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Physical Chemistry

2012

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Articles 1 - 26 of 26

Full-Text Articles in Physics

Structure And Chemistry Of Model Catalysts In Ultrahigh Vacuum, Joshua D. Walker Dec 2012

Structure And Chemistry Of Model Catalysts In Ultrahigh Vacuum, Joshua D. Walker

Theses and Dissertations

The study of catalysis is a key area of focus not only in the industrial sector but also in the nature and biological systems. The market for catalysis is a multi-billion dollar industry. Many of the materials and products we use on a daily basis are formed through a catalytic process. The quest to understanding and improving catalytic mechanisms is ongoing. Many model catalysts use transition metals as a support for chemical reactions to take place due to their selectivity and activity. Palladium, gold, and copper metals are studied in this work and show the ability to be catalytically reactive ...


Confinement Effects Of Solvation On A Molecule Physisorbed On A Metal Particle, Jacob Fosso Tande Dec 2012

Confinement Effects Of Solvation On A Molecule Physisorbed On A Metal Particle, Jacob Fosso Tande

Doctoral Dissertations

We describe and present results of the implementation of the surface and volume polarization for electrostatics~(SVPE) and the iso-density surface solvation models. Unlike most other implementation of the solvation models where the solute and the solvent are described with multiple numerical representation, our implementation uses a multiresolution, adaptive multiwavelet basis to describe both solute and the solvent. This requires reformulation to use integral equations throughout as well as a conscious management of numerical properties of the basis.

Likewise, we investigate the effects of solvation on the static properties of a molecule physisorbed on a spherical particle, modeled as a ...


Charge, Bonding, And Magneto-Elastic Coupling In Nanomaterials, Qi Sun Dec 2012

Charge, Bonding, And Magneto-Elastic Coupling In Nanomaterials, Qi Sun

Doctoral Dissertations

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials because they are intimately connected to charge, structure, and magnetism, and a quantitative analysis of their behavior can reveal microscopic aspects of chemical bonding and spin-phonon coupling. To investigate these effects, we measured infrared vibrational properties of bulk and nanoscale MoS2 [molybdenum disulfide], MnO [manganese(II) oxide], and CoFe2O4 [cobalt iron oxide]. From an analysis of frequencies, oscillator strengths, and high-frequency dielectric constants, we extracted Born and local effective charges, and polarizability for MoS2 and MnO. For MoS2 nanoparticles ...


Capacitively Coupled Radio-Frequency Discharges In Nitrogen At Low Pressures, L. L Alves, L. Marques, C. D Pintassilgo, W. Wattieaux, Et. Es-Sebbar, J. Berndt, E. Kovačević, N. Carrasco, L. Boufendi, G. Cernogora Jul 2012

Capacitively Coupled Radio-Frequency Discharges In Nitrogen At Low Pressures, L. L Alves, L. Marques, C. D Pintassilgo, W. Wattieaux, Et. Es-Sebbar, J. Berndt, E. Kovačević, N. Carrasco, L. Boufendi, G. Cernogora

Dr. Et-touhami Es-sebbar

This paper uses experiments and modelling to study capacitively coupled radio-frequency (rf) discharges in pure nitrogen, at 13.56 MHz frequency, 0.1–1 mbar pressures and 2–30 W coupled powers. Experiments performed on two similar (not twin) setups, existing in the LATMOS and the GREMI laboratories, include electrical and optical emission spectroscopy (OES) measurements. Electrical measurements give the rf-applied and the direct-current-self-bias voltages, the effective power coupled to the plasma and the average electron density. OES diagnostics measure the intensities of radiative transitions with the nitrogen second-positive and first-negative systems, and with the 811.5 nm atomic line ...


Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig Jun 2012

Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig

Yevgeniya V. Zastavker

The transition metal chalcogenide Ni(S,Se)2 is one of the few highly correlated, Mott-Hubbard systems without a strong first-order structural distortion that normally cuts off the critical behavior at the metal-insulator transition. The zero-temperature (T) transition was tuned with pressure, and significant deviations were found near the quantum critical point from the usual T1/2 behavior of the conductivity characteristic of electron-electron interactions in the presence of disorder. The transport data for pressure and temperature below 1 kelvin could be collapsed onto a universal scaling curve.


