Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session DT2: Electron Impact Ionization and Excitation I |
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Chair: Jim Colgan, Los Alamos National Laboratory Room: Holiday Inn Salon B |
Tuesday, October 10, 2006 1:30PM - 2:00PM |
DT2.00001: Latest Developments in the Theoretical Calculation of Atomic Ionization by Charged Particle Impact Invited Speaker: The ionization of atoms by electron or ion impact for highly differential scattering has primarily concentrated on the traditional (e, 2e) scattering plane. The initial and final momentum vectors of the projectile define the scattering plane. The assumption has been that all the important physical effects would be observed in the scattering plane due to symmetry. 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 C6+ projectile ions. In this presentation, we will show that the same out-of-plane effects can be observed for electron-impact ionization of magnesium. Proper quantum mechanical distorted wave treatment of electron-impact ionization involves fewer approximations than heavy ion ionization. These electron-impact ionization 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] |
Tuesday, October 10, 2006 2:00PM - 2:30PM |
DT2.00002: Electron Excitation and Ionization of the Chlorine Molecule Invited Speaker: Despite its technological importance, many of the emission systems in molecular chlorine have received surprisingly little study. I will present our experimental measurements of absolute emission cross sections for 10 to 700 eV electrons incident on chlorine molecules. The emission systems include the dominant $\mbox{Cl}_2^+ \quad A\,^2\Pi \,-\,X\,^2\Pi $ and the Cl$_{2}$ systems at 256 nm and 306 nm. The $A-X$ system possesses a very dense band spectrum and I will discuss our efforts to extract individual vibrational cross sections and discuss this system's contribution to the total chlorine ionization cross section. [Preview Abstract] |
Tuesday, October 10, 2006 2:30PM - 3:00PM |
DT2.00003: Dynamics of resonant excitation and attachment processes in electron-molecule collisions Invited Speaker: Vibrational excitation and dissociation of small molecules by low-energy electron imapct are dominated by resonant processes. In the collision of electrons with molecules and molecular ions, are dominated by resonant processes, Our theoretical understanding of these basic processes comes principally from resonance scattering theory and simple one-dimensional models of the reaction dynamics. This talk will focus on dramatic effects in low-energy dissociative electron attachment (DEA) that are purely polyatomic in origin and that can only be studied with a multi-dimensional treatment of the dissociation dynamics. These effects will be illustrated by our studies of DEA in water, hydrogen disulfide and formic acid. [Preview Abstract] |
Tuesday, October 10, 2006 3:00PM - 3:15PM |
DT2.00004: Near-threshold absolute angle-differential cross sections for electron-impact excitation of argon and xenon. Michael Allan, Oleg Zatsarinny, Klaus Bartschat Following up on our recent work on e$-$Ne collisions [1], absolute angle-differential cross sections for electron-impact excitation of argon and xenon atoms to the lowest four $np^{5}(n+1)s$ levels, and the $5p^{5}5d[\frac{7}{2}]_3$ level in xenon, have been measured and calculated as a function of electron energy up to a few eV above threshold. For argon, excellent agreement is observed between the experimental data and predictions from a Breit-Pauli \hbox{$B$-spline} \hbox{$R$-matrix} (BSR) method, in which non-orthogonal orbital sets are used to optimize the target description [2,3]. The agreement is still satisfactory for the more complex xenon target, suggesting that predictions from the BSR model should already be sufficiently accurate for many modelling applications. Nevertheless, the remaining discrepancies indicate the need for further refinement of the theoretical model. \par\noindent \par\noindent [1] M. Allan, K. Franz, H. Hotop, O. Zatsarinny and K. Bartschat, J.~Phys. B \textbf{39} L139, 2006. \par\noindent [2] O. Zatsarinny and K. Bartschat, J.~Phys. B {\bf 37} (2004) 4693. \par\noindent [3] O. Zatsarinny, Comp. Phys. Commun. {\bf 174} (2006) 274. [Preview Abstract] |
Tuesday, October 10, 2006 3:15PM - 3:30PM |
DT2.00005: Fluorescence Polarization of Helium Negative Ion Resonances Excited by Polarized Electron Impact T.J. Gay, J.W. Maseberg The helium triply-excited negative ion $2s^22p\,^2\!P$ and $2s2p^2\,^2\!D$ resonance states can autoionize to populate the singly excited $3\,^3\!D$ level. Optical observation of interference from these resonant channels in the $3\,^3\!D\rightarrow2\,^3\!P$ 587.5 nm transition is possible and measurements of the intensity and linear polarization fraction of this line are available [1-4]. In contrast to previous work, we utilize spin-polarized electrons and report the integrated Stokes parameters P$_1$, P$_2$, and P$_3$ in the 55-60 eV region. Our null result for P$_2$ indicates that even though these resonances are long lived ($\sim$200 ps), magnetic forces acting on the temporarily-captured electron are negligible. Values of P$_3$ show no statistically-significant variation from their asymptotic non-resonant levels. \newline \newline [1] A. Defrance, J. Phys. B \textbf{13}, 1229 (1980). \newline [2] D. Cvejanovi\'{c} \textit{et al}., J. Phys. B \textbf{33}, 2265 (2000). \newline [3] H. Batelaan \textit{et al}., J. Phys. B \textbf{24}, 5151 (1991). \newline [4] P. J. M. van der Burgt \textit{et al}., J. Phys. B \textbf{19}, 2015 (1986). [Preview Abstract] |
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