Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session T4: Atomic and Molecular Structure, Including in Static Fields |
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Chair: Yuri Ralchenko, National Institute of Standards and Technology Room: Knoxville Convention Center 301E |
Friday, May 19, 2006 10:30AM - 10:42AM |
T4.00001: Measurement of pressure broadening of the 2S-3S transition of $^{7}$Li by noble gases Mark Rosenberry, Kristin Burgess, Kok Win Goh, Michael Reuter, Brian Stewart Doppler-free two-photon spectroscopy offers a unique combination of advantages for line-broadening studies. The narrow lines make resolution of small changes in linewidth more easily observable, while the fact that entire velocity distribution is excited ensures that a thermal distribution at the temperature of the sample is being studied. We have employed this technique in studying line broadening of the 2s-3s state of $^{7}$Li by Ne, Ar, Kr, and Xe. Experimental broadening rates are modeled in the impact approximation using available ab initio potentials. [Preview Abstract] |
Friday, May 19, 2006 10:42AM - 10:54AM |
T4.00002: Precision calculations of atomic properties of Ga and Ga-like ions U.I. Safronova, M.S. Safronova, T.E. Cowan Energies of the $4s^2np_j$ ($n$ = 4-8), $4s^2ns_{1/2}$ ($n$=5- 8), $4s^2nd_j$ ($n$= 4-7), $4s^2nf_{j}$ ($n$= 4-5), and $4s^25g_ {j}$ states in neutral gallium are obtained using relativistic all-order method. Reduced matrix elements, oscillator strengths, and transition rates are determined for the 130 possible $4s^2nl_j-4s^2n'l'_{j'}$ electric-dipole transitions. Electric-quadrupole and magnetic-dipole matrix elements are evaluated to calculate the lifetime of the $4s^24p\ ^2P_{3/2}$ state in Ga-like ions with $Z$ = 30--100. The hyperfine constants $A$ are determined for 28 $4s^2nl_j$ states in $^{69}$Ga~I and $^{71}$Ga~I isotopes. All above mentioned properties are obtained in the relativistic single-double (SD) approximation, where single and double excitations of Dirac-Fock wave functions are included to all orders of perturbation theory. Using SD wave functions, accurate values are obtained for various matrix elements. The resulting data are used to determine transition rates, oscillator strengths, and lifetimes. These calculations provide a theoretical benchmark for comparison with experiment and theory. [Preview Abstract] |
Friday, May 19, 2006 10:54AM - 11:06AM |
T4.00003: The He-He dimer binding energy: A new computational method.. George Rawitscher, Israel Koltracht An iterative method has been developed for calculating negative energy eigenvalues, based on the Lippmann-Schwinger integral equation [1]. A reliable method for finding approximate starting values for the iteration will be described. The He-He dimer is used to test the method, using the He-He TTY potential [2]. Due to the weak binding, the wave function extends out to large distances. For a distance of 3,000 a.u., 208 mesh points suffice to obtain an accuracy of three significant figures for the binding energy, while with 320 mesh points the accuracy is increased to six significant figures. [1] G. Rawitscher and I. Koltracht, ``A new method to calculate Dimer binding energies with an economical number of mesh-points'', submitted for publication. [2] K. T. Tang, J. P. Toennies, and C. L. Yiu, Phys. Rev. Lett. 74, 1546 (1995). [Preview Abstract] |
Friday, May 19, 2006 11:06AM - 11:18AM |
T4.00004: Triple excitations in the relativistic coupled-cluster formalism and calculation of Na properties Sergey Porsev, Andrei Derevianko The coupled-cluster (CC) formalism is a highly-accurate method of atomic, molecular and nuclear structure. We have implemented a CC-inspired relativistic method for univalent atoms that includes a nonperturbative treatment of single and double excitations from the core and single, double, and triple excitations involving valence electron. Triple excitations of core electrons are included in the fourth order of many-body perturbation theory. In addition, we incorporate all-order dressing of lines and vertices of the matrix-element diagrams. The resulting formalism for matrix elements is complete through the fourth order and subsumes certain chains of diagrams in all orders. With the developed method we computed removal energies, magnetic-dipole hyperfine-structure constants, and electric- dipole amplitudes for atomic Na. We find that the removal energies are reproduced within 0.01-0.03\% and the hyperfine constants of the $3s_{1/2}$ and $3p_{1/2}$ states with a better than 0.1\% accuracy. The computed dipole amplitudes for the principal $3s_{1/2} - 3p_{1/2;3/2}$ transitions are in an agreement with 0.05\%-accurate experimental data. Details can be found in the paper: S.G.Porsev and A.Derevianko, Phys. Rev. A 73, 012501 (2006) [Preview Abstract] |
Friday, May 19, 2006 11:18AM - 11:30AM |
T4.00005: Quantitative Theory for Electron-Atom Scattering Colm T. Whelan, Robert K. Nesbet, Jason. Martinez The aim of this work is to develop a general approach to electron and photon impact ionization. This approach should \begin{enumerate} \item be non-perturbative, \item not be restricted to simple systems, \item be straightforward to systematically improve, \item be computationally efficient, \item treat symmetric problems symmetrically. \end{enumerate} \underline {R operator formalism} The concept of an R-matrix has been extended to a general coordinate hyperspace by the introduction of an R-operator, [1]. We have developed an approach to electron-atom scattering within the context of the R-operator formalism. Results will be presented for the Temkin-Poet problem [2, 3] as well as for e-H collisions. [1] R. K. Nesbet, Phys. Rev. B, \textbf{30}, 4230, 1984 [2] A.Temkin, Phys. Rev. A, \textbf{126}, 130, 1962 [3] R. Poet, J. Phys. B, \textbf{13,}2995,1980 [Preview Abstract] |
