Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session T7: Spectroscopy, Lifetimes, Oscillator StrengthsFocus
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Chair: Marianna Safronova, University of Delaware Room: 553AB |
Friday, May 27, 2016 8:00AM - 8:24AM |
T7.00001: Apker Award Talk: Atomic Beam Measurement of the Indium $6p_{1/2}$ Scalar Polarizability Invited Speaker: Benjamin Augenbraun We report on the first measurement of the scalar polarizability of the indium $6p_{1/2}$-excited state using two-step laser spectroscopy in an atomic beam. This is one in a series of precise atomic structure measurements by the Majumder lab at Williams College, which serve as stringent tests of $\textit{ab initio}$ calculation methods for three-valence-electron systems. We stabilize a laser to the indium $5p_{1/2}\rightarrow6s_{1/2}$ 410 nm transition and scan a second laser across the $6s_{1/2}\rightarrow6p_{1/2}$ 1343 nm transition. The two laser beams are overlapped and interact transversely with a collimated atomic beam of indium. Two-tone FM spectroscopy allows us to observe the small ($<$1 part in $10^3$) IR absorption, and characteristic sideband features in the RF-demodulated lineshape provide built-in frequency calibration. Application of DC electric fields up to 20 kV/cm give rise to Stark shifts of order 100 MHz. Because our group has previously measured the difference in polarizabilities within the 410 nm transition, we can determine the $6p_{1/2}$ polarizability with no loss of precision. Preliminary results are in excellent agreement with recent theoretical calculations and can be used to infer accurate values for the indium $6p$-$5d$ matrix elements. [Preview Abstract] |
Friday, May 27, 2016 8:24AM - 8:36AM |
T7.00002: Advances in Low-Frequency 3-color Broadband Coherent Raman Spectroscopy of Condensed Phase Samples Laszlo Ujj Low-frequency dispersive spontaneous Raman spectroscopy is a very useful method to measure phonon frequencies in crystals or characterize collective vibrational motions of macromolecules. The coherent version of the method has not been fully explored yet. It is shown here that the 3-color Broadband Coherent Raman scattering can be a very powerful extension to not only gas phase but condensed phase low frequency (5-500 cm$^{\mathrm{-1}})$ vibrational measurements with large frequency separation between the narrowband and broadband radiation generating the signal. The spectral measurements presented here used volumetric Brag filters for the first time to record coherent Raman spectra. Specific spectral analysis using model independent methods to derive the vibrational information is also presented. The technic can be extended to measure electronic resonance enhanced spectra by tuning only the frequency of the narrowband laser close to the electronic transition frequencies. This makes the method suitable for coherent Raman microscopy. The polarization properties of the signal is also explained and experimentally verified. [Preview Abstract] |
Friday, May 27, 2016 8:36AM - 8:48AM |
T7.00003: Effective three-particle interactions in atoms with partly filled f-shell Mikhail Kozlov, Elena Konovalova, Anna Viatkina, Marianna Safronova Three particle forces are known to be very important in nuclear physics. In atoms such forces appear between valence electrons in the second order of many-body perturbation theory due to the exchange interaction with the core. Usually their contribution to the valence energy is very small, of the order of few inverse centimeters. However, for atoms and ions with partly filled d and f shells the overlap between valence and core electrons may be large. This leads to significant enhancement of the effective three particle interactions. In Ti II (ground configuration (GC) 3d$^2$4s) these interactions change binding energy by few hundred inverse centimeters [Berengut et al., J. Phys. B, {\bf 41}, 235702 (2008)]. In Ce I (GC 4f5d6s$^2$) these interactions contribute few thousand inverse centimeters. Three particle forces are also important for highly charged ions with low-lying f shell, such as Pr$^{9+,10+}$, Nd$^{10+,11+}$, and Sm$^{13+}$. These ions may have narrow optical transitions [Safronova et al., Phys. Rev. Lett., {\bf 113}, 030801 (2014)] and are now considered for the new generation of optical clocks. [Preview Abstract] |
