Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R11: Focus Session: Aerosols, Clusters, Droplets: Physics and Chemistry of Nanoobjects III: Molecular Clusters |
Hide Abstracts |
Sponsoring Units: DCP Chair: David Nesbit, University of Colorado Room: Baltimore Convention Center 303 |
Wednesday, March 15, 2006 2:30PM - 3:06PM |
R11.00001: Unraveling proton accommodation in water with cluster spectroscopy Invited Speaker: We describe how argon-nanomatrix spectroscopy, implemented with broadly tunable solid state infrared laser sources, allows us to establish how water networks flex and distort to accommodate elementary aqueous species like protons and electrons. We will focus on the hydrated proton, as this charge defect accounts for charge conduction in many biological processes that occur in a hydrophobic environment. By freezing the water clusters to their minimum energy structures, sharp, characteristic bands are recovered very low in energy that reveal how the local solvent arrangement dictates the spatial extent of the excess charge delocalization. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R11.00002: Excess Electrons in Water Clusters Ying Li, Robert Barnett, Uzi Landman Excess electrons in water systems are always a research topic of interest. In this talk, we will discuss the behavior and formation of the excess electrons in water cluster using DFT ab-initio simulations with a combination of quantum mechanics and molecular mechanics. System size is chosen so that the excess electrons will form a bound state rather than a surface state. Measurements will be performed to test the stability of the electron structure. [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R11.00003: Surface-trapped excess electrons on ice Francesca Baletto, Mal-Soon Lee, Sandro Scamdolo Local surface trapping of excess electrons has recently been observed in large water clusters and at the ice/vacuum interface. The existence of stable surface-bound states for the excess electron may have important implications in atmospheric chemistry, electrochemistry, and radiation physics. By means of first-principles molecular dynamics we find that excess electrons induce a structural reconstruction of the ice surface on a time scale of a fraction of a picosecond [Baletto et al., PRL 95, 176801 (2005)]. Preliminary results on small neutral water clusters indicate that fast (on a picoseconds scale) structural changes occur already at the lowest atmospheric temperatures, suggesting that addition of excess electrons may lead to even more substantial structural rearrangements than those found for the ice surface. [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R11.00004: Hole-filling spectroscopy of the \textit{trans}-formanilide-H$_{2}$O and tryptamine-H$_{2}$O complexes: Solvent shuttling and solvent loss Timothy Zwier, Jasper Clarkson Studies of molecular clusters formed and cooled in a supersonic expansion offer unique opportunities to study novel types of dynamical processes under well-defined conditions. This talk will highlight recent studies in our laboratory at Purdue involving water-containing complexes with \textit{trans}-formanilide (TFA) and tryptamine (TRA). In TFA-H$_{2}$O, stimulated emission pumping is used to initiate a unique type of reaction in which a single water molecule is shuttled between remote hydrogen-bonding sites on the same solute molecule. The energy barrier to isomerization is measured for shuttling the molecule in either direction. In TRA-H$_{2}$O and TRA(ND$_{2})$-D$_{2}$O, infrared excitation is used to dissociate the water molecule from a flexible molecule with well-defined starting geometry. Isomer-specific product quantum yields of the TRA monomer product will be reported as a function of the XH or XD oscillator excited. The interplay between water loss and conformational isomerization of the flexible TRA molecule will be discussed. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R11.00005: Anharmonic Vibrational Spectra of Hydrogen Bonded Clusters Sotiris S. Xantheas We report anharmonic vibrational spectra for a variety of hydrogen bonded clusters such as (H$_{2}$O)$_{n}$ and (HF)$_{n}$, $n$=1-5. We investigate the convergence of the hydrogen bonded frequencies with basis set and level of electron correlation and compare with the available experimental data. For this purpose we employ the correlation-consistent basis sets up to quintuple zeta (5z) quality and compute the spectra at the second order M{\o}ller-Plesset (MP2) and Coupled Cluster plus Single and Double with perturbative estimate of Triple excitations [CCSD(T)]. The correlation between the calculated elongations in the hydrogen bonding stretches and the corresponding computed/observed vibrational frequencies suggest an extension of Badger's rule for these hydrogen bonded systems. [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R11.00006: Probing the Stepwise Solvation of the Sulfate Dianion: Gas Phase Infrared Spectroscopy of SO$_{4}^{2-}$$\cdot$(H$_{2}$O)$_{n}$ Clusters (n=3-24) Knut R. Asmis, Gerard Meijer, Gabriele