Bulletin of the American Physical Society
45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 59, Number 8
Monday–Friday, June 2–6, 2014; Madison, Wisconsin
Session B8: Electron-Atom and -Molecule Collisions |
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Chair: Sultana Nahar, Ohio State University Room: Hall GJ |
Tuesday, June 3, 2014 10:30AM - 10:42AM |
B8.00001: Benchmark calculation of total cross sections for ionization-excitation of helium Oleg Zatsarinny, Klaus Bartschat The total cross section for simultaneous ionization-excitation of helium by electron impact has been revisited within the framework of the fully non\-perturbative $B$-spline $R$-matrix with pseudo\-states (BSRMPS) approach~[1]. This is a highly challenging 4-body Coulomb problem that cannot be simplified by effectively treating one of the target electrons as a spectator. After successfully applying the BSRMPS method to the energy- and angle-differential problem~[2], we investigated a long-standing discrepancy regarding the absolute normalization of the cross section for ionization with simultaneous excitation of the residual ion into the He$^+$(2p) state. Our calculations strongly favor the values suggested in [3,4] rather than the re\-normalization proposed in~[5].\\[4pt] [1]~O.~Zatsarinny and K.~Bartschat, J.~Phys.~B~{\bf 46} (2013) 112001.\\[0pt] [2]~O.~Zatsarinny and K.~Bartschat, Phys.~Rev.~Lett.~{\bf 107} (2011) 023203.\\[0pt] [3]~E.W.O.~Bloemen, H.~Winter, T.D.~M\"ark, D.~Dijkkamp, D.~Barends, and F.J.~de~Heer, J.~Phys.~B {\bf~14} (1981) 717.\\[0pt] [4]~J.J.~Forand, K.~Becker, and J.W.~McConkey, J.~Phys.~B {\bf~18} (1985) 1409.\\[0pt] [5]~H.~Merabet, R.~Bruch, S.~F\"ulling, K.~Bartschat, and A.L.~Godunov, J.~Phys.~B~{\bf~36} (2003) 3383. [Preview Abstract] |
Tuesday, June 3, 2014 10:42AM - 10:54AM |
B8.00002: Momentum Imaging of the Dynamics of Dissociative Electron Attachment to Molecules of Biological Significance Daniel Slaughter, Yosuke Kuriyama, Yu Kawarai, Yoshiro Azuma, Ali Belkacem Direct observations of dynamics following dissociative electron attachment (DEA) in biologically-relevant molecules are presented. These experiments employ a 3D momentum-imaging spectrometer (the DEA reaction microscope), a pulsed low-energy electron gun and an effusive gas target. This approach allows the measurement of kinetic energy and angular distributions of ionic fragments produced by DEA, in some cases elucidating the total kinetic energy release following two-body breakup. Significant progress has been made in describing the dynamics of the dissociating transient anion formed by electron attachment to relatively simple molecules [1-4]. Building upon that prior work, we present several aspects of the rich dynamics of DEA to nucleobases and related compounds.\\[4pt] [1] Slaughter et al. Physical Review A 87 052711 (2013)\\[0pt] [2] Moradmand et al. Physical Review A 88 032703 (2013)\\[0pt] [3] Haxton et al. Physical Review A 84 030701 (2011)\\[0pt] [4] Adaniya et al. Physical Review Letters 103 233201 (2009) [Preview Abstract] |
Tuesday, June 3, 2014 10:54AM - 11:06AM |
B8.00003: Indirect dissociative recombination of water molecule at low electronic energies Samantha Fonseca, Nicolas Douguet, Viatcheslav Kokoouline, Ann Orel We present a theoretical study of the indirect dissociative (DR) recombination of the water molecular ion H$_{2}$O$^{+}$ at low collisional energies. The approach is based on the computation of the scattering matrix just above the ionization threshold and enables the explicit determination of all diabatic electronic couplings responsible for dissociative recombination. We use the multi-channel quantum- defect theory to demonstrate the precision of the scattering matrix by reproducing accurately ab initio Rydberg state energies of the neutral molecule. We also present our latest results on H$_{2}$O$^{+}$ with our previous results on the DR of linear molecular ions N$_{2}$H$^{+}$ and HCO$^{+}$ and demonstrate the crucial role of the previously overlooked longitudinal modes for linear polyatomic ions with large permanent dipole moment. [Preview Abstract] |
Tuesday, June 3, 2014 11:06AM - 11:18AM |
