Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session F3: Ionization and Charge Transfer |
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Chair: Colm Whelan, Old Dominion University Room: Burnham Yates Conference Center Olive Branch |
Thursday, May 19, 2005 10:30AM - 10:42AM |
F3.00001: Electron Capture Processes Following Collisions of He$^{2+ }$ Ions with Molecular Targets O. Abu-Haija, E.Y. Kamber, S.M. Ferguson Energy-gain spectra, absolute state-selective and total cross sections have been measured for single-electron capture processes in collisions of He$^{2+}$ ions with O$_{2}$, H$_{2}$O, CO$_{2}$, N$_{2}$, and NH$_{3}$ at impact energies between 100 eV and 1600 eV and scattering angles between 0$^{o}$ and 6$^{o}$ using the translational energy-gain spectroscopy (TES) technique. As apparent from the translational energy-gain measurements, single-electron capture (SEC) from O$_{2}$ and H$_{2}$O proceeds by both dissociative and non-dissociative channels, whereas for N$_{2 }$and CO$_{2}$ only dissociative SEC has been observed. However, for NH$_{3 } $the non-dissociative SEC channel is found to be predominantly populated. Total cross sections have also been compared with available measurements and theoretical calculations based on Landua-Zener model and Demkov model. [Preview Abstract] |
Thursday, May 19, 2005 10:42AM - 10:54AM |
F3.00002: Excitation and Charge Transfer in p + H(2s) Collisions D.R. Schultz, T-G Lee, T. Minami, M.S. Pindzola The time-dependent lattice method for ion-atom collisions is used to calculate excitation and charge transfer cross sections for proton collisions with excited state Hydrogen. A non-perturbative calculation on a 59.0 million point lattice yields $\Delta n = 0$ amd $\Delta n = 1$ excitation and charge transfer cross sections at 5, 10, and 15 keV incident energy. The non-perturbative cross sections serve as benchmarks for atomic orbital close-coupling and classical trajectory Monte-Carlo calculations performed over a much wider energy range. [Preview Abstract] |
Thursday, May 19, 2005 10:54AM - 11:06AM |
F3.00003: Electron capture cross sections for C(6+)+H collisions at low energies Chien-Nan Liu, Shu Chun Cheng, Anh-Thu Le, Chii-Dong Lin The hyperspherical close-coupling method has been used to calculate electron capture cross sections for$C^{6+}$+H collisions for energies from 1 keV/amu down to 0.1 eV/amu. Total electron capture cross sections and partial cross sections to n=4 and n=5 states of $C^{5+}$ were obtained. For energies above 500 eV/amu our results agree with the semiclassical molecular orbital calculations but disagree with the more recent semiclassical atomic orbital calculations. For energies below 3 eV/amu the electron capture to n=5 becomes dominant and at energies below 3 eV/amu the electron capture cross sections show the Langevin 1/v dependence. [Preview Abstract] |
Thursday, May 19, 2005 11:06AM - 11:18AM |
F3.00004: Slow B$^{5+}$+ H$_{2}$ Collisions Bidhan Saha, Dwayne Joseph The charge-exchange processes involving ions and atomic targets have received considerable theoretical and experimental considerable attentions over the last decades owing to its immense applications in both astrophysical and magnetically confined thermonuclear fusion plasmas. However, for molecular targets there are not many accurate calculations although the charge-exchange processes provide valuable inputs on the radiation research, multi-charged ion source developments, and lasers radiating in the visible ultraviolet (VUV) and X-ray regions. The electron capture cross sections in such an environment are appreciably larger. The recently observed X-ray emission data from the comets suggest that the charge exchange between solar wind and cometary gases is the most likely mechanism for X-ray production. We report our MO calculation for the process B$^{5+}$+ H$_{2}$ $\diamondsuit $ B$^{4+}$(nl) + H$^{+}_{2}$ at low energies. We use a semi-classical, impact parameter, close coupling approach based on the molecular-state expansion augmented with the plane-wave electron translation factor, freezing the molecular details of the target [1], the effective binding of the active electron inside the transient molecule is simulated employing the pseudo-potential techniques [2]. Details will be presented at the conference. [1] B. C. Saha and A. Kumar, Theo. Chem 487, 11 (1999). [2] A. Kumar and B. C. Saha, Phys. Rev. A.59, 1273 (1999). [Preview Abstract] |
Thursday, May 19, 2005 11:18AM - 11:30AM |
F3.00005: A Four-Body Theoretical Approach to Proton Impact Ionization of Helium Matt Foster, Jerry L. Peacher, Don H. Madison, Michael Schulz, Nataliya Maydanyuk, Ahmad Hasan Very recently, experimental measurements have been made for single ionization of helium by 75 keV proton impact for fixed ejected electron energies and different momentum transfers. These experiments further demonstrate the fact that the fundamental physics governing a simple collision process is still not well understood. The fully quantum mechanical model 3DW-EIS (three-distorted-wave-eikonal-initial-state), which worked well for higher energy C$^{6+}$ ionization of helium, does not give good agreement with absolute experiment for this case. However, the 3DW-EIS model treats the collision as a three-body process (projectile, ion, ejected electron). This suggests that a three-body model may not be appropriate for lower collision energies. Consequently, we will present a complete four-body model which takes all two particle Coulomb interactions (six in total) into account on equal footing. [Preview Abstract] |
