Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V43: Atomic/Molecular Structure and AMO Processes on Surfaces and in Condensed Matter |
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Sponsoring Units: DAMOP Chair: M. Safronova, University of Delaware Room: Baltimore Convention Center 346 |
Thursday, March 16, 2006 11:15AM - 11:27AM |
V43.00001: Oscillating Mechanical Electron Cloud Due to Nuclear Vibration Stewart Brekke The nucleus is vibrating rapidly thereby creating a mechanical sphere of charge as the electrons vibrate due to the moving electric field. The mechanical sphere of charge reconciles the Bohr concept of a circular orbit with Schrodinger's idea of an electon cloud in which the electron is a DeBroglie wave surrounding the nucleus. If the electron is vibrating rapidly in itself as well as due to the vibrating electric field of the nucleus we also have an electon cloud. The resulting mechanical electron cloud is a combination of the two vibrational components. Effectively, there is a vibrating sphere of electronic charge surrounding the nucleus. If r, the distance to the electron from the center of the nucleus minus the Amplitude of nuclear vibration, Acos2($\pi$)ft, then a spherical shell of charge S = 4 ($\pi$)(r - Acos2($\pi$)ft)$^2$ is created. [Preview Abstract] |
Thursday, March 16, 2006 11:27AM - 11:39AM |
V43.00002: Hydrogen Molecule in the Frame of the Three-Body Santilli-Shillady Model Raul Perez-Enriquez, J. Marin, R. Riera We analyze the charge distribution structure of a Hydrogen molecule under the Restricted Three-body Santilli-Shillady Model. Using the stable isoelectronium model, a particle with $M=2\,m_e $ and $q=-2\,e$, we found a compatible ground state of $H_2 $ which overcomes the problems of that developed by Aringazin and Kucherenko. Our model makes use of energies and bond lengths of the ground state of Hydrogen as calculated by Kolos and Wolniewicz in 1968, and assumes that the isoelectronium is restricted to move over a confined region of space around the nuclei. This compatible ground state can be obtained following the Ley-Koo solution to Schr\"{o}dinger equation for Hydrogen molecular ion confined by a spheroidal box and we think it could be used for a better understanding of phenomena associated with correlated electrons in molecular bonds as it is observed in double photoionization and neutron scattering experiments. The self consistency of our results comes right from the correlation between the protons bond length, $R$, and the size of the spheroidal box, $a=\textstyle{1 \over 2}\xi _0 \cdot R$. [Preview Abstract] |
Thursday, March 16, 2006 11:39AM - 11:51AM |
V43.00003: Explicitly Correlated Wavefunctions for Few-Body Problems Frank E. Harris Explicitly correlated wavefunctions enable far more compact, yet accurate descriptions of few-body systems than are possible using basis functions built from orbital products. The most efficient functions of this type contain all the interparticle distances as exponentials. Progress in evaluating the matrix elements for such a basis is reviewed for three and four-body systems, with particular attention to the difficult analytical problems posed by the four-body system and the challenges associated with highly singular integrals in the three-body system (which arise in the computation of relativistic effects). An alternative basis is provided by Gaussians in all the interparticle distances; recent contributions toward systematizing the use of such functions are also reported. Application of the exponential basis to the He isoelectronic series is described; the results differ from those reported by others in that their quality does not decrease with increasing nuclear charge $Z$. This feature permits an improved characterization of the coefficients in the $1/Z$ expansion. Also disscused is the cancellation of divergences in the combinations of individually divergent integrals arising in the treatment of relativistic effects in the He system. [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:03PM |
