Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session G11: Focus Session: Promises and Challenges in Chemical Dynamics IV |
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Sponsoring Units: DCP Chair: Sunita Satyapal, Department of Energy Room: Baltimore Convention Center 303 |
Tuesday, March 14, 2006 8:00AM - 8:12AM |
G11.00001: Phase and curvature Curt Wittig It is known that geometric phases play important roles in atomic and molecular science, from the Aharonov-Bohm effect including flux quantization to the Born-Oppenheimer approximation and its conical intersections. When judged from a geometrical perspective, these and related phenomena can be assigned the common parentage of quantum holonomy on curved surfaces. Moreover, this perspective can be extended to larger arenas. For example, adiabatic transport of a state in phase space is nonzero if and only if [$x$, $p$] is nonzero. This yields a curvature that is equal to $\hbar ^{-1}$. This talk will explore additional aspects of geometric phase: (i) the origin of the curvature in parameter space imposed by $\hbar $, and therefore by the existence of quantum mechanics; and (ii) the relationship of the curvature to matrix elements, $e.g.$, between which kinds of states. [Preview Abstract] |
Tuesday, March 14, 2006 8:12AM - 8:48AM |
G11.00002: A zero magnetic moment molecular probe of the electron's electric dipole moment. Invited Speaker: The stationary states of a molecule in a pure electric field are degenerate in the sign of the projection of total angular momentum on the field axis. A lifting of this $\pm $M$_{F}$ degeneracy would be an indication of CP (time reversal) symmetry violation. For heavy paramagnetic molecules, this CP violation would be attributed to an electron electric dipole moment (e-EDM) and could at once separate Supersymmetric models from the Standard Model and explain why we are made of matter instead of antimatter. A major obstacle to observing CP violation in this way is that the background magnetic-field induced splitting of the $\pm $M$_{F}$ degeneracy normally dwarfs any possible electric-field induced splitting. Here we report how the physics of $^{2}\Pi _{1/2}$ PbF can be exploited to gain extraordinary sensitivity to the e-EDM while reducing the magnetic g factor to less than 10$^{-7}$. The construction of a radical beam source of PbF, sensitive resonance enhanced multi-photon ionization (REMPI) detection of PbF, and progress toward measurement of the e-EDM are reported. [Preview Abstract] |
Tuesday, March 14, 2006 8:48AM - 9:00AM |
G11.00003: Ion Imaging Studies of Ultra-Cold Molecule Production David W. Chandler We report the cooling of molecules in a single collision between an atom and a molecule in a crossed molecular beam apparatus. In particular we will show data on cooling NO by collision with Ar and NH3 in collisiosn with Ne. We have produced in significant numbers ($\sim $10$^{8}$ molecules cm$^{-3}$ per quantum state) translationally cold NO($^{2}\Pi _{1/2}$,v$'$=0,j$'$=7.5) molecules in a specific quantum state with an upper-limit laboratory-frame rms velocity of 14.8$\pm $1.1 m/s, corresponding to a temperature of 406$\pm $28 mK. The translational cooling results from the kinematic collapse of the velocity distribution of the NO molecules after collision. We present experimental evidence to show that increasing the collision energy by a factor of $\sim $2.6 does not change the velocity spread of the cold NO molecules. Similarly, the energy condition for producing the cold NO does not depend on the energy of the Ar beam. However, the energy of the Ar beam does shift the scattering angle at which the cold molecules appear. We will highlight new studies on utilizing these cold molecules for collisional studies. This work was done in collaboration with Professor James Valentini of Columbia University. [Preview Abstract] |
Tuesday, March 14, 2006 9:00AM - 9:12AM |
