Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session PR4: Electron Collisions |
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Chair: Igor Bray, Curtin University Room: 303 AB |
Thursday, October 15, 2015 1:30PM - 2:00PM |
PR4.00001: Ion Momentum Imaging of Dissociative Electron Attachment to Small Molecules Invited Speaker: Michael Fogle In recent years, low energy dissociative electron attachment (DEA) interactions have been of interest to varying biological and technological applications. To study the dynamics resulting from DEA, we used an ion-momentum imaging apparatus based on the Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) technique in which a molecular beam is crossed by a pulsed electron beam. The beam interaction takes place in a 4$\pi$ pulsed electrostatic spectrometer that collects the anion fragments resulting from DEA. The molecular beam is formed by a supersonic expansion which results in a well-localized and cold target. Using this apparatus we have investigated the DEA dynamics for several small molecules: CO$_2$ at the 4 eV shape resonance and the 8 eV Feshbach resonance; N$_2$O at the 2.3 eV shape resonance; HCCH at the 3 eV shape resonance; and CF$_4$ near the 7 eV resonance. An overview of these experimental ion-momentum results will be compared to ab initio electronic structure and fixed-nuclei scattering calculations to gauge the resulting dynamics driven by DEA. In many cases, conical intersections play a pivotal role in driving the dynamics. Some of these systems exhibit non-axial recoil conditions indicative of a bending dynamics in the transitory negative ion state while others exhibit a direct axial recoil dissociation without any bending. [Preview Abstract] |
Thursday, October 15, 2015 2:00PM - 2:30PM |
PR4.00002: Electron Scattering by biomass molecular fragments Invited Speaker: Marco Lima The replacement of fossil fuels by biofuels from renewable sources may not be a definite answer for greenhouse gas emissions problems, but it is a good step towards a sustainable energy strategy. Few per cent of ethanol is being mixed to gasoline in many countries and in some of them, like Brazil, a very aggressive program has been developed, using, in large scale, flex fuel engines that can run with any mixture of gasoline and ethanol, including 100{\%} ethanol. Important points are how to produce ethanol in a sustainable way and with which technology? Biomass is a good candidate to enhance the first generation (produced from Corn in USA and from sugarcane in Brazil) production towards the so-called second-generation ethanol, since it has cellulose and hemicellulose as source of sugars. In order to liberate these sugars for fermentation, it is important to learn how to separate the main components. Chemical routes (acid treatment) and biological routes (enzymatic hydrolysis) are combined and used for these purposes. Atmospheric plasmas can be useful for attacking the biomass in a controlled manner and low energy electrons may have an important role in the process. Recently, we have been studying the interaction of electrons with lignin subunits (phenol, guaiacol, p-coumaryl alcohol), cellulose components, $\beta $-D-glucose and cellobiose ($\beta $(1-4) linked glucose dimer) and hemicellulose components [2] ($\beta $-D-xylose). We also obtained results for the amylose subunits $\alpha $-D-glucose and maltose ($\alpha $(1-4) linked glucose dimer). Altogether, the resonance spectra of lignin, cellulose and hemicellulose components establish a physical--chemical basis for electron-induced biomass pretreatment that could be applied to biofuel production. In order to describe a more realistic system (where molecules are ``wet''), we have obtained the shape resonance spectra of phenol-water clusters, as obtained previously from elastic electron scattering calculations. Our results, obtained in a simple model (phenol in the presence of one and two water molecules), indicate that the well-known indirect mechanism for hydrogen elimination in the gas phase is significantly impacted on by microsolvation, due to the competition between vibronic couplings on the solute and solvent molecules. This fact suggested how relevant the solvation effects could be for the electron-driven damage of biomolecules and the biomass delignification. We have also discussed microsolvation signatures in the differential cross sections that could help to identify the solvated complexes and access the composition of gaseous admixtures of these species. In a collaboration project involving Australia (within the Brazilian Science Without Borders program), Portugal, Spain and Brazil, we have focused on obtaining theoretical and experimental electronic excitation cross sections of phenol and furfural for 10-50 eV electron impact energies. Convergence on electronic multichannel coupling stands as the biggest challenge to obtain agreement between theory and experiments. In my presentation, I will discuss the current status of this project. [Preview Abstract] |
Thursday, October 15, 2015 2:30PM - 2:45PM |
PR4.00003: Coherence parameter measurements for neon and hydrogen Robert Wright, Leigh Hargreaves, Murtadha Khakoo, Oleg Zatsarinny, Klaus Bartschat, Al Stauffer We present recent coherence parameter measurements for excitation of neon and hydrogen by 50eV electrons. The measurements were made using a crossed electron/gas beam spectrometer, featuring a hemispherically selected electron energy analyzer for detecting scattered electrons and double-reflection VUV polarization analyzer to register fluorescence photons. Time-coincidence counting methods on the electron and photon signals were employed to determine Stokes Parameters at each scattering angle, with data measured at angles between 20 -- 115 degrees. The data are compared with calculated results using the B-Spline R-Matrix (BSR) and Relativistic Distorted Wave (RDW) approaches. Measurements were made of both the linear (P$_{\mathrm{lin}}$ and $\gamma$) and circular (L$_{\mathrm{perp}}$) parameters for the lowest lying excited states in these two targets. We particularly focus on results in the L$_{\mathrm{perp}}$ parameter, which shows unusual behavior in these particular targets, including strong sign changes implying reversal of the angular momentum transfer. In the case of neon, the unusual behavior is well captured by the BSR, but not by other models. [Preview Abstract] |
Thursday, October 15, 2015 2:45PM - 3:00PM |
PR4.00004: Orientation Effects in Excitation-Ionization of Helium A.L. Harris, T.P. Esposito We present fully differential cross sections (FDCS) for electron-impact excitation-ionization of helium when the ionized electron is found outside of the scattering plane. When the final state He$+$ ion is left in a non-spherically symmetric state, such as a p-state, an orientation for the ion can be defined. Using our 4-Body Distorted Wave and First Born Approximation models, we examine FDCS in search of effects due to the orientation of the final state He$+$ ion. [Preview Abstract] |
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