Ionization Photophysics And Rydberg Spectroscopy Of Diacetylene, M. Schwell, Y. Benilan, N.. Fray, M.-C. Gazeau, Et. Es-Sebbar, F.-G. Levrel, N. Campion, S. Leach Jun 2012

Ionization Photophysics And Rydberg Spectroscopy Of Diacetylene, M. Schwell, Y. Benilan, N.. Fray, M.-C. Gazeau, Et. Es-Sebbar, F.-G. Levrel, N. Campion, S. Leach

Dr. Et-touhami Es-sebbar

Photoionization of diacetylene was studied using synchrotron radiation over the range 8–24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron–photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IEad = (10.17 ± 0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE = (16.15 ± 0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions , C3H+, and C2H+. Structured autoionization features observed in the PEPICO spectrum of ...


Generalized Hydrodynamic Treatment Of The Interplay Between Restricted Transport And Catalytic Reactions In Nanoporous Materials, David M. Ackerman, Jing Wang, James W. Evans Jun 2012

Generalized Hydrodynamic Treatment Of The Interplay Between Restricted Transport And Catalytic Reactions In Nanoporous Materials, David M. Ackerman, Jing Wang, James W. Evans

Physics and Astronomy Publications

Behavior of catalytic reactions in narrow pores is controlled by a delicate interplay between fluctuations in adsorption-desorption at pore openings, restricted diffusion, and reaction. This behavior is captured by a generalized hydrodynamic formulation of appropriate reaction-diffusion equations (RDE). These RDE incorporate an unconventional description of chemical diffusion in mixed-component quasi-single-file systems based on a refined picture of tracer diffusion for finite-length pores. The RDE elucidate the nonexponential decay of the steady-state reactant concentration into the pore and the non-mean-field scaling of the reactant penetration depth.


Electrohydrodynamic Enhancement Of Heat Transfer And Mass Transport In Gaseous Media, Bulk Dielectric Liquids And Dielectric Thin Liquid Films, Seyed Reza Mahmoudi May 2012

Electrohydrodynamic Enhancement Of Heat Transfer And Mass Transport In Gaseous Media, Bulk Dielectric Liquids And Dielectric Thin Liquid Films, Seyed Reza Mahmoudi

Electronic Thesis and Dissertation Repository

Controlling transport phenomena in liquid and gaseous media through electrostatic forces has brought new important scientific and industrial applications. Although numerous EHD applications have been explored and extensively studied so far, the fast-growing technologies, mainly in the semiconductor industry, introduce new challenges and demands. These challenges require enhancement of heat transfer and mass transport in small scales (sometimes in molecular scales) to remove highly concentrated heat fluxes from reduced size devices. Electric field induced flows, or electrohydrodynamics (EHD), have shown promise in both macro and micro-scale devices.

Several existing problems in EHD heat transfer enhancements were investigated in this thesis ...


Volatile Products Controlling Titan’S Tholins Production, N. Carrasco, T. Gautier, Et. Es-Sebbar, P. Pernot, G. Cernogora Mar 2012

Volatile Products Controlling Titan’S Tholins Production, N. Carrasco, T. Gautier, Et. Es-Sebbar, P. Pernot, G. Cernogora

Dr. Et-touhami Es-sebbar

A quantitative agreement between nitrile relative abundances and Titan’s atmospheric composition was recently shown with a reactor simulating the global chemistry occurring in Titan’s atmosphere [Gautier et al. (2011) Icarus, 213: 625]. Here we present a complementary study on the same reactor using an in-situ diagnostic of the gas phase composition. Various initial N2-CH4 gas mixtures (methane varying from 1 to 10%) are studied, with a monitoring of the methane consumption and of the stable gas neutrals by in-situ mass spectrometry. Atomic hydrogen is also measured by optical emission spectroscopy. A positive correlation is found between atomic hydrogen ...


K-Shell X-Ray Spectroscopy Of Atomic Nitrogen, M. M. Sant'anna, Gunnar Ohrwall, Wayne C. Stolte, Alfred S. Schlachter, Dennis W. Lindle, B. M. Mclaughlin Mar 2012

K-Shell X-Ray Spectroscopy Of Atomic Nitrogen, M. M. Sant'anna, Gunnar Ohrwall, Wayne C. Stolte, Alfred S. Schlachter, Dennis W. Lindle, B. M. Mclaughlin

Chemistry and Biochemistry Faculty Publications

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64 ± 0.02 eV was determined for the K-shell binding energy.


