Bulletin of the American Physical Society
64th Annual Gaseous Electronics Conference
Volume 56, Number 15
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session JW2: Electron-Molecule Collisions |
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Chair: Michael Brunger, Flinders University Room: 255E |
Wednesday, November 16, 2011 9:30AM - 10:00AM |
JW2.00001: Low-energy electron molecule collision calculations with the R-matrix method Invited Speaker: The R-matrix method is widely used to study electron -- and positron -- molecule collisions.\footnote{J. Tennyson, 2010, Phys. Rep., 491, 29.} It is now being systematically applied constituent molecules of technological plasmas where it is particularly useful for studying collision processes with open shell species for which experimental studies are particularly difficult. Sample results for collision calculations will be given at the meeting. Such calculations can now be performed by the non-specialist using the Quantemol-N expert system. The R-matrix with pseudo-states method has been implemented as part of the UK molecular R-matrix codes. This method extends the energy range treatable by the method as well as significantly improving the treatment of polarization effects. [Preview Abstract] |
Wednesday, November 16, 2011 10:00AM - 10:15AM |
JW2.00002: Electronic Excitation of Furan by Low Energy Electrons Leigh R. Hargreaves, Murtadha A. Khakoo, Maria Cristina A. Lopes, Romarly da Costa, Marcio H.F. Bettega, Marco A.P. Lima We present absolute differential cross section (DCS) measurements and calculations of electron impact excitation of the lowest lying triplet $^{3}$B$_{2}$ and $^{3}$A$_{1}$ electronic states of furan. The incident electron energy range of the present study was 5-15eV. The experimental data were normalized to the elastic DCS data of [1]. The cross sections were determined by unfolding electron energy loss spectra, using an open source data analysis package and the spectroscopic assignments of [2]. The calculations employ a Multichannel Schwinger method with a 9-state closed coupling CI configuration including polarized pseudo-potentials. The preliminary theoretical results show reasonable agreement with experiment below 10eV, but differ at higher energies. \\[4pt] [1] M. A. Khakoo et al., Phys. Rev. A, 81, 062716 (2010) \\[0pt] [2] A. Guiliani and M.-J. Hubin-Franskin, Int. J. Mass Spec., 205, 163 (2001) [Preview Abstract] |
Wednesday, November 16, 2011 10:15AM - 10:30AM |
JW2.00003: Low Energy Elastic Electron Scattering from Gaseous Isopropanol Amos Jo, Alexsander Gauf, Joshua Tanner, Leigh R. Hargreaves, Murtadha A. Khakoo, Carl Winstead, B. Vincent McKoy, Marcio H.F. Bettega Normalized absolute experimental electron scattering differential cross-sections (DCS) for electron energies of 1.5eV to 30eV and scattering angles from 10$^{\circ}$ to 130$^{\circ}$, for elastic electron scattering from isopropyl alcohol will be presented. The experimental method employs the relative flow method using an aperture gas collimator source of isopropanol and helium as the calibration gas. It also employs a moveable source arrangement to accurately determine the experimental background. The theory is a multi-channel Schwinger method with polarization effects included. On average, agreement between theory and experiment is found to be very good. [Preview Abstract] |
Wednesday, November 16, 2011 10:30AM - 10:45AM |
JW2.00004: Low Energy Elastic Electron Scattering from Gaseous Tetrahydrofuran Alexsander Gauf, Amos Jo, Todd Walls, Leigh Hargreaves, Murtadha A. Khakoo Normalized absolute experimental electron scattering differential cross-sections (DCS) for electron energies of 1.5eV to 50eV from tetrahydrofuran will be presented. The experimental method employs the relative flow method using helium as the calibration gas, but a moveable source arrangement to accurately determine the experimental background. The results extend experimentally available DCS at lower energies and are found to be in very good agreement with earlier measurements in general. However, our results, using a thin aperture gas source, are not constrained by molecular diameter requirements [1] and serve as a useful systematic check of earlier results (see [2] and the references therein). \\[4pt] [1] M. A. Khakoo et al., J. Phys. B. 40, 3601(2007). \\[0pt] [2] M. Allan, J. Phys. B.40, 3531 (2007). [Preview Abstract] |
Wednesday, November 16, 2011 10:45AM - 11:00AM |
