Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P11: Focus Session: Aerosols, Clusters, Droplets: Physics and Chemistry of Nanoobjects II: Helium Nanodroplets II, Aerosols, and Miscellaneous |
Hide Abstracts |
Sponsoring Units: DCP Chair: Geoffrey Smith, University of Georgia Room: Baltimore Convention Center 303 |
Wednesday, March 15, 2006 11:15AM - 11:27AM |
P11.00001: High resolution infrared and microwave spectra of OCS solvated in helium clusters. Wolfgang Jaeger, Robert McKellar, Yunjie Xu In recent years, exciting progress has been made in determining the onset and following the evolution of a bulk phase property, namely superfluidity, in the microscopic size regime. Our previous microwave and infrared studies of small He$_{N}$-OCS and He$_{N}$-N$_{2}$O clusters extended up to N=8 and N=19, respectively, and the infrared spectra with CO or CO$_{2}$ as probe reached almost up to N=20. We have now been able to extend the studies on He$_{N}$-OCS to much larger N-values in both the infrared and microwave regions. The B rotational constants that were extracted from the spectra show unexpected, non-classical behavior as a function of N, the number of helium atoms. We will present the experimental techniques used and an interpretation of the observed trends in spectroscopic observables. [Preview Abstract] |
Wednesday, March 15, 2006 11:27AM - 11:39AM |
P11.00002: Recurrences in rotational dynamics and superfluid response in doped He-HCCCN and He-N${}_2$O clusters Nikolay Blinov, Pierre-Nicholas Roy, Wolfgang J\"ager Recent experiments on He-N${}_2$O complexes revealed the oscillatory behavior of the rotational constant in the range of cluster sizes corresponding to the completion of the first solvation shell. We use the path-integral Monte Carlo approach to show that this phenomenon can be associated with a non-monotonic size evolution of the non-classical rotational inertia and superfluidity, the origin of which can be traced back to combined solvent layering and bosonic exchange effects. Using the dopant molecule as an experimental microscopic probe of superfluidity, we show that in small doped helium clusters superfluidity builds up in stages correlated with the filling and completion of solvation shells. [Preview Abstract] |
Wednesday, March 15, 2006 11:39AM - 11:51AM |
P11.00003: Infrared spectra and intensities of H$_{2}$O-N$_{2}$, H$_{2}$O-O$_{2}$ and H$_{2}$O-Ar complexes in superfluid He droplets. Susumu Kuma, Mikhail N. Slipchenko, Kirill Kuyanov, Takamasa Momose, Andrey F. Vilesov The infrared spectra of H$_{2}$O-N$_{2}$, H$_{2}$O-O$_{2}$ and H$_{2}$O-Ar complexes in superfluid He droplets were measured in the range of the stretching vibrational bands of water molecules. The infrared intensities of anti-symmetric stretching band of these complexes showed no significant increase with respect to that of a single H$_{2}$O molecule as opposed to the predicted intensities in previous theoretical calculations. From the analysis of the observed spectra, it was found that H$_{2}$O in H$_{2}$O-O$_{2}$ and H$_{2}$O-Ar rotates nearly freely inside the complexes, while that in H$_{2}$O-N$_{2}$ does not. The conformation of these complexes were estimated from the rotational constants obtained from the analysis. [Preview Abstract] |
Wednesday, March 15, 2006 11:51AM - 12:27PM |
P11.00004: Spectroscopic Properties of Aerosols and their Microscopic Origin Invited Speaker: Large molecular aggregates with sizes ranging from less than nanometers up to microns play an important role in atmospheric processes, as components of the interstellar medium, and as drug delivery systems in medicine. The vibrational dynamics of these particles can be strongly influenced by intrinsic particle properties such as size, shape, or surface area. These phenomena are discussed here for several pure and composite ice particles which consist of CO$_{2}$, N$_{2}$O, NH$_{3}$, SO$_{2}$, their isotopomers, and different carbohydrates. The aerosol are generated in collisional cooling cells, by supersonic expansions, and by rapid expansion of supercritical solutions [1]. The vibrational dynamics is studied in situ with a rapid scan Fourier transform infrared spectrometer. We demonstrate that only the combination of experiments with microscopic models leads to a comprehensive understanding of the various features observed in the infrared spectra. The corresponding molecular model (exciton model [1,2]) allows us not only to calculate spectra for large molecular aggregates, but also to derive propensity rules for the occurrence of characteristic effects in infrared spectra of particles. \newline \newline [1] R. Signorell, \textit{Mol. Phys}. \textbf{101}, 3385, (2003). \newline [2] R. Disselkamp and G. E. Ewing, \textit{J. Chem. Soc. Faraday Trans. }\textbf{86}, 2369, (1990). [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 12:39PM |