Vuv Photoionization Of Acetamide Studied By Electron / Ion Coincidence Spectroscopy In The 8-24 Ev Photon Energy Range, M. Schwell, Y. Bénilan, N. Fray, M.-C Gazeau, Et. Es-Sebbar, Gustavo A. Garcia, L. Nahon, N. Champion, S. Leach Jan 2012

Vuv Photoionization Of Acetamide Studied By Electron / Ion Coincidence Spectroscopy In The 8-24 Ev Photon Energy Range, M. Schwell, Y. Bénilan, N. Fray, M.-C Gazeau, Et. Es-Sebbar, Gustavo A. Garcia, L. Nahon, N. Champion, S. Leach

Dr. Et-touhami Es-sebbar

A VUV photoionization study of acetamide was carried out over the 8-24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E (12A’) = (9.71±0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 12A”, was determined to be ≈ 10.1 eV. Assignments of the ...


Water Diffusion In And Out Of The Β-Barrel Of Gfp And The Fast Maturing Fluorescent Protein, Turbogfp, Marc Zimmer, Binsen Li, Ramza Shahid, Paola Peshkepija Jan 2012

Water Diffusion In And Out Of The Β-Barrel Of Gfp And The Fast Maturing Fluorescent Protein, Turbogfp, Marc Zimmer, Binsen Li, Ramza Shahid, Paola Peshkepija

Chemistry Faculty Publications

The chromophore of fluorescent proteins is formed by an internal cyclization of the tripeptide 65SYG67 fragment and a subsequent oxidation. The oxidation is slow – the kinetics of this step is presumably improved in fast maturing GFPs. Water molecules can aid in the chromophore formation. We have used 50ns molecular dynamics simulations of the mature and immature forms of avGFP and TurboGFP to examine the diffusion of water molecules in-and-out of the protein β-barrel. Most crystal structures of GFPs have well-structured waters within hydrogen-bonding distance of Glu222 and Arg96. It has been proposed that they have an important role in chromophore ...


Ogólnotechniczne Podstawy Biotechnologii Z Elementami Grafiki Inżynierskiej Ćw., Wojciech M. Budzianowski Jan 2012

Ogólnotechniczne Podstawy Biotechnologii Z Elementami Grafiki Inżynierskiej Ćw., Wojciech M. Budzianowski

Wojciech Budzianowski

No abstract provided.


Materiały Odstresowujące, Wojciech M. Budzianowski Jan 2012

Materiały Odstresowujące, Wojciech M. Budzianowski

Wojciech Budzianowski

No abstract provided.


Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy Into The Short-Wave Infrared, Trevor Laurence Courtney Jan 2012

Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy Into The Short-Wave Infrared, Trevor Laurence Courtney

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Two-dimensional Fourier Transform (2D FT) spectroscopy in the short-wave infrared (1-2 &mu) enables high frequency and time resolution experiments of molecular dyes, third-generation photovoltaic systems, and carotenoids - all rich in electronic transitions in this spectral region. Such experiments require short pulses with broad spectra to probe fast dephasing or solvation dynamics as well as couplings between widely spaced electronic transitions. Stable, low-dispersion interferometers at Brewster's angle are introduced for multioctave-spanning nonlinear spectroscopies. We adapt a compact, phase-characterized Mach-Zehnder interferometer to the short-wave infrared; active stabilization produces accurate and evenly spaced time delays between the two excitation pulses in 2D FT spectroscopy. An intrinsically phase-stable Sagnac interferometer is introduced to enhance the interferometric signal detection with respect to the copropagating local oscillator in partially collinear 2D FT spectroscopy. These interferometers exploit the air-glass interface Brewster's angle of thin-film metallic beam splitters to preserve expected output phase shifts and to minimize secondary reflections over multiple octaves. A homebuilt short-wave IR noncollinear optical parametric amplifier with a periodically poled crystal provides broadband excitation and ...


Nanostructures Of Liquid Crystal Phases, Dong Chen Jan 2012

Nanostructures Of Liquid Crystal Phases, Dong Chen

Physics Graduate Theses & Dissertations

Bent-core liquid crystals have attracted intense interest in recent years, exhibiting a wide variety of novel structural phenomena involving the interplay of chirality, molecular bend and molecular tilt. Freeze-fracture transmission electron microscopy together with other experimental methods has been used to characterize the nanostructures of bent-core liquid crystal phases in which the molecules undergo complex self-assembly, forming, for example, helical nanofilaments (the B4 phase), disordered focal conics (the DC phase), and layer undulations (the B7 phase) in the bulk. These studies have helped us better understand the complex nature of these and other liquid crystal phases. For example, the investigation ...


