Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session K6: Ion-Atom and Ion-Molecule Collisions |
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Chair: John Tanis, Western Michigan University Room: Knoxville Convention Center 301C |
Thursday, May 18, 2006 8:00AM - 8:12AM |
K6.00001: Angular and High-Frequency Analysis of Interference Structures in Electron Emission Spectra from 60 MeV/u Kr$^{34+}$ + H$_{2}$. J.A. Tanis, J.-Y. Chesnel, A. Cassimi, J.-P. Grandin, L. Adoui, D. Hennecart, B. Sulik, B. Skogvall, P. Sobocinski, N. Stolterfoht New measurements of interference structures associated with electron emission have been made for 60 MeV/u Kr$^{34+}$ + H$_{2}$ collisions to characterize the angular dependence of the primary interference structures over a wide range including backward ejection angles, and, additionally, to search for high-frequency structures as reported for 1-5 MeV/u H$^{+}$ + H$_{2}$ collisions.$^{1}$ Comparison of the data with several theories over the range 30$^{o}$--150$^{o}$ shows the theories to follow the trend of the data but underestimate the measured oscillation frequencies by as much as 50{\%} for backward angles. High-statistics measurements of electron spectra for 90$^{o}$ and 150$^{o}$ were subjected to Fourier analysis to determine if components corresponding to high-frequencies exist in the inverse spectrum but no evidence was found, in contrast to the results reported for H$^{+}$ + H$_{2}$. $^{1}$S. Hossain \textit{et al}., Phys. Rev. A \textbf{72}, 010701(R) (2005).. [Preview Abstract] |
Thursday, May 18, 2006 8:12AM - 8:24AM |
K6.00002: Simultaneous electron capture to bound an continuum states in 90 AMeV U$^{88+}$+N$_{2}$ collisions Siegbert Hagmann, Muaffaq Nofal, Thomas Stoehlker, Christophor Kozhuharov, Xincheng Wang, Alexander Gumberidze, U. Spillmann, Regina Reuschl, Sebastian Hess, Fritz Bosch, Dieter Liesen, Doris Jakubassa, Joachim Ullrich, Robert Moshammer, Reinhard Doerner Electron transfer processes at relativistic collision velocities are an essential ingredient in relativistic accelerator design. The large recombination energy of highly charged ions contributes to extended multiple ionization of target atoms, and thus population of multiply excited configurations in the projectile. Theories have widely failed to describe the intrinsic many-electron processes in the capture channel. Using the imaging forward electron spectrometer in the ESR we have searched for many body processes in the capture channel and measured for 90AMeV U$^{88+}$ + N$_{2} \quad \to $U$^{87+}$ + N$^{+\ast }$ + e$_{cusp }$coincidences between the cusp electron and the projectile having captured one electron into a bound state. We find that the cusp in the coincident 0$^{0}$--electron spectrum shows still a clear asymmetric shape skewed to the low energy side as predicted for a single active electron ECC. Further experiments are in progress. [Preview Abstract] |
Thursday, May 18, 2006 8:24AM - 8:36AM |
K6.00003: Radiative Electron Capture to Continuum in 90 AMeV U88+ + N2 : the Short Wavelength Limit of Electron Nucleus Bremsstrahlung Siegbert Hagmann, Muaffaq Nofal, Thomas Stoehlker, Christophor Kozhuharov, Xincheng Wang, Alexander Gumberidze, Uwe Spillmann, Regina Reuschl, Sebastian Hess, Fritz Bosch, Dieter Liesen, Doris Jakubassa, Joachim Ullrich, Robert Moshammer, Reinhard Doerner At relativistic velocities, the radiative electron capture to the continuum (RECC) increasingly competes with the non-radiative capture to continuum ECC. This allows investigating the role of the additional radiative degree of freedom in relativistic collisions dynamics. Using the imaging forward electron spectrometer in the ESR storage ring at GSI we have measured coincidences between x rays and cusp electrons$_{ }$and identified the coincident photons as coming from the short wavelength limit of electron nucleus bremsstrahlung. We show that this technique using inverse kinematics is the only one to allow measuring kinematically complete differential cross sections for electron nucleus bremsstrahlung at the theoretically important short wavelength limit. [Preview Abstract] |
Thursday, May 18, 2006 8:36AM - 8:48AM |
K6.00004: Fragmentation of H$_{2}$O by 1 -- 5 keV He$^{2+}$ ions: Experiment and Theory N. Stolterfoht, R. Hellhammer, P. Sobocinski, R. Cabrera-Trujillo, Y. Ohrn, E. Deumens, J. Sabin Fragmentation of H$_{2}$O molecules induced by $^{3}$He$^{2+}$ impact was investigated experimentally as a function of the energy in the range from 1-5 keV. Collisions at large impact parameters are found to produce fragment protons with energies centered around peaks at 6 eV and 15 eV. The H$^{+}$ fragments were detected in the angular range from 25\r{ } to 135\r{ } with respect to the incident beam direction. Absolute fragmentation cross sections d$\sigma $/d$\Omega $, differential in the emission angle are found to be anisotropic, with protons preferentially emitted at angles near 90\r{ }. In addition to the experiments, we performed quantum-mechanical calculations to understand the fragmentation mechanisms producing protons at preferred energies and angles. The theoretical results are obtained using the Electron-Nuclear Dynamics formalism (END), which solves the time-dependent Schr\"{o}dinger equation. [Preview Abstract] |
