. Elastic collisions control the energy transfer between the ion and the atoms. The study of collisions at the $\mu$K range has thus far been impeded by the effect of the ion's micromotion which limited collision energy to mK scale. Unraveling this limit will allow to investigate few partial wave and even S-wave collisions. Our system is capable of trapping Sr$^{+}$ ions and Rb and Sr atoms and cooling them to their quantum ground state. Atoms and ions are trapped and cooled in separate chambers. Then, the atoms are transported using an optical conveyer belt to overlap the ions. In contrast to other experiments in this field where the atoms are used to sympathetic cool the ion, our system is also capable of ground state cooling the ion before immersing it into the atom cloud. By this method, we would be able to explore heating and cooling dynamics in the ultracold regime. [Preview Abstract] |
Thursday, June 11, 2015 3:24PM - 3:36PM |
P5.00008: Analysis of the Frozen Core Approximation in Heavy-Ion Impact Ionization of Helium Allison Harris The frozen core approximation has been successfully used for decades to model 4-Body collisions as 3-Body processes. Recently, computational advancements have allowed for full 4-Body models to be used to calculate fully differential cross sections (FDCS) for single ionization of helium. These 4-Body models show discrepancies with their 3-Body model counterparts. For heavy-ion impact ionization, we have identified four possible sources of the discrepancies between the models. These four possible sources are: the initial state helium wave function, the final state He$+$ wave function, the final state potential for the outgoing electrons, and the perturbation. To identify which of these four sources causes the differences in the FDCS, we have performed a comprehensive study of 3-body and 4-body models for several different heavy-ion projectiles, as well as for a wide range of incident projectile energies, ionized electron energies, and momentum transfer values. [Preview Abstract] |
Thursday, June 11, 2015 3:36PM - 3:48PM |
P5.00009: Three dimensional imaging technique suitable for the measurements of the internal energies of asymmetrical diatomic molecular ions J.B. Sauza, D.I. Panchenko, A.C. Duot, R.A. Strom, V.M. Andrianarijaona We propose a three dimensional imaging technique that could be used to measure the internal energy of asymmetrical diatomic molecular ions such as HeH$^{+}$ and CO$^{+}$. The detection scheme is similar to the one used for symmetrical diatomic molecular ions, which accesses the internal energy of the ion through the kinetic energy release in a resonant dissociative charge transfer (see for instance Phys. Rev. Lett. \textbf{92} 163004 (2004)). In that technique, the fragments hit two detectors which send the positions of the impacts along with the difference between the times of impacts to a computer. The computed kinetic energy release is related to the vibrational excitation level of the initial molecular ion. In the case of an asymmetrical ion, the lighter fragment has a higher recoil velocity and goes further away transversally from the center of mass direction. The heavier fragment would not hit the first detector if the beam is judiciously misaligned. Therefore, we make distinction between the two particles. Details of the technique will be presented. [Preview Abstract] |
Thursday, June 11, 2015 3:48PM - 4:00PM |
P5.00010: Evidence of Double-Electron Capture by Highly-ionized Atoms Isolated at Very Low Energy Shannon Fogwell Hoogerheide, Arda Sahiner, Joseph N. Tan Electron capture processes are important in the study of comets [1], controlled fusion energy [2], anti-matter atoms [3], and proposed one-electron ions in Rydberg states. There are few studies for low energy. At NIST, highly-charged ions extracted from an electron-beam ion trap can be isolated with $<$ 10 eV energy using a recently developed compact Penning trap. By controlling the background gas pressure and composition, the charge exchange rates can be studied. Fully stripped neon ions are held in the trap for varying lengths of time and allowed to interact with different background gases at multiple pressures. The ions are then pulsed to a time-of-flight detector, to count the population of each charge state. Analysis yields information about the trap loss and single-electron capture rates. Moreover, evidence of double-electron capture is observed at low background gas pressures. Related work involves the resonant charge exchange of fully-stripped neon ions with laser-excited rubidium atoms to produce highly-excited one-electron ions, enabling a new measurement of the Rydberg constant.\\[4pt] [1] T. E. Cravens, Science 296, 1042 (2002)\\[0pt] [2] R. C. Isler, Plasma Phys. Control. Fusion 36, 171-208 (1994)\\[0pt] [3] C. H. Storry, et. al., Phys. Rev. Lett. 93, 263401 (2004) [Preview Abstract] |
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