A Comprehensive Search For Stable Pt–Pd Nanoalloy Configurations And Their Use As Tunable Catalysts, Teck L. Tan, Lin-Lin Wang, Duane D. Johnson, Kewu Bai Jan 2012

A Comprehensive Search For Stable Pt–Pd Nanoalloy Configurations And Their Use As Tunable Catalysts, Teck L. Tan, Lin-Lin Wang, Duane D. Johnson, Kewu Bai

Ames Laboratory Publications

Using density-functional theory, we predict stable alloy configurations (ground states) for a 1 nm Pt–Pd cuboctahedral nanoparticle across the entire composition range and demonstrate their use as tunable alloy catalysts via hydrogen-adsorption studies. Unlike previous works, we use simulated annealing with a cluster expansion Hamiltonian to perform a rapid and comprehensive search that encompasses both high and low-symmetry configurations. The ground states show Pt(core)–Pd(shell) type configurations across all compositions but with specific Pd patterns. For catalysis studies at room temperatures, the ground states are more realistic structural models than the commonly assumed random alloy configurations. Using ...


Surface And Particle-Size Effects On Hydrogen Desorption From Catalyst-Doped Mgh2, J. M. Reich, Lin-Lin Wang, Duane D. Johnson Jan 2012

Surface And Particle-Size Effects On Hydrogen Desorption From Catalyst-Doped Mgh2, J. M. Reich, Lin-Lin Wang, Duane D. Johnson

Ames Laboratory Publications

With their high capacity, light-metal hydrides like MgH2 remain under scrutiny as reversible H-storage materials, especially to develop control of H-desorption properties by decreasing size (ball-milling) and/or adding catalysts. By employing density functional theory and simulated annealing, we study initial H2 desorption from semi-infinite stepped rutile (110) surface and Mg31H62 nanoclusters, with(out) transition-metal catalyst dopants (Ti or Fe). While Mg31H62structures are disordered (amorphous), the semi-infinite surfaces and nanoclusters have similar single, double, and triple H-to-metal bond configurations that yield similar H-desorption energies. Hence, there is no size effect on desorption energetics with reduction in sample size, but dopants ...


Nmr And Conductivity Studies Of The Mixed Glass Former Effect In Lithium Borophosphate Glasses, Michael Storek, Roland Böhmer, Steve W. Martin, Dirk Larink, Hellmut Eckert Jan 2012

Nmr And Conductivity Studies Of The Mixed Glass Former Effect In Lithium Borophosphate Glasses, Michael Storek, Roland Böhmer, Steve W. Martin, Dirk Larink, Hellmut Eckert

Materials Science and Engineering Publications

Alkali ion charge transport has been studied in a series of mixed glass former lithium borophosphate glasses of composition 0.33Li2O + 0.67[xB2O3 + (1 – x)P2O5]. The entire concentration range, 0.0 ≤ x ≤ 1.0, from pure glassy Li2P4O11 to pure glassy Li2B4O7 has been examined while keeping the molar fraction of Li2O constant. Electrical conductivity measurements and nuclear magnetic resonance techniques such as spin relaxometry, line shape analysis, and stimulated-echo spectroscopy were used to examine the temperature ...


Applications Of Density Functional Theory In Materials Science And Engineering, Manuel Alvarado Jan 2012

Applications Of Density Functional Theory In Materials Science And Engineering, Manuel Alvarado

Open Access Theses & Dissertations

Density Functional Theory (DFT) is a powerful tool that can be used to model various systems in materials science. Our research applies DFT to two problems of interest. First, an organic/inorganic complex dye system known as a Mayan pigment is modeled to determine chemical binding sites, verifying each model with physical data such as UV/Vis spectra. Preliminary studies on palygorskite-based mayan pigments (mayacrom blue, mayacrom purple) show excellent agreement with experimental studies when using a dimer dye geometry binding with tetrahedrally-coordinated aluminum impurity sites in palygorksite. This approach is applied to a sepiolite-based organic/inorganic dye system using ...


