Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session C5: Laboratory Astrophysics and Molecular Collisions |
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Chair: Hossein Sadeghpour, ITMAP Room: Fairfield |
Tuesday, June 9, 2015 2:00PM - 2:12PM |
C5.00001: Atomic Uncertainties and their Effects on Astrophysical Diagnostics Robert Sutherland, Stuart Loch, Adam Foster, Randall Smith The astrophysics and laboratory plasma modeling community have been requesting meaningful uncertainties on atomic data for some time. This would allow them to determine uncertainties due to the atomic data on a range of plasma diagnostic quantities and explain some of the important discrepancies. In recent years there have been much talk, although relatively little progress, on this for theoretical cross section calculations. We present here a method of generating ``baseline'' uncertainties on atomic data, for use in astrophysical modeling. The uncertainty data was used in a modified version of the APEC spectral emission code, to carry these uncertainties on fundamental atomic data through to uncertainties in astrophysical diagnostics, such as fractional abundances and emissivities, providing uncertainties on line ratios. We use a Monte-Carlo method to propagate the uncertainties through to the emissivities, which were tested using a variety of distribution functions. As an illustration of the usefulness of the method, we show results for oxygen, and compare with an existing line ratio diagnostic which has a currently debated discrepancy. [Preview Abstract] |
Tuesday, June 9, 2015 2:12PM - 2:24PM |
C5.00002: New measurement scheme to investigate low energy charge transfer in H $+$ H$_{2}^{+}$ V.M. Andrianarijaona The merged-beam apparatus at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, can reliably access low energy charge transfer in H $+$ H$_{2}^+ \to $ H$^{+} + $ H$_{2}$ and is able to benchmark the total cross section at 200 to under 0.1 eV/u, but is not equipped with a device that would provide the ro-vibrational state distribution of the primary molecular ions. A new experimental scheme, which will allow to upgrade the heretofore only total absolute cross section measurements to vibrationally resolved cross section measurements and will make comparison to state-to-state calculations (PRA \textbf{67} 022708 (2003) possible, will be presented. [Preview Abstract] |
Tuesday, June 9, 2015 2:24PM - 2:36PM |
C5.00003: Uncertainties in X-ray Opacities: Investigating Problems in Precision Modeling of Laboratory and Astrophysical Plasmas Chris Orban, Mark Schillaci, Franck Delahaye, Sultana Nahar, Marc Pinsonneault, Paul Keiter, Katie Mussack, Anil Pradhan Despite significant experimental and theoretical advances in our understanding of x-ray opacities that were gained in the mid-1990s, there remain important discrepancies between experimental and theoretical opacity models that impair efforts to model laboratory and astrophysical systems such as stars and inertial confinement fusion experiments. I will briefly describe a few different projects that I contribute to in efforts to both test and improve opacity models. Specifically, I have compared theoretical opacities developed by the Opacity Project collaboration to experiments at the Sandia Z pinch. I also collaborate on an opacity-related laser experiment led by the University of Michigan that will be conducted at the OMEGA laser in April 2015. Finally, I will discuss, from an astrophysical point of view, the question of how precise opacity models and tabulated opacity data need to be in order to adequately model main sequence stars. [Preview Abstract] |
Tuesday, June 9, 2015 2:36PM - 2:48PM |
C5.00004: Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Pb II N. Heidarian, R.E. Irving, A.M. Ritchey, S.R. Federman, D.G. Ellis, S. Cheng, L.J. Curtis, W.A. Furman Interpreting astronomical observations of atomic ions requires knowledge of their oscillator strengths and transition rates. Also, in order to understand the atomic structure for these ions, experimental lifetimes are necessary to confirm theoretical predictions. We present the results of lifetime measurements taken with the Toledo Heavy-Ion Accelerator using beam-foil techniques on levels of astrophysical interest in Pb II producing lines of 1203.6 {\AA} and 1433.9 {\AA} ($6s6p^{2}$ \ $^{2}D_{3/2}$ and $6s^{2}6d$ \ $^{2}D_{3/2}$, respectively). Oscillator strengths are derived from the lifetimes, and our experimental results will be compared with theoretical calculations obtained by others as well as astronomical observations. The measurements may guide us toward understanding the relativistic effects involved in these energy levels better. [Preview Abstract] |
Tuesday, June 9, 2015 2:48PM - 3:00PM |
C5.00005: Predicting high-$j$, high-energy collisional rate coefficients for the H-CO system using ultracold scattering calculations Kyle Walker, Lei Song, Benhui Yang, Gerrit Groenenboom, Ad van der Avoird, Balakrishnan Naduvalath, Robert Forrey, Phillip Stancil Collisional excitation rate coefficients of carbon monoxide with light colliders such as H, H$_{2}$, He, and electrons are necessary to produce accurate models of many astrophysical environments. CO, the second most abundant molecule in the universe after molecular hydrogen, has an excitation temperature of just $\sim$5.5 K for its lowest rotational transition, and so it can be collisionally excited to high rotational levels in moderately energetic environments. However, in these regions it is not appropriate to assume a thermal population of levels, and therefore collisional rate coefficients must be provided to model the non-thermal gas. We present a zero-energy scaling technique for predicting rate coefficients for CO($v=0,j$) deexcitation induced by H for temperatures below 3000 K for transitions from $j=1-70$ to all lower $j'$ levels, where $j$ is the rotational quantum number. We use explicit quantum scattering calculations and our predicted rates to form the most extensive set of collisional excitation rate coefficients for the H-CO system. [Preview Abstract] |
