Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Y45: Atom Interactions with Molecules, Surfaces, and X-Rays |
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Sponsoring Units: DAMOP Chair: Han Pu, Rice University Room: A310 |
Friday, March 25, 2011 8:00AM - 8:12AM |
Y45.00001: ABSTRACT WITHDRAWN |
Friday, March 25, 2011 8:12AM - 8:24AM |
Y45.00002: Dissipative Effects on Quantum Sticking Yanting Zhang, Dennis Clougherty Using variational mean-field theory, many-body dissipative effects on the threshold law for quantum sticking and reflection of neutral particles are examined. For the case of an ohmic bosonic bath, we study the effects of the infrared divergence on the probability of sticking and obtain an analytic expression for the rate of sticking as an asymptotic expansion in the incident energy $E$. The low-energy threshold law for quantum sticking is found to be robust with respect to many-body effects and remains a universal scaling law to leading order in $E$. Non-universal many-body effects alter the coefficient of the rate law and the exponent of a subdominant term. [Preview Abstract] |
Friday, March 25, 2011 8:24AM - 8:36AM |
Y45.00003: Breaking Quantum Mirrors with Thermal Fluctuations Ian Goyette, Dennis Clougherty We study ultracold atoms interacting with a surface at finite temperature. For the case where the surface is out of thermal equilibrium with the environment, the asymptotic form of the Casimir-Polder potential decays as an inverse square law and can be either attractive or repulsive, depending on the temperature difference. We analyze the effect of this interaction on the threshold law for quantum sticking, the probability that an atom will stick to the surface $s(E)$ as the incident energy tends to zero. We predict a new threshold law for neutral atoms interacting with a surface out of thermal equilibrium with its environment: $s(E)\sim E^\gamma$ as $E\to 0$ where $\gamma$ ($0\le\gamma\le 1/2$) depends on the strength of the non-equilibrium Casimir-Polder interaction which can be tuned with temperature. [Preview Abstract] |
Friday, March 25, 2011 8:36AM - 8:48AM |
Y45.00004: ABSTRACT WITHDRAWN |
Friday, March 25, 2011 8:48AM - 9:00AM |
Y45.00005: Temperature dependence of the depolarization rates of Ne$^{\ast }$(2p$_{i}$ [J=1]) atoms induced by He atom collisions Vaibhav Khadilkar, Christian Bahrim Our theoretical depolarization rates for the disalignment, disorientation, and alignment relaxation of Ne$^{\ast }$(2p$_{i}$ [J=1]) atoms at temperatures between 10 K and 3000 K are compared with various experiments. We perform quantum close-coupling many-channel calculations using a new model potential for the interaction between Ne$^{\ast }$(2p$_{i}$ [J=1]) and He atoms [1]. We analyze isotropic collisions in a gaseous mixture at thermal equilibrium, and find excellent agreement between our calculations and the experimental data above 77 K [1, 2]. We explain the temperature dependence of the depolarization rates using the anisotropy of the collisional channels [2]. For T $<$ 77 K, our disalignment rates for the Ne$^{\ast }$(2p$_{2}$ [J=1]) and Ne$^{\ast }$(2p$_{10}$ [J=1]) atoms are larger than the experimental data. The experiment predicts a linear variation of the intra-multiplet cross sections to zero-energy. Our calculations indicate that for the 2p$_{2}$ and 2p$_{10}$ states, at low collision energies, the nuclear rotation at large atomic separation has a stronger influence in the molecular Hamiltonian than the electrostatic interaction. This situation does not occur for the 2p$_{5}$ and 2p$_{7}$ states, where the agreement between theory and experiment is found even at 20K [1]. [1] Bahrim C and Khadilkar V 2009 \textit{Phys Rev A} \textbf{79} 042715. [2] Khadilkar V and Bahrim C 2010 \textit{J Phys B }\textbf{43 }(in press). [Preview Abstract] |
Friday, March 25, 2011 9:00AM - 9:12AM |
Y45.00006: Dipole Transitions for the hydrogen molecule using Fully Nonadiabatic Wavefunctions Steven Alexander, R.L. Coldwell Using variational Monte Carlo and simple, explicitly-correlated fully-nonadiabatic wavefunctions we have computed highly accurate trial wavefunctions for the lowest rovibrational state of several states of the hydrogen molecule. With these wavefunctions we have calculated the transition moments for all possible dipole transitions and we compare our results with those from more traditional calculations. [Preview Abstract] |
Friday, March 25, 2011 9:12AM - 9:24AM |
Y45.00007: Formation of the negative molecular ion MH- by radiative association of a neutral molecule M with H- Viatcheslav Kokoouline, Mehdi Ayouz, Maurice Raoult, Olivier Dulieu We consider the formation of negative molecular ions MH$^{-}$ through the reaction of radiative association: M+H$^{-} \quad \to $ MH$^{-}$ + ?$\omega $, where M is a diatomic or triatomic neutral molecule. We present a theoretical approach to calculate the cross-section and the rate constant for the reaction and apply the theory to study formation of molecular ions from H$^{-}$ and neutral molecules abundant in the interstellar medium (ISM): We consider H$_{2}$, CO, and H$_{2}$O as possible candidates to form negative ions. Such ions have never been observed in the ISM. Their eventual observation would serve as a proof of presence of H$^{-}$ in the ISM too. The H$^{-}$ ion cannot be detected directly by the photoabsorption spectroscopy. Supported by Triangle de la Physique contract QCCM and the National Science Foundation grant PHY-0855622 [Preview Abstract] |