Friday, May 27, 2016 8:48AM - 9:00AM |
T7.00004: Relativistic atomic data for Rb-like tungsten U. I. Safronova, A. S. Safronova, P. Beiersdorfer Accurate calculations of the atomic properties of Rb-like W$^{37+}$ are needed for studying high energy density plasma as well as for magnetic fusion applications. In this work, we have calculated energy levels, radiative transition probabilities, and autoionization rates for [Ni]$4s^24p^6nl$, [Ni]$4s^24p^54l'nl$ ($l'=d, f, n$ = 4-7), [Ni]$4s4p^64l'nl$,($l'=d, f, n$ =4-7), [Ni]$4s^24p^55l'nl$ ($n$ = 5-7), and [Ni]$4s4p^646l'nl$ ($n$ =6-7) states in Rb-like tungsten (W$^{37+}$) using the relativistic many-body perturbation theory and the Hartree-Fock-relativistic method. Branching ratios and intensity factors were calculated for satellite lines, and dielectronic recombination rate coefficients were determined for the [Ni]$4s^24p^6nl$ ($n$=4-7) singly excited states, as well as for the [Ni]$4s^24p^54dnl$, [Ni]$4s^24p^54fnl$, [Ni]$4s4p^64dnl$, [Ni]$4s24p^64fnl$, ($n$ = 4-6), and [Ni]$4s^24p^55l'5l$ doubly excited nonautoionizing states. Contributions from the [Ni]$4s24p^64fnl$ ($n$ = 6 - 7), [Ni]$4s^24p^55l'nl$ ($n$ = 5 - 6), and [Ni]$4s^24p^56l'nl$ $n$ = 6 - 7) doubly excited autoionizing states are evaluated numerically. Contributions from high-n states (n $\leq$ 200) were determined by using a scaling procedure and found to be very important for high temperatures. [Preview Abstract] |
Friday, May 27, 2016 9:00AM - 9:12AM |
T7.00005: Observation of vibrational overtones by single molecule resonant photodissociation Gang Shu, Ncamiso Khanyile, Kenneth Brown Molecular ions sympathetically cooled by a chain of laser-cooled atomic ions are ideal for performing high-precision molecular spectroscopy with applications in astrochemistry and fundamental physics. The same system can be coupled with a broadband laser to perform survey spectroscopy and discover new molecular transitions. Here we present our results using three-ion chains of Ca$^{+}$ and CaH$^{+}$ to observe vibrational transitions via resonance enhanced multiphoton dissociation detected by Ca$^{+}$ fluorescence [1]. Based on theoretical calculations, the observed peaks are assigned to two vibrational overtones corresponding to transitions from the ground vibrational state, $\nu \quad =$ 0, to the excited vibrational states, $\nu \quad =$ 9 and $\nu \quad =$10. Our method allows us to track single molecular events, and it can be extended to handle any molecule by monitoring normal mode frequency shifts to detect the dissociation. [1] N. B. Khanyile, G. Shu, and K. R. Brown, Nat. Comm.~\textbf{6}, 7825~(2015) [Preview Abstract] |
Friday, May 27, 2016 9:12AM - 9:24AM |
T7.00006: Two-electron R-matrix approach to calculations of potential-energy curves of long-range Rydberg molecules Michal Tarana, Roman \v{C}ur\'ik We introduce a computational method developed for study of long-range molecular Rydberg states of such systems that can be approximated by two electrons in a model potential of the atomic cores [1]. The method is based on a two-electron R-matrix approach inside a sphere centered on one of the atoms. The wave function is then connected to a Coulomb region outside the sphere via a multichannel version of the Coulomb Green's function. This approach is applied to a study of Rydberg states of Rb$_2$ for internuclear separations $R$ from 40 to 320 bohrs and energies corresponding to $n$ from 7 to 30. We report bound states associated with the low-lying $^3P^o$ resonance and with the virtual state of the rubidium atom that turn into ion-pair-like bound states in the Coulomb potential of the atomic Rydberg core. The results are compared with previous calculations based on single-electron models employing a zero-range contact-potential [2] and short-range modele potential [3]. [1] M. Tarana and R. \v{C}ur\'ik, Phys. Rev. A 93, 012515 (2016). [2] C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour, Phys. Rev. Lett. 85, 2458 (2000). [3] A. A. Khuskivadze, M. I. Chibisov, and I. I. Fabrikant, Phys. Rev. A 66, 042709 (2002). [Preview Abstract] |
