Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session TF5: Electron-Molecule Collisions |
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Chair: Don Madison, Missouri University of Science and Technology Room: Village Square |
Friday, October 4, 2013 10:30AM - 11:00AM |
TF5.00001: The Dynamics of Dissociative Electron Attachment to Small Polyatomic Molecules Invited Speaker: Thomas Rescigno Dissociative electron attachment (DEA) is a resonant process in which an electron attaches to a molecule to form an unstable anion which subsequently fragments into stable products. DEA to small polyatomic molecules is often governed by complex electronic and nuclear dynamics that is intrinsically multi-dimensional. One-dimensional treatments of the dissociation dynamics based on resonance scattering theory, while often successful in modeling the energy dependence of total cross sections, can mask the complexity of post-attachment dynamics which is revealed by the observed angular dependence of the reaction products. The dissociation evolves on transient anion potential energy surfaces and often involves conical intersections which can result in a complete breakdown of the axial recoil approximation. I will use the examples of DEA to water, carbon dioxide and methanol to illustrate the discussion. [Preview Abstract] |
Friday, October 4, 2013 11:00AM - 11:15AM |
TF5.00002: Electron scattering from H$^{+}_2$ molecule Dmitry V. Fursa, Mark C. Zammit, Jeremy S. Savage, Igor Bray We have extended the {\em ab initio} convergent close-coupling (CCC) method to electron scattering from molecules within the adiabatic approximation. As a first application of the method we consider the most fundamental molecule: molecular hydrogen ion. Experimentally H$^{+}_2$ is produced in a number vibrationally excited states (up to $\nu=18$ in some experiments). Fixed-nuclear scattering calculations have been performed at a number internuclear distances within the CCC method formulated in both spherical and spheroidal coordinates. We have calculated potential energy curve and the required vibrational wave functions, and produced adiabatic approximation cross sections for dissociative excitation and ionisation processes. Comparison with available experimental and theoretical results will be presented. [Preview Abstract] |
Friday, October 4, 2013 11:15AM - 11:30AM |
TF5.00003: Fully Differential Cross Sections for Electron-Impact ionization of aligned molecules Esam Ali, Don Madison, Julian Lower, Erich Weigold, Susan Bellm, Allison Harris, Chuangang Ning Most experiments measuring electron-impact ionization of molecules do not determine the orientation of the molecule at the time of ionization. One way to determine the orientation is to simultaneously ionize the molecule and excite the residual ion to a state that will dissociate. The orientation of the molecule can then be determined by detecting one of the dissociation fragments since the fragments will leave in the direction of orientation. We will present Fully differential cross sections for 176 eV electron-impact dissociative excitation-ionization of oriented H2. These results show a strong dependence of the dissociative ionization-exictation process on the alignment of the internuclear axis with respect to the projectile momentum and emission directions of the scattered and ejected electrons. [Preview Abstract] |
Friday, October 4, 2013 11:30AM - 12:00PM |
TF5.00004: Recent Theoretical Studies of Dissociative Recombination Invited Speaker: Steven Guberman After decades of progress, quantitative agreement between theory and experiment for dissociative recombination (DR) cross sections has remained elusive. Using ab initio potential curves, widths and the MQDT approach (Guberman, 2012) the DR of N2$+$, i.e. N2$+ \quad +$ e$^{-}$ $\to$ N $+$ N, has been analyzed for each of the lowest 5 ion vibrational levels. It is shown that agreement with future high resolution experiments requires that theory account for minor dissociative routes. The cross sections and rate constants are compared to the results of afterglow and merged beam experiments. Good agreement is obtained for the v $=$ 0 rate constant. The only storage ring experiment (CRYRING) to measure cross sections and rate constants found that two unknown ion vibrational distributions gave similar values, (Peterson et al., 1998) leading to the conclusion that the rate constants must be similar for each of the lowest 4 ion vibrational levels. The theory finds that at low electron temperatures the rate coefficients are indeed similar but above room temperature the larger rate coefficient for v $=$ 0 diverges from the others by factors of 2 -- 3. The rate constant for ``elastic'' capture in which the electron is captured but emitted before dissociation has been calculated and allows for the determination of the fraction of collisional captures that lead to DR. For v $=$ 0, DR results from 2 out of every 10 captures. Guberman, S. L., J. Chem. Phys. \textbf{137}, 074309 (2012); Peterson, J. R. et al., J. Chem. Phys. \textbf{108}, 1978 (1998). [Preview Abstract] |
Friday, October 4, 2013 12:00PM - 12:15PM |
TF5.00005: Electron and photon excitation and ionization of tetrahydrofurfuryl alcohol Michael J. Brunger, Luca Chiari, Darryl Jones, Penny Thorn, Zoe Pettifer, George Barbosa da Silva, Gustavo Garcia, Francisco Blanco, F. Ferreira da Silva, P. Limao-Vieira, M.-J. Hubin-Franskin, J. Delwiche We present differential cross section measurements for the low-energy electron-impact excitation of the electronic states of the biologically important molecule tetrahydrofurfuryl alcohol (THFA). Electron energy loss spectra have been measured at selected incident energies between 15 eV and 50 eV and for scattering angles in the 15-90 degrees range using an electron spectrometer. The absolute scale of the inelastic DCSs is set by the elastic DCSs calculated with the Independent Atom Model with Screening Corrected Additivity Rule approach between 1 and 1000 eV. We also present results from VUV photoabsorption and He(I) photoelectron spectra for THFA. A comparison between the results obtained with these different techniques is provided. [Preview Abstract] |
Friday, October 4, 2013 12:15PM - 12:30PM |
TF5.00006: Electron impact total cross sections for components of DNA and RNA molecules Minaxi Vinodkumar, Chetan Limbachiya, Mayuri Barot, Avani Barot, Mohit Swadia Biomolecules, in particular DNA/RNA components are prone to high energy radiation damage which can occur due to primary, secondary or reactive processes [1]. We report electron impact total cross sections (Q$_{T})$, total elastic cross sections (Q$_{el})$ and total inelastic cross sections (Q$_{inel})$ for components of DNA and RNA molecules from threshold to 2000 eV. These components include Uracil (C$_{4}$H$_{4}$N$_{2}$O$_{2})$, Thymine (C$_{5}$H$_{6}$N$_{2}$O$_{2})$, Cytosine (C$_{4}$H$_{5}$N$_{3}$O), Adenine (C$_{5}$H$_{5}$N$_{5})$, Guanine (C$_{5}$H$_{5}$N$_{5}$O) and Phosphoric acid (H$_{3}$PO$_{4})$. We have employed Spherical Complex Optical Potential (SCOP) formalism [2] to calculate the total elastic cross sections, total inelastic cross sections and total cross sections.\\[4pt] [1] L. Sanche ``Radical and Radical Ion Reactivity in Nucleic Acid Chemistry (Greenberg, M. ed.), John Wiley {\&} Sons, Inc. 239 (2009)\\[0pt] [2] Minaxi Vinodkumar and Chetan Limbachiya, Molecular Physics \textbf{111} 213(2013) [Preview Abstract] |
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