Tuesday, June 9, 2015 3:00PM - 3:12PM |
C5.00006: Quantum reaction dynamics of ultracold O + OH collisions Brian Kendrick, Jisha Hazra, Gagan Pradhan, Naduvalath Balakrishnan Quantum scattering calculations of the O + OH($v=0$, $j=0$) $\to$ H + O$_2$($v'=0-3$, $j'$) reaction are presented for the electronically adiabatic ground state $^2A''$ potential energy surface of HO$_2$. A numerically exact three-dimensional time-independent scattering method based on hyperspherical coordinates is used to compute rotationally resolved reaction probabilities, cross sections, and non-thermal rate coefficients. Total and vibrationally resolved scattering results are also presented. The scattering calculations span a wide range of collision energies between ultra-cold ($1.16\,\mu$K) and thermal ($298$ K) and include several values of total total angular momentum $J=0-3$. Interesting enhancements in the ultra-cold cross sections are observed for many of the transitions which are attributed to the presence of quantum resonances associated with the HO$_2$ complex. [Preview Abstract] |
Tuesday, June 9, 2015 3:12PM - 3:24PM |
C5.00007: Tunable inelastic collisions between magnetically trapped hydroxyl radicals (OH) Hao Wu, David Reens, Tim Langen, Goulven Qu\'em\'ener, Jun Ye We experimentally study collisional properties of cold polar hydroxyl (OH) molecules, which are directly loaded from a Stark-decelerated beam into a strongly confining permanent magnet trap. The OH molecule is both magnetically and electrically polar, which enables the tuning of inelastic collisions as a function of an applied electric field. Based on the experimental data and detailed simulations of the in-trap evolution we find that the OH two-body loss rate depends not only on the magnitude of the magnetic and electric fields, but also on their relative angles. This provides an important step towards a quantitative understanding of the inelastic collisional property and for further evaporative cooling of the molecular sample. [Preview Abstract] |
Tuesday, June 9, 2015 3:24PM - 3:36PM |
C5.00008: Dynamics of Dissociative Electron Attachment to Methane T.N. Rescigno, N. Douguet, S. Fonseca, A.E. Orel, D.S. Slaughter, A. Belkacem We present the results of a theoretical ad experimental study of dissociative electron attachment (DEA) to CH$_4$. The total DEA cross section is dominated by a single broad peak centered near 10 eV, leading predominantly to H$^-$/CH$_4$ and CH$_2^-$/CH$_4$ dissociation channels. We will present evidence that both of these ion channels result from excitation of a triply degenerate Feshbach resonance (doubly excited negative ion state) of $^2T_2$ symmetry whose parent is the lowest excited triplet state of the neutral molecule. We will present calculated angular distributions based on analysis of the entrance amplitudes obtained from the results of complex Kohn scattering calculations along with experimentally measured angular distributions obtained using the COLTRIMS method. [Preview Abstract] |
Tuesday, June 9, 2015 3:36PM - 3:48PM |
C5.00009: Dissociative Electron Attachment Dynamics in the Nucleobase Uracil and Related Molecules Daniel Slaughter, Yosuke Kuriyama, Yu Kawarai, Yoshiro Azuma, Carl Winstead, Vincent McKoy, Thorsten Weber, Ali Belkacem We report the dynamics of dissociative electron attachment (DEA) in the biologically-relevant molecule uracil and the diazines pyrazine and pyrimidine. Our DEA reaction microscope [1] consists of a 3D momentum-imaging spectrometer, a pulsed low-energy electron gun and an effusive gas target. The experimental approach allows the measurement of kinetic energy and angular distributions of ionic fragments produced by DEA, in some cases elucidating the total kinetic energy release following two-body breakup. By comparison of calculations of the electron attachment probability in the molecular frame with measured ion angular distributions, we determine that one of the uracil anion resonances could be a Feshbach resonance [2] and we compare the dynamics of the dissociation of the uracil anion with the diazines.\\[4pt] [1] Adaniya et al. Review of Scientific Instruments 83 (2) 023106 (2012)\\[0pt] [2] Kawarai et al. The Journal of Physical Chemistry Letters 5 (21) 3854 (2014) [Preview Abstract] |
Tuesday, June 9, 2015 3:48PM - 4:00PM |
C5.00010: Calculation of Molecular Shape Resonances Using Grid Based Exterior Complex Scaling and N$^2$-Term Separable Potentials Brant Abeln, Thomas N. Rescigno, C. William McCurdy A novel approach employing Exterior Complex Scaling (ECS) and discrete grid methods is used to calculate molecular resonance energies and widths for the $^2\Pi_g$ shape resonance state of N$_2^{-}$ and $^2\Pi_u$ shape resonance of CO$_2^{-}$. These calculations are performed using a Finite Element Discrete Variable Representation (FE-DVR) in prolate spheroidal coordinates with an atomic center placed at each of the foci of the coordinate system, thereby preserving the cusp condition at those sites. A separable approximation to the interaction potential is made from the matrices of the nuclear attraction, direct and exchange operators generated by an existing quantum chemistry structure code in a Gaussian basis. These potentials are then represented on our ECS FE-DVR grid allowing the calculation of complex-valued resonance energies. The method is demonstrated here in the static-exchange approximation. [Preview Abstract] |
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