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Articles 1 - 12 of 12

Full-Text Articles in Physics

Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta Oct 2008

Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta

Chemistry Publications and Other Works

Inelastic neutron scattering is used to probe the dynamical response of H2 films adsorbed on MgO(100) as a function of film thickness. Concomitant diffraction measurements and a reduced-dimensionality quantum dynamical model provide insight into the molecule-surface interaction potential. At monolayer thickness, the rotational motion is strongly influenced by the surface, so that the molecules behave like quasiplanar rotors. These findings have a direct impact on understanding how molecular hydrogen binds to the surface of materials used in catalytic and storage applications.


Dynamics Of Apomyoglobin In The Α-To-Β Transition And Of Partially Unfolded Aggregated Protein, E. Fabiani, A. M. Stadler, D. Madern, M. M. Koza, M. Tehei, M. Hirai, G. Zaccai Oct 2008

Dynamics Of Apomyoglobin In The Α-To-Β Transition And Of Partially Unfolded Aggregated Protein, E. Fabiani, A. M. Stadler, D. Madern, M. M. Koza, M. Tehei, M. Hirai, G. Zaccai

Faculty of Science - Papers (Archive)

Changes of molecular dynamics in the α-to-β transition associated with amyloid fibril formation were explored on apo-myoglobin (ApoMb) as a model system. Circular dichroism, neutron and X-ray scattering experiments were performed as a function of temperature on the protein, at different solvent conditions. A significant change in molecular dynamics was observed at the α-to-β transition at about 55 ˚C, indicating a more resilient high temperature β structure phase. A similar effect at approximately the same temperature was observed in holo-myoglobin, associated with partial unfolding and protein aggregation. A study in a wide temperature range between 20 K and 360 K …


Linear Dichroism In Resonant Inelastic X-Ray Scattering To Molecular Spin-Orbit States, Renaud Guillemin, Stephane Carniato, Wayne C. Stolte, Loic Journel, Richard Taieb, Dennis W. Lindle, Marc Simon Sep 2008

Linear Dichroism In Resonant Inelastic X-Ray Scattering To Molecular Spin-Orbit States, Renaud Guillemin, Stephane Carniato, Wayne C. Stolte, Loic Journel, Richard Taieb, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

Polarization-dependent resonant inelastic x-ray scattering (RIXS) is shown to be a new probe of molecular-field effects on the electronic structure of isolated molecules. A combined experimental and theoretical analysis explains the linear dichroism observed in Cl 2p RIXS following Cl 1s excitation in HCl and CF3Cl as due to molecular-field effects, including singlet-triplet exchange, indicating polarized-RIXS provides a direct probe of spin-orbit-state populations applicable to any molecule.


Inverse Velocity Dependence Of Vibrationally Promoted Electron Emission From A Metal Surface, N. H. Nahler, J. D. White, Jerry L. Larue, Daniel J. Auerbach, Alec M. Wodtke Aug 2008

Inverse Velocity Dependence Of Vibrationally Promoted Electron Emission From A Metal Surface, N. H. Nahler, J. D. White, Jerry L. Larue, Daniel J. Auerbach, Alec M. Wodtke

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

All previous experimental and theoretical studies of molecular interactions at metal surfaces show that electronically nonadiabatic influences increase with molecular velocity. We report the observation of a nonadiabatic electronic effect that follows the opposite trend: The probability of electron emission from a low–work function surface—Au(111) capped by half a monolayer of Cs—increases as the velocity of the incident NO molecule decreases during collisions with highly vibrationally excited NO(X2π½, V = 18; V is the vibrational quantum number of NO), reaching 0.1 at the lowest velocity studied. We show that these results are consistent with a vibrational …


An Extended Multireference Study Of The Electronic States Of Para-Benzyne, Carol A. Parish, Evan B. Wang, Hans Lischka Jul 2008

An Extended Multireference Study Of The Electronic States Of Para-Benzyne, Carol A. Parish, Evan B. Wang, Hans Lischka

Chemistry Faculty Publications

A state-averaged, multireference complete active space (CAS) approach was used for the determination of the vertical excitation energies of valence and Rydberg states of para-benzyne. Orbitals were generated with a 10- and 32-state averaged multiconfigurational self-consistent field approach. Electron correlation was included using multireference configuration interaction with singles and doubles, including the Pople correction for size extensivity, multireference averaged quadratic coupled cluster (MR-AQCC) and MR-AQCC based on linear response theory. There is a very high density of electronic states in this diradical system—there are more than 17 states within 7 eV of the ground state including two 3s …


Real-Time Plasma Controlled Chemistry In A Two-Frequency, Confined Plasma Etcher, Vladimir Milosavljevic, Albert R. Ellingboe, Cezar Gaman, John V. Ringwood Apr 2008

Real-Time Plasma Controlled Chemistry In A Two-Frequency, Confined Plasma Etcher, Vladimir Milosavljevic, Albert R. Ellingboe, Cezar Gaman, John V. Ringwood

Articles

The physics issues of developing model-based control of plasma etching are presented. A novel methodology for incorporating real-time model-based control of plasma processing systems is developed. The methodology is developed for control of two dependent variables (ion flux and chemical densities) by two independent controls (27 MHz power and O2flow). A phenomenological physics model of the nonlinear coupling between the independent controls and the dependent variables of the plasma is presented. By using a design of experiment, the functional dependencies of the response surface are determined. In conjunction with the physical model, the dependencies are used to deconvolve the sensor …


