Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session B11: Focus Session: Promises and Challenges in Chemical Dynamics II |
Hide Abstracts |
Sponsoring Units: DCP Chair: Jim Valentini, Columbia University Room: Baltimore Convention Center 303 |
Monday, March 13, 2006 11:15AM - 11:51AM |
B11.00001: Adventures in Cluster Dynamics Invited Speaker: We report on the exploration of new scientific territories of energetics, response, dynamics and function of large, finite atomic and molecular systems. Studies of ultrafast (attosecond to femtosecond) electron and nuclear dynamics of clusters in ultraintense laser fields (peak intensity 10$^{15}$--10$^{20}$Wcm$^{-2})$ led to the advent of table-top nuclear fusion driven by cluster Coulomb explosion. The eighty years' quest for nuclear fusion driven by chemical reactions was achieved by ``hot--cold'' fusion in the chemical physics laboratory. Moving from femtosecond nuclear dynamics in the energy domain of nuclear physics (1keV--1MeV) towards ultralow energies and ultraslow millisecond dynamics in ultracold (T = 100$\mu $K--1nK) finite systems, we address the bridging between the nuclear dynamics of clusters and of finite, ultracold atomic clouds. \newline \newline References \newline [1] I. Last, Y. Levy, J. Jortner. PNAS \underline {99}, 9107 (2002).\newline [2] I. Last, J. Jortner. Phys. Rev. Letts. \underline {87}, 033401-1 (2001); Phys. Rev. A \underline {64}, 063201-1 (2001); J. Chem. Phys. \underline {120}, 1336 (2004); \underline {120}, 1348 (2004); \underline {121}, 3030 (2004); \underline {121}, 8329 (2004); Phys. Rev. A \underline {71}, 063204-1 (2005).\newline [3] J. Jortner, M. Rosenblit, Adv. Chem. Phys. \underline {132}, 247 (2005). [Preview Abstract] |
Monday, March 13, 2006 11:51AM - 12:03PM |
B11.00002: Isomer morphology and vibrational mode dependence of the coupling between an excess electron and small water networks. Mark Johnson Negatively charged water clusters are presently the subject of intense study because of their promise to unravel the surprisingly complex dynamics of the hydrated electron. We focus on the use of vibrational spectroscopy to establish the morphologies and local binding motifs of the water networks that bind an electron. Here we will discuss the rearrangement pathways of the H-bond network in the elementary act of free electron accommodation, where we use argon-mediated population modulation to isolate the geometries of the neutral cluster precursors. We then obtain isomer-selective vibrational spectra of the anions that produced, where we correlate the local binding motifs with the overall electron binding energies. Finally, in the small cluster limit, we reveal how different intramolecular vibrational motions interact with the diffuse electron cloud by analysis of the resulting ``Fano'' lineshapes when vibrations are embedded in the electron continuum. These interactions vary by over an order of magnitude for various ``free OH'' bands. The implications of these observations on the extrapolation to bulk behavior will be considered in light of the trends displayed by the cluster properties up n=30 or so. [Preview Abstract] |
Monday, March 13, 2006 12:03PM - 12:15PM |
B11.00003: Vibrational energy at interfaces Dana Dlott New advances in ultrafast vibrational spectroscopy now permit the real-time observation of vibrational energy at interfaces. Using a liquid suspension of reverse micelles, consisting of a nanodroplet of water separated from an organic solvent by a monolayer of surfactant, we pumped vibrational energy into either the water or surfactant layer using an ultrashort IR laser pulse. Incoherent anti-Stokes Raman probe techniques were used to watch the vibrational energy move across this surfactant monolayer. The results were quite different that what would be expected if we were watching heat flow. The specific pathways of vibrational energy are invoked to explain these results. [Preview Abstract] |
Monday, March 13, 2006 12:15PM - 12:27PM |
