Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session NR3: Electron Collisions with Atoms and Molecules |
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Chair: Michael Brunger, Flinders University Room: Petit Amphitheatre |
Thursday, October 7, 2010 10:30AM - 11:00AM |
NR3.00001: Calculation of excitation and ionization processes using relativistic CCC method Invited Speaker: The recently formulated relativistic convergent close-coupling (RCCC) method has been applied to electron scattering from quasi-one electron atoms [1] and also highly charged hydrogenlike ions [2]. In the latter case it has been used to resolve discrepancies between theory and experiment for the polarization of x-rays emitted by hydrogenlike ions (Ti$^{21+}$, Ar$^{17+}$, Fe$^{25+}$) during electron impact excitation and make predictions for cross sections and radiation polarization for hydrogen-like uranium ion. Here we report on the extension of the RCCC method to accommodate electron scattering from two electron targets and quasi-two electron targets. We apply the theory to electron scattering from mercury which serves as a testing ground for relativistic theories due to its high atomic number, $Z=80$. Furthermore, electron-mercury scattering plays an important practical role in the physics of fluorescent and high intensity discharge lamps. In our calculations the mercury atom was modeled as a quasi-two electron atom consisting of two valence electrons above an inert $[Xe]4f^{14}5d^{10}$ frozen core. One- and two-electron polarization potentials have been used to model more accurately the valence-core-electrons correlations. We have calculated cross sections for electron impact excitations of mercury for a large number of transitions. Good agreement was found with our previous nonrelativistic results for the transitions that are not strongly affected by relativistic effects (e.g., $(6s6p){}^1P^o_{1}$). For the transitions that are strongly affected by relativistic effects (e.g., $(6s6p){}^3P^o_{1}$) we find good agreement with recent DBSR calculations [3] and available experiment.\\[4pt] [1] D. V. Fursa and I. Bray, Phys. Rev. Lett. {\bf 100}, 113201 (2008).\\[0pt] [2] C. J. Bostock, D. V. Fursa, and I. Bray, Phys. Rev. A {\bf 80}, 052708 (2009).\\[0pt] [3] O. Zatsarinny and K. Bartschat, Phys. Rev. A {\bf 79}, 042713 (2009). [Preview Abstract] |
Thursday, October 7, 2010 11:00AM - 11:15AM |
NR3.00002: Benchmark data for elastic and inelastic electron collisions with krypton atoms Oleg Zatsarinny, K. Bartschat, H. Hotop, M. Allan We have further extended our recent work [1] on elastic and inelastic electron scattering from Kr atoms and obtained new datasets for angle-differential cross sections at selected scattering angles as a function of the projectile energy. Our energy resolution of about 10~meV made it possible to separate many structures and to analyze the resonances in detail. Comparison of the measured data with theoretical predictions from a fully relativistic Dirac $B$-spline $R$-matrix (DBSR) method~[2] shows very encouraging agreement.\\[4pt] [1] T.H.~Hoffmann, M.-W.~Ruf, H.~Hotop, O.~Zatsarinny, K.~Bartschat, and M.~Allan, J. Phys. B {\bf 43} (2010) 085206.\\[0pt] [2] O.~Zatsarinny and K.~Bartschat, Phys. Rev. A~{\bf 77} (2008) 062701. [Preview Abstract] |
Thursday, October 7, 2010 11:15AM - 11:30AM |
NR3.00003: The Sherman function for Kr and Xe Allan Stauffer, Robert McEachran The Sherman function is a measure of the left-right asymmetry in the elastic differential scattering of spin-polarized electrons from atomic systems. We have carried out detailed calculations of certain elaborate structures in this function for scattering from krypton and xenon using a relativistic complex optical potential method. These structures show rapid variation as a function of both scattering angle and energy. We will illustrate this behaviour with several examples which show a variety of distinctive forms. [Preview Abstract] |
Thursday, October 7, 2010 11:30AM - 12:00PM |
NR3.00004: Electron Impact Ionisation of Molecules Invited Speaker: Electron impact ionisation studies can be used to fully characterise the collision dynamics of a system. Collisions with atomic systems are now relatively well understood, as evidenced by the excellent agreement between experimental measurements and theoretical predictions over a wide range of impact energies. Molecular targets provide a new challenge for both experiment and theory. Detailed studies have now been carried out using diatomic targets such as H$_{2}$ and N$_{2}$, and reasonable agreement with theory is obtained for these simple systems. However, for more complex polyatomic molecules, large discrepancies are seen between theory and experiment. A possible cause of this is due to the theoretical approximations required to account for all orientations of the molecule (as is necessary to compare to current experiments). The inherent symmetry of methane (CH$_{4})$ makes it an ideal molecule to study, since in this target the orientational variance of the wavefunctions needed to predict the collision dynamics are minimised. The experimental restrictions due to the random orientation of effusive molecular targets is also being addressed in our laboratory by developing a method of pre-aligning the molecules using a laser field. Progress towards these goals will also be discussed. [Preview Abstract] |
Thursday, October 7, 2010 12:00PM - 12:15PM |
NR3.00005: How Good is Theory for Predicting the Absolute Value of (e,2e) Ionization Cross Sections? Don Madison, Sadek Amami, Adam Upshaw, Hari Saha Very recently Hargreaves, Stevenson, and Lohmann [to be published] reported measurements of absolute differential cross sections for electron-impact ionization of neon and argon. They compared their absolute measurements with DWBA (distorted wave Born), DW2-RM (second order distorted wave R-matrix), CCC (convergent close coupling), and 3DW (3 body distorted wave) calculations. While none of the theories were in overall very good agreement with experiment, the best agreement was found for the DWBA which is the least sophisticated of all the theoretical approaches. We have improved the DWBA and 3DW calculations by including correlation-polarization effects and by replacing the static exchange continuum waves with Hartree-Fock continuum waves. The sensitivity of the magnitude and shape of cross section to these effects will be presented. [Preview Abstract] |
Thursday, October 7, 2010 12:15PM - 12:30PM |
NR3.00006: Optimal Sturmian basis functions for atomic three-body systems Juan Martin Randazzo, Lorenzo Ugo Ancarani, Gustavo Gasaneo, Ana Laura Frapiccini, Flavio Colavecchia We discuss the optimisation of the Configuration Interaction method for three-body atomic systems in which the configurations are defined as products of Sturmian functions (SF). Our study in the case of two-electron atoms [1] clearly shows that the use of basis functions which fulfil the electron-nucleus cusp conditions and with adequate asymptotic behavior considerably improves the energy convergence rate. Using the SF basis, we transform the two-electron Schrodinger equation into a matrix eigenvalue problem. The results of the diagonalization are better than those obtained with highly accurate calculations which use Coulomb Sturmians Functions (CSF) [2]. Our results can be considered as the most accurate results obtained with uncorrelated basis functions [1]. An extension to atomic three-body systems with general masses will be presented. \\[4pt] [1] J.M. Randazzo, L.U. Ancarani, G. Gasaneo, A..L. Frapiccini and F.D. Colavecchia, Phys. Rev. A 81, 042520 (2010). \\[0pt] [2] M.W.J. Bromley and J. Mitroy, Int. J. Quantum Chem. 107, 1150 (2007). [Preview Abstract] |
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