JW2.00005: Computational studies of inelastic electron-molecule scattering processes with the Quantemol-N system Brent Walker, Jonathan Tennyson Data for cross-sections of electron-molecule scattering processes is an important ingredient in the study of plasmas, especially in undertaking reactor scale computer simulations of industrial plasmas. Such cross-section data can be obtained computationally from first principles, where a highly successful and accurate approach is the \textbf{R}-matrix method. In the \textbf{R}-matrix method, to approach the quantum-mechanical problem of the electron molecule interaction, space is divided into two regions: the \textit{inner} region, in which the (complicated) $N+1$ electron problem of the interaction between the scattering electron and the $N$ electron molecule is solved in detail; and the \textit{outer} region, where a much simpler scattering problem is solved. We report on recent developments in the \textit{Quantemol-N} package -- which provides an expert system interface to the state-of-the-art UK Molecular R- matrix codes -- for taking account of \textit{inelastic} electron- molecule scattering processes. The electron-impact processes we will focus on are: (1).~dissociative attachment; (2).~impact ionization; and (3).~electron impact excitation/dissociation. Example calculations will be presented. We will also illustrate how data obtained from calculations of such inelatic scattering processes has been incorporated into reactor-scale plasma simulations at Quantemol Ltd. [Preview Abstract] |
Wednesday, November 16, 2011 11:00AM - 11:30AM |
JW2.00006: Low energy electron collision parameters for modeling auroral/dayglow phenomena Invited Speaker: From the tenuous atmospheres of Pluto and Triton to the higher pressure atmospheres of Earth and Titan, electron-collisions with molecular nitrogen continue to warrant attention. The airglow emissions of N$_{2}$ from the atmospheres of Earth and planetary satellites have been extensively observed. Accurate, consistent cross section data is a necessity for accurate models of how upper atmospheres behave. This enables determinations of solar energy inputs and atmospheric expansion and contraction, which influences satellite orbits for instance. Recent work by Lean \textit{et al.} [1], Stevens \textit{et al.} [2], and Kato \textit{et al.} [3] appear to substantiate our $e^{-}$+N$_{2}$ excitation and emission work (e.g., Johnson \textit{et al.} [4], Malone \textit{et al.} [5], Young \textit{et al.} [6] and references therein). Recently, we have focused on the near-threshold-to-peak region of N$_{2}$ with the goal of providing low energy collision parameters of the $X^{1}\Sigma _{g}^{+}$(0)--$A^{3}\Sigma _{u}^{+}$, $B^{3}\Pi _{g}$, $W^{3}\Delta _{u}$, $B^{\prime 3}\Sigma _{u}^{-}$, $a^{\prime 1}\Sigma _{u}^{-}$, $a^{1}\Pi _{g}$, $w^{1}\Delta _{u}$, $C^{3}\Pi _{u}$, and $E^{3}\Sigma _{g}^{+}$ transitions for modeling auroral and dayglow phenomena in these N$_{2}$-rich atmospheres. The Lyman-Birge-Hopfield (LBH) emissions, from $a^{1}\Pi _{g}(v^{\prime })$--$X^{1}\Sigma _{g}^{+}(v^{\prime \prime })$ transitions, are `bellwether' measurements for diurnal Terrestrial Space Weather variations [7]. However, near-threshold cross section data is still lacking for the $a^{1}\Pi _{g}$ state, as well as the `\textit{slow-cascade}' $a^{\prime 1}\Sigma _{u}^{-}$ and $w^{1}\Delta _{u}$ contributors to LBH emissions. In addition, Vegard-Kaplan (VK) emissions, from the $A^{3}\Sigma _{u}^{+}(v^{\prime })$--$X^{1}\Sigma _{g}^{+}(v^{\prime \prime })$ transitions, recently observed in Titan's thermosphere [2], require further improved monoenergetic laboratory measurements. New electron energy-loss measurements, along with direct excitation (integral) cross sections, are presented for excitation of the lower states of N$_{2}$, with finely-spaced impact energy increments in the threshold-to-peak region. Our recent work, including vibrationally resolved excitation, addresses these atmospheric data needs.\\[4pt] [1] Lean \textit{et al.}, 2011, JGR, 116, A01102. $\quad \quad \quad \quad \quad \quad \,$ [4] Johnson \textit{et al.}, 2005, JGR, 110, A11311. \newline [2] Stevens \textit{et al.}, 2011, JGR, 116, A05304. $\quad \quad \quad \quad \quad $ [5] Malone \textit{et al.}, 2009, J. Phys. B, 42, 135201. \newline [3] Kato \textit{et al.}, 2010, PRA, 81, 042717. $\quad \quad \quad \quad \quad \quad \;\;\,{\kern 1pt}$ [6] Young \textit{et al.}, 2010, J. Phys. B, 43, 135201. \newline [7] Ajello \textit{et al.}, 2011, UV Molecular Spectroscopy from Electron Impact for Applications to Planetary Atmospheres and Astrophysics, Book Chapter 28, published in ``Charged Particle and Photon Interactions with Matter'' Recent Advances, Applications, and Interfaces-Eds., Hatano \textit{et al.}, Taylor {\&} Francis, Boca Raton, FL. [Preview Abstract] |
Wednesday, November 16, 2011 11:30AM - 11:45AM |
