Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session PW1: Collisional Processes and Related TopicsLive
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Chair: Zoran Petrovic, Serbian Academy of Sciences and Arts |
Wednesday, October 7, 2020 1:00PM - 1:30PM Live |
PW1.00001: Precision Spectroscopy of Trapped Yb$^+$ in Search for Dark Matter Invited Speaker: Vladan Vuletic Recently it has been proposed to search for particles outside the Standard Model (SM) in an intermediate mass range (100 eV to 100 MeV) by means of precision isotope shift spectroscopy on narrow optical transitions. We perform such measurements on two quadrupole S$\rightarrow$D transitions and one octupole S$\rightarrow$F transition for five bosonic isotopes of Yb$^+$ with an accuracy below 1kHz, and observe nonlinearities in the corresponding King plots. Such a nonlinearity can indicate physics beyond the SM, or higher-order effects within the SM. Our data indicate that there are at least two distinct sources of nonlinearity. We identify the second-order field shift as the leading-order effect within the SM for Yb$^+$, and discuss possibilities for the other source of nonlinearity. In the future, more precise measurements on more transitions available for Yb$^+$ and Yb, in combination with improved electronic-structure calculations, can be used to distinguish between effects within and outside the SM.\\ \\ $^1$ This work was performed in collaboration with I. Counts, J. Hur, D.P.L. Aude Craik, H. Jeon, C. Leung, J. Berengut, A. Geddes, A. Kawasaki, L. Caldwell, and W. Jhe. It is supported by the NSF. [Preview Abstract] |
Wednesday, October 7, 2020 1:30PM - 1:45PM Live |
PW1.00002: The Role of Transverse Momentum in Electron Vortex Beam Ionization Collisions Alexander Plumadore, Allison Harris The recent experimental realization of electron vortex beams (EVB) has prompted numerous proposed applications in fields from electron microscopy to control and manipulation of individual molecules. These new beams have many unique characteristics, such as transverse momentum and quantized orbital angular momentum. Despite the growing interest in applications of EVBs, there is a limited understanding of their fundamental interactions with matter at the atomic scale. Collisions between EVBs and atomic targets can provide insight into these interactions. I present fully differential cross sections for the ionization of ground and excited state atomic hydrogen using EVBs. I show that the projectile's transverse momentum can significantly alter the ionized electron angular distributions in both the scattering plane and the full three-dimensional geometry. Additionally, the ionized electron's ejection angle can be controlled by the vortex opening angle, a feature unique to vortex projectiles. Finally, I demonstrate that the inherent uncertainty in the vortex projectile's momentum transfer leads to a broadening of the classical binary peak, making signatures of the target electron density more readily observable and can be used to infer target structure information. [Preview Abstract] |
Wednesday, October 7, 2020 1:45PM - 2:00PM Live |
PW1.00003: Ionization of Two-Electron Targets by Electron Vortex Beam Allison Harris In the last decade, a new type of electron wave packet has been experimentally realized that has transverse linear momentum and non-zero orbital angular momentum. Known as electron vortex beams (EVBs), these particles have many proposed applications, such as the control and rotation of nanoparticles and improved resolution in electron microscopy. Unfortunately, very little is known about how EVBs interact with individual atoms, and there are no experimental results yet for collisions between EVBs and atoms. There is also very little theoretical work on this topic, with only a handful of studies to date for EVB collisions with hydrogen atoms. If EVBs are to be used for any of the proposed applications, it is crucial to understand how they interact with atoms on a fundamental level. We present ionization cross sections for EVB projectiles colliding with two-electron targets and examine whether EVBs can be used to probe electron correlation effects. [Preview Abstract] |
Wednesday, October 7, 2020 2:00PM - 2:15PM Live |