Stability And Equation Of State Of A Nanocrystalline Ga-Ge Mullite In A Vitroceramic Composite: A Synchrotron X-Ray Iffraction Study, Kristina E. Lipinska-Kalita, Patricia Kalita, Cedric Gobin, Oliver Hemmers, Thomas Hartmann, Gino Mariotto Apr 2008

Stability And Equation Of State Of A Nanocrystalline Ga-Ge Mullite In A Vitroceramic Composite: A Synchrotron X-Ray Iffraction Study, Kristina E. Lipinska-Kalita, Patricia Kalita, Cedric Gobin, Oliver Hemmers, Thomas Hartmann, Gino Mariotto

Environmental Studies Faculty Publications

Synchrotron x-ray diffraction and diamond anvil cell techniques were used to characterize the phase transformations and to evaluate the structural stability at elevated pressures of a developed nanocrystalline composite. The optically transparent material was built of a germanium oxide-based amorphous host matrix with homogeneously dispersed 13±3 nm Ga-Ge mullite-type nanocrystals, which had a structure similar to the conventional Al2O3-SiO2 mullite. The equation of state of the nanocrystals and the overall structural integrity of the nanocomposite were investigated in quasihydrostatic conditions on compression to 36 GPa and on the following decompression to ambient conditions. The overall …


Equation Of State Of Gallium Oxide To 70 Gpa: Comparison Of Quasihydrostatic And Nonhydrostatic Compression, Kristina E. Lipinska-Kalita, Patricia Kalita, Oliver Hemmers, Thomas Hartmann Mar 2008

Equation Of State Of Gallium Oxide To 70 Gpa: Comparison Of Quasihydrostatic And Nonhydrostatic Compression, Kristina E. Lipinska-Kalita, Patricia Kalita, Oliver Hemmers, Thomas Hartmann

Environmental Studies Faculty Publications

Synchrotron x-ray diffraction and diamond-anvil cell techniques were used to characterize pressure induced structural modifications in gallium oxide. Gallium oxide was studied on compression up to 70 GPa and on the following decompression. The effect of the pressure-transmitting medium on the structural transformations was investigated in two sets of compression and decompression runs, one with nitrogen as a quasihydrostatic pressure-transmitting medium and the other in nonhydrostatic pressure conditions. The x-ray diffraction data showed gradual phase transition from a low-density, monoclinic β-Ga2O3 to a high-density, rhombohedral α-Ga2O3. With the use of nitrogen as a …


A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde Jan 2008

A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde

Chemistry Publications and Other Works

We present a six-dimensional potential energy surface for the (H2)2 dimer based on coupled-cluster electronic structure calculations employing large atom-centered Gaussian basis sets and a small set of midbond functions at the dimer’s center of mass. The surface is intended to describe accurately the bound and quasibound states of the dimers (H2)2, (D2)2, and H2–D2 that correlate with H2 or D2 monomers in the rovibrational levels (v, j) =(0,0), (0,2), (1,0), and (1,2). We employ a close-coupled approach to compute the …


Solution-Based Synthesis Of Nitride Fuels, Kenneth Czerwinski, Tyler A. Sullens Jan 2008

Solution-Based Synthesis Of Nitride Fuels, Kenneth Czerwinski, Tyler A. Sullens

Fuels Campaign (TRP)

One of the original synthetic routes devised for the synthesis of U (III)N involved the entire reaction taking place in liquid ammonia. Several experimental reactions were conducted in an attempt to synthesize the UI3(NH3)x and U(NH2)3(NH3)x precursors of U(III) N. Each attempt involved cleaning of the uranium metal to remove the oxide coating of the metal reagent with 3 washes of concentrated nitric acid, each followed by a rinse with liquid ammonia. Success of this cleaning procedure was varied, with a majority of cleaned metal oxidizing rapidly once …


Photofragmentation Of Sif4 Upon Si 2p And F 1s Core Excitation: Cation And Anion Yield Spectroscopy, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, Dennis W. Lindle Jan 2008

Photofragmentation Of Sif4 Upon Si 2p And F 1s Core Excitation: Cation And Anion Yield Spectroscopy, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We have studied the fragmentation dynamics of core-excited SiF4 by means of soft-x-ray photoexcitation and partial positive and negative ion yield measurements around the Si L2,3-shell and F K-shell ionization thresholds. All detectable ionic fragments are reported and we observe significant differences between the various partial ion yields near the Si 2p threshold. The differences are similar to our previous results from CH3Cl showing more extended fragmentation in correspondence to transitions to Rydberg states. At variance with smaller systems, we observe negative ion production in the shape resonance region. This can be related …


Activation Energy Of Surface Diffusion And Terrace Width Dynamics During The Growth Of In (4×3) On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali Jan 2008

Activation Energy Of Surface Diffusion And Terrace Width Dynamics During The Growth Of In (4×3) On Si (100) - (2×1) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The nucleation and growth of indium on a vicinal Si (100) - (2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In (4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1) × 1011 s-1. The RHEED specular …