JW2.00007: Cross sections and spin asymmetries for e-Cd scattering Dmitry Fursa, Christopher Bostock, Igor Bray Electron scattering from the ground state of cadmium atoms has been investigated theoretically using the convergent close-coupling (CCC), and relativistic convergent close-coupling (RCCC) methods. Elastic and inelastic differential cross sections, integrated cross sections, and electron impact coherence parameters and spin-asymmetries have been calculated and compared with available experimental and theoretical results. We find, in general, good agreement between the theories and experiment. In particular we find very good agreement with measurements of the Sherman function in elastic scattering of spin-polarized electrons from the ground state of cadmium atom by Bartsch {\it et~al.} [\textit{J.~Phys.~B} {\textbf{25}}, 1511 (1992)] that have been in serious disagreement with scattering theories for nearly two decades. The unusually rapid variation in the spin asymmetry parameter in the vicinity of 4~eV projectile energy is now explained in terms of unitarity of the close-coupling formalism. [Preview Abstract] |
Wednesday, November 16, 2011 11:45AM - 12:00PM |
JW2.00008: Electron impact total cross sections for H$_{2}$S and PH$_{3}$ for a wide energy range Chetan Limbachiya, Minaxi Vinodkumar, Nigel Mason In this paper we have computed total cross sections for H$_{2}$S and PH$_{3}$ using two different molecular codes, Quantemol N for low energy calculations and Spherical Complex Optical Potential for intermediate and high energies. We present rotationally elastic total cross sections for electron scattering from H2S and PH3, to demonstrate the possibility of producing robust cross sections from 0.01 eV to 2 keV using two different theoretical formalisms[1]. We use the commercial Quantemol-N formalism[2] for calculating total cross sections up to threshold of the target and the Spherical Optical Complex Potential (SCOP) method for calculating total sections beyond threshold up to 2 keV [3]. \\[4pt] [1] C. G. Limbachiya, M. Vinodkumar, N. J. Mason, Phys. Rev. A (in press)\\[0pt] [2] J.Tennyson \textit{et al }2007 \textit{J. Phys.Conf. Series }\textbf{86, }012001\\[0pt] [3] M. Vinodkumar \textit{et al }2010 \textit{International Journal of Mass Spectrometry }\textbf{294, }54 [Preview Abstract] |
Wednesday, November 16, 2011 12:00PM - 12:15PM |
JW2.00009: Distribution Function Shape Relaxation in Electron Atom Systems; the Kullback-Leibler Entropy Bernie Shizgal, Reinel Sospedra-Alfonso The relaxation of energetic electrons in an equilibrium background gas is an important fundamental problem in kinetic theory with important applications to devices in plasma processing of materials, plasma displays and other technologies. The objective is to study the electron-atom relaxation process in terms of the evolution of the shape of the distribution function (DF) and the relaxation time for the approach of the DF to equilibrium. We consider two rare gas atom moderators, Argon and Neon, characterized by different electron-atom momentum transfer cross sections. The isotropic portion of the DF is given by the Fokker-Planck equation. A measure of the departure of the DF from the steady state distribution is the Kullback-Leibler entropy (KLE). The relaxation time for the KLE is compared to the relaxation time for the electron temperature. The results presented include the heating of the electrons by an external electric field and the relaxation of the initial DF to the steady Davydov DF. The multi-exponential decay in these systems is interpreted approximately in terms of a single relaxation time for both the DF and the average energy. [Preview Abstract] |
Wednesday, November 16, 2011 12:15PM - 12:30PM |
JW2.00010: Low Energy Electron Impact Excitation of Water Kevin Ralphs, Gabriela Serna, Leigh R. Hargreaves, Murtadha A. Khakoo, Carl Winstead, B. Vincent McKoy We present normalized absolute differential and integral cross-section measurements for the low energy electron impact excitation of the lowest dissociative $^{3}$B$_{1}$, $^{1}$B$_{1}$,$^{3}$A$_{1}$ and $^{1}$A$_{1}$ states of H$_{2}$O. The DCS were taken at incident energies of 9eV, 10eV, 12eV, 15eV and 20eV and scattering angles of 15$^{\circ}$ to 130$^{\circ}$ and normalized to the elastic electron scattering measurements of [1]. The DCS were obtained after a sophisticated unfolding of the electron energy loss spectrum of water using photoabsorption data in the literature as investigated by Thorn et al. [2]. Our measurements extend those of [2] to near-threshold energies. We find both important agreements and differences between our DCS and those of [2]. Comparison to our theory (multi-channel Schwinger) and that of earlier work [3] will also be presented. \\[4pt] [1] M. A. Khakoo et al. Phys. Rev. A 78, 052710 (2008).\\[0pt] [2] P. A. Thorn et al. J. Phys. B.: At. Mol. Phys. 40 697 (2007).\\[0pt] [3] T. J. Gil Phys. Rev. A 49, 2642 (1994) [Preview Abstract] |
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