Thursday, May 19, 2005 11:30AM - 11:42AM |
F3.00006: Second-order distorted wave calculation for electron impact ionization of helium to He$^{+}$(n=1 and 2) Zhangjin Chen, Don H. Madison Second-order distorted wave calculations are presented for electron impact ionization of helium with the residual ion left in n=1 and 2 states at intermediate energies in coplanar asymmetric geometry. Whereas previous second-order calculations have used the plane wave Born approximation and have used approximations to simplify the evaluation of the second-order term, we perform a full distorted wave calculation and make no approximations in the evaluation of the second-order amplitude (i.e. we sum over all contributing intermediate states). The triple differential cross sections are compared with experimental measurements and other theoretical results. [Preview Abstract] |
Thursday, May 19, 2005 11:42AM - 11:54AM |
F3.00007: Electron-Impact Ionization of Atomic Ions in the W Isonuclear Sequence J.A. Ludlow, S.D. Loch, M.S. Pindzola, A.D. Whiteford, D.C. Griffin A configuration-average distorted-wave method is used to calculate electron-impact ionization cross sections and rate coefficients for atomic ions in the W isonuclear sequence. Besides direct ionization, the indirect process of excitation-autoionization is also included. Checks on the validity of the configuration-average approximation are made by comparison with detailed calculations using the level to level multi-configuration distorted-wave method for selected ionization stages. Indirect ionization is found to be greatly reduced due to radiation damping for the higher ionization stages. [Preview Abstract] |
Thursday, May 19, 2005 11:54AM - 12:06PM |
F3.00008: Time-Dependent Close-Coupling Calculations for Electron-Impact Ionization of H$^+_2$ S.D. Loch, M.S. Pindzola, J. P. Colgan The time-dependent close-coupling method for two electron molecular systems is used to calculate electron-impact dissociative excitation and ionization cross sections for H$^+_2$. A perturbative distorted-wave method is also formulated to calculate the same cross sections for H$^+_2$. For low total azimuthal symmetry, a 6 coupled-channels non-perturbative calculation on a 9.4 million point radial and angular lattice yields partial cross sections that are in reasonable agreement with the first-order perturbation theory results. When the non-perturbative results for low symmetry are combined with the perturbative results for high symmetry, the resulting dissociative ionization cross section is in excellent agreement with experiment. [Preview Abstract] |
Thursday, May 19, 2005 12:06PM - 12:18PM |
F3.00009: Double Autoionization of Hollow Atom States M.S. Pindzola, F.J. Robicheaux, J.P. Colgan The time-dependent close-coupling method for three electron systems is used to calculate the double autoionization of hollow atom states. Initial excited states are obtained by relaxation of the Schr\"odinger equation in imaginary time, while autoionization rates are obtained by propagation in real time. A 12 coupled-channels non-perturbative calculation on a 7.1 million point radial lattice yields a double autoionization rate for the Li($2s^22p$) $\rightarrow$ Li$^{2+}$ +2e$^-$ transition that is somewhat smaller than earlier many-body perturbation theory calculations and in reasonable agreement with rates extracted from resonance profiles found in e + Li$^+$ and $\gamma$ + Li experiments. [Preview Abstract] |
Thursday, May 19, 2005 12:18PM - 12:30PM |
F3.00010: Model electron impact ionization from highly excited states of hydrogen-like ions Turker Topcu, Francis Robicheaux We present results from fully quantal and classical Monte Carlo calculations of the electron impact ionization of hydrogen-like ions within a simple two-dimensional model. We study the ionization probability from the ground state and highly excited states as function of incident energy, charge of the ion, and principle quantum number. The motivation is to investigate the correspondence between the quantal and classical ionization probabilities as the principal quantum number of the initial state increases. The quantal calculation was carried out by direct time propagation of the Schrodinger equation using a split operator method. The two dimensional s-wave model potential was chosen to have the form $V(r_1,r_2) = -Z/r_1 - Z/r_2 + 1/(r_1+r_2)$. [Preview Abstract] |
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F3.00011: Semiclassical treatment of $\bar{p}p$ formation in $\bar{p}$-H collisions R. Cabrera-Trujillo, B.D. Esry As the energy of an antiproton colliding with a hydrogen atom decreases, the probability for formation of protonium ($\bar{p}p$) increases. In this work, we present a calculation of protonium formation using the Electron-Nuclear Dynamics (END)\footnote{ E. Deumens, A. Diz, R. Longo, and Y. {\"O}hrn, Rev. Mod. Phys. {\bf 66}, 917 (1994).} theory for projectile energies from 1~eV to 10~eV. We present preliminary results for the protonium formation cross section, the stopping cross section (nuclear and electronic). In particular, we explore the role of non-adiabatic effects and the ionization channel within the END formalism. [Preview Abstract] |
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