Bulletin of the American Physical Society
2006 73rd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 9–11, 2006; Williamsburg, Virginia
Session BC: Atomic, Molecular, Optical |
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Chair: Adrian Daw, Appalachian State University Room: Williamsburg Hospitality House Yorktown |
Thursday, November 9, 2006 8:30AM - 8:54AM |
BC.00001: Time variation of the fine structure constant $\alpha$ from realistic models of Oklo reactors. C.R. Gould, E.I. Sharapov, S.K. Lamoreaux The topic of whether the fundamental constants of nature vary with time has been a subject of great interest since Dirac originally proposed the possibility that $G_N \sim 1/t_{universe}$. Recent observations of absorption spectra lines from distant quasars appeared to indicate a possible increase in the fine structure constant $\alpha$ over ten billion years. Contrarily, analyses of the time evolution of $\alpha$ from Oklo natural nuclear reactor data have yielded inconsistent results, some indicating a decrease over two billion years while others indicated no change. We have used known Oklo reactor epithermal spectral indices as criteria for selecting realistic reactor models. Reactors RZ2 and RZ10 were modeled with MCNP and the resulting neutron spectra were used to calculate the change in the $^{149}$Sm capture cross section as a function of a possible shift in the energy of the 97.3-meV resonance. Our study resolves the contradictory situation with previous Oklo $\alpha$-results. Our suggested $2 \sigma$ bound on a possible time variation of $\alpha$ over two billion years is stringent: $ -0.11 \le \frac{\Delta \alpha}{\alpha} \le 0.24$, in units of $10^{-7}$, but model dependent in that it assumes only $\alpha$ has varied over time. [Preview Abstract] |
Thursday, November 9, 2006 8:54AM - 9:06AM |
BC.00002: The Quantum, Semiclassical {\&} Classical Monodromy of Hydrogenic Atomic States in Perpendicular and Near Perpendicular External Electric and Magnetic Fields Chris Schleif, John Delos We construct a classical integrable approximation for Hydrogen in perpendicular and nearly perpendicular external electric and magnetic fields and show that for a certain range of field strength ratios and angles, classical action variables can only be consistently defined locally on connected integrable regions of phase space. This effect, called classical Monodromy, is a result of the global organizational structure of the invariant manifolds in the phase space of this approximate system. EBKM quantization of classical actions is then used to construct a lattice of semiclassical eigenstates. For n manifolds containing a sufficient number of eigenstates, the semiclassical spectrum contains a lattice defect whenever the underlying classical system has classical Monodromy. Finally we use standard quantum perturbation theory to produce a quantum spectrum for Hydrogenic states in external fields. We find that for system parameters where the classical Monodromy is present, a lattice defect appears in the spectrum of quantum eigenstates. We find that our classical system accurately predicts all features of this Quantum Monodromy including excellent agreement between the classical bifurcation of a doubly pinched torus into 2 singly pinched tori, and a Quantum bifurcation of the lattice defect from a single [1 2 ; 0 1 ] defect into two distinctive [ 1 1 ; 0 1 ] defects. [Preview Abstract] |
Thursday, November 9, 2006 9:06AM - 9:18AM |
BC.00003: Longitudinal Stern-Gerlach Douglas Higinbotham In 1922 Otto Stern and Walther Gerlach split a beam of silver atoms using a transverse gradient field. This experiment, which lead to the understanding that electrons have intrinsic spin, oddly enough does not work for free electrons due to the interplay between the Lorentz force and Heisenberg uncertainly principle. Recent calculations, Phys. Rev. Lett. 79 (1997) 4517 and Phys. Rev. Lett. 86 (2001) 4508, have shown that a dismissed idea of L. Brillouin from 1928 to use a longitudinal gradient field to minimize the effect of the Lorentz force may in fact be possible. The history of the Stern-Gerlach device will be presented along with the revived ideas for separating a beam of free electrons into its two spin states. [Preview Abstract] |
Thursday, November 9, 2006 9:18AM - 9:30AM |
BC.00004: Using Time of Flight Mass Spectrometry to Determine Temperature James Gleeson, James Cowart, Anthony Calamai, Adrian Daw In support of measurements of rate coefficients and other atomic and molecular parameters for astronomy and astrophysics, we are developing a method of obtaining and analyzing time of flight spectra (TOFS). This is analogous to obtaining temperatures from profiles of optical emission lines. Using a cylindrical RF ion trap, ion clouds were generated by bombarding H$_{2}$ and N$_{2}$ gas at nano-torr pressures with electrons having roughly 100 eV of kinetic energy. The ion clouds were ejected from the trap by applying voltage pulses to the trap end caps, and detected using an electron multiplier. The voltage, rise time, and RF phase of the ejection pulse were varied to obtain either the best charge-to-mass resolution or to obtain the best information on the energy distribution of stored ions. The TOFS produced under these conditions were modeled and simulated using Sim-Ion 7.0 ion optics software. The experiment and simulation data are compared and information pertaining to the kinetic energies of the ions in the generated ion cloud is presented. [Preview Abstract] |
