Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session HW3: Heavy Particle Collisions |
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Chair: Don Madison, Missouri University of Science and Technology Room: Classroom 202 |
Wednesday, October 24, 2012 8:00AM - 8:30AM |
HW3.00001: Kinematically complete study on ion-impact induced ionization of laser-cooled lithium Invited Speaker: Daniel Fischer The study of atomic fragmentation processes due to charged particle impact provides insight in the dynamics of correlated few-particle Coulomb-systems, and thus advances our understanding of the fundamentally important few-body problem. In this respect, Fully differential data represent the most sensitive test of the theoretical treatment of the few-body dynamics. For ion-atom collisions such data became available exploiting the technique of ``Reaction Microscopes.'' Here we report on the first operation of a new experimental tool, a MOTReMi, i.e. a Reaction Microscope equipped with a magneto-optically trapped target. This setup allows for the first time using lithium as a target for kinematically complete ion collision experiments. The lithium atom is particularly interesting for its simple, but at the same time asymmetric structure with one weakly bound outer shell electron and two strongly correlated K-shell electrons. In first experiments in the ion storage ring TSR at the MPIK in Heidelberg, for the first time initial state selective cross sections for ion impact ionization became available by means of optical excitation. Fully differential cross sections will be presented which reveal detailed information on interference and polarization effects in the scattering dynamics. [Preview Abstract] |
Wednesday, October 24, 2012 8:30AM - 8:45AM |
HW3.00002: Strong multiple-capture effect in slow Ar$^{17+}$-Ar collisions: a quantum mechanical analysis Arash Salehzadeh, Tom Kirchner A recent X-ray spectroscopy experiment on 255 keV Ar$^{17+}$-Ar collisions [1] provided evidence for strong multiple-electron capture --- a feature that is supported by classical trajectory Monte Carlo calculations for similar collision systems [2]. We have coupled a quantum-mechanical independent-electron model calculation for the Ar$^{17+}$-Ar system with (semi-) phenomenological Auger and radiative cascade models to test these findings. The capture calculations are performed using the basis generator method and include single-particle states on the projectile up to the 10th shell. The cross sections obtained for shell-specific multiple capture are fed into a stabilization scheme proposed in Ref. [3] in order to obtain n-specific cross sections for {\it apparent} single (and double) capture that in turn are fed into a radiative cascade code [1] to obtain X-ray emission intensities that can be compared with the experimental data. Good agreement is found for the Lyman series from n=3 to n=7 if the multiple-capture contributions are included, whereas calculations that ignore them are in stark conflict with the data. \\[4pt] [1] M. Trassinelli et al., J. Phys. B 45, 085202 (2012)\\[0pt] [2] S. Otranto and R. Olson, Phys. Rev. A 83, 032710 (2011)\\[0pt] [3] R. Ali et al., Phys. Rev A 49, 3586 (1994). [Preview Abstract] |
Wednesday, October 24, 2012 8:45AM - 9:00AM |
HW3.00003: Application of Neural Networks to Atomic and Molecular Collisions A.L. Harris, J.A. Darsey Traditional methods of studying atomic and molecular collisions begin with the classical equations of motion for the particles involved in the system, or the Schr\"{o}dinger equation. Both of these methods are clearly rooted in the physics of the collision, but they are often computationally difficult and require approximations in order to make the problem tractable. Unlike the traditional methods of studying collision processes, neural networks do not begin with the physics of the problem, but instead employ a semi-empirical method that recognizes patterns in data to make predictions about systems where data is unavailable. Neural networks have been successfully utilized in many different fields, but to our knowledge have never been applied to collision processes. While the premise of a neural network is not based in physics, its output can provide useful data for processes that may be too difficult experimentally or computationally to explore. We will present results from the NNETS neural network code for different collision systems and discuss what role neural networks may play in collision physics. [Preview Abstract] |
Wednesday, October 24, 2012 9:00AM - 9:15AM |
HW3.00004: STUDENT AWARD FINALIST: Projectile Coherence Effects in Single and Dissociative Electron Capture in Collision of Protons with H$_{2}$ and He Sachin Sharma, Ahmad Hasan, Kisra Egodapitiya, Thusitha Arthanayaka, Giorgi Sakhelashvili, Michael Schulz Recently, we have observed that interference effects, similar to optical Young double-slit interference, in the projectile scattering angle dependent ionization cross sections of H$_{2}$ by 75 k$e$V proton impact are present or not depending on the projectile coherence. This suggests that atomic scattering cross sections in general are sensitive to the projectile coherence, an aspect which has been overlooked for decades. To investigate this effect further, we have measured differential cross sections for single and dissociative capture for 75 and 25 k$e$V protons colliding with H$_{2}$ and He. A significant sensitivity of the cross sections to the projectile coherence was confirmed. For 25 k$e$V we found that interference due to different impact parameters leading to the same scattering angle dominates over molecular two-center interference. This important observation sets the stage for resolving heatedly debated discrepancies between theory and experiment for ionization of He by 100 MeV/amu C$^{6+}$ impact. [Preview Abstract] |
Wednesday, October 24, 2012 9:15AM - 9:30AM |
HW3.00005: Calculations for ion-impact induced ionization and fragmentation of water molecules Tom Kirchner, Mitsuko Murakami, Marko Horbatsch, Hans J\"urgen L\"udde Charge-state correlated cross sections for single- and multiple-electron removal processes in proton-water-molecule collisions are calculated by using the non-perturbative basis generator method adapted for ion-molecule collisions [1,2]. A fragmentation model is then applied to calculate the yields of $\rm H_2O^+$, $\rm OH^+$, $\rm H^+$, and $\rm O^+$ ions emerging after $\rm H_2O^{q+}$ formation [3]. A detailed comparison is made with experimental data from three groups covering the energy range from 20--5000 keV. It is found that multiple electron processes with $q\le 3$ play an important role at the lower end of this range and are calculated accurately within an independent particle model. We are currently completing the analogous analysis for He$^+$-$\rm H_2O$ collisions for which the presence of the projectile electron poses some additional challenges. \\[4pt] [1] H.J. L\"udde et al, Phys. Rev. A 80, 060702(R) (2009)\\[0pt] [2] M. Murakami et al, Phys. Rev. A 85, 052704 (2012)\\[0pt] [3] M. Murakami et al, Phys. Rev. A 85, 052713 (2012) [Preview Abstract] |
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