Friday, March 25, 2011 9:24AM - 9:36AM |
Y45.00008: Terahertz Time-Domain Spectroscopy of Ices of N$_{2}$, CO$_{2}$, and Ar Bagvanth R. Sangala, Perry A. Gerakines, David J. Hilton We used Terahertz Time-Domain Spectroscopy (THz- TDS) to study thin ice films of N$_{2}$, CO$_{2}$, and Ar from 0.1 -1.6THz. We observed an absorption line for N$_{2}$ ice films at 1.46THz in the temperature range of 10-28K. Ar ice films have absorption lines at 0.47THz and 0.97THz in the temperature range of 10-30K. We observed no absorption line for CO$_{2}$ ice films in the temperature range of 10-40K from 0.1-1.6THz. These results will be helpful in analyzing the data terms from observations of THz radiation from astronomical sources impinging upon interstellar materials. [Preview Abstract] |
Friday, March 25, 2011 9:36AM - 9:48AM |
Y45.00009: Collision-Induced Infrared Absorption by Collisional Complexes in dense Hydrogen-Helium gas mixtures at Thousands of Kelvin Martin Abel, Lothar Frommhold, Xiaoping Li, Katharine L.C. Hunt The interaction-induced absorption by collisional pairs of H$_{2}$ molecules is an important opacity source in the atmospheres of the outer planets and cool stars. The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H$_{2}$--H$_{2}$, H$_{2}$--He, and H$_{2}$--H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin [1]. Laboratory measurements of interaction-induced absorption spectra by H$_{2}$ pairs exist only at room temperature and below. We show that our results reproduce these measurements closely [1], so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures [1]. \\[4pt] [1] Xiaoping Li, Katharine L. C. Hunt, Fei Wang, Martin Abel, and Lothar Frommhold, ``Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin'', International Journal of Spectroscopy, vol. 2010, Article ID 371201, 11 pages, 2010. doi: 10.1155/2010/371201 [Preview Abstract] |
Friday, March 25, 2011 9:48AM - 10:00AM |
Y45.00010: Size dependent ionization dynamics of argon clusters in intense x-ray pulses Sebastian Schorb, M. Swiggers, R. Coffee, M. Messerschmidt, S. Moeller, G. Williams, J. Bozek, T. Osipov, S. Wada, D. Rupp, T. Moeller, C. Bostedt Free Electron Lasers open the door for novel experiments in many science areas ranging from ultrafast chemical dynamics to single shot imaging of molecules. For the success of virtually all experiments with free electron lasers a detailed understanding of the light - matter interaction in the x-ray regime is pivotal. The Linac Coherent Light Source (LCLS) free electron laser in Stanford allows for the first time to study innershell ionization dynamics of intense x-ray pulses on a femtosecond time scale. We performed experiments on the ionization dynamics of Argon clusters at different pulse length using the slotted spoiler foil in the second LCLS bunch compressor [1]. The Auger rate of argon clusters is predicted to be size dependent and lower than in atoms due to delocalization of the valence electrons [2]. We observe a dependence of the ionization dynamics on pulse length and cluster size. The results are discussed and also compared to recent atomic and molecular data from LCLS.\\[4pt] [1] P. Emma et al. PRL 92, 074801 (2004)\\[0pt] [2] U. Saalmann, JM Rost PRL 89, 14 (2002) [Preview Abstract] |
Friday, March 25, 2011 10:00AM - 10:12AM |
Y45.00011: {\it Ab initio} calculations of atomic coherence excited by optical pulses: CEP effects and generation of X-ray radiation Suman Dhayal, Yuri Rostovtsev Recent progress in ultrashort, e.g. attosecond, laser technology allows to obtain ultra-strong fields which can be of the same order of magnitude as the electric field created by an atomic nucleus. Interaction of such strong and broadband field with atomic systems even under the action of a far-off resonance strong pulse of laser radiation should be revisited. As we have shown, such pulses can excite remarkable coherence on high frequency transitions. We have found and analyzed analitical solutions for various pulse shapes. We have developed new mechanisms of efficient atomic coherent excitation by using two-frequency laser pulses and via tunneling through electric fields. We have done {\it ab initio} calculations using TDDFT for several atoms and simple molecules interacting with strong optical fields. We compare efficiency generation with the efficiency of high harmonic generation approach, and discuss the CEP effects and possible applications of the results obtained to cooperative generation of XUV radiation. The efficiency of XUV generation is calculated for particular candidates for XUV radiation such as H (100 nm) and He (50 nm) atoms and H-like ions (Li$^{2+}$ (30 nm), as well as Ar$^{8+}$ and Xe$^{8+}$ (30-50 nm). [Preview Abstract] |