P11.00005: Kinetics and Products of Radical-Initiated Oxidation of Organic Particles Using Aerosol CIMS Geoffrey Smith, John Hearn Ambient aerosol can contain a significant fraction of organic material which may react with trace gases in the atmosphere. Recently, it has been proposed that reactions with radical species, such as OH and Cl, may constitute a substantial loss mechanism for organic particles. In particular, the radical-initiated oxidation could lead to the creation of smaller, more volatile species which remove mass from the particles. An accurate assessment of the importance of these radical reactions requires measurements of their rates of reaction as well as identification of the subsequent products. We are exploring OH- and Cl-initiated reactions using Aerosol CIMS (chemical ionization mass spectrometry) to monitor changes in the compositions of the aerosol as well as the gas phase. This technique is well-suited to the study of organic species since the mass spectra contain very little fragmentation. These experiments provide insight into the oxidative processing which may potentially alter many critical properties of organic aerosol, including hygroscopicity and their ability to act as cloud condensation nuclei. [Preview Abstract] |
Wednesday, March 15, 2006 12:39PM - 12:51PM |
P11.00006: Gas-phase infrared spectroscopy of ionic uranyl coordination complexes David Moore, Anita Gianotto, Nick Polfer, Jos Oomens, Mike van Stipdonk, Gary Groenewold The uranyl dication (UO$_{2}^{2+})$ is the primary carrier of uranium in environmental and biological systems, yet relatively little is known about its chemical properties. Mass spectrometric studies have confirmed that the properties, and in particular the reactivity of the uranyl center is rather dependent on its coordination environment. The current study uses IRMPD spectroscopy of ionic uranyl complexes, recorded using a free-electron laser coupled to an FTICR mass spectrometer, to investigate the effects of cluster size and composition on the infrared spectra. The central observation from the current study is that the asymmetric uranyl stretch is quite sensitive to the coordination environment, showing clear, reproducible, incremental redshifts as the number and electron donating ability of the ligands is increased. These spectral trends are accurately reproduced by computed frequencies from DFT calculations. Results from complexes containing anionic ligands are also presented, and are consistent with the presence of a significant barrier to electron transfer within the complexes. [Preview Abstract] |
Wednesday, March 15, 2006 12:51PM - 1:03PM |
P11.00007: Stable highly symmetric dopant encapsulated binary clusters Peter Lievens, Sven Neukermans, Ewald Janssens While clusters composed of rare gas atoms exhibit enhanced stabilities for high symmetry geometries, magic numbers in simple metal clusters are determined by the number of delocalized valence electrons. Altering the composition of binary clusters allows to tailor independently the cluster geometry (number of atoms) and electronic properties (number of delocalized electrons). We produce beams of binary clusters with a dual-target dual-laser vaporization source. Size and composition dependent stability fluctuations are investigated with photofragmentation and mass spectrometry, and ionization energies with threshold laser ionization spectroscopy. We recently studied clusters of noble metals doped with transition metal atoms, and of group IVa elements doped with di- and trivalent metal atoms. Evidence is presented for the existence of combined closures of shells of atoms and shells of electrons for specific binary species. Phenomenological interpretations of new electronic shell closures are compared with DFT calculations of their geometry and electronic structure. [Preview Abstract] |
Wednesday, March 15, 2006 1:03PM - 1:15PM |
P11.00008: Factors Controlling Polymorph Formation in Nonphotochemical Laser-Induced Nucleation (NPLIN) of Aqueous Glycine Solutions Xiaoying Sun, Bruce A. Garetz The supersaturation and polarization dependence of nonphotochemical laser-induced nucleation (NPLIN) was studied in aqueous glycine solutions at wavelengths of 532 and 1064 nm, using linearly, circularly and elliptically polarized light. We observed a narrow supersaturation window (SS=1.45-1.54) for ``polarization switching,'' i.e. different polarizations producing different polymorphs. We also observed that, within this window, a small range of ellipticities near unity could induce the nucleation of the alpha polymorph, and that this range depended on supersaturation. Similar ``polarization switching'' behavior was observed at wavelengths of 1064 and 532 nm, although the supersaturation window became narrower at lower laser intensities at both wavelengths. Order-parameter ellipsoids and triangles based on optical Kerr alignment are presented to aid the interpretation of the experimental results. [Preview Abstract] |
Wednesday, March 15, 2006 1:15PM - 1:27PM |