Thursday, May 18, 2006 8:48AM - 9:00AM |
K6.00005: Measurements of Total Cross Sections of the n = 2 Excitation of Helium from the Impact of 10-25 keV Protons T.J. Kvale, G.S. Hodges, J. Kang, J.D. Thomas, D.G. Seely Absolute, total cross sections for the n = 2 excitation of helium by intermediate-energy proton impact were measured using the energy-loss experimental technique. The incident proton beam was accelerated to kinetic energies of 10-25 keV and directed through a target cell containing helium gas at room temperature. The scattered proton beam was then energy analyzed to obtain energy-loss spectra. The excitation cross sections were calculated by comparing the amplitudes of the energy-loss peaks corresponding to excitation of the n=2 states of helium with the zero-energy-loss peak. As such, the cross sections have been determined on an absolute scale, without the need to normalize the results to any other experiments or theories. The cross sections are compared to theoretical results, including the First Born, Distortion Glauber, VPS, and Multi-State Approximation methods. The theories that incorporate many-state calculation methods such as the Multi-State Approximation are in reasonable agreement with the present data, suggesting that strong coupling between states must be considered in intermediate-energy, multi-electron ion-target collision systems. [Preview Abstract] |
Thursday, May 18, 2006 9:00AM - 9:12AM |
K6.00006: Using Electron-Impact Ionization results to Understand Out-of-the-Scattering Plane Structure seen For Heavy Particle Impact M. Foster, J.L. Peacher, M. Schulz, D.H. Madison The ionization of atoms by electron or ion impact has histortically concentrated on the scattering plane. The scattering plane is defined by the initial and final momentum vectors of the projectile. The assumption has been that all the important physical effects would be observed in the scattering plane. Previous work on ion impact ionization of helium showed that experiment and theory are in good agreement in the scattering plane and in poor agreement out-of-the-scattering plane for C$^{6+}$ projectile ions. In this paper, we will show that the same out-of-plane effects can be observed for electron-impact ionization of magnesium. Since the proper quantum mechanical treatment for electron-impact ionization involves fewer approximations than heavy ion ionization, the electron results can be used to determine the physical effects causing the unexplained out-of-the-plane structure for heavy particle collisions. This process revealed that the out-of-plane structure was caused by very close collisions between the projectile and nucleus. [Preview Abstract] |
Thursday, May 18, 2006 9:12AM - 9:24AM |
K6.00007: Laser-Phase Dependence for Electron Capture in Laser-Assisted Proton -- Hydrogen Collisions Thomas Niederhausen, Uwe Thumm We calculate electron capture probabilities for ion--atom collisions in a strong laser field ($5\times10^{13}~\mathrm{W/cm^2}$) by numerically solving the 3-dimensional time--dependent Schr\"{o}dinger equation. For circularly polarized laser fields and an impact energy of $1.2~\mathrm{keV}$, we find a substantial modification of the electronic dynamics in the $p$--$H$ collision system as compared to field-free collisions. In particular, we observe a strong dependence on the laser phase and the impact parameter for electron capture, which can be explained using semi-classical arguments. [Preview Abstract] |
Thursday, May 18, 2006 9:24AM - 9:36AM |
K6.00008: Local Momenta and Weak Quantum Measurements in Massive Three-Body Coulomb Systems Michael Schillaci In recent years researchers have attempted to improve the continuum state three-body wavefunction for three, mutually interacting Coulomb particles by including, so called, local momentum effects. Numerical calculations confirm that while ignoring these local momentum effects for \emph{light-ion--atom} processes, may be appropriate, three-body effects may dominate in the reaction zone for \emph{heavy-ion--atom} processes involving massive, Coulomb interacting particles. It is also shown that a real-valued, position-dependent phase is added to a locally distorted two-body coulomb wave, which may be detectable in continued studies of massive coulomb systems at near threshold energies. [Preview Abstract] |
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