B8.00004: Transmission of electrons through tapered glass capillaries: Temporal dependence S. Wickramarachchi, D. Keerthisinghe, J.A. Tanis, T. Ikeda, B.S. Dassanayake Electron transmission through a funnel-shaped borosilicate glass capillary as a function of the time evolution of the charge deposition has been studied for 500 and 1000 eV incident electrons. These measurements were done at Western Michigan University. The capillary had inlet/outlet diameters of 800 $\mu $m/100 $\mu $m and a length of 35 mm. The time dependence was studied for deposited charge in the range 0 - 1000 nC for each angle investigated, except for 5$^{\circ}$ at 1000 eV for which the measurements extended to 7000 nC. Measurements were obtained for the \textit{direct }region near zero degree tilt angle where there are no collisions with the capillary walls, and for the \textit{indirect} region for larger tilt angles (up to 5$^{\circ})$ where electrons are deflected by the deposited charge or they collide with the capillary walls. In the direct region, the transmission showed no stable behavior with erratic fluctuations occurring for all deposited charges. In the indirect region, the transmission showed some fluctuations with rapid self-discharging but the transmission slowly increased with deposited charge. Total blocking was observed for 1000 eV at the tilt angle of 5$^{\circ}$ when the incident charge was higher than 6500 nC. [Preview Abstract] |
Tuesday, June 3, 2014 11:18AM - 11:30AM |
B8.00005: Exploration of the Dissociative Recombination following DNA ionization to DNA$^{+}$ due to ionizing radiation Richard A. Strom, Andrew T. Zimmerly, Vola M. Andrianarijaona It is known that ionizing radiation generates low-energy secondary electrons, which may interact with the surrounding area, including biomolecules, such as triggering DNA single strand and double strand breaks as demonstrated by Sanche and coworkers (\textit{Radiat. Res.} \textbf{157} 227(2002)). The bio-effects of low-energy electrons are currently a topic of high interest. Most of the studies are dedicated to dissociative electron attachments; however, the area is still mostly unexplored and still not well understood. We are computationally investigating the effect of ionizing radiation on DNA, such as its ionization to DNA$^{+}$. More specifically, we are exploring the possibility of the dissociative recombination of the temporary DNA$^{+}$ with one of the low-energy secondary electrons, produced by the ionizing radiation, to be another process of DNA strand breaks. Our preliminary results, which are performed with the binaries of ORCA, will be presented. [Preview Abstract] |
Tuesday, June 3, 2014 11:30AM - 11:42AM |
B8.00006: Electron elastic scattering off high spin atoms: the Cr and Mn case V. Dolmatov, M. Amusia, L. Chernysheva The Cr(...$3d^{5}$$4s^{1}$, $^{7}S$) and Mn(...$3d^{5}$$4s^{2}$, $^{6}S$) atoms belong to the cohort of high spin atoms, owing to their semifilled $3d^{5}$ and $4s^{1}$ (in Cr) subshells. The current understanding of low-energy electron scattering off such atoms is rudimentary. Here, we scrutinize the impacts of electron correlation, exchange, and electron spin-polarization on elastic scattering phase shifts and total cross sections of $\rm e^{-}$ $+$ Cr and $\rm e^{-}$ $+$ Mn scattering, as well as Wigner time delays of the scattering processes in question, in the electron energy interval where most interesting effects occur, $E= 0$--$15$ eV. We also provide an update to our earlier calculated results for $\rm e^{-}$ $+$ Mn scattering [1]. The findings of this work identify some of the most intrinsic properties of electron elastic scattering off semifilled shell atoms. As in [1], a ``spin-polarized'' Hartree-Fock approximation, random phase approximation with exchange, and the Dyson theory for the self-energy part of the Green function of a scattered electron have been blended in together in order to advance into the understanding of electron scattering off semifilled shell atoms.\\[4pt] [1] V. K. Dolmatov, M. Ya. Amusia, and L. V. Chernysheva, Phys. Rev. A \textbf{88} 042706 (2013). [Preview Abstract] |
Tuesday, June 3, 2014 11:42AM - 11:54AM |
B8.00007: Calculations of Stopping Powers for Electron in Bio-molecules A.K.F Haque, M.A. Uddin, A.K. Basak, M.I. Hossain, M. Hasan, F.B. Malik, B.C. Saha Accurate information for the stopping powers (\textbf{SP}s) of various media including various complicated molecules for energetic electrons becomes essential in many areas of current research including health sciences. Few easy to implement formulas have enjoyed much use for atomic targets [1]. Molecular media, especially the bio-molecules, poses stringent test of any available relied theories. A semi empirical model including the accurate density distributions of the media is proposed to investigate complex molecular targets; our calculated \textbf{SP}s for \textbf{H}$_{2}$\textbf{O and C}$_{\mathbf{5}}$\textbf{H}$_{\mathbf{5}}$\textbf{N}$_{\mathbf{5}}$\textbf{O }are found in good agreement with available experimental findings for E $=$1 to 10 GeV region. \\[4pt] [1] A. K. F. Haque, M. a. Uddin, A. K. Basak, M. I. Hossain, M. Hasan, B. C. Saha. and F. B. Malik and, \textit{Electron impact stopping powers for } \textit{atomic and molecular media:} \textit{A simplified semi-empirical model}, \textbf{EPL }(\textit{under} \textit{consideration)} 2014. [Preview Abstract] |
