Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session RR3: Electron-Molecule Collisions |
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Chair: Murtakha Khakoo, California State University, Fullerton Room: Oakmont Junior Ballroom |
Thursday, November 9, 2017 10:00AM - 10:30AM |
RR3.00001: Adiabatic-nuclei calculations of electron and positron scattering from molecular hydrogen and its ion Invited Speaker: Dmitry Fursa We report the extension of the convergent close-coupling (CCC) method for electron-molecule scattering [1] to the adiabatic-nuclei (AN) formulation which allows us to study the effects of nuclei motion and electron-impact dissociation processes. For H$_2^+$ and its isotopologues [2] we have modeled collisions with hot (vibrationally excited) molecules and compared with available experimental data for dissociative ionization, proton production, and the dissociative products kinetic energy release distributions. For H$_2$ we have performed AN calculations of positron scattering with emphasis on establishing convergent low-energy total and vibrational $0 \rightarrow 1$ excitation cross sections. To study electron collisions with H$_2$ we have developed a spheroidal coordinate formulation of the CCC method that allows for an accurate description of the target wave functions to large inter-nuclei distances. Excitation cross sections for vibrationally resolved transitions between low-lying H$_2$ states have been calculated and used to determine vibrational excitation of the H$_2$ ground state via excitation of electronically excited singlet states and radiative cascade. [1] Zammit et al., J. Phys. B {\bf 50}, 123001 (2017). [2] Zammit et al., Phys. Rev. A {\bf 90} 022711 (2014)\\ \\In collaboration with: M. C. Zammit, J. S. Savage, L. H. Scarlett, J. Tapley, I. Bray [Preview Abstract] |
Thursday, November 9, 2017 10:30AM - 11:00AM |
RR3.00002: Fragmentation dynamics of simple molecules by electron collision Invited Speaker: Xiangjun Chen The dissociation of multi-charged molecule is of great importance in various fields, such as plasma physics and planetary atmospheric chemistry. Most of the multi-charged molecules are in transient states that always dissociate through various pathways, which contain valuable information of the potential energy surfaces of the molecular ions. Recently, the three-body fragmentation dynamics of multi-charged CO$_{\mathrm{2}}$, OCS, CS$_{\mathrm{2}}$ molecules have been studied by electron collision using momentum imaging technique in my group. Nonsequential and sequential fragmentation dynamics of CO$_{\mathrm{2}}^{\mathrm{3+}}$ has been investigated by electron collision at an impact energy of 500 eV. The dissociation mechanisms are clearly distinguished by combined use of the Dalitz plot together with momentum correlation spectra. The angular distributions and kinetic-energy releases (KERs) of different fragmentation processes are obtained. By analyzing KERs together with the help of potential-energy curves exploration at the multi-reference configuration interaction level, we conclude that the sequential fragmentation occurs in the ground state and the first two low-lying electronic excited states of the CO$_{\mathrm{2}}^{\mathrm{3+}}$ ion. Fragmentation dynamics of CO$_{\mathrm{2}}^{\mathrm{4+\thinspace }}$are also analyzed and the distributions of momentum correlation angles between ionic fragments and the KERs are obtained. Based on the Coulomb explosion model, the bond angle and the bond length of CO$_{\mathrm{2}}^{\mathrm{4+}}$ before fragmentation are reconstructed. The results agree quite well with the geometry parameters of neutral CO$_{\mathrm{2}}$ molecule. We also investigated the fragmentation dynamics of OCS$^{\mathrm{q+}}$ and CS$_{\mathrm{2}}^{\mathrm{q+}}$ (q $=$ 2, 3, 4) induced by electron collision at an impact energy of 500 eV using the momentum imaging technique. Various dissociation channels are analyzed in details. Recently, we have performed molecular dynamics simulation of the ground state of CO$_{\mathrm{2}}^{\mathrm{3+}}$. The evolution of the molecular bond breakage in time range of 0-200 fs is investigated. The results will be presented in the talk. [Preview Abstract] |
Thursday, November 9, 2017 11:00AM - 11:15AM |
