Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session LT1: Electron-Molecule Collisions |
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Chair: Michael Brunger, Flinders University Room: Doubletree Hotel Pine |
Tuesday, October 18, 2005 1:30PM - 2:00PM |
LT1.00001: Low-Energy Electron-Molecule Collision Experiments Invited Speaker: The talk will report on the recent improvements of the techniques to measure elastic and inelastic electron-molecule cross sections. Emphasis will be given on the measurement of the cross sections as a function of scattering angle over a large angular range using the `magnetic angle changer' (MAC) invented by Frank Read and co-workers, and on the measurements at low energies. It will be shown that measurement of cross sections in general and the use of the MAC device in particular require complex strategies to control instrumental drift and to determine the instrumental response function over wide ranges of energies and scattering angles, and that the results may to some degree depend on the details of these strategies. The procedures will be illustrated with measurement of elastic and vibrational cross sections in N$_2$. The $v=0\rightarrow 1$ cross section in the resonance region was measured in the full angular range $0^\circ - 180^\circ$, elastic cross sections in the range of about $10^\circ - 180^\circ$, the lower limit being dependent on the electron energy. The results agree well with high quality theoretical results of Morrison, Sun and Hao. The integral and momentum transfer cross sections derived from the differential data agree well with swarm data. The talk will then present applications of these experimental techniques to study elastic and vibrational cross sections in NO, CH$_4$, cyclopropane and other molecules. Emphasis will be given on threshold peaks and near threshold structures due to vibrational Feshbach resonances. The vibrational excitation of NO $via$ the low-lying shape resonances will also be presented and compared to the recent theoretical results \{C. S. Trevisan, K. Houfek, Z. Zhang, A. E. Orel, C. W. McCurdy, and T. N. Rescigno, {\it Phys. Rev.} A {\bf 71}, 052714 (2005)\}. [Preview Abstract] |
Tuesday, October 18, 2005 2:00PM - 2:30PM |
LT1.00002: New trends in low--energy electron collisions with molecules Invited Speaker: Experimental studies on electron-polyatomic molecular collisions are reviewed in connection with the plasma processing and environmental issues. Recent developments in electron scattering experiments on differential cross sections (DCSs) are summarized for various processes such as elastic scattering, vibrational, and electronic excitations, including the dissociative attachments as well as the radical formation. Three illustrative examples are described specifically as follows: 1) perfluocarbons as the main feed gases in the plasma etching industry and the need to replaced by alternative compounds that have low global warning potentials, e.g. COF$_{2}$, C$_{3}$F$_{6}$, and $l-$C$_{4}$F$_{6}$; 2) detection of non-emissive CH$_{3}$ radicals via the low-lying electronic states of CH$_{4}$ by electron impact; and 3) the electronic spectra of thymine by electron impact methods, also including H$_{2}$O. This work was supported by the Ministry of Education, Sport, Culture and Technology, the Japan Society for Promotion of Science, the Japan Atomic Energy Research Institute, and the CUP program between Japan and South Korea. In collaboration with Masamitsu Hoshino, Department of Physics, Sophia University, Chiyoda-ku, Japan; Casten Makochekanwa, Department of Physics, Sophia University, Chiyoda-ku, Japan, Graduate School of Sciences, Kyushu University, Japan; Hyuck Cho, Physics Department, Chungnam National University, South Korea. [Preview Abstract] |
Tuesday, October 18, 2005 2:30PM - 3:00PM |
LT1.00003: Physics with Cooled and Trapped Molecular Ions Invited Speaker: Modern techniques developed during the last decade have open several new opportunities to study low energy collision processes between molecular ions and electrons, such as dissociative recombination and electron impact excitation, with the help of fast molecular ion beams. The heavy-ion storage ring technique, together with cold electron beams produced by cryogenically cooled photocathode allow to reach center-of-mass resolution of the order of 500 $\mu$eV, permitting the observation of well separated Rydberg resonances in the recombination process. Also, manipulation and probing of the vibrational and rotational excitation of the stored molecular ions is now made possible with these tools. Observation of the molecular dynamics taking place during theses collisions can be made via three-dimensional imaging detectors. In this lecture, several examples will be shown which demonstrate the advantages of these techniques for simple molecular ions such as HD$^+$ and H$_3^+$. Comparison with recent theoretical calculations will be presented as well. Also, the next generation of experiments which will be performed by the end of this decade using the Cryogenic Storage Ring (CSR) will be described. [Preview Abstract] |
Tuesday, October 18, 2005 3:00PM - 3:15PM |
LT1.00004: Low Energy Electron Scattering from Formic Acid Violaine Vizcaino, Milica Jelisavcic, James Sullivan, Stephen Buckman Formic acid (HCOOH) is the simplest of the organic acids and it is thought that it could play a key role in the formation of simple biomolecules such as glycine and acetic acid in the interstellar medium. We have studied elastic electron scattering from formic acid using a crossed-beam electron spectrometer. Absolute cross sections are obtained using the relative flow technique. Flow rates for HCOOH, and the reference gas He, are measured at a number of temperatures, including both room temperature and 70$^{\circ}$C, in order to investigate the effects of molecular dimers which are thought to dominate at room temperature. Measurements at energies in the range 10-50 eV will be presented at the meeting and compared, where possible, with recent theoretical calculations. [Preview Abstract] |
Tuesday, October 18, 2005 3:15PM - 3:30PM |
LT1.00005: Resonance Processes in Electron-CF Collisions Cynthia Trevisan, Ann Orel, Thomas Rescigno CF radicals are by-products of semiconductor processing reactant gas C$_2$F$_4$ under electron bombardment. Since they are highly reactive and difficult to isolate under laboratory conditions, theoretical calculations are the only practical source for electron-CF collision cross section estimates. We have carried out an extensive set of {\em ab initio} calculations aimed at quantifying the various resonant collision processes that could lead to significant vibrational excitation and/or ion production in e$^-$-CF collisions. Near equilibrium geometry, CF and its negative ion states are similar to NO, which is isoelectronic with CF and which has been the subject of much recent theoretical and experimental study. The binding energy of CF, however, is significantly smaller than that of NO and, unlike NO, there are negative ion states that correlate with both F$^-$+C and F+C$^-$ (N$^-$ does not exist). These differences make for some interesting comparisons and differences between e$^-$-CF and e$^-$-NO cross sections, which will be the focus of this work. [Preview Abstract] |
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