Santambrogio, Mathias Bruemmer, Ludger Woeste, Jia Zhou, Dave T. Moore, Daniel M. Neumark Hydrated sulfate dianions are of paramount importance in diverse branches of science. However, a microscopic, molecular level understanding of the nature of the solute-solvent interaction as well as the composition of the solvation shell has not yet been achieved. Here we report the first gas phase infrared spectra of multiple charged anions in general, namely of mass-selected SO$_{4}^{2-}\cdot $(H$_{2}$O)$_{n}$ dianions ($n$=3-24) employing the infrared multiple photon dissociation technique in combination with radiation from the free electron laser FELIX. The infrared spectra (550-1800 cm$^{-1})$ were measured in the region of the stretching and bending modes of the sulfate core as well as characteristic intra- and intermolecular water modes, allowing an unprecedented, atomic level insight into structure of the complex as well as the nature and strength of the underlying hydrogen bonding interaction. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R11.00007: Effective polarizabilities of water clusters Ramiro Moro, Roman Rabinovitch, Chunlei Xia, Vitaly Kresin We report the measurement of electrical polarizabilities of water clusters [(H$_{2}$O)$_{n}$, n=3-18] by deflection of a supersonic beam in an inhomogeneous field. In all the clusters studied, the deflections are only towards higher fields, indicating a polarizability-like behavior. The highest polarizability per one water molecule is seen in the trimer (7.9 $\pm $ 0.3 {\AA}$^{3})$ and it quickly decreases for larger clusters to about 4 {\AA}$^{3}$ per molecule for n=6-18. These values are large and could be explained by the addition of two parts: an intrinsic electronic polarizability plus a contribution from a permanent dipole moment responding with a Langevin-like behavior. With a cluster temperature of $\sim $200 K, estimated from the evaporative ensemble picture, the permanent dipole moments are $\sim $1-2 Debye per cluster. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R11.00008: Experimental Evidence for Internal Structure in Aqueous -- Organic Nanodroplets Gerald Wilemski, Barbara E. Wyslouzil, Reinhard Strey, Christopher H. Heath, Uta Dieregsweiler The spatial distribution of species within an aerosol droplet influences how it interacts with its environment. Despite the ubiquity of multicomponent nanodroplets in natural and technological aerosols, there are no published measurements of their internal structure. In a recent paper [Wyslouzil, et. al., Phys. Chem. Chem. Phys. \textbf{8}, xxx, (2006)], we report the first experimental results for structure in aqueous organic nanodroplets based on small angle neutron scattering by high number density aerosols. For H$_{2}$O -- n-butanol droplets, fitting of the diffraction patterns confirms the picture of an aqueous core containing $\sim $3 mol{\%} alcohol covered by a shell of densely packed alcohol molecules. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R11.00009: Imaging predissociation dynamics and energy flow pathways in vibrationally excited acetylene-HCl dimers Guosheng Li, Jessica Parr, Igor Fedorov, Hanna Reisler We report photofragment imaging studies of the predissociation of acetylene-HCl dimers. The dimer is vibrationally excited by laser irradiation either in the CH asymmetric stretch mode of the acetylene subunit or in the HCl subunit. Photofragment ion images of HCl in specific rotational states are obtained from which kinetic energy release patterns are analyzed. The predissociation behavior in the two cases is different. CH stretch excitation is followed by IVR in acetylene and results in an acetylene fragment with one quantum of CC stretch excitation (in agreement with results of Roger Miller and coworkers) and a statistical rotational energy distribution. HCl excitation results in acetylene fragments with one or two quanta of bending excitation with no clear preference for a specific mode. In both cases HCl rotations are nonstatistical. The different predissociation outcomes reflect the different energy flow pathways followed in each case. Research supported by the US National Science Foundation. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R11.00010: Monte Carlo simulations of Phase Changes in Lennard-Jones nanoclusters. Silvina Gatica, Xiao Dong, Estela Blaisten-Barojas Monte Carlo simulations of Lennard-Jones clusters of less than 100 atoms are performed to explore the possible phase changes. The simulation is made at constant pressure and temperature. In the Monte Carlo the volume of the cluster is evaluated during the calculation in terms of the mean quadratic radius, and the reduced temperature is kept below 0.4 to avoid the evaporation of the cluster. We obtain a PV diagram and calculate the energy per particle, the radial distribution function, the coordination number and displacement function, to look for signatures of the presence of a solid-liquid-like phase change. The equilibrium structure and number of layers in the cluster at each pressure and temperature are also computed. We compare our findings with predictions of other authors. