Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session SF3: Electron Collisions with Atoms and Molecules |
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Chair: Allan Stauffer, York University Room: State D |
Friday, November 7, 2014 8:30AM - 9:00AM |
SF3.00001: Angular distributions for ionization from excited states of atoms Invited Speaker: James Colgan We present recent theoretical work examining cross sections for electron-impact ionization of excited states of atoms. Our work is motivated by recent measurements of the angular differential cross sections from electron-impact single ionization of Mg atoms in the $3s3p$ excited state [1], which were prepared by laser excitation of the Mg target. We use the time-dependent close-coupling approach to electron-impact ionization [2] and explore the angular distributions from excited state Na and Mg, building on recent work by us in which we examined the angular distributions from the ground states of Na and Mg [3]. We examine the differences between the angular distributions resulting from ionization of the ground and excited states. Our calculations are also compared to the recent measurements [1], and we highlight where further work would be desirable in this area.\\[4pt] [1] K. L. Nixon and A. J. Murray, Phys. Rev. Letts. {\bf 106}, 123201 (2011); Phys. Rev. Letts. {\bf 112}, 023202 (2014).\\[0pt] [2] J. Colgan and M. S. Pindzola, Eur. J. Phys. D {\bf 66}, 284 (2012).\\[0pt] [3] G. S. J. Armstrong, J. Colgan, and M. S. Pindzola, Phys. Rev. A {\bf 88}, 042713 (2013). [Preview Abstract] |
Friday, November 7, 2014 9:00AM - 9:15AM |
SF3.00002: Theoretical and experimental results for electron-impact ionization of the 3p state of Mg that has been laser aligned Sadek Amami, Don Madison, Kate Nixon, Andrew Murray, James Colgan Low energy theoretical and experimental quadruple differential cross sections (QDCS) will be presented for electron impact ionization of magnesium atoms that have been aligned by lasers. The incident projectile electron has an energy of 43.31eV, the scattered and ejected electrons were detected with equal energies (E1$=$E2$=$20eV), one of the final state electrons was detected at a fixed scattering angle of 30 degrees, and the other final state electron is detected at angles ranging between 0 degrees and 180 degrees. The Mg atoms are excited to the 3p state using a linearly polarized laser which produces a standing wave aligned perpendicular to the laser beam direction. Theoretical results will be compared with the experimental data for several different alignment angles both in the scattering plane as well as in the plane perpendicular to the incident beam direction. [Preview Abstract] |
Friday, November 7, 2014 9:15AM - 9:30AM |
SF3.00003: Quasi-Sturmian basis functions for two- and three-body scattering problems. Jessica A. Del Punta, Lorenzo Ugo Ancarani, Gustavo Gasaneo For quantum three-body scattering processes, one important theoretical issue is how to impose to the wave function the correct asymptotic behavior. In many methods the problem is solved using basis functions that generally do not possess the correct behavior at large distances. One exception is given by the Generalized Sturmian Functions (GSF) [1] which are defined taking into account the interactions of the problem under consideration, thus making them an efficient basis set. We present in this work an alternative set of basis functions, named Quasi Sturmian Functions (QSF). Starting with the two-body case [2], QSF satisfy a non-homogeneous differential equation, and may be constructed with a selected asymptotic behavior (e.g. outgoing). Contrary to GSF, these basis functions have analytical closed form for the case of a Coulomb potential. Moreover, we showed that the QSF provide a superior convergency rate when solving a two-body scattering problem. For the three-body case, we propose a representation using hyperspherical coordinates. While the angular variables are treated in a parametric way, the hyperradial part of these new QSF basis functions are obtained by a generalization of the method used for the two-body problem. As a consequence, analytical expressions can be given for these new QSF and the desired Coulomb asymptotic behavior in the hyperradial coordinate can be imposed. \\[4pt] [1] G. Gasaneo et al, Adv. Quantum Chem., 67, 153 (2013) [2] J. A. Del Punta el al, J. Math. Phys., 55, 052101 (2014). [Preview Abstract] |
Friday, November 7, 2014 9:30AM - 10:00AM |
SF3.00004: Low energy electron-molecule scattering using the R-matrix method Invited Speaker: Jimena Gorfinkiel The study of electron-molecule collisions continues to attract significant interest stimulated, in no small part, by the need for collisional data to model a number of physical environments and applied processes (e.g. the modelling of focused electron beam induced deposition and the description of the interaction of radiation with biological matter). This need for electron scattering data (cross sections but also information on the temporary negative ions, TNI, that can be formed) has motivated the renewed development of theoretical methodology and their computational implementation. I will present the latest developments in the study of low energy electron scattering from molecules and molecular clusters using the R-matrix method. Recent calculations on electron collisions with biologically relevant molecules have shed light on the formation of core-excited TNI these larger targets. The picture that emerges is much more complex than previously thought. I will discuss some examples as well as current and future developments of the methodology and software in order to provide more accurate collisional data (in particular cross sections) for bigger targets.\\[4pt] In collaboration with Zdenek Masin, The Open University. [Preview Abstract] |
Friday, November 7, 2014 10:00AM - 10:15AM |
SF3.00005: Theoretical and Experimental Triple Differential Cross Sections for Electron Impact Ionization of SF$_{6}$ Hari Chaluvadi, Kate Nixon, Andrew Murray, Chuangang Ning, James Colgan, Don Madison Experimental and theoretical Triply Differential Cross Sections (TDCS) will be presented for electron-impact ionization of sulfur hexafluoride (SF6) for the molecular orbital 1t1g. M3DW (molecular 3-body distorted wave) results will be compared with experiment for coplanar geometry and for perpendicular plane geometry (a plane which is perpendicular to the incident beam direction). In both cases, the final state electron energies and observation angles are symmetric and the final state electron energies range from 5eV to 40eV. It will be shown that there is a large difference between using the OAMO (orientation averaged molecular orbital) approximation and the proper average over all orientations and also that the proper averaged results are in much better agreement with experiment. [Preview Abstract] |
Friday, November 7, 2014 10:15AM - 10:30AM |
SF3.00006: Importance of projectile-target interactions in the triple differential cross sections for Low energy (e,2e) ionization of aligned H$_{2}$ Esam Ali, Don Madison, X. Ren, A. Dorn, Chuangang Ning Experimental and theoretical Triple Differential Cross Sections (TDCS) are presented for electron impact ionization-excitation of the $2s\sigma_{g} $state of H$_{2}$ in the perpendicular plane. The excited $2s\sigma _{g} $ state immediately dissociates and the alignment of the molecule is determined by detecting one of the fragments. Results are presented for three different alignments in the xy-plane (scattering plane is xz) - alignment along y-axis, x-axis, and 45$^{\circ}$ between the x- and y-axes for incident electron energies of 4, 10, and 25 eV and different scattered electron angles of 20$^{\circ}$ and 30$^{\circ}$ in the perpendicular plane. Theoretical M4DW (molecular 4-body distorted wave) results are compared to experimental data, and overall we found reasonably good agreement between experiment and theory. The Results show that (e,2e) cross sections for excitation-ionization depend strongly on the orientation of the H$_{2}$ molecule. [Preview Abstract] |
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