Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session PR2: Electron Attachment and Recombination |
Hide Abstracts |
Chair: Murtadha Khakoo, California State University, Fullerton Room: Doubletree Crystal City Crystal Ballroom B |
Thursday, October 4, 2007 8:00AM - 8:15AM |
PR2.00001: Collisions of thermal electrons and electron affinities of SF$_{6}$, C$_{6}$F$_{6}$ and nucleic acids Edward C.M. Chen, Edward S. Chen New electron affinities of the subject molecule are reported from the temperature dependence of thermal electrons measured with the electron capture detector and negative ion mass spectra. The electron affinities are compared with values obtained from anion photoelectron spectra. Multiple negative ion potential energy curves are calculated to consolidate all experimental data The adiabatic electron affinities are: in eV SF$_{5}$, 3.80(12), SF$_{6}$ 2.45(10), C$_{6}$f$_{6}$, 1.40(10), Adenine, 1.08(5), Guanine, 1.60(10), Cytosine, 1.04(5), Thymine, 0.93(5), Uracil, 0.96(5). Excited state for all of these except for guanine have been observed in photoelectron spectra. Parent negative ions of the nucleic acids are observed in mass spectra. The as phase acidities of the deprotonated nucleic acids are reported. [Preview Abstract] |
Thursday, October 4, 2007 8:15AM - 8:30AM |
PR2.00002: Dissociative electron attachment to molecules and unstable species relevant in plasma processing Karola Graupner, Thomas Field Collisions between low energy electrons (0 to 10 eV) and molecules can lead to formation of negatively charged fragment ions by dissociative electron attachment. Electron attachment to plasma species, such as unstable molecules, formed in 2.45 GHz microwave discharges of CS$_2$/He [1], C$_3$F$_6$/He, SF$_6$/He, CH$_4$/He and CCl$_4$/He has been investigated with ERIC (Electron Radical Interaction Chamber), which includes a trochoidal electron monochromator and time-of-flight mass spectrometer. Knowledge of the spectra of negative ions formed as a function of electron energy for unstable molecules may be useful for understanding chemical processes and negative ion formation in plasmas. It may also be possible to identify unstable molecules in gas sampled from plasmas with these characteristic negative ion spectra. \newline \newline [1] Dissociative electron attachment to the unstable carbon monosulfide molecule CS, K. Graupner, T. A. Field and L. Feketeova, New J. Phys, \textbf{8} (2006) 314. [Preview Abstract] |
Thursday, October 4, 2007 8:30AM - 8:45AM |
PR2.00003: Dissociative Electron Attachment to HCN and HNC S.T. Chourou, A.E. Orel HCN and its isomer HNC are known to be among the initial species that drive synthesis of amino acid and protein in interstellar media. Dissociative electron attachment (DEA) to those molecules may thus have an impact on these chemical processes of relevance in astrophysics. Previous experimental and theoretical studies have indicated both $\sigma$ and $\pi$ low-lying resonances. These resonant states are expected to depend on stretching and bending of the molecule and to lead to competing ($CN^-$ + H) and (CN + $H^-$) products. In this work, we present a comparative study of the dissociation mechanism. We carried out electron scattering calculations using the Complex Kohn Variational Method as a function of the three internal degrees of freedom to obtain the resonance energy surface and autoionization widths. We use this as input to a dynamics calculation using the multiconfiguration time-dependant Hartree (MCTDH) approach. We finally compare our DEA cross sections and branching ratios to available findings. [Preview Abstract] |
Thursday, October 4, 2007 8:45AM - 9:00AM |
PR2.00004: Dissociative Electron Attachment to C$_2$HCl V. Ngassam, A.E. Orel Studies of dissociative electron attachment (DEA) to acetylene have shown a dramatic effect as a function of bending the molecule. We have begun an investigation of such multidimensional effect on mono-chloro substitute of hydrocarbons. This work concentrates on chloroacetylene. We study the system in limited dimensionality (\textit{i.e.} as a diatomic) and then contrast this with multidemension studies. We perform electron scattering calculations using the complex Kohn variational method to determine the resonance parameters of this system. The results show a two low lying resonance state of $\Sigma$ and $\Pi$ symmetry. Resonant potential energy surfaces are then constructed as a function of the Cl--C and C--C internuclear distances as well as the Cl--C angle. Stretching the C--H distance does not significantly the position and shape of the resonance states, thus the problem is reduced to 3 active degrees of freedom and the DEA dynamics can be study. The time dependent wave packet method is used to solve the one dimension problem and the Multi-Configuration Time-Dependant Hartree method is used for wavepacket propagation on the computed resonant potential energy surfaces in three-dimension. We discuss the mechanisms leading to dissociation into the product channels and report the computed DEA cross sections. [Preview Abstract] |
Thursday, October 4, 2007 9:00AM - 9:15AM |
PR2.00005: Branching fraction for radiating products of the dissociative recombination of N$_{2}$H$^{+}$, HCO$^{+}$, HOC$^{+ }$, and HNC$^{+}$.. R. Johnsen, M.F. Golde, R. Rosati, D. Pappas, M. Skrzypkowski We present the results of a series of flowing-afterglow studies of the emission spectra produced by dissociative electron-ion recombination (DR) of the ions N$_{2}$H$^{+}$, HCO$^{+}$, HOC$^{+}$, and HNC$^{+}$. Yields of product states were determined by comparing emission band intensities to model calculations of the afterglow. We find that DR of N$_{2}$H$^{+}$ results in emission of the N$_{2}$(B-A) 1$^{st}$ positive system (yield of (19$\pm $8){\%}), but the vibrational distribution indicates that the B-state, in part, is populated by collisional and radiative coupling from other triplet states. DR of HCO$^{+}$ forms the long-lived CO($a ^{3}\Pi )$ state with a yield of (23 $\pm $ 12){\%} while DR of HOC$^{+}$ populates the triplet states CO($a' \quad ^{3}\Sigma ^{+})$ and CO($d \quad ^{3}\Delta)$ with a combined yield of $>$ 40{\%}. Observations of the red and violet CN bands show that DR of HNC$^{+ }$ results in CN(B) and CN(A) with yields of (22$\pm $8){\%} and (14$\pm $5){\%}, respectively. The vibrational distributions of the product electronic states do not seem to follow a simple pattern: In some cases, a monotonic decline with increasing v' is observed that can be understood on the basis of Bates'' impulse model, but other distributions are partially inverted and extend to very high vibrational quantum numbers. [Preview Abstract] |
Thursday, October 4, 2007 9:15AM - 9:30AM |
PR2.00006: Four-Particle Dalitz Plots to Visualize Atomic Break-Up Processes Michael Schulz, Daniel Fischer, Thomas Ferger, Robert Moshammer, Joachim Ullrich We introduce a new method to analyze four-body fragmentation processes, which is basically an extension of Dalitz plots commonly used in particle physics to analyze three-body fragmentation processes. It enables for the first time to present multiple differential cross sections as a function of all four fragments without loss of any part of the total cross section in the integral spectrum. As a first example, the technique is applied to ionization processes in atomic collisions. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700