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R11.00011: Infrared spectroscopy of metal-solvent clusters: Li(NH$_{3})_{n}$ and Li(MeNH$_{2})_{n}$ Andrew Ellis, Tom Salter, Corey Evans, Victor Mikhailov Mass-selected infrared spectra of the uncharged metal-solvent clusters Li(NH$_{3})_{n}$ and Li(MeNH$_{2})_{n}$ in the N-H stretching region have been recorded using two techniques, photodepletion spectroscopy and two-colour (IR+UV) REMPI. Infrared REMPI is the most suitable for the smaller clusters, since the energy input into the cluster by the IR photon is insufficient to cause dissociation. Our latest findings for this technique will be presented alongside computational predictions of the cluster spectra. For the larger clusters, injection of an IR photon in the N-H stretching region causes rapid dissociation and offers the opportunity to record mass-selected IR spectra by photodepletion spectroscopy. IR photodepletion spectra of Li(NH$_{3})_{n}$ near 3 $\mu $m recorded for $n$ = 4-7 show vibrational structure that points to completion of the first solvation shell at $n$ = 4, with additional ammonia molecules entering a second shell in which the solvent molecules are more weakly bound to the cluster. Photodepletion spectra have also been recorded for other clusters, including Li(MeNH$_{2})_{n}$, and the latest findings for these species will be described. [Preview Abstract] |
Wednesday, March 15, 2006 5:06PM - 5:18PM |
R11.00012: Rings, Towers and Cages in Zn$_{n}$O$_{n}$ Clusters Arthur Reber, Shiv Khanna, Jagtar Hunjan, Marcela Beltran It is shown that the transition from an elementary ZnO molecule to compact bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. First principles electronic structure calculations within a gradient corrected density functional framework have been carried out to investigate the progression of geometries and electronic properties of Zn$_{n}$O$_{n}$ (n=2-12,15,16,21) clusters. It is shown that Zn$_{n}$O$_{n}$ (n=2, 3, 4, 5, 6, 7) clusters are all single, highly stable rings and that Zn$_{3}$O$_{3}$ is particularly stable. Starting at Zn$_{8}$O$_{8}$, these elementary rings begin to assemble into column structures that begin to distort at n=10. The ground states of Zn$_{12}$O$_{12}$, and Zn$_{16}$O$_{16}$ are single cages while the structure of Zn$_{11}$O$_{11}$, Zn$_{15}$O$_{15}$ and Zn$_{21}$O$_{21}$ can be described as barrels. The Zn$_{12}$O$_{12}$ cage has a high dissociation energy and a large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of 2.51 eV making it a potential candidate for cluster assemblies. [Preview Abstract] |
Wednesday, March 15, 2006 5:18PM - 5:30PM |
R11.00013: On the Aluminum Cluster Superatoms acting as Halogens and Alkaline-earth Metals Dennis E. Bergeron, Patrick J. Roach, A. Welford Castleman, Naiche O. Jones, J. Ulises Reveles, Shiv Khanna It is shown that a new class of super-polyhalides can be formed by combining the Al$_{13}$ super-halogen with the conventional halogen, I. Experimental reactivity studies demonstrate that the new super-polyhalides, Al$_{13}$I$_{x}^{-}$, exhibit pronounced stability for even numbers of I atoms. Theoretical investigations probing the geometry and the electronic structure reveal that the enhanced stability is associated with pairs of I atoms occupying the on-top sites around the Al$_{13}^{-}$ core. We also demonstrate another series, Al$_{14}$I$_{x}^{-}$, that exhibits stability for odd numbers of I atoms. It is shown that this series can be described as consisting of an Al$_{14}$I$_{3}^{-}$ core upon which the I atoms occupy on-top locations around the Al atoms. The potential synthetic utility of superatom chemistry built upon these motifs will be addressed. [Preview Abstract] |
Wednesday, March 15, 2006 5:30PM - 5:42PM |
R11.00014: Induced super-halogen behavior of metal moieties in halogen-doped metal clusters Fedor Naumkin, Hobart Leung Recent studies of the Al$_{13}$I$^{-}$ cluster ion have shown negative charge localization on the aluminum core and associated this with its super-halogen character resulting from a high electron affinity EA of Al$_{13}$ (exceeding that of the I atom). The present work reports results of ab initio calculations for a similar halogen-doped metal cluster, M$_{13}$X$^{-}$. The charge is found to be localized on the M$_{13}$ core as well, even though its EA is lower than that of X. Other properties such as structure and stability for different spin-states are also investigated and compared with those for the neutral counterparts. Comparison to the corresponding smaller metal-halide species is made as well. The charge localization on the metal moieties is concluded to be associated not only with the relative EA values. An alternative, physically transparent interpretation is given, which explains the observed charge distributions on electrostatic basis. The super-halogen behavior of the metal moieties is linked to the presence of the halogen atom in the systems. [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