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 J07: Applications of Electron and Photon-Molecule Collisions |
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Sponsoring Units: GEC Chair: James Colgan, Los Alamos National Laboratory Room: Grand D |
Wednesday, May 30, 2018 10:30AM - 11:00AM |
J07.00001: Electron-molecule collision calculations for plasma physics applications Invited Speaker: Jonathan Tennyson Plasma models require data on electron driven process for a wide variety of species. Cool plasmas such as those that occur naturally in the Earth's ionosphere and the interstellar medium or those harnessed for a wide variety of technological processes are largely molecular. These molecular plasma include many transient species whose behavior when colliding with electrons is poorly known and hard to characterize experimentally. My group performs calculations which use the fully quantum-mechanical R-matrix method to perform calculations on a variety of plasma problems including rotational excitation of interstellar molecular ions, excitation of fusion plasma edge species and collisions with molecules important for plasma etching. My talk will feature illustrative examples of such applications including: \begin{itemize} \item Rotational excitation and dissociative recombination of the argonium ion (ArH$^+$) which was recently been found to be ubiquitous in diffuse interstellar molecular clouds; \item Development of a radiative-collisional model for BeH/BeD/BeT, a species whose emission spectra is being actively monitored in fusion plasmas; \item An electron chemistry of NF$_3$ and its fragments (NF$_2$ and NF) which are important in remote plasma sources which are being developed for isotropic etching and thin film deposition in microelectronics fabrication. \end{itemize} [Preview Abstract] |
Wednesday, May 30, 2018 11:00AM - 11:30AM |
J07.00002: Molecular data for hydrogen plasmas Invited Speaker: Mark Zammit Low-temperature hydrogen plasmas are ubiquitous throughout the Universe. They exist in fusion plasmas, solar atmospheres, planetary atmospheres, primordial gas clouds, and determined much of the chemistry of the early Universe. To accurately model these plasmas requires a vast amount of atomic and molecular collision data. \\ Recently we have embarked on the projects of calculating \textit{ab~initio} electron- and photon-molecule data of important diatomics. In this talk, I will present our results on the hydrogen molecule $\mathrm{H}_2$, its ion $\mathrm{H}_2^+$, the isotopologues, and discuss possible implications of these new results. \\ To model electron-molecule collisions we have developed the molecular convergent close-coupling method [1-3]. Results from these studies are the first of their kind: calculating cross sections of all electronically driven processes and explicitly demonstrating convergence of the cross sections over a broad range of impact energies. Generally, the results are in good agreement with experiments, however, for some major processes large discrepancies are seen with generally ``accepted" and used data. \\ For the photon-molecule project, we have recently developed our own code with the goal of calculating comprehensive opacity tables that are accurate across the entire range of temperature space, from molecular dominated opacities through to ion dominated opacities. Recently we calculated state-resolved photodissociation cross sections of $\mathrm{H}_2^+$ [4] via the electronically excited states, and investigated isotopic effects. We also explored radiative association via excited states. We close by briefly discussing how the radiative association cross sections computed here may be of use in modeling the formation of anti-hydrogen molecular ions. \\ $[1]$~M. C. Zammit~\textit{et al.}~\textit{Phys.~Rev.~Lett.} {\bf 116}, 233201 (2016) \\ $[2]$~M. C. Zammit~\textit{et al.}~\textit{Phys.~Rev.~A} {\bf 95}, 022708 (2017) \\ $[3]$~M. C. Zammit~\textit{et al.}~\textit{Phys.~Rev.~A} {\bf 90}, 022711 (2014) \\ $[4]$~M. C. Zammit~\textit{et~al.}~\textit{Astrophys.~J.} {\bf 851}, 64 (2017) [Preview Abstract] |
Wednesday, May 30, 2018 11:30AM - 12:00PM |
J07.00003: Ultrafast transient polarization spectroscopy as a sensitive probe of photon-driven excited state dynamics of nitrobenzene. Invited Speaker: Niranjan Shivaram I will discuss a novel approach to measure ultrafast processes in molecules based on the technique of Optical Kerr-effect (OKE) spectroscopy. In conventional OKE spectroscopy, two pulses (drive and probe) with a relative polarization of 45 degrees interact via the third order susceptibility of a medium. The signal generated along the probe direction with a polarization orthogonal to the input probe polarization is measured using a crossed polarizer, resulting in a near-background free, highly sensitive measurement. In our adaptation of the method, we use an additional pulse to first pump the system to an excited state and use the drive/probe pulse-pair to probe the dynamics that follow. We demonstrate this method in liquid Nitrobenzene using a femtosecond ultraviolet pulse as pump and near infrared pulses as drive and probe. We perform this measurement in an optical heterodyne configuration which enhances signal levels in addition to allowing a direct extraction of the non-linear response of the medium. This method has the potential to be more sensitive than transient absorption by about three orders of magnitude without the requirement of resonant transitions to probe the dynamics. [Preview Abstract] |
Wednesday, May 30, 2018 12:00PM - 12:30PM |
J07.00004: Low Energy Electron Scattering from Molecular Hydrogen and Carbon Monoxide Invited Speaker: Murtadha Khakoo We will present measurements of differential cross sections for excitation of the valence states of molecular hydrogen using conventional electron spectroscopy as well as the b-state of molecular hydrogen using electron time-of-flight spectroscopy. Comparisons with the Convergent Close-coupling theory for molecular hydrogen will be made and shows excellent agreement with the b-state and very good with the valence states. We will also present measurements of differential cross sections for excitation of valence and Rydberg states of carbon monoxide from near-threshold for the a-state up to 20 eV and make comparisons with available measurements and theory for excitation of 9 electronic states. [Preview Abstract] |
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