Friday, May 27, 2016 9:24AM - 9:36AM |
T7.00007: The atom in a molecule: Implications for molecular structure and properties Peter Langhoff, Jeffrey Mills, Jerry Boatz The apparent impossibility of meaningful assignments of indistinguishable electrons to particular atomic nuclei in a molecule seemingly precludes quantum-mechanical definition of fragment atomic Hamiltonian operators. Structural symmetry, conformations, and isomers, as well as the electronic energies and properties of constituent atoms are accordingly perceived as ill defined. Here we provide assignments of electrons to atoms in molecules and define their energies and properties. A separable Hilbert space in the form of orthonormal (Eisenschitz-London) outer-products of atomic eigenstates facilitates assignments of electrons to particular atomic nuclei and also provides support for totally antisymmetric solutions of the Schr\"odinger equation. Self-adjoint atomic operators within a molecule are shown to have Hermitian matrix representatives and physically significant expectation values in molecular eigenstates. Nuanced descriptions of molecular structures and properties emerge naturally from this representation in the absence of additional subjective conditions, including the interplay between atomic promotion and interaction energies, atomic hybridization and charge apportionment, and atomic-state entanglements upon dissociation, attributes revealed by illustrative calculations. [Preview Abstract] |
Friday, May 27, 2016 9:36AM - 9:48AM |
T7.00008: Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Sn~{\sc ii} Negar Heidarian, Richard Irving, Steven Federman, David Ellis, Song Cheng, Larry Curtis In order to understand the atomic structure for atomic ions, experimental lifetimes are necessary to confirm theoretical predictions. Also, interpreting astronomical observations of atomic ions requires knowledge of their oscillator strengths and transition rates. We present the results of lifetime measurements taken with the Toledo Heavy-Ion Accelerator using beam-foil techniques on levels of interest in Sn~{\sc ii} producing lines at 1811.2 {\AA} and 1699.4 {\AA} ($5s5p^{2}$ \ $^{2}D_{5/2}$ and $5s5p^{2}$ \ $^{2}D_{3/2}$, respectively). Oscillator strengths are derived from the lifetimes, and our experimental results will be compared with our MCDHF calculations using the development version\footnote[2]{P. J{\"{o}}nsson et al., The Computational Atomic Structure Group (2014)} of the GRASP2K package\footnote[3]{P. J{\"{o}}nsson et al., Comput. Phys. Commun. 184, 2197 (2013)} as well as the latest calculations done by others. [Preview Abstract] |
Friday, May 27, 2016 9:48AM - 10:00AM |
T7.00009: Detection of precise quantum defects of the 6snd, 6sng and 6sni Rydberg states of Ytterbium. Fathima Niyaz, Jirakan Nunkaew, Thomas Gallagher We use a selective field ionization technique to observe the microwave transitions of Ytterbium Rydberg states, from the 6s(n$+$3)d states to the 6sng and 6snh states for 27$\le $n$\le $33. We also observe the microwave transitions from 6snd to 6s(n$+$1)d for states 33$\le $n$\le $38. Our measurements and previous 6snd to 6s(n$+$1)d measurements give precise values for the 6snd quantum defects which indicate the presence of a previously undetected perturbation in the series. This work has been supported by the U. S. Department of Energy, Office of Basic Energy Sciences. [Preview Abstract] |
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