Computational Study Of The Hydration Of Sulfuric Acid Dimers: Implications For Acid Dissociation And Aerosol Formation, Berhane Temelso, Thuong Ngoc Phan, George C. Shields Jan 2012

Computational Study Of The Hydration Of Sulfuric Acid Dimers: Implications For Acid Dissociation And Aerosol Formation, Berhane Temelso, Thuong Ngoc Phan, George C. Shields

Faculty Journal Articles

We have investigated the thermodynamics of sulfuric acid dimer hydration using ab initio quantum mechanical methods. For (H2SO4)2(H2O)n where n = 0−6, we employed high-level ab initio calculations to locate the most stable minima for each cluster size. The results presented herein yield a detailed understanding of the first deprotonation of sulfuric acid as a function of temperature for a system consisting of two sulfuric acid molecules and up to six waters. At 0 K, a cluster of two sulfuric acid molecules and one water remains undissociated. Addition of a second water ...


Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering For Gas-Phase Temperature Measurements, Joseph Daniel Miller Jan 2012

Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering For Gas-Phase Temperature Measurements, Joseph Daniel Miller

Graduate Theses and Dissertations

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) is employed for quantitative gas-phase temperature measurements in combustion processes and heated flows. In this approach, ultrafast 100-fs laser pulses are used to induce vibrational and rotational transitions in N2 and O2, while a third spectrally narrowed picosecond pulse is used to probe the molecular response. Temporal suppression of the nonresonant contribution and elimination of collisional effects are achieved by delay of the probe pulse, while sufficient spectral resolution is maintained for frequency-domain detection and thermometry. A theoretical framework is developed to model experimental spectra by phenomenologically describing ...


Hyperfine Structure In The Electronic Spectrum Of Tas, Andrew Bendelsmith, Keith Kuwata, Thomas Varberg Dec 2011

Hyperfine Structure In The Electronic Spectrum Of Tas, Andrew Bendelsmith, Keith Kuwata, Thomas Varberg

Thomas D. Varberg

No abstract provided.


Hydrogen Production From Biogas By Oxy-Reforming: Reaction System Analysis, Aleksandra Terlecka, Wojciech M. Budzianowski Dec 2011

Hydrogen Production From Biogas By Oxy-Reforming: Reaction System Analysis, Aleksandra Terlecka, Wojciech M. Budzianowski

Wojciech Budzianowski

Oxy-reforming is emerging as an interesting alternative to conventional methods of hydrogen generation. The current article characterises this process through analysis of individual reactions: SMR (steam methane reforming), WGS (water gas shift) and CPO (catalytic partial oxidation). Analyses relate to optimisation of thermal conditions thus enabling cost-effectivenes of the process.


Using Frequency-Narrowed, Tunable Laser Diode Arrays With Integrated Volume Holographic Gratings For Spin-Exchange Optical Pumping At High Resonant Fluxes And Xenon Densities, Nicholas Whiting, Panayiotis Nikolaou, Neil A. Eschmann, Michael J. Barlow, R Lammert, J Ungar, W Hu, Laurent Vaissie, Boyd M. Goodson Dec 2011

Using Frequency-Narrowed, Tunable Laser Diode Arrays With Integrated Volume Holographic Gratings For Spin-Exchange Optical Pumping At High Resonant Fluxes And Xenon Densities, Nicholas Whiting, Panayiotis Nikolaou, Neil A. Eschmann, Michael J. Barlow, R Lammert, J Ungar, W Hu, Laurent Vaissie, Boyd M. Goodson

Nicholas Whiting

Next-generation laser diode arrays with integrated ‘on-chip’ volume holographic gratings can provide high power with spectrally narrowed output that can be tuned about the rubidium D1 line—without causing significant changes to the laser’s flux or spectral profile. These properties were exploited to independently evaluate the effects of varying the laser centroid wavelength and power on batch-mode Rb/129Xe spin-exchange optical pumping (SEOP) as functions of xenon partial pressure and cell temperature...


Cavity Ringdown Spectroscopy Of 13c2h2 In The 12900-13400 Region.Pdf, Christopher J. Lue, Michael Sullivan, Mark Draganjac, Scott Reeve Dec 2011

Cavity Ringdown Spectroscopy Of 13c2h2 In The 12900-13400 Region.Pdf, Christopher J. Lue, Michael Sullivan, Mark Draganjac, Scott Reeve

Scott Reeve

No abstract provided.