V43.00004: Lattice Regularized Diffusion Monte Carlo Simulations of iron dimer Michele Casula, Leonardo Guidoni, Sandro Sorella Transition metal compounds play a crucial role in various fields, ranging from biomolecular reactions to magnetic solid state properties. On the other hand, the strong dynamic correlation present in the unfilled d-shell makes the predictions of the density functional theory unreliable and requires the use of post-Hartree-Fock methods, limited however to small systems. The Lattice Regularized Diffusion Monte Carlo (LRDMC) method, recently introduced [M. Casula, C. Filippi, and S. Sorella, Phys. Rev. Lett. 95, 100201 (2005)], seems to be an effective alternative, since it can provide accurate results with a favorable size scaling. One of the main advantages of this framework is the possibility to include non-local potentials in a consistent variational scheme, substantially improving both the accuracy and the computational stability upon previous non-variational diffusion Monte Carlo approaches. Here, we apply the LRDMC framework to the iron dimer, by using a fully optimized Jastrow geminal wave function as guiding state. Despite its simplicity, its neutral and anionic ground states are controversial, and we try to clarify their symmetry by comparing our LRDMC results with experimental spectroscopic data. [Preview Abstract] |
Thursday, March 16, 2006 12:03PM - 12:15PM |
V43.00005: Regionally specific hyperfine polarization of Rb atoms at micron/submicron distance from the Pyrex glass surfaces in optical pumping cells K. Zhao, Z. Wu We made {\it regionally specific} measurement of the hyperfine polarization of Rb atoms in the vicinity ($\sim 10^{-5}\,\rm cm$) of coated and uncoated Pyrex glass surfaces in optical pumping cells. This is in contrast to the previous hyperfine polarization studies, where the quantity measured is the bulk hyperfine polarization, which depends on surface interactions {\it averaged over the entire cell surfaces}. We probe the hyperfine polarization of the Rb atoms in the vicinity of cell surfaces using the evanescent wave of a weak laser beam. We find that the polarization in the vicinity of uncoated surfaces is significantly lower than that in the bulk. The polarization decreases rapidly with decreasing distance from the surface. By contrast, the polarization in the vicinity of a silicone coated Pyrex glass surface is independent of the distance from the cell surface and is equal to the bulk polarization. Regionally specific measurement of the hyperfine polarization as a function of the penetration depth of the evanescent wave allows us to deduce the hyperfine polarization, its normal gradient and normal gradient coefficient at the cell surface. We present the values of these quantities for three representative uncoated cells. [Preview Abstract] |
Thursday, March 16, 2006 12:15PM - 12:27PM |
V43.00006: Q-factor spoiling of a fused silica microsphere Pablo Bianucci, John Robertson, Andreas Muller, C. K. Shih When a planar transparent surface if brought close to a microsphere resonator, the induced leakage will result in a decrease of the Q-factor of the resonant modes. We present a systematic study of the Q-factor spoiling on a fused silica microsphere using a tapered optical fiber as a waveguide and a cleaved fiber as a planar surface. The Q-spoiling is measured as function of the distance between the microsphere and the cleaved fiber. Different modes show quite different deterioration rate for the Q-value as a function of sphere-fiber distance. This Q-decay rate is directly related to the evanescent nature of the cavity modes. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 12:39PM |
V43.00007: Radiation Patterns of Electric Dipoles Close to a Plane Interface LAN LUAN, Paul Sievert, John Ketterson The radiation pattern of an electric dipole is modified when located in the vicinity of a dielectric or metal interface. We have investigated this phenomenon through numerical simulations and direct measurements. Our simulations are based on the Sommerfeld integral formalism. The effects of the dipole position and orientation, the dielectric constants of the media, and the observation position on the radiation pattern for TE and TM modes were studied. On the experimental side, we used fluorescent molecules to simulate the electric dipoles. The angular distribution of the fluorescence emission was recorded. Both our simulations and the experiments showed that the dipole radiation pattern is strongly modified from the free space form. Our results are potentially important for optical signal collection associated with spectroscopic studies of molecules bound to a surface. [Preview Abstract] |
Thursday, March 16, 2006 12:39PM - 12:51PM |
