Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session C2: Focus Session: Molecular Spectroscopy |
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Chair: Ben McCall, University of Illinois-Urbana Champaign Room: Imperial Center |
Wednesday, May 26, 2010 2:00PM - 2:30PM |
C2.00001: Laser-cooled atomic ions as tools for molecular ion spectroscopy Invited Speaker: Kenneth Brown Laser cooled ions in linear Paul traps are an ideal tool for studying gas phase atomic and molecular ions at very low temperatures. The large trapping depth and the wide mass acceptance range allows the simultaneous trapping of different ion species for long times. The laser cooled ions sympathetically cool other ion species in the trap through the Coulombic interaction. At cold temperatures the ions will form an ordered structure, a Coulomb crystal. This presents an opportunity to heat the crystal with one ion and detect that heating with another. Our work is focused on using this effect to non-destructively detect molecular spectra by changes in the laser-cooled atomic fluorescence. We will compare our technique to two similar procedures: resonance enhanced multi-photon dissociation in Coulomb crystals and quantum logic spectroscopy. [Preview Abstract] |
Wednesday, May 26, 2010 2:30PM - 3:00PM |
C2.00002: Studies of Photosynthetic Energy and Charge Transfer by Two-dimensional Fourier transform electronic spectroscopy Invited Speaker: Jennifer Ogilvie Two-dimensional (2D) Fourier transform electronic spectroscopy has recently emerged as a powerful tool for the study of energy transfer in complex condensed-phase systems. Its experimental implementation is challenging but can be greatly simplified by implementing a pump-probe geometry, where the two phase-stable collinear pump pulses are created with an acousto-optic pulse-shaper. This approach also allows the use of a continuum probe pulse, expanding the available frequency range of the detection axis and allowing studies of energy transfer and electronic coupling over a broad range of frequencies. We discuss several benefits of 2D electronic spectroscopy and present 2D data on the D1-D2 reaction center complex of Photosystem II from spinach. We discuss the ability of 2D spectroscopy to distinguish between current models of energy and charge transfer in this system. [Preview Abstract] |
Wednesday, May 26, 2010 3:00PM - 3:12PM |
C2.00003: Precision Spectroscopy of Nanoparticles Frank Li, Robert Schafer, Ching-Ting Hwang, Steven Ruggiero, Carol Tanner We describe a new approach for characterizing nanoparticles in suspension using laser transmission spectroscopy. Our apparatus precisely measures light transmission as a function of wavelength from the near UV to the near IR. The transmittance versus wavelength is inverted using a theoretical model to obtain particle size, geometry, and density information. The precision of our measurements allows us to determine both the particle size distribution and the absolute number of particles with diameters ranging of $\sim$5 nm to $\sim$3000 nm with $\sim$1 nm resolution. The size range of applicability is comparable to that of dynamic light scattering, but with approximately six orders of magnitude higher sensitivity (down to $\sim$1000 particles/mL). The technique also allows us to determine the length and width of rod shaped particles including biological objects. We will present results for a variety of systems including metal, polystyrene, and metal-oxide particles, and organisms including viruses and bacteria. [Preview Abstract] |
Wednesday, May 26, 2010 3:12PM - 3:24PM |
C2.00004: Quantum defect analysis of $\rm{H_3^+}+\rm{e^-}$ system Jia Wang, Chris Greene The neutral triatomic hydrogen molecule ($\rm{H_3}$) plays an important role in astrophysics because its cation form $\rm{H_3^+}$ acts as a proton donor in chemical reactions occurring in interstellar clouds. As the simplest triatomic neutral molecule, $\rm{H_3}$ also attracts fundamental interest. Treating the system of $\rm{H_3}$ molecule as a Rydberg electron attaching to a $\rm{H_3^+}$ ion, we carry out \emph{ab initio} study of the system with quantum defect theory, improving on some approximations used in existing theory. [Preview Abstract] |
Wednesday, May 26, 2010 3:24PM - 3:36PM |
C2.00005: Potential energy and dipole moment surfaces of H$_3^-$ molecule Olivier Dulieu, Mehdi Ayouz, Romain Gu\'erout, Jacques Robert, Viatcheslav Kokoouline A new potential energy surface for the electronic ground state of the simplest triatomic anion H$_3^-$ is determined for a large number of geometries. Its accuracy is improved at both short and large distances compared to previous studies. The permanent dipole moment surface of this state is also computed for the first time. Nine vibrational levels of H$_3^-$ and fourteen levels of D$_3^-$ are obtained, bound by at most $\sim 70$cm$^{-1}$ and $\sim 126$cm$^{-1}$ respectively. These results should guide the spectroscopic search of the H$_3^-$ ion in cold gases (below 100K) of molecular hydrogen in the presence of H$^-$ ions. [Preview Abstract] |
Wednesday, May 26, 2010 3:36PM - 3:48PM |
C2.00006: Calculation of potential curves for the $X^2 \Sigma_{u}^+$ and $A^2 \Sigma_{g}^+$ states of Be$_{2}^+$ : Existence of a double minimum Sandipan Banerjee, John Montgomery, Jason Byrd, Harvey Michels, Robin C\^ot\'e We report \textit{ab initio} calculations performed on the ground $X^2 \Sigma_{u}^+ $ and $A^2 \Sigma_{g}^+$ states of the Be$_{2}^+$ dimer. We have analyzed the ground $X^2 \Sigma_{u}^+ $ state and predict the location of all bound vibrational levels. We have also found two local minima, separated by a large barrier, in the otherwise expected repulsive $A^2 \Sigma_{g}^+$ state. Bound vibrational levels have been calculated for both wells. Spectroscopic constants, Frank-Condon factors, transition dipole moments and lifetimes of these levels have also been calculated. For the \textit{ab initio} calculations we have used a full valence CI , taking into account core-core and core-valence correction separately. We have also predicted some of the long-range van der Waals coefficients by extrapolating our \textit{ab initio} data at large separations. [Preview Abstract] |
Wednesday, May 26, 2010 3:48PM - 4:00PM |
C2.00007: Large scale valence-bond calculations on diatomic molecules: Aspects of spectral compression Peter W. Langhoff, Michal Ben-Nun, Jeffrey Mills, Kyle Rollin, Michael Bromley, Jerry Boatz, Gordon Gallup Progress is reported in performing large scale valence-bond calculations of the ground and electronically excited Born-Oppenheimer eigenstates of diatomic molecules. A code suite for this purpose has been devised which combines spin-free methods in enumerating electronic configurations in terms of the standard tableau functions devised by one of us (GG - Crunch Code) with an efficient Slater-orbital-based integrals package (Smiles Code) modified for present purposes. Slater orbitals are employed in the forms of standard valence basis sets supplemented with diffuse terms, Sturmian sets with high powers of the radial coordinate, and even-tempered sets with low radial powers. Previously devised (Stieltjes) methods are employed to compress the resulting large SCF spectra to obtain reduced numbers of configurations which can nevertheless describe the complexities of Rydberg-valence mixing and avoided crossings common in excited diatomic eigenstates. The calculated results are of spectroscopic interest and also form the basis of a recently devised exact-pair atomic spectral method for {\it ab initio} calculations of polyatomic molecules, the implementation of which is facilitated by the use of a valence-bond description of the interacting atomic pairs. [Preview Abstract] |
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