Friday, May 19, 2006 11:30AM - 11:42AM |
T4.00006: Complete treatment of the non-linear terms in the single-double all-order method Rupsi Chandra, M.S. Safronova, W.R. Johnson The implementation of the single-double (SD) relativistic all-order method yielded accurate results for a number of atomic properties in alkali-metal atoms and other systems with one valence electron. This method is a linearized coupled-cluster method, where single and double excitations of Dirac-Fock wavefunctions are included to all orders of perturbation theory. Partial triples excitations are also included in the SDpT extension of the SD method. However, further progress in the study of fundamental symmetries in heavy atoms calls for the improvement of the current methodology. This work represents a complete restoration of all six non-linear coupled-cluster terms that contribute at the SD level. The contributions of the non-linear terms to various atomic properties is investigated. [Preview Abstract] |
Friday, May 19, 2006 11:42AM - 11:54AM |
T4.00007: $B$-spline calculations of oscillator strengths in noble gases. Oleg Zatsarinny, Klaus Bartschat The $B$-spline box-based close-coupling method [1] was applied for extensive calculations of the transition probabilities in the noble gases Ne, Ar, Kr and Xe for energy levels up to $n$ = 12. An individually optimized, term-dependent set of non-orthogonal one-electron radial functions was used to account for the strong term dependence in the valence orbitals. The core-valence correlation was introduced through multi-channel expansions, which include the $n$s$^{2}n$p$^{5}$, $n$s$n$p$^{6}$ and $n$s$^{2}n$p$^{4}(n$+1)$l$ target states. The inner-core correlation was accounted for by employing multi-configuration target states. Energy levels and oscillator strengths for transitions from the $n$p$^{6}$ ground-state configuration as well as transitions between excited states were computed in the Breit-Pauli approximation. The inner-core correlation was found to be very important for most of the transitions considered. The good agreement with the available experimental data shows that the $B$-spline method can be used for accurate calculations of oscillator strengths for states with intermediate $n$-values, i.e. exactly the region where it is difficult to apply standard MCHF methods. At the same time the accuracy for the low-lying states is close to the accuracy obtained in large-scale MCHF calculations [2]. [1] O. Zatsarinny and C. Froese Fischer, J. Phys. B \textbf{35, }4669 (2002). [2] A. Irimia and C. Froese Fischer, J. Phys. B \textbf{37,} 1659 (2004). [Preview Abstract] |
Friday, May 19, 2006 11:54AM - 12:06PM |
T4.00008: The correlation of nucleon mass to nuclear stability is investigated Eugene Pamfiloff The decay chains and series of unstable isotopes are studied with particular detailed analysis of nuclei masses and the change in mass experienced by individual nucleons of parent, daughter and product isotopes or other emissions. The data shows a direct correlation between the nucleon mass of a stable product nucleus and that of an unstable parent or daughter nucleon during the transition. This suggests that in addition to proton and neutron quantities, nuclear stability is dependent upon specific nucleon mass benchmarks. It also indicates the probability that 238U is the parent of a series of stable and unstable isotopes situated below the Pb threshold with an unambiguous connection to stable 56Fe nucleons. To confirm these conclusions, the natural and artificial alpha emitter isotopes were also evaluated by the meticulous analysis of all nucleon masses relative to the 1H proton. The developed database and system of evaluation allow those decay chain products of uncertain origin to be traced from unstable or stable nuclei back to the immediate source isotope in the series and then to the most probable origin. Often, more than one possible transition source isotope is identified. The system provided good results when tested against the incident and product particles of high and low energy interactions, including events of nuclear transmutation. Every transition to a stable product demonstrates a strong correlation with a specific mass per nucleon benchmark as a third condition of nuclear stability. [Preview Abstract] |
Friday, May 19, 2006 12:06PM - 12:18PM |
T4.00009: Energetics and structural properties of bosonic three-dimensional clusters near threshold D. Blume, G. J. Hanna We treat three-dimensional bosonic clusters with up to N=40 atoms, interacting additively through two-body van der Waals potentials, in the near-threshold regime using the diffusion quantum Monte Carlo method. Our study focuses on super-Borromean systems with N atoms for which all subsystems are unbound. We determine the energetics and structural properties such as the expectation value of the interparticle distance as a function of the coupling strength. It has been shown that the coupling strength $g_N^*$, for which the N-body system becomes unbound, is bounded by the coupling constant $g_{N-1}^*$, for which the next smaller system with N-1 atoms becomes unbound. By fitting our numerically determined ground state energies to a simple functional form with three fitting parameters, we determine the relationship between $g_N^*$ and $g_{N-1}^*$. [Preview Abstract] |
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