V43.00008: Quadrupole $nd \rightarrow nl$ resonances in valence ns-photoelectron angular distributions from half-filled shell atoms. Valeriy Dolmatov Nondipole photoelectron angular distributions from atoms have become an \textit{ad hoc} topic of intensive research in recent years. To date, such distributions have largely remained unstudied, with a few exceptions, in open-shell atoms in view of difficulties in handling such atoms. Therefore, we have unfolded a theoretical program focusing on studies of nondipole photoelectron angular distributions from open-shell atoms. In the present work, we choose the Mn(3d$^{5}$4s$^{2}$, $^6$S) atom as a case study owing to its relative ``simplicity'' because its open 3d$^{5}$ subshell is only half-filled. We explore features of nondipole angular asymmetries for valence 4s-photoelectrons in a region of $3d \rightarrow nl$($l=0,2,4$) quadrupole resonances. A removal of a 4s electron leaves the Mn atom either in a 3d$^{5}$4s,($^{7}$S) or 3d$^{5}$4s,($^{5}$S) final state. It is found that, due to demonstrated exclusive for a half-filled shell atom electron correlation effects, resonance enhancements of 4s nondipole angular asymmetry parameters depend markedly on final state terms of the atom, both in their magnitudes and shapes, with one of them overshooting the other by almost an order of magnitude at the resonance maximum, and with both of them far overshooting the dipole approximation value of 2. A ``spin-polarized'' RPAE has been employed in this study. [Preview Abstract] |
Thursday, March 16, 2006 12:51PM - 1:03PM |
V43.00009: Cooperative Emission from Semiconductor Quantum Wells in High Magnetic Fields D. H. Reitze, Y. D. Jho, X. Wang, J. Kono, A. A. Belyanin, V. V. Kocharovsky, G. Solomon, X. Wei Stochastically oriented, spectrally-peaked emissions is generated in In$_{0.2}$Ga$_{0.8}$As/GaAs multiple quantum wells (QW). Using intense 150 fs, 775 nm pulses for excitation, we investigate the spatial and temporal characteristics of the emission in dense magneto-plasmas in high magnetic fields (30 T) and at carrier densities approaching 10$^{13}$ cm$^{-2}$. Above a threshold intensity and magnetic field, the emission from Landau levels exhibit anomalous narrow features appearing asymmetrically on the high-energy side of the peaks. An examination of the spot size dependence of emission strength relative to the coherence length, temperature dependence of threshold magnetic field, and differential transmission spectra suggest that the inter-LL emission arises from the spontaneous polarization of the dense magneto-plasma. [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:15PM |
V43.00010: Dielectric Modification of the Casimir force between a gold sphere and a silicon surface Feng Chen, Umar Mohideen The Casimir force (retarded van der Waals force) can become very large at micron and nano distance scales and can affect the performance and fabrication of microelectromechanical (MEMS) and nanoelectromechanical systems (NEMS). Here we demonstrate that it is possible to modify the Casimir force in the microelectromechanical systems, through alteration of the dielectric properties of the silicon boundary. This will open new opportunities for the application of the Casimir force in MEMS and NEMS. This experiment also helps improve our understanding of the Casimir force between dielectric surfaces. [Preview Abstract] |
Thursday, March 16, 2006 1:15PM - 1:27PM |
V43.00011: Analysis of van der Waals Interaction Energies from Quantum Chemistry: Aromatic Clusters and Rare Gas Dimers Stephen Garrison, Inez Gonzalez, Carlos Gonzalez, Manuel Marquez, Edward Lim The weak van der Waals (vdW) interactions in aromatic clusters and rare gas systems are studied using ab initio quantum chemistry and the Hartree-Fock Dispersion (HFD) method. The results, extrapolated to the complete basis set limit and along with comparisons to experiment, are used to understand and explain a fortuitous cancellation of errors in the benzene interaction calculations. Additionally, interesting results are found for the all-electron calculations for argon. [Preview Abstract] |
Thursday, March 16, 2006 1:27PM - 1:39PM |
V43.00012: Energy Distribution of Cluster Assemble with Isomers Songbai Ye, Louis Bloomfield The internal energy of cluster assemble without isomers will be a single-peak distribution in thermal equilibrium. However, if it has several isomers and each isomer has different state density distribution, the internal energy distribution will be structured in certain circumstance. By destroying the equilibrium of isomer populations and observing the building-up of the new equilibrium, we can gain information of the internal energy of the cluster assemble. We can also study the change of the internal energy of the cluster assemble by selectively burning some isomers before we proceed the deplete-probe method. This presentation is based upon work supported by the National Science Foundation under Grant No. DMR-0405203. [Preview Abstract] |
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