Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session NR3: Heavy Particle Collisions |
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Chair: Michael Schulz, Missouri S&T Room: State D |
Thursday, November 6, 2014 10:00AM - 10:30AM |
NR3.00001: Antimatter-matter scattering including rearrangement Invited Speaker: Alisher Kadyrov Two distinct versions of the convergent close coupling (CCC) approach to ion-atom and ion-molecule collisions have been developed in the impact parameter representation. The first method starts from the exact three-body Schr\"odinger equation for the total scattering wave function and leads to coupled-channel Lippmann-Schwinger type integral equations for the transition amplitudes, with the relative motion of the heavy particles treated fully quantum mechanically. The second approach utilises a traditional semi-classical approximation. It is based on the time-dependent Schr\"odinger equation for the electronic part of the scattering wave function and leads to a system of coupled differential equations. This allows one to test the quality of approximations used in standard approaches to the problem. Both methods are applied to calculate antiproton collisions with inert gases and simple molecular targets in the energy range from 1 keV to 1 MeV. The methods are also applied to proton collisions including rearrangement channels. Interplay of direct ionisation and electron capture to continuum in target breakup is investigated. The first CCC calculations of the antiproton and proton stopping power in atomic and molecular hydrogen are presented. [Preview Abstract] |
Thursday, November 6, 2014 10:30AM - 10:45AM |
NR3.00002: Fully Differential Study of Projectile Coherence Effects in Ionization of H2 Thusitha Arthanayaka, Sachin Sharma, Basu Lamichhane, Ahamad Hasan, Juan Remolina, Susmitha Akula, Don Madison, Michael Schulz In recent years, the important role of the projectile coherence properties in ionization of H$_{2}$ has been demonstrated in measured double differential cross sections (DDCS). Here, we report the first fully differential study of such effects. The additional kinematic information was used to further ``clean'' the data from any background which may have survived the coincidence condition and the results show that the observed coherence effects are not just due to an experimental artifact. Furthermore, interference effects could be studied in unprecedented detail by comparing fully differential cross sections (FDCS) for a coherent and an incoherent projectile beam. For relatively small ejected electron energies we observe pronounced single-center interference, for which the molecular structure of the target is not of primary importance. Rather, this type of interference is due to a coherent superposition of different transition amplitudes leading to the same final state. However, for larger electron energies (corresponding to a speed close to the projectile speed) clear signatures of molecular two-center interference are observed in addition to single-center interference. [Preview Abstract] |
Thursday, November 6, 2014 10:45AM - 11:00AM |
NR3.00003: Excitation-ionization of lithium atoms by fast ion impact: the independent-electron model and beyond Tom Kirchner, Nariman Khazai, Laszlo Gulyas We report on a theoretical study of one-electron and two-electron processes in the ion-impact-induced ionization of lithium atoms [1]. An independent-electron model (IEM) description based on basis-generator-method and continuum-distorted-wave-eikonal-initial-state single-particle probabilities is applied to calculate $1s$ and $2s$ vacancy production single-differential cross sections, which were measured with the recently developed MOTReMi apparatus [2]. We find that the IEM predicts a considerable role of two-electron excitation-ionization processes in $1s$-vacancy production, but is not sufficient to explain the data. Replacing the IEM by an independent-event model for one of the contributing excitation-ionization processes and also taking a shake-off process into account improves the comparison with the measurements significantly. \\[4pt] [1] T. Kirchner {\it et al.}, Phys. Rev. A {\bf 89}, 062702 (2014).\\[0pt] [2] D. Fischer {\it et al.}, Phys. Rev. Lett. {\bf 109}, 113202 (2012). [Preview Abstract] |
Thursday, November 6, 2014 11:00AM - 11:30AM |
