Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session R07: Electron and Ion Reactions at Low Energy |
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Chair: Joan Marler, Clemson University Room: Grand D |
Thursday, May 31, 2018 10:30AM - 11:00AM |
R07.00001: Rydberg molecules, electron collisions, and associative ionization Invited Speaker: Chris Greene A mechanism for associative ionization in the reaction between a Rb(nl) Rydberg atom and a ground state Rb atom that forms Rb$_{\mathrm{2}}^{\mathrm{+}}$ will be discussed, along with experimental evidence from the Stuttgart group. This talk will also consider the low energy dissociative recombination reaction in which a colliding electron can destroy a simple diatomic positive ion with surprising efficiency. Time permitting, progress in our studies of negative ion photodetachment processes occurring in the vicinity of Rydberg states with huge positive or negative polarizability will also be addressed. [Preview Abstract] |
Thursday, May 31, 2018 11:00AM - 11:30AM |
R07.00002: Merged Beam Measurements of Mutual Neutralization at Subthermal Collision Energies Invited Speaker: Xavier Urbain We have measured the total cross sections and kinetic energy distributions for the mutual neutralization of a large ensemble of atomic anions and cations with a merged beam apparatus. An unprecedented resolution in the kinetic energy spectra allows us to identify the states of both reactants and products down to their fine structure. Knowing the angular distribution of the products in the laboratory and center-of-mass frame, allows for total, partial, and differential cross sections to be retrieved. Multi-channel Landau-Zener calculations have been performed with an asymptotic method for the evaluation of ionic-covalent coupling matrix elements. The systematic analysis of branching ratios has shed new light on the electron transfer mechanism. These single pass measurements prepare similar studies involving molecular ions, to be performed with the double electrostatic ion storage ring DESIREE operating at cryogenic temperature. [Preview Abstract] |
Thursday, May 31, 2018 11:30AM - 12:00PM |
R07.00003: Electron and Ion Reactions at Low Energies. Invited Speaker: Asa Larson Theoretical studies of low-energy electron-molecule and ion-ion scattering processes require computations of highly excited electronic states. Non-adiabatic effects are crucial to consider and structure calculations are combined with electron scattering calculations. Ab initio and fully quantum mechanical studies limit the investigations to diatomic or triatomic molecular scattering complexes. Often various strictly or quasi-diabatic representations of the electronic states are applied. We have studied various processes such as dissociative recombination, ion-pair formation, dissociative attachment, vibrational or dissociative excitations following electron collisions with diatomic and triatomic molecules. We also investigate the mutual neutralization reaction following collisions of oppositely charged ions. Calculated cross sections and final state distributions are compared with experimental data. Theoretical challenges that remain to be solved will be discussed. [Preview Abstract] |
Thursday, May 31, 2018 12:00PM - 12:30PM |
R07.00004: Kinetics of transient species with cations and electrons at thermal energies. Invited Speaker: Nicholas Shuman Weakly ionized plasma will generally contain some concentrations of transient species, e.g. small fluorocarbon radicals in a discharge through CF4 . Experimental measurements of the kinetics of these species with electrons and with ions are scarce in the literature, in part due to the difficulty in producing and quantifying transient species. We have developed a technique, termed variable electron and neutral density attachment mass spectrometry (VENDAMS), employing a flowing afterglow- Langmuir probe apparatus that provides access to the kinetics of a wide range of radical or otherwise unstable species reacting with electrons or with cations. Rate coefficients and product branching fractions of electron attachment to small fluorocarbon radicals and hydrofluorocarbon radicals have been measured at thermal conditions from 300 – 1000 K. The results are interpreted using a kinetic modeling approach rooted in statistical theory, which allows extrapolation of the results to conditions not accessible by the experiment, including to extreme temperatures, pressures, or non-thermal conditions. The ion- molecule kinetics of small hydrocarbon, fluorocarbon, and hydrofluorocarbon radicals with a number of cations were also studied under thermal conditions. The results show that surprisingly the radical species react less efficiently and with a lower likelihood of long-range charge transfer than similar reactions of stable, closed-shell species with the same cations. The VENDAMS technique is also used to study ion-ion mutual neutralization processes. [Preview Abstract] |
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