PW1.00004: Electron recombination of CH$^+ $ and its rotational state dependence Daniel Paul, K. Blaum, J. G\"ock, M. Grieser, F. Grussie, R. von Hahn, N. Jain, C. Krantz, H. Kreckel, C. Meyer, D. M\"ull, O. Novotn\´{y}, F. Nuesslein, S. Saurabh, V. Schmidt, P. Wilhelm, A. Wolf, S. George, \´{A}. K\´{a}losi, X. Urbain, D.W. Savin Molecular cations in the interstellar medium (ISM) are used to trace the properties of diffuse interstellar clouds, out of which stars and planets are formed. These cations can be destroyed by dissociative recombination (DR) with electrons. Laboratory studies of DR are needed to understand molecular evolution in space. Here we have studied DR of CH$ ^+ $, which is of particular interest for understanding the diffuse cloud dynamics. In the electrostatic cryogenic storage ring CSR, CH$ ^+ $ in their lowest rovibrational states can be stored for DR studies at ISM-relevant conditions. Using merged ion and electron beams in an electron cooler, low energy (meV) collisions can be studied. Here we report experimental DR rate coefficient measurements for CH$^+ $, including new results at ISM-relevant meV collision energies. We furthermore studied the rotational state dependence of the DR rate coefficient. [Preview Abstract] |
Wednesday, October 7, 2020 2:15PM - 2:30PM Live |
PW1.00005: Endothermic electron attachment to N$_{\mathrm{2}}$O. Thomas M. Miller, Jordan C. Sawyer, Brendan C. Sweeny, Shaun G. Ard, Albert A. Viggiano, Nicholas S. Shuman Rate constants for dissociative electron attachment (DEA) to N$_{\mathrm{2}}$O yielding O$^{\mathrm{-}}$ have been measured as a function of temperature from 400-1000 K. In the 400-600 K range, upper limits are given. The data from 700 -1000 K follow Arrhenius behavior described by 2.4 x 10$^{\mathrm{-8}}$ exp(-0.29 eV / kT) cm$^{\mathrm{3}}$ s$^{\mathrm{-1}}$. The activation energy derived from the Arrhenius plot is equal to the endothermicity of the reaction. However, calculations at the CCSD(T)/CBS level suggest the lowest energy crossing between the neutral (linear) and anion (bent) surfaces lies 0.6 eV above the N$_{\mathrm{2}}$O equilibrium geometry, 0.3 eV above the endothermicity of the DEA. Kinetic modeling under this assumption is in modest agreement with the experimental data. The data are best explained by DEA occurring below the lowest energy crossing of the neutral and valence anion surfaces via vibrational Feshbach resonances. The latter were earlier observed directly by Allan and Skallck\'{y} (J. Phys. B. \textbf{36}, 3397, 2003). [Preview Abstract] |
Wednesday, October 7, 2020 2:30PM - 2:45PM |
PW1.00006: Electron collision cross sections for molecules Satyendra Pal, Manoj Kumar Indispensable input for modelling processes in plasma physics involves the complete cross section data sets for all interactions processes. Compilation of these data includes elastic and all inelastic processes (electronic and vibrational excitation, partial and total ionization, dissociative electron attachment, etc.) Data are needed for ground state species as well as metastables and other excited atomic particles and/or radicals. [1-2]. We present the calculations for the ionization cross sections and the averaged energy of the secondary electrons released in the partial ionization of the C$_{\mathrm{2}}$H$_{\mathrm{2}}$ molecule by electron impact. The JK semi empirical formulation is employed to evaluate the cross sections in the energy range ionization threshold to 1 keV. We have also derived the cross sections in the higher energy range upto 10 keV using Bethe analysis [3-4]. The evaluated results show the good comparison with other available experimental and theoretical results. \textbf{References} \textbf{[1] }B.P. Marinkovi \textit{et al.; J. Phys.: Conf. Ser. }\textbf{86 (}2007) 012006. \textbf{[2]} H. Kubo, Proc. 3rd International Conference on Atomic and Molecular Data and Their Applications, Eds. D. R. Schulz, P. S. Krsti\'{c} and F. Own by AIP Conference Proceedings \textbf{636} (2002) 161. \textbf{[3]} S. Pal et al.; \textit{J. Phys. Chem}.$ A$ \textbf{123 }(2019) 4314. \textbf{[4]} S. Pal et al.; \textit{Rad. Phys. Chem}. \quad \textbf{173 }(2020) 108877. this text with your abstract body. [Preview Abstract] |
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