Thursday, November 9, 2006 9:30AM - 9:42AM |
BC.00005: Effects of ion trap electrode geometry on ion storage and extraction James Cowart, James Gleeson, Anthony Calamai, Adrian Daw The ion trap laboratory at Appalachian State University is measuring rate coefficients and other fundamental atomic and molecular parameters for astronomy and astrophysics. To obtain more detailed information on the energy distribution of ions stored in an RF ion trap, a detailed model of the trap has been constructed using IDL and Simion 7.0. Effects of details of the trap electrode geometry on ion storage and the process for ion extraction and detection are presented. [Preview Abstract] |
Thursday, November 9, 2006 9:42AM - 9:54AM |
BC.00006: Photodetachment spectroscopy near the lowest threshold of the S$^{-}$ ion John N. Yukich, James E. Wells Numerous experiments have investigated photodetachment spectroscopy in a magnetic field at the $^{2}$P$_{3/2 }\to \quad ^{3}$P$_{2}$ threshold, also known as the \textit{electron affinity} for S$^{-}$. In this work we have investigated detachment at the $^{2}$P$_{1/2 }\to \quad ^{3}$P$_{2}$ threshold, which is the lowest-lying threshold for the S$^{-}$ ion. Our experimental apparatus includes a Penning ion trap in which the ions are created, trapped and stored. Our observations yield a quantitative measurement for the threshold energy and an indirect measurement for the spin-orbit splitting of the ion. [Preview Abstract] |
Thursday, November 9, 2006 9:54AM - 10:06AM |
BC.00007: Rotational Spectroscopy of the Excited States of Nitric Acid Paul Helminger, Douglas T. Petkie, Ivan Medvedev, Atsuko Maeda, Frank C. De Lucia Because it is an important molecular species in the ozone cycle in the upper atmosphere, nitric acid (HNO3) has been the subject of many studies in both the infrared and in the microwave region of the spectrum. Our microwave studies of the rotational spectrum of nitric acid now includes work on all of the excited states below 1200 cm-1 in energy as well a few states at higher energy, such as the v2 state at 1700 cm-1. Microwave studies of the rotational spectrum of HNO3 in excited vibration states contribute both to a better understanding of this fundamental molecule and to the construction of accurate spectral maps for infrared remote sensing. An overview of our studies of the rotational spectroscopy of the excited states will be presented, including our observation of torsion splitting in a number of states. Our recent progress on the assignment and analysis of transitions other states will also be presented. [Preview Abstract] |
Thursday, November 9, 2006 10:06AM - 10:18AM |
BC.00008: Resonantly Enhanced Multiphoton Ionization Circular Dichroism (REMPICD) Watheq Al-Basheer, Runhua Li, Rodney Sullivan, Richard Pagni, Robert Compton Linear and non-linear circular dichroism of $R$-(+)-3-methylcyclopentanone is reported in the gas and liquid phase. Measurements of (2+1) resonance-enhanced multiphoton ionization circular dichroism (REMPICD) for nozzle-jet expanded molecular beams of the equatorial conformer of $R$-3MCP are presented. Monitoring either mass-selected cations or photo-electrons produced via (2+1) REMPI through the $n \to $ 3s Rydberg transition yielded a REMPICD of +1.5$\pm $ 0.5{\%} [ REMPICD $\equiv $ 2(I$_{L}$ -- I$_{R})$/( I$_{L}$ + I$_{R})$, where I$_{L/R}$ refers to the ion/electron signal for left-/right-circularly polarized light. A racemic mixture of 3-methylcyclopentanone showed no significant CD. The REMPICD is larger and of opposite sign than the 1-photon CD at the $n \to $ 3s transition. It appears that the REMPICD is dominated by the continuum transition. Measurements of 1-photon CD as a function of temperature provides information on the enthalpy difference between the equatorial and axial conformers of 3MCP. Density Function Theory calculations also support these measurements. [Preview Abstract] |
Thursday, November 9, 2006 10:18AM - 10:30AM |
BC.00009: Negative Power Subflows in High Contrast Step-Index Cylindrical Fibers Sergiy Mokhov Single-mode waveguides with high contrast between guiding and cladding refractive indices become experimentally available. Strong modal dispersion of them significantly changes properties of propagation of pulses. The hybrid-mode analysis of step-index cylindrical fiber expresses basic dispersion properties of fibers with high contrast. In this case analitical dispersion relation depends on dimensionless contrast and normalized frequency. It's interesting that the fundamental mode $HE_{11}$ in fiber with contrast more than 2.7 can have the distribution of power flow with regions of negative values. This slightly investigated effect can have some nano-technological applications. The analytic form of dispersion equations for fibers with simple profiles are useful because propagation constants and their derivatives can be calculated with high accuracy. The problem of the coaxial step- index fiber is considered in details. Distortions of transversal electromagnetic fields are stronger due to the presence of the low index inner cylinder so the occurrence of negative power subflows is possible at smaller contrast in comparison with the simple step-index fiber. [Preview Abstract] |
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