G11.00004: Supersonic Molecular Beam Optical Stark Spectroscopy of MnH. Jamie Gengler, Tongmei Ma, Jeremy Harrison, Timothy Steimle The large moment of inertia, large magnetic moment, and possible large permanent electric dipole moment of manganese monohydride, MnH, makes it a prime candidate for ultra-cold molecule production via Stark deceleration and magnetic trapping\footnote {J.R. Bochinski, E.R. Hudson, H.J. Lewandowski, and J. Ye, \textit{Phys. Rev. A} \textbf{70}, 043410 (2004).}'\footnote {S.Y.T. van de Meerakker, R.T. Jongma, H.L. Bethlem, and G. Meijer, \textit{Phys. Rev. A} \textbf{64}, 041401(R) (2001).}. Here we report the first molecular beam production of MnH and the analysis of the Stark effect in the (0,0) $A^{7} \Pi $ -- $X^ {7}\Sigma ^{+}$ band. The sample was prepared by laser ablation of solid Mn in an H$_ {2}$ supersonic expansion. The low rotational temperature ($<$50 K) and near natural linewidth resolution ($\sim$50 MHz) facilitated analysis of the $^{55}$Mn (I=5/2) and $^{1}$H (I=1/2) hyperfine structure. A comparison of the derived field-free parameters with those obtained from sub- Doppler optical\footnote{T.D. Varberg, J.A. Gray, R.W. Field, and A.J. Merer, \textit{J. Mol. Spec.} \textbf{156}, 296-318 (1992).} and Doppler limited infrared\footnote{I.E. Gordon, D.R.T. Appadoo, A. Shayesteh, K.A. Walker, and P.F. Bernath, \textit{J. Mol. Spec}., \textbf{229}, 145-149 (2005).} measurements will be made. Progress on the analysis of the Stark effect will be given. [Preview Abstract] |
Tuesday, March 14, 2006 9:12AM - 9:24AM |
G11.00005: Rotation of a generalized Eckart frame in atom-diatomic molecule scattering Florence J. Lin A cyclic change in the shape of an atom-diatomic molecule complex can lead to net rotation of not only the complex, but also the rotating axes of a generalized Eckart frame of the complex. Large-amplitude, ``internal'' motions of an atom-diatomic molecule van der Waals complex can lead to overall rotation of the complex in the center-of-mass frame. When the total angular momentum is conserved, the net angle of overall rotation is the sum of a dynamic phase plus a geometric phase. The classical geometric phase is describable in terms of molecular rotational constants. The scattering angle of the atom in a nonreactive ``slightly sticky collision'' between an atom and a diatomic molecule in molecular beams depends on an analogous ``internal'' motion. Thus, the scattering angle of the atom is also given by the sum of a dynamic phase plus a geometric phase. [Preview Abstract] |
Tuesday, March 14, 2006 9:24AM - 9:36AM |
G11.00006: Two- and three-state conical intersections in complex systems Spiridoula Matsika, Kurt Kistler, ZongRong Xu, Akihiko Yoshikawa Nonadiabatic processes play an important role on the excited state dynamics of chemical systems. Conical intersections (actual potential energy surface crossings) of two states have been established to facilitate nonadiabatic processes of molecules and radicals in the gas phase. More recently three-state conical intersections have made their appearance and may also play a key role in nonadiabatic processes. Here we present studies where the importance of conical intersections is being investigated in photoinitiated processes of biologically relevant systems, and particularly the nucleobases and their analogs. Large scale ab initio multireference configuration interaction methods (MRCI) are being used. Our results show the presence of many seams of two- or three-state conical intersections that can complicate the potential energy surfaces and dynamics of these systems. Solvent effects on conical intersections are first being investigated using clusters of water with the system. A mixed quantum mechanical/ classical mechanical (QM/MM) approach where the solute is described with the MRCI method will also be presented as a means to study the effect of the solvent on excited states. [Preview Abstract] |
Tuesday, March 14, 2006 9:36AM - 9:48AM |
G11.00007: Saturation transfer studies on doorway states for CH$_{2}$ intersystem crossing Yangsoo Kim, Anatoly Komissarov, Gregory Hall, Trevor Sears Double-resonance transient photobleaching kinetics of singlet and mixed singlet-triplet eigenstates of CH$_{2}$ to characterize the closely related processes of rotational energy transfer and collision induced intersystem crossing in methylene will be reported. Qualitative features of the state-to-state rotational energy transfer matrix are revealed. Selective bleaching of individual eigenstates of mixed state (doorway) pairs shows very efficient collisional interconversion within the mixed-state pair. [Preview Abstract] |