NR3.00004: Signatures of the electron saddle swaps mechanism in the photon spectra following charge-exchange collisions Invited Speaker: Sebastian Otranto During the last few years, several experimental and theoretical studies have focused on state selective charge exchange processes between charged ions and alkali metals. These data are of particular importance for the tokamak nuclear fusion reactor program, since diagnostics on the plasma usually rely on charge-exchange spectroscopy. In this sense, alkali metals, have been proposed as potential alternatives to excited hydrogen/deuterium for which laboratory experiments are not feasible at present. In this talk, we present our recent work involving ion collisions with alkali metals. Oscillatory structures in the angular differential charge-exchange cross sections obtained using the MOTRIMS technique are correctly described by classical trajectory Monte Carlo simulations. These oscillations are found to originate from the number of swaps the electron undergoes around the projectile-target potential saddle before capture takes place and are very prominent at impact energies below 10 keV/amu. Moreover, cross sections of higher order of differentiability also indicate that the swaps leave distinctive signatures in the (n,l)-state selective cross sections and in the photon line emission cross sections. Oscillatory structures for the x-ray hardness ratio parameter are also predicted.\\[4pt] In collaboration with Ronnie Hoekstra, Zernike Institute for Advanced Materials, University of Groningen and Ronald Olson, Department of Physics, Missouri University of Science and Technology. [Preview Abstract] |
Thursday, November 6, 2014 11:30AM - 11:45AM |
NR3.00005: Development of Ultra-Accelerated Quantum Chemical Molecular Dynamics Method for Gaseous Electronics Applications Akira Miyamoto, Kenji Inaba, Ryuji Miura, Ai Suzuki, Nozomu Hatakeyama, Masaaki Matsukuma, Kazuyoshi Matsuzaki Much attention has been given to the computational design of complex chemical dynamic processes including various solid surface reactions including gaseous electronics. For this purpose we have developed novel quantum chemical molecular dynamics method called ultra-accelerated quantum-chemical molecular dynamics (UA-QCMD) method which is around 10,000,000 times faster than the conventional first principles molecular dynamics method. In the present study we demonstrated that the quantum chemical calculation in UA-QCMD, that is Colors, has high accuracy in comparison with DFT and thermodynamic data. On the basis of high speed and high accuracy calculation of the UA-QCMD method we have confirmed that the method is effective for investigating dynamic mechanism of a variety of gaseous electronics processes including oxidation process of Si crystal with O$_{2}$, H$_{2}$O and O radical, oxidation process of Ge crystal with O radical and planarization process of Ru with the gas cluster ion beam (GCIB). The calculated results have been demonstrated to agree well with experimental results and give detailed mechanism of these gaseous electronics reaction processes. [Preview Abstract] |
Thursday, November 6, 2014 11:45AM - 12:00PM |
NR3.00006: Electron detachment from O$_{2}^{-}$ ions in oxygen and air in a strong electric field Alexandr Ponomarev, Nickolay Aleksandrov Electron detachment from O$_{2}^{-}$ ions have been theoretically studied in oxygen and O$_{2}$-N$_{2}$ mixtures when the ions are heated in a strong external electric field. Properties of the ions were studied by a Monte Carlo simulation technique. Collisional cross sections for ion-molecule scattering was calculated on the basis of the statistical approach for the vibrational transfer and relaxation in collisions between O$_{2}^{-}$ ions and O$_{2}$ molecules. To validate the statistical approach used, we calculated ion mobility and diffusion coefficients under conditions under which experiments are available and obtained good agreement with measurements in pure oxygen. The detachment rate was determined under the assumption that electron detachment proceeds via the formation of vibrationally excited temporary O$_{2}^{-}$ ions. The obtained detachment rate constants turned out to agree well with available measurements in oxygen. This method was extended to calculate detachment rates in air and other O$_{2}$:N$_{2}$ mixtures. It was shown that, for a given value of the reduced electric field, the detachment rate coefficient increases with decreasing mole fraction of oxygen in mixtures. In particular, the detachment rate in air is much higher than that in oxygen. The reason is that the effect of resonant charge transfer in collisions between O$_{2}^{-}$ and O$_{2}$ is less profound in the mixtures with lower fraction of oxygen; as a result, the average ion energy is higher. [Preview Abstract] |
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