RR3.00003: Low energy (e, 2e) study for N$_{\mathrm{\mathbf{2}}}$ in coplanar and non-coplanar geometries for symmetric and asymmetric angles and final state electron energies Sadek Amami, Ahmad Sakaamini, Matthew Harvey, Andrew Murray, Don Madison Triple differential cross sections (TDCS) have been calculated and compared with experimental data for electron impact ionization of the neutral molecule N$_{\mathrm{2}}$ over a range of geometries from coplanar to the perpendicular plane. Experiment and theory will be compared for incident electron energies of 10eV and 20eV above the ionization potential of the 3$\sigma_{\mathrm{g}}$, 1$\pi_{\mathrm{u}}$ and 2$\sigma _{\mathrm{g}}$ states, using both equal and non-equal outgoing electron energies. Also, we have measured and calculated TDCS for equal outgoing electron energies of 10eV and 20eV for ionization of the N$_{\mathrm{2}}$ 3$\sigma_{\mathrm{g}}$, and 1$\pi_{\mathrm{u\thinspace }}$states for one of the electrons having a fixed scattering angle of 45$^{\mathrm{o}}$, 90$^{\mathrm{o}}$, and 125$^{\mathrm{o}}$. Calculations have been done for experimental data taken with the incident electron beam in the scattering plane, at 45\textdegree to this plane and orthogonal to the scattering plane. Experimental data will be compared to three different theoretical approximations - the three body distorted wave (3DW) approximation, the Distorted wave Born approximation (DWBA), and the Ward-Macek approximation. [Preview Abstract] |
Thursday, November 9, 2017 11:15AM - 11:30AM |
RR3.00004: Electron impact single ionization of methane. Lorenzo Ugo Ancarani, Carlos Mario Granados-Castro The electron impact single ionization of the outer valence 1t$_{\mathrm{2}}$ and the inner valence 2a$_{\mathrm{1\thinspace }}$orbitals of methane is investigated theoretically. In a first Born approximation, the scattering wave function describing the ejected electron is expanded in a set of Generalized Sturmian Functions [1] with appropriate Coulomb asymptotic conditions; this allows us to extract the scattering amplitude directly from the expansion coefficients, without the need of calculating a transition matrix element. Triple differential cross sections, calculated for several coplanar asymmetric geometries, are compared with other theoretical models (in an absolute scale), and with two sets of relative scale measurements with incident energies of 500 eV or 250 eV [2,3]. The binary to recoil ratio is analyzed as a function of the momentum transfer. For the outer valence 1t$_{\mathrm{2}}$ and for given kinematical conditions, we predict a double peak structure in the cross section binary region, a clear signature of the p-nature of the molecular orbital. [1] C. M. Granados-Castro and L. U. Ancarani, Eur. J. Phys. D 71, 65 (2017). [2] A. Lahmam--Bennani et al., J. Phys. B, 42, 165201 (2009). [3] N. Isik et al., J. Phys. B, 49, 065203 (2016). [Preview Abstract] |
Thursday, November 9, 2017 11:30AM - 11:45AM |
RR3.00005: Self-consistent electron impact cross-sections for THF: A swarm investigation Madalyn Casey, Daniel Cocks, Gregory Boyle, Jaime de Urquijo, Darryl Jones, Michael Brunger, Ronald White An accurate quantitative description of electron transport in biological systems is necessary for applications in medical imaging and dosimetric treatments. Modelling charged particle transport in the human body on a molecular level involves interactions with many complex molecules but is often reduced to the comprehensively studied surrogate of water. Simple analogues for the sugars and DNA bases, such as tetrahydrofuran (THF), a sugar linking the phosphate groups in the DNA backbone, represents a first step to include the structure of DNA. The first experiments of macroscopic transport of electrons in pure THF and mixtures with N$_{2}$ and Argon have become available, and we use these measurements to perform rigorous testing of existing THF cross-sections. To model transport through THF we solve Boltzmann's equation to iteratively modify cross-sections and obtain a set that best reproduces the experimental transport coefficients. Negative differential conductivity is present in mixtures with THF, but is absent in the pure gas, and we observe the thermal activation of this phenomenon. [Preview Abstract] |
Thursday, November 9, 2017 11:45AM - 12:00PM |
RR3.00006: Theoretical and experimental study of electron impact ionization (e,2e) of para-benzoquinone for an intermediate incident electron energy Esam Ali, Darryl Jones, Oddur Ingólfsson, Chuangang Ning, James Colgan, Michael Brunger, Don Madison We will present a theoretical and experimental study of electron impact single ionization of para-benzoquinone [1]. Experimental data were taken for the unresolved combination of the 4 highest occupied molecular orbitals (4b3g, 5b2u, 1b1g, and 2b3u) of para-benzoquinone. The theoretical results are compared with experimental data measured in an asymmetric coplanar geometry for a 250 eV incident electron energy, an ejected electron energy of 20 eV, and for four fixed scattered electron angles of 7.5$^{\mathrm{o}}$, 10$^{\mathrm{o}}$, 12.5$^{\mathrm{o}}$, and 15$^{\mathrm{o}}$. Theoretical M3DW (molecular 3-body distorted wave) results summed over the four unresolved states will be compared to the experimental data. As the experimental TDCS measurements for each scattering angle are cross normalized, we fully assess the ability of the theoretical model to reproduce the experimental data in terms of angular distribution and intensity. [1] Jones \textit{et al.,} J. Chem. Phys. \textbf{145}, 164306 (2016). [Preview Abstract] |
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