Bulletin of the American Physical Society
2005 Joint Spring Meeting Ohio Section of APS and the Southern Ohio Section of AAPT
Friday–Saturday, April 8–9, 2005; Dayton, OH
Session D1: Atomic and Molecular Physics |
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Chair: Paul Wolf Room: SC 320 |
Saturday, April 9, 2005 8:00AM - 8:12AM |
D1.00001: Measurements of Total Cross Sections of the n=2 Excitation of Helium from the Impact of 10-25 keV Protons G.S. Hodges, J. Kang, J.D. Thomas, T.J. Kvale, D.G. Seely Absolute, total cross sections of the n=2 excitation of helium by intermediate-energy proton impact are measured using the energy-loss experimental technique. The incident proton beam is accelerated to kinetic energies of 10-25 keV, and is focused into a target cell containing helium gas at room temperature. A hemispherical energy analyzer is used to measure the energy-loss spectra of the incident and scattered proton beams. The excitation cross sections are determined by measuring the amplitudes of the energy-loss peaks corresponding to excitation of the n=2 states of helium. These measurements are compared to theoretical results, including the First Born, Distortion, Glauber, VPS, and Multi-State Impact Parameter Approximation methods. The calculations that incorporate many-state calculation methods such as the Multi-State Impact Parameter Approximation are in reasonable agreement with the present data, suggesting that strong coupling between states must be considered in intermediate-energy, multi-electron ion-target collision systems. [Preview Abstract] |
Saturday, April 9, 2005 8:12AM - 8:24AM |
D1.00002: Two-Photon Polarization Spectroscopy of atomic Cs over the $6s^{2}S_{1/2}\rightarrow6p^{2}P_{3/2}\rightarrow9d^{2}D_{5/2}$ transition Morgan J. Welsh, Seda Kin, Jacob D. Hinkle, S. Burcin Bayram An experimental investigation of collisional depolarization of the atomic cesium $6s^{2}S_{1/2}\rightarrow 9d^{2}D_{5/2}$ two- color two-photon polarization spectrum with Ar buffer gas has been made. In the vicinity of the$6s^{2}S_{1/2}\rightarrow6p^{2} P_{3/2}\rightarrow9d^{2}D_{5/2}$~stepwise resonances the dependence of the Ar pressure revealed strong depolarization on the polarization spectrum. Measurements of the linear polarization degree were made with the first laser tuned to resonance and the second laser tuned within a $\pm~11$ cm$^{-1}$ range over the final state. In the absence of collisions, the measurements of the polarization spectrum is in agreement with calculations. The polarization measurement on the $6s^{2}S_{1/2} \rightarrow6p^{2}P_{3/2}\rightarrow9d^{2}D_{5/2}$ transition and an overview of the experimental techniques of our results are also presented. [Preview Abstract] |
Saturday, April 9, 2005 8:24AM - 8:36AM |
D1.00003: A theory of the N-clock Michael Crescimanno, Irina Novikova, David Phillips, Alexander Zibrov, Ron Walsworth There is great current interest in developing compact, robust atomic clocks with low power consumption and fractional frequency stability better than a part per trillion. In recent years, significant progress toward this goal has been achieved using coherent population trapping (CPT) resonances in atomic vapor. An alternative to the CPT clock scheme is the N-resonance clock, an all-optical three-photon-absorption resonance (in Rb vapor) discovered in 2002. I review the current state of the experimental characterization of the N-resonance, and describe a preliminary comparison between these data and a theoretical (quantum-optics based) model. [Preview Abstract] |
Saturday, April 9, 2005 8:36AM - 8:48AM |
D1.00004: Intensity Calculations of CO2 Molecule using Schwenke PES Kausar Yasmin Due to its strong opacity in the IR region, CO$_{2}$ has a major impact of the Earth's atmosphere and the climate. Spectroscopic investigation of CO$_{2}$ will enable scientists develop an understanding of the impact of human induced and natural changes on the Earth's atmosphere. Results will aid the prediction of weather and climate changes and help inhibit the development of Greenhouse effect. Computations of line intensity of CO$_{2}$ were carried out using the Schwenke potential energy surface$^{1}$ and dipole moment surface$^{2}$. Computations were done using the SCF$^{3}$ and the CCSDT$^{4}$ models. Results were compared with the data listed in Hitran96$^{5}$. [Preview Abstract] |
Saturday, April 9, 2005 8:48AM - 9:00AM |
D1.00005: Non-Adiabatic Dynamics of B + H$_{2}$ David Weeks, Lachlan Belcher A description of the non-adiabatic molecular dynamics of B + H$_{2}$ requires knowledge of the derivative coupling terms usually ignored in the standard Born-Oppenheimer approximation. These coupling terms are functions of the nuclear degrees of freedom, and for three body dynamics calculations, Jacobi coordinates are often employed because they separate the asymptotic Hamiltonian. On the other hand, code we use to compute derivative coupling terms produces output in Cartesian coordinates. The derivative coupling terms must therefore be transformed to Jacobi coordinates using the Jacobian matrix of the Jacobi to Cartesian transformation equations. This procedure is somewhat complicated by an ambiguity in the choice of the overall rotation coordinate in the plane containing the B and H$_{2}$ nuclei. This ambiguity is exacerbated by the fact that many choices of overall rotation angle will yield the same derivative coupling term with respect to the overall rotation coordinate, while at the same time producing disparate results for the derivative coupling term with respect to the Jacobi angle between the H$_{2}$ bond and the line between the B atom and H$_{2}$ center of mass. We discuss this ambiguity and its resolution using a collinear two body problem, and apply the resolution to the B + H$_{2}$ system to obtain derivative coupling terms and associated diabatic surfaces suitable for dynamics calculations. [Preview Abstract] |
Saturday, April 9, 2005 9:00AM - 9:12AM |
D1.00006: Modeling DNA unzipping in the presence of bound proteins Farhat Habib, Ralf Bundschuh Unzipping Force Analysis of Protein Association (UFAPA) is a novel technique to investigate protein-DNA interactions by mechanically unzipping DNA. We computationally investigate the limits of this technique under quasi-static conditions. We find the minimum binding energy of a protein for which the protein can be detected using this technique and the minimum distance between the binding sites of two proteins of varying binding energies that can be resolved unambiguously with this technique. [Preview Abstract] |
Saturday, April 9, 2005 9:12AM - 9:24AM |
D1.00007: Diffusion in Entangled Polymer Solutions: Constraint Release E. von Meerwall, J. Randall, S.-Q. Wang We have used the proton pulsed-gradient spin-echo NMR method to measure the self-diffusion D of entangled polybutadienes (PBD) in tetrachloromethane at 70$^{\circ}$C, in order to elucidate the origins of the departure of the molecular-weight (M) exponent of D from the reptational -2.0, and to characterize any differences between melt and solution behavior. M(PBD) ranged from 12 kDa to 100 kDa; PBD concentration (volume fraction ) v was 0.350, 0.422, and 0.514. Entanglement ratios R were calculated as M/M$_{e}$(v), where for PBD M$_{e}$(1) = 4.5 kDa and M$_{e}$(v) = M$_{e}$(1)/v$^{1.2}$, yielding a range of R between 2 and 25. Preliminary results, plotted in the form log (DM$^{2}$v$^{1.2})$ \textit{vs.} log R, adhere to a master curve with slope near -1, suggesting at most modest differences from the known behavior of melts. The relatively rapid approach to the melt asymptote, near R = 20, supports our earlier contention that constraint release rather than contour length fluctuation is the cause of the observed M-exponent of D. Further work, using solutions of binary blends based on high-M PBD, is in progress. [Preview Abstract] |
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