Friday, March 25, 2011 10:12AM - 10:24AM |
Y45.00012: XAS measurements at LCLS: Investigating Electronic Damage at an X-Ray FEL Catherine Graves, David Bernstein, Joshua Turner, William Schlotter, Hermann D\"{u}rr, Andreas Scherz, Joachim St\"{o}hr As X-ray FEL sources such as the LCLS ramp up scientific studies, the damage caused by the intense x-ray pulses has become a central question. X-ray FEL investigations of solid-state materials must consider the change in the electronic system during the x-ray pulse, in contrast to proposed biomolecular imaging experiments which must suppress atomic motion.\footnote{Neutze, R. et. al. Nature 406, 752 (2000).} The potential electronic damage to the system is also amplified in many materials investigations which probe absorption edges. Therefore, a key need of all studies involving materials research with X-ray FELs is to mitigate or overcome the electronic damage when probing the system. We report the first x-ray absorption spectroscopy (XAS) results from LCLS, which show significant line shape changes dependent on the fluence and x-ray pulse length. We employ a technique previously developed at FLASH which also allows us to visualize the beam dispersion.\footnote{Bernstein, D.P. et al. Appl. Phys. Lett. 95, 134102 (2009).} Our spectroscopy results from LCLS demonstrate a safe fluence and pulse length regime at which material investigations can be conducted without perturbing the ground state of the system during the probing x-ray pulse. [Preview Abstract] |
Friday, March 25, 2011 10:24AM - 10:36AM |
Y45.00013: Berry phase-like effect near DOS singularity in continuum models coupled with discrete states Savannah Garmon, Dvira Segal, Ingrid Rotter Threshold effects in a continuum model (cut-off frequency in a waveguide or the band edge in tight-binding chains) may significantly modify the single-particle discrete eigenvalue spectrum resulting from coupled discrete states. Focusing on tight-binding chains as an example we reveal a Berry phase-like effect as the system parameters are adiabatically varied about certain exceptional points (non-analytic points in the eigenvalue spectrum) that are related to the threshold (van Hove) singularity in the density of states. We show that this effect is related to the form of the eigenvalue expansion in the vicinity of the band edge. In particular, for a semi-infinite model with a side-coupled impurity the eigenvalues in this vicinity may be expanded in powers of the coupling $g$, rather than the more usual $g^{2}$. In another example, in the case of an infinite tight-binding chain with a side-coupled impurity (or a two-level atom traveling in an infinite waveguide) the DOS singularity results in a $g^{4/3}$ amplification of the decay width of the resonant state [1, 2]. \\[4pt] [1] Phys. Rev. B \textbf{73}, 115340 (2006). \\[0pt] [2] Phys. Rev. Lett \textbf{94}, 043601 (2005). [Preview Abstract] |
Friday, March 25, 2011 10:36AM - 10:48AM |
Y45.00014: A Novel Geometric Effect of the Sunbeam (NGES) and Geometric Spin Hall Effect of Light (GSHEL) due to the Earth Rotation Sangboo Nam Recently there are reports of NGES\footnote{S. B. Nam, arXiv \textbf{0910.5767} (2009).} based on geometrical optics, and GSHEL\footnote{A. Aiello, et al., Phys. Rev. Lett. \textbf{103}, 100401 (2009).} based on electrodynamics in vacuum. Here, I discuss the nature of NGES, using the Berry notion of the classical parallel transport,\footnote{M. V. Berry, ``Geometric Phases in Physics'' (Ed. by A. Shapere and F. Wilczek, Singapore, 1989) \textbf{pp7-28}.} and present GSHEL due to the earth rotation. For both NGES and GSHEL, the observing frame (detecting plane) should be tilted with respect to the light beam propagation direction. Setups to detect simultaneously both GNES and GSHEL are discussed. Descriptions given here are applicable to any beams such as electronic and atomic beams. [Preview Abstract] |
Friday, March 25, 2011 10:48AM - 11:00AM |
Y45.00015: Observation of a Passive PT Phase Transition A. Guo, C. Furrow, Vas. P. Kunets, S.-Q. Yu , G. Salamo, G.A. Siviloglou, R. El-Ganainy, K.G. Makris, D.N. Christodoulides, D. Duchesne, R. Morandotti, M. Volatier-Ravat, V. Aimez In 1998 Bender and Boettcher discovered that the spectrum of a system with PT-symmetric Hamiltonian can still be entirely real. This subject attracts more and more attention during the last few years. One of the intriguing characteristics of PT-symmetric systems is the possibility of a\textit{ phase transition} beyond which the spectrum ceases to be entirely real. This symmetry breaking occurs suddenly once the imaginary component of the potential exceeds a certain critical level. Here we report the observation of a phase transition in a passive PT-symmetric optical structure once the loss exceeds a certain critical value. This counterintuitive loss-enhanced transmission is purely an outcome of a spontaneous PT symmetry breaking. [Preview Abstract] |
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