P11.00009: Density Functional Studies of Magic Metal-(C$_{60}$)$_2$ Clusters Eva Zurek, Jochen Autschbach Previous experimental studies of C$_{60}$-metal clusters revealed that clusters with composition C$_{60}$Ba$_{32}$ and (C$_{60}$K$_6$)$_n$K$^+$ appeared as magic peaks in the Time-of-Flight mass spectra due to geometric and electronic stability, respectively. Recent experiments using a new heating technique have revealed a different set of magic peaks, which cannot be explained by either one of the aforementioned mechanisms. We present theoretical studies addressing the stability and bonding of these newly observed magic clusters. Molecular density functional calculations have been performed to determine the most energetically stable geometrical configurations for $M_n$(C$_{60}$)$_2$ clusters, with $M=$ K, Ba and $1 \leq n \leq 6$. The bonding mechanisms have been analyzed in some detail. The results indicate that for barium containing clusters, ionic bonding (transfer of the valence $6s$ electrons to the C$_{60}-\pi^*$ orbitals) and covalent bonding (between the barium $5d$ and C$_{60}-\pi^*$ orbitals) are the dominant mechanisms. Moreover, a metal cluster is formed between the two fullerenes (Ba-Ba bonding). For the potassium containing clusters, only ionic bonding was found. Calculations of the Gibbs free energies indicate that Ba$_3$(C$_{60}$)$_2$ and K$_4$(C$_{60}$)$_2$ are the most stable structures, in agreement with experimental results. The role of the entropy is found to be very important in determining which clusters are magic. [Preview Abstract] |
Wednesday, March 15, 2006 1:27PM - 1:39PM |
P11.00010: Photoelectron spectroscopy as a structural probe of intermediate size clusters Leeor Kronik, Olga Guliamov, Koblar A. Jackson We examine the utility of photoelectron spectroscopy (PES) as a structural probe of Si$_{n}^{-}$ in the n = 20 -- 26 size range by determining isomers and associated photoelectron spectra from first principles calculations. Across the entire size range, we consistently obtain good agreement between theory and experiment [Hoffmann et al., \textit{Eur. Phys. J. D} \textbf{16}, 9 (2001)]. We find that PES can almost invariably distinguish between structurally distinct isomers at a given cluster size, but that structurally similar isomers usually cannot be reliably distinguished by PES. For many, but not all, sizes the isomer giving the best match to experiment is the lowest-energy one found theoretically. Thus, combining theory with PES experiments emerges as a useful source of structural information even for intermediate size clusters. [Preview Abstract] |
Wednesday, March 15, 2006 1:39PM - 1:51PM |
P11.00011: Nearly Free Electron Gas in a Silicon Cage J. Ulises Reveles, Shiv Khanna Theoretical investigations of the ground state geometries, electronic structure, spin magnetic moment and the stability of the metal encapsulated MSi$_{12}$ ( M= Sc, Ti, V, Cr, Mn, Fe, Co, Ni) clusters have been carried out within a gradient corrected density functional formalism. The ground state of most MSi$_{12}$ clusters are shown to have the lowest spin multiplicity as opposed to the high spin multiplicity of free transition metal atoms. Consequently, a proper inclusion of the spin conservation rules is needed to understand the variation of the binding energy of M to Si$_{12}$ clusters. Using such rules, CrSi$_{12}$ and FeSi$_{12}$ are found to exhibit the highest binding energy across the neutral while VSi$_{12}^{-}$ has the highest binding energy across the anionic MSi$_{12}^{- }$series. It is shown that the variations in binding energy, electron affinity and ionization potential can be rationalized within an 18-electron sum rule commonly used to understand the stability of chemical complexes and shell filling in a confined free electron gas. [Preview Abstract] |
Wednesday, March 15, 2006 1:51PM - 2:03PM |
P11.00012: Single and Multiple Rings, and Cages in SiO$_{x}$ Clusters Penee Clayborne, Arthur Reber, J. Ulises Reveles, Shiv Khanna, A. Welford Castleman, Ashraf Ali Theoretical studies on the geometry, electronic structure and stability of Si$_{n}$O$_{m}$ clusters have been carried out within a gradient corrected density functional formalism. It is shown that the ground states of small Si$_{n}$O$_{n}$ clusters containing upto 4 units are single rings. The first Si-Si bond appears at Si$_{5}$O$_{5}$, and starting at this size, the elementary rings begin to assemble into multiple rings that eventually lead to cages. The ground state structures at larger sizes have a central core of pure Si atoms decorated by outer shell of SiO units. An analysis of the fragmentation patterns shows that Si$_{7}$O$_{7}$ and Si$_{10}$O$_{10}$ are particularly stable species. The results of our investigations on the Si$_{n}$O$_{n-1}$ and Si$_{n}$O$_{n+1}$ species will also be presented. In particular, we will examine possible reaction mechanisms that could lead to the formation of SiO$_{2}$ from SiO molecules in interstellar space. [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