B11.00004: Atomic Beam Scattering as a Probe of the Glass Transition of Polymer Thin Films Miriam Freedman, Aaron Rosenbaum, Steven Sibener We have investigated the thin film dynamics of poly(methyl methacrylate) (PMMA) using inelastic helium atom scattering. The glass transition in the surface region of a polymer film is thought to be at a lower temperature than the bulk, but it is unclear whether this reduction is due to the film surface or the near-surface layer. Because helium atom scattering is a surface sensitive, non-perturbative technique with which we can directly probe the surface dynamics, we hope to be able to clarify this debate. We obtain broad time of flight spectra, which are well fit by a semi-classical scattering model. From these fits, we note deviations near the bulk glass transition that could be due to changes in surface presentation or dynamics. At low beam energies and sample temperatures, we observe elastic scattering from which we calculate Debye-Waller factors that are similar to other organic thin films. This study has shown that helium atom scattering provides a unique means of exploring the glass transition of polymer thin films. [Preview Abstract] |
Monday, March 13, 2006 12:27PM - 1:03PM |
B11.00005: Optical Spectroscopy and Photophysics of Single Wall Carbon Nanotubes Invited Speaker: We explore the fundamental nature and dynamics of excited electronic states in SWNT. Psec luminescence and photobleaching dynamics of SWNTs in micellar solution show that non-radiative Auger recombination is extremely fast. At low pH, nanotube surface endoperoxides protonate and introduce holes that quench the luminescence. At higher concentration these holes also bleach the band gap optical absorption. Near infrared two photon luminescence excitation spectra quantitatively reveal the importance of excitons. In order to characterize excited states in both metallic and semiconducting SWNTs at the single-tube level, we detect white-light Rayleigh scattering from individual tubes suspended over an open slit in a substrate. Diagnostic spectra with high signal to noise are obtained in just a few minutes. [Preview Abstract] |
Monday, March 13, 2006 1:03PM - 1:15PM |
B11.00006: First hyperpolarizability ($\beta )$ of bare and polymer protected copper nanoparticles Puspendu Das, Manabendra Chandra We have prepared bare as well as polyvinyl pyrrollidone (PVP) capped Cu nanoparticles (NPs) of $<$10 nm size by laser ablation and measured their first hyperpolarizabilities ($\beta $ values) using the hyper-Rayleigh scattering technique in solution. The $\beta $ values for the bare and capped NPs are 414 ($\pm $19) x 10$^{-30 }$and 808 ($\pm $12) x 10$^{-30 }$esu/atom$^{1/2}$, respectively. The bare NPs are stable in isopropanol for weeks but are short-lived compared to the capped particles. Our results of capped NPs having a $\beta $ value twice as high compared to the bare NPs of the same size show that surface capping is necessary for enhancing $\beta $ in noble metal NPs. In addition to the bulk and surface quadrupolar contributions which exist in bare NPs, dipolar contribution to $\beta $ becomes important for the capped NPs due to the destruction of centro-symmetry at the surface, leading to a significant increment in $\beta $. Experiments with smaller size NPs show that $\beta $ goes down with size. The bulk quadrupolar polarization which decreases with particle size, perhaps, rationalizes the size dependence of $\beta $. [Preview Abstract] |
Monday, March 13, 2006 1:15PM - 1:27PM |
B11.00007: RRKM Theory at the Gas-Surface Interface: Hydrogen Dissociation Dynamics on Cu(111) Heather Abbott, Ian Harrison A simple picture of the hydrogen dissociation/associative desorption dynamics on Cu(111) emerges from a two-parameter, full dimensionality microcanonical unimolecular rate theory (MURT) model of the gas-surface reactivity. Vibrational frequencies for the reactive transition state were taken from 6D density functional theory calculations [Hammer, \textit{et al. Phys. Rev. Lett.} \textbf{73}, 1400 (1994)]. The MURT's parameters were fixed by simulation of experiment as: a H$_{2}$ dissociation threshold energy of $E_{0}$ = 79 kJ/mol and $s$ = 1 surface atoms that actively exchange energy within the reactive transition state. Remarkably, MURT quantitatively predicts much of the dynamical behavior observed. The divergence of the statistical theoretical predictions from the experimental results at low rotational quantum numbers, $J\le 5$, points towards the importance of dynamical steering at low J. The surface degrees of freedom are calculated to provide $\sim $30{\%} of the energy required to surmount E$_{0}$ under thermal equilibrium conditions. Explicit treatment of the surface (i.e., $T_s >0\mbox{ }K)$ is a novel aspect of the MURT theoretical approach. [Preview Abstract] |