Tuesday, March 14, 2006 9:48AM - 10:00AM |
G11.00008: Spectroscopic Identification of Multiple Conformers of $o,p$-H$_{2}\cdot \cdot \cdot $ICl and $o,p$-H$_{2}\cdot \cdot \cdot $I$_{2}$ Complexes Joshua Darr, Richard Loomis Laser-induced fluorescence and action spectroscopy experiments have identified ro-vibronic transitions associated with multiple conformers of the $o,p$-H$_{2}\cdot \cdot \cdot $ICl(X,v²=0) and $o,p$-H$_{2}\cdot \cdot \cdot $I$_{2}$(X,v²=0) complexes. For each complex, the conformers with the hydrogen molecule localized at the end of the dihalogen, with a $C_{2v}$ symmetry, are more stable than the conformers with the hydrogen molecule localized in the T-shaped well, which lies orthogonally about the dihalogen bond axis. Furthermore, the conformers containing $o$-H$_{2}$(j=1) and $p$-D$_{2}$(j=1) are found to be more strongly bound than those containing $p$-H$_{2}$(j=0) and $o$-D$_{2}$(j=0). The role of multi-pole electrostatic interactions is elucidated by comparing the binding energies of the H$_{2}\cdot \cdot \cdot $ICl(X,v²=0) and H$_{2}\cdot \cdot \cdot $I$_{2}$(X,v²=0) complexes with $C_{2v}$ symmetries. The relative populations of the $C_{2v}$ and T-shaped conformers can be altered by changing the properties of the supersonic expansion used to stabilize the complexes. The relative populations of the $o$-H$_{2}\cdot \cdot \cdot $ICl(X,v²=0) and $p$-H$_{2}\cdot \cdot \cdot $ICl(X,v²=0) conformers can also be manipulated, with a population ratio of 3:1 approached by decreasing the hydrogen concentration in helium. [Preview Abstract] |
Tuesday, March 14, 2006 10:00AM - 10:12AM |
G11.00009: Double Resonance Spectroscopy of the $B"\overline B { }^1\Sigma _u^+ $state of H$_{2 }$above the double well barrier. Robert Ekey, Aaron Marks, Elizabeth McCormack Double resonance spectroscopy via the$EF{ }^1\Sigma _g^+ ,v'_{EF} =6,J'$ state has been used to probe the rovibrational the \textit{ungerade} double-well $B"\overline B { }^1\Sigma _u^+ $state of H$_{2}$. Many transitions to levels of the outer-well and the combined inner and outer-well above the barrier have been observed for the first time by detecting both molecular and atomic ion production as a function of energy by using a time of flight mass spectrometer. While significant perturbations are observed in the energy region above the double-well barrier, assignments to states with dominant inner and outer-well characteristics can still be made. Distinct dynamical behaviors of the levels below, at and above the barrier have also been observed. [Preview Abstract] |
Tuesday, March 14, 2006 10:12AM - 10:24AM |
G11.00010: The Department of Energy's Hydrogen Storage Activities: Challenges and Needs in Chemistry and Chemical Dynamics Sunita Satyapal, Grace Ordaz, John Petrovic, Carole Read, George Thomas Hydrogen storage is a key area of research funded by the Department of Energy. Hydrogen, the simplest diatomic molecule known, has the highest energy content of all known fuels by mass, but the practical storage of sufficient hydrogen on-board a vehicle is a significant technological challenge. Hydrogen can be stored via various mechanisms within materials such as metal hydrides (e.g. LiBH$_{4}$, AlH$_{3})$ chemical hydrides (e.g. organic liquids), and nanostructured sorbents (e.g. carbon nanotubes, clathrates). Examples of mechanisms include physisorption, chemisorption, dissociative adsorption or combinations of the above. In addition to weight and volume, the kinetics of hydrogen charging and discharging as well as durability must be addressed. A fundamental understanding of hydrogen storage to help optimize materials is critical. The technical requirements for hydrogen storage, as well as some of the promises and challenges will be presented, with a focus on what chemical dynamics and chemistry can offer in solving the challenge of hydrogen storage for transportation applications. [Preview Abstract] |
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