Tuesday, June 3, 2014 11:54AM - 12:06PM |
B8.00008: Direct and indirect transmission of electrons through insulating PET nanocapillaries D. Keerthisinghe, S. Wickramarachchi, J.A. Tanis, N. Stolterfoht, B.S. Dassanayake The transmission of 300--800 eV electrons through insulating PET nanocapillaries has been studied to further understand the mechanism following our earlier work [1]. The measurements were done at Western Michigan University for two samples having the same thickness 12 $\mu$m, but with capillary diameters 100 nm and 200 nm and pore densities 5 x 10$^{8}$ /cm$^{2}$ and 5 x 10$^{7}$/cm$^{2}$, respectively. The samples were coated with a thin layer of gold ($\sim$ 20 nm) to prevent charge up of the sample from the incident beam. The experiment was conducted at energies of 300, 500, and 800 eV for the sample with 100 nm diameters and at 500 and 800 eV for the sample with 200 nm diameters. Observations showed angular distributions with two peaks for both samples [2]. Based on the peak centers, which are related to the sample tilt angles, three different regions were identified as direct, guiding and transition (from direct to guiding). Variation of the FWHM (deg) of the angular distributions and the energy of the transmitted electrons will be discussed for the three regions. \\[4pt] [1] S. Das \textit{et al}., Phys. Rev A \textbf{76} 042716 (2007)\\[0pt] [2] D. Keerthisinghe \textit{et al.,} AIP Conf. Proc. \textbf{1525}, 36 (2013) and references therein [Preview Abstract] |
Tuesday, June 3, 2014 12:06PM - 12:18PM |
B8.00009: Electron Excitation of Tin and Tin ion Lalita Sharma, Rajesh Srivastava There is a great requirement of accurate atomic data of tin and its ions to understand the properties of laser produced tin plasma, one of the sources of extreme ultraviolet (EUV) radiation. The constant efforts are being made under various international programs viz., International SEMATECH's EUV Source Program, Intel Lithography Roadmap etc., to improve the efficiency of the EUV sources which can meet the requirements of high volume manufacturing of commercial chips. For optimizing the efficiency of EUV device the plasma modeling should be accurate which in turn, would rely on the accuracy of atomic data used. In this connection we have undertaken the study of electron impact excitation of Sn and Sn$^{+}$. Since the atomic number of Sn is 50, it is sufficiently heavy atom to manifest relativistic spin -- orbit and exchange effects. Therefore, we have used a fully relativistic distorted wave (RDW) theory to calculate results for cross sections corresponding to various transitions as well as polarization of photons due to decay of excited states of Sn and Sn$^{+}$ In our RDW theory wavefunctions for both, the target electrons and projectile electrons are obtained by solving Dirac equations. Thus the relativistic effects are incorporated in consistent manner to ensure the reliability of the cross section and polarization results which will be presented in detail at the conference. [Preview Abstract] |
Tuesday, June 3, 2014 12:18PM - 12:30PM |
B8.00010: A method to obtain static potential for electron-molecule scattering Rajesh Srivastava, Tapasi Das, Allan Stauffer Electron scattering from molecules is complicated by the fact that molecules are a multi-centered target with the nuclei of the constituent atoms being a center of charge. One of the most important parts of a scattering calculation is to obtain the static potential which represents the interaction of the incident electron with the unperturbed charge distribution of the molecule. A common way to represent the charge distribution of molecules is with Gaussian orbitals centered on the various nuclei. We have derived a way to calculate spherically-averaged molecular static potentials using this form of molecular wave function which is mostly analytic. This method has been applied to elastic electron scattering from water molecules and we obtained differential cross sections which are compared with previous experimental and theoretical results. The method can be extended to more complex molecules. [Preview Abstract] |
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