Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session B8: Invited Session: Low-Energy Collision ApplicationsInvited
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Sponsoring Units: GFB GEC Chair: Thomas M. Miller, Boston College Room: 555AB |
Tuesday, May 24, 2016 10:30AM - 11:00AM |
B8.00001: Plasma Modeling Enabled Technology Development Empowered by Fundamental Scattering Data Invited Speaker: Mark J. Kushner Technology development increasingly relies on modeling to speed the innovation cycle. This is particularly true for systems using low temperature plasmas (LTPs) and their role in enabling energy efficient processes with minimal environmental impact. In the innovation cycle, LTP modeling supports investigation of fundamental processes that seed the cycle, optimization of newly developed technologies, and prediction of performance of unbuilt systems for new applications. Although proof-of-principle modeling may be performed for idealized systems in simple gases, technology development must address physically complex systems that use complex gas mixtures that now may be multi-phase (e.g., in contact with liquids). The variety of fundamental electron and ion scattering, and radiation transport data (FSRD) required for this modeling increases as the innovation cycle progresses, while the accuracy required of that data depends on the intended outcome. In all cases, the fidelity, depth and impact of the modeling depends on the availability of FSRD. Modeling and technology development are, in fact, empowered by the availability and robustness of FSRD. In this talk, examples of the impact of and requirements for FSRD in the innovation cycle enabled by plasma modeling will be discussed using results from multidimensional and global models. Examples of fundamental studies and technology optimization will focus on microelectronics fabrication and on optically pumped lasers. Modeling of systems as yet unbuilt will address the interaction of atmospheric pressure plasmas with liquids. [Preview Abstract] |
Tuesday, May 24, 2016 11:00AM - 11:30AM |
B8.00002: Chiral Sensitivity in the Dissociative Electron Attachment of Halocamphor Molecules Invited Speaker: Joan Dreiling We have demonstrated chirally-dependent molecular destruction when incident longitudinally-spin-polarized (chiral) electrons break bonds in chiral molecules. This chiral sensitivity was observed through an asymmetry in the dissociative electron attachment (DEA) reaction rate with chiral 3-bromocamphor (C$_{\mathrm{10}}$H$_{\mathrm{15}}$BrO) [1]. Such an observation provides an unambiguous demonstration of the idea underlying the Vester-Ulbricht hypothesis [2], which attempts to explain the origins of the homochirality that is observed in many biological systems. While the lack of inversion symmetry in these reactions allows the effects we observe to occur, their dynamic causes are poorly understood [3]. We have further studied the asymmetries in the DEA rates for two additional halocamphor molecules, 3-iodocamphor (C$_{\mathrm{10}}$H$_{\mathrm{15}}$IO) and 10-iodocamphor, in a systematic effort to illuminate the mechanisms responsible for the chiral sensitivity. The DEA signal depends on the sign of the incident electron helicity for a given target handedness in all molecules, and it varies with both the atomic number and the location of the heaviest atom in the molecule. Surprisingly, the DEA asymmetries for 10-iodocamphor, in which the heaviest atom is farther from a chiral center than for the other molecules, produced the largest asymmetries. This work was performed at the University of Nebraska-Lincoln. [1] J.M. Dreiling and T.J. Gay, Phys. Rev. Lett. \textbf{113}, 1181 (2014). [2] T.L.V. Ulbricht and F. Vester, Tetrahedron \textbf{18}, 629 (1962). [3] T.J. Gay, in Advances in Atomic, Molecular, and Optical Physics, \textbf{57}, 157 (Academic Press, Burlington, 2009). [Preview Abstract] |
Tuesday, May 24, 2016 11:30AM - 12:00PM |
B8.00003: Collisions between low-energy electrons and small polyatomic targets of biological relevance Invited Speaker: Leigh Hargreaves Over the last decade, cross section measurements and calculations for DNA prototype molecules have received significant attention from the collisions community, due to the potential applications of this data in modelling electron transport through biological matter with a view to improving radiation dosimetry. Such data are additionally interesting from a fundamental aspect, as small carbon-based molecules are ideal targets for considering effects including target conformation, long-range dynamical interactions and coupling effects between the various degrees of freedom on the scattering properties of the target. At the California State University Fullerton, we have made a series of measurements of the elastic, vibrationally inelastic and electronically inelastic cross sections for a variety of small polyatomic targets, including water and the basic alcohols, ethylene, toluene and several fluorinated alkanes. These processes are important in a range of applications, primarily for modelling electron transport and thermalization, and energy deposition to a biological media. The data were obtained using a high resolution electron energy-loss spectrometer, operating in a crossed beam configuration with a moveable aperture gas source. The gas source design facilitates both an expedient and highly accurate method of removing background signal, and removes uncertainties from the data due to uncertainties in the beam profile. We have also performed scattering calculations employing the Schwinger Multichannel method, in collaboration with the California institute of technology, to compare with our measurements. In this talk, I will present an overview of our recent data and future research plans. [Preview Abstract] |
Tuesday, May 24, 2016 12:00PM - 12:30PM |
B8.00004: Adventures in Gaseous Positronics - An Ultra-High-Energy-Resolution Cryogenic Beam Invited Speaker: Mike Natisin While positron interactions with matter are important in a variety of contexts, many important experiments have been inhibited due to the difficulties encountered in creating beams with narrow energy spreads. This talk focuses on the development of a pulsed positron beam with a total energy spread of 7 meV FWHM; this represents a factor of five improvement over the previous state-of-the-art. Current positron atomic physics experiments rely on high quality beams from buffer gas traps. Although widely used, the physical phenomena operative in beam formation had not previously been fully investigated, and understanding these processes proved crucial to improving beam quality. Experimental measurements and simulation results of positron cooling and beam formation are discussed, with an emphasis on beam energy resolution.\footnote{M. R. Natisin, \emph{et al.}, Phys. Plasmas \textbf{22}, 033501 (2015)}$^,$\footnote{M. R. Natisin, \emph{et al.}, Phys. Plasmas in press (2016)}$^,$\footnote{M. R. Natisin, \emph{et al.}, J. Phys. B \textbf{47}, 225209 (2014)} Using these results, a new cryogenic, trap-based beam system was built. Positrons are cooled to 50 K using a CO buffer gas, resulting in beams with total energy spreads as low as 6.9 meV FWHM, sub-microsecond temporal spreads and beam diameters as small as 1~mm.\footnote{M. R. Natisin, \emph{et al.}, App. Phys. Lett \textbf{108}, 024102 (2016)} Details of this beam system, as well as new experiments that will be enabled by it, will be discussed. [Preview Abstract] |
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