Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session T1: Focus Session: Electronic, Atomic, and Molecular Collision Studies |
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Chair: Steven Manson, Georgia State University Room: A601 |
Friday, June 17, 2011 8:00AM - 8:30AM |
T1.00001: Coupling of Photonic and Electronic Spin Catalyzed by Diatomic Molecules Invited Speaker: Recent experiments involving the collisions of polarized photons or polarized electrons with simple diatomic molecules have shown novel ways in which the net spin of electrons can be converted into the net spin of photons following the collisions, or vice versa. I will discuss three recent experiments that illustrate such transformations: the production of nuclear rotational spin in nitrogen molecules excited by polarized electrons with the subsequent emission of polarized photons [1], the excitation by polarized electrons of rotational eigenstates of hydrogen molecules and the subsequent emission of circularly-polarized light [2], and the photolysis of hydrogen molecules by circularly-polarized light yielding photofragments that ``spin the wrong way.'' To our knowledge, these latter measurements represent the first observation of photofragment orientation by direct observation of the polarization of the photofragment fluoresence. \\[4pt] [1] J.W.Maseberg and T.J.Gay, PRA \textbf{79}, 022705 \\[0pt] [2] J.W.Maseberg and T.J.Gay, J.Phys.Conf.Ser.\textbf{212}, 01221 [Preview Abstract] |
Friday, June 17, 2011 8:30AM - 8:42AM |
T1.00002: Theoretical and Experimental Three-Dimensional Triple Differential Cross Sections for Electron Impact Ionization of Neon S.M. Amami, Thomas Pflueger, Don Madison, Xueguang Ren, Arne Senftleben, Alexander Dorn, Joachim Ullrich Three-dimensional triple differential cross sections have been calculated and measured for 61 eV electron-impact ionization of the 2p state of neon. Three-dimensional distributions for the ejected electron will be presented for fixed incident projectile energy and scattering angle. Comparison between theoretical DWBA (distorted wave Born approximation), M3DW (molecular 3-body distorted wave), and experiment will be given for ejected electron energies ranging between 2 eV to 20 eV and scattered projectile angles ranging between 20 degrees and 70 degrees. Although the M3DW is in much better agreement with experiment than the DWBA, the experiment exhibits some structure not predicted by theory. [Preview Abstract] |
Friday, June 17, 2011 8:42AM - 8:54AM |
T1.00003: ABSTRACT WITHDRAWN |
Friday, June 17, 2011 8:54AM - 9:06AM |
T1.00004: Radiative Double Electron Capture in F$^{9+}$ + C Collisions T. Elkafrawy, J.A. Tanis, A. Simon, A. Warczak Radiative double electron capture (RDEC) is a fundamental process involving the capture of two electrons with the simultaneous emission of a single photon. For loosely bound target electrons RDEC can be treated as time reversed double photoionization in which the photon-electron interaction is the origin of electron emission, offering a tool for the exploration of problems in atomic systems such as the electron-electron interaction in electromagnetic fields or the search for a proper description of a two electron-continuum wave function. In the present work, both radiative electron capture (REC) and RDEC were investigated in collisions of 2.21 MeV/u bare and H-like fluorine ions with carbon foils. This experiment was conducted at Western Michigan University using the tandem Van de Graaff accelerator, with the emitted x-rays at 90\r{ } to the beam line measured in coincidence with singly- and doubly-charge changed ions. Current results are compared with previous measurements for O$^{8+}$ + C collisions [1] and with recent theoretical calculations [2-4].\\[0pt][1] A. Simon \textit{et al}., Phys. Rev. Lett. \textbf{104} (12), 123001 (2010) [2] A. I. Mikhailov \textit{et al}., Phys. Lett. A \textbf{328}, 350 (2004) [3] A. I. Mikhailov \textit{et al}., Phys. Rev. A \textbf{69}, 032703 (2004) [4] A. Nefiodov \textit{et al}., Phys. Lett. A \textbf{346}, 158 (2005). [Preview Abstract] |
Friday, June 17, 2011 9:06AM - 9:36AM |
T1.00005: Electron-Nitrogen Collision Processes Relevant to Planetary Atmospheres Invited Speaker: Electron-N$_{2}$ collisions play an important role in the nitrogen-rich upper atmospheres of Titan, Triton, and Earth. Modeling these processes requires accurate laboratory data. Despite the recognized importance of such data, there remained an unsatisfactory degree of consensus among much of the available laboratory collision cross section data. To address this situation, our group has devoted considerable effort over the past decade to improve the status of low energy electron collision data. In doing so, we have measured direct excitation cross sections for at least 17 electronic states of neutral N$_{2}$ and a variety of key UV emission cross sections. Here we review the result of this effort, highlighting how the picture of electron collision processes has evolved, where consensus has been reached and where discrepancies still exist. New electron energy-loss measurements will be presented for excitation of the valence states, with finely spaced ($<$1eV) impact energy increments in the threshold-to-peak region where excitation is not in proportion to the Franck-Condon factors. These data are novel in that they include measurements at fixed electron scattering angles, differential in impact energy over a range of scattering angle. Also, new near-threshold integral cross sections are provided and compared to existing data. [Preview Abstract] |
Friday, June 17, 2011 9:36AM - 9:48AM |
T1.00006: Energy transfer in collisions of atmospheric O and H$_2$ Marko Gacesa, Peng Zhang, Vasili Kharchenko We report new differential and total cross sections calculated quantum mechanically for O($^3$P) + H$_2(v,j)$ reactive collision using the most recent chemically accurate potential energy surfaces for $^3$A$'$ and $^3$A$''$. Reactive state-to-state calculations were performed at energies important for astrophysical environments and planetary atmospheres for total angular momenta up to $J=100$, and non-reactive cross sections were constructed for higher values of $J$. Corresponding differential cross sections were used to construct the kernel of Boltzmann equation and calculate energy relaxation of hot oxygen atoms in collisions with H$_2$. Escape of molecular hydrogen from planetary atmospheres and the role of angular anisotropy of the scattering are also discussed. [Preview Abstract] |
Friday, June 17, 2011 9:48AM - 10:00AM |
T1.00007: Nonlinear pressure shifts of alkali-metal atoms in xenon Bart McGuyer, Tian Xia, Yuan-Yu Jau, William Happer Compact, portable atomic frequency standards are based on the microwave resonance frequencies of alkali-metal atoms in inert buffer gases. The frequency shift of these resonances due to collisions with the buffer gas is known as the pressure shift. We demonstrate that the microwave resonance frequencies of ground-state $^{87}$Rb and $^{133}$Cs atoms have a nonlinear dependence on the pressure of the buffer gas Xe. Previous work has demonstrated a nonlinear dependence in Ar and Kr, but not He and N$_2$, which is thought to be due to the loosely-bound van der Waals molecules that are known to form between alkali-metal and buffer-gas atoms in Ar, Kr, and Xe, but not He and N$_2$. Surprisingly, we find that the nonlinearities in Xe are of the opposite sign to those in Ar and Kr, even though the overall shifts for each of these gases are negative. This discrepancy suggests that though the shifts due to the molecules in Ar and Kr are positive, the shifts due to the molecules in Xe are negative. No nonlinearities were observed in the buffer gas Ne to within our experimental accuracy, which suggests that molecules do not form in Ne. Additionally, we present improved measurements of the shifts of Rb and Cs in He and N$_2$ and of Rb in Ar and Kr. [Preview Abstract] |
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