Monday, March 13, 2006 1:27PM - 1:39PM |
B11.00008: An STM and Theoretical Study of the Interaction of hexabenzocorone on a Ru(0001) Surface Kwang Taeg Rim, Li Liu, Chaochin Su, Shengxiong Xiao, Michael Steigerwald, Mark Hybertsen, Colin Nuckolls, George Flynn The interaction of hexabenzocorone (hbc) with a metal surface has been investigated using Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS) in ultrahigh vacuum. The images obtained at room temperature, after hbc molecules were vacuum deposited at 325$^{o}$C onto a pristine ruthenium (0001) surface, exhibit surface bound molecules with off-centered bonding sites. I(V) curves over hbc molecules show high tunneling current at positive bias voltages. After annealing of the hbc-bonded Ru sample surface at 600$^{o}$C for 15min, hbc molecules appear to aggregate laterally and to bond symmetrically to the surface. The possibility of growing carbon nanotubes on the hbc-Ru precursor surface upon dosing with C$_{2}$H$_{2}$ will also be discussed along with a theoretical model for bonding and growth of nanotubes. [Preview Abstract] |
Monday, March 13, 2006 1:39PM - 1:51PM |
B11.00009: Single-molecule vibrational spectroscopy of water molecules using an LT-STM Chikako Matsumoto, Yousoo Kim, Kenta Motobayashi, Maki Kawai Single-molecule vibrational spectroscopy has attracted considerable attention as a powerful tool for nanoscale chemistry. The adsorption of water molecules on metal surfaces plays an important role in understanding many phenomena in nature, such as heterogeneous catalysis and corrosion, etc. The structure of water at low coverage has been investigated on a variety of transition-metal surfaces with various techniques. But the microscopic understanding of the adsorption feature of single water molecules is still unclear. We report molecular scale study of adsorption behaviors of water molecules on Pt (111) surface at 4.7 K by use of single-molecule vibrational spectroscopy with the scanning tunneling microscopy (STM). The Pt (111) surface was dosed with a small amount of water molecules ($<$ 0.01 ML) at the temperature less than 20 K. A water monomer appears as a single protrusion in the STM images. A dimer was formed by manipulating monomers with an STM tip. The shape of a water dimer looks like\textbf{ `}cherry blossom', which can be explained by one of the water molecules rotating around the other\textbf{.} Inelastic electron tunneling spectroscopy using the STM was utilized to determine vibrational modes of individual water dimers. [Preview Abstract] |
Monday, March 13, 2006 1:51PM - 2:03PM |
B11.00010: A Novel Vibrational Spectroscopic Study of a Single Molecule using an STM -- Measurement and Selection rules of Action spectroscopy Yousoo Kim, Yasuyuki Saino, Toshiro Okawa, Tadahiro Komeda, Hidemi Shigekawa, Maki Kawai The excitation of molecular vibration by means of the inelastically tunneled electrons from the tip of a scanning tunneling microscope (STM) can lead to various dynamical processes at surfaces. In addition, inelastic electron tunneling spectroscopy with the STM (STM-IETS) is now applicable to the vibrational spectroscopy of the individual molecules. The vibrational spectrum of a single molecule provides useful information not only for the chemical identification of the molecule but also for investigating how molecular vibration can couple with the relevant dynamical processes. Inelastically tunneled electrons from the STM were used to induce vibrationally mediated motions of a single \textit{cis-}2-butene molecule among four equivalent orientations on Pd(110) at 4.7 K. Action spectrum obtained from the motions clearly detects more vibrational modes than STM-IETS. We demonstrate the usefulness of the action spectroscopy as a novel single molecule vibrational spectroscopic method. We also discuss its selection rules in terms of the resonance tunneling. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700