Biological and Chemical Physics Commons^™

Magnetic Ordering And Structural Phase Transition In Strained Ultrathin Srruo3/Srtio3 Superlattice, Mingquiang Gu, Xiaoshan Wu, Guoping Zhang

Symposium 2012

No abstract provided.

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 Research

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.

Crystal Structural Behavior Of Cocu₂O₃ At High Temperatures, April Jeffries, Ravhi S. Kumar, Andrew L. Cornelius

Undergraduate Research Opportunities Program (UROP)

High temperature structure of CoCu₂O₃ The spin ladder compounds have received much attention recently due to their relation to the high transition temperature superconductivity. Also the study of spin ladder compounds is of great interest to explore the specific characteristics that result in their behavior. The CoCu₂O₃ spin ladder crystal structure is similar to SrCu₂O₃, which is apparent composition for many high temperature superconductors. The effects of temperature on structural change are investigated for this system. High temperature x-ray diffraction patterns were collected up to 1000⁰C and the variation of lattice parameters as a function of temperature up to decomposition …

The Economics Of The Atomic Bomb: Cost And Utilization, Jonathan M. Davis Mr.

Senior Honors Theses

Few moments in human history can be compared to the culmination of events that brought the atomic bomb into creation.  It is incredible to contemplate that while a nation was fighting a two front war that spanned from Europe into the Pacific, that the United States was able to utilize the time, energy, brains, materials, manpower, and capital to complete a project in four years. That under any other circumstances would have taken greater than half a century to complete.

First, this thesis will discuss breakthroughs in research that led scientists to believe that the atomic weapons could be built, …

Hipsec X-Ray Diffraction And Infrared Spectroscopy Studies On Energetic Materials Under Extreme Conditions, Mai Huong Bausch, Yu Liu

Festival of Communities: UG Symposium (Posters)

We conducted a series of experiments on the decompositions of the energetic materials NaBH4, NH3BH3, HMX, and RDX under different pressures using the x-ray diffraction (XRD) technique; we also studied the lesser known but high-performance explosive FOX-7’s behaviors under high pressures using the infrared spectroscopy (IR) technique. For the chemical decomposition of NaBH4 and NH3BH3 we discovered possible x-ray induced hydrogen gas generation; for the decomposition of HMX and RDX, we discovered that the decay rates of these two materials vary with pressure respectively; for the study of FOX-7’s high pressure behaviors we discovered potential phase changes and pressure induced …

Ultrafast Rempi In Benzene And The Monohalobenzenes Without The Focal Volume Effect, Timothy D. Scarborough, James Strohaber, David B. Foote, Collin J. Mcacy, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We report on the photoionization and photofragmentation of benzene (C₆H₆) and of the monohalobenzenes C₆H₅–X (X = F, Cl, Br, I) under intense-field, single-molecule conditions. We focus 50-fs, 804-nm pulses from a Ti:sapphire laser source, and record ion mass spectra as a function of intensity in the range ~10¹³ W/cm² to ~10¹⁵ W/cm². We count ions that were created in the central, most intense part of the focal area; ions from other regions are rejected. For all targets, stable parent ions (C₆H₅X+) are …

Site-Specific Photocatalytic Splitting Of Methanol On Tio2(110), Chuanyao Zhou, Zefeng Ren, Shijing Tan, Zhibo Ma, Xinchun Mao, Dongxu Dai, Hongjun Fan, Xueming Yang, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Zhou Wang, Zhenyu Li, Bing Wang, Jinlong Yang, Jianguo Hou

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Clean hydrogen production is highly desirable for future energy needs, making the understanding of molecular-level phenomena underlying photocatalytic hydrogen production both fundamentally and practically important. Water splitting on pure TiO₂ is inefficient, however, adding sacrificial methanol could significantly enhance the photocatalyzed H₂ production. Therefore, understanding the photochemistry of methanol on TiO₂ at the molecular level could provide important insights to its photocatalytic activity. Here, we report the first clear evidence of photocatalyzed splitting of methanol on TiO₂ derived from time-dependent two-photon photoemission (TD-2PPE) results in combination with scanning tunneling microscopy (STM). STM tip induced molecular manipulation …

Measurement Of Γ-Emission Branching Ratios For 154,156,158Gd Compound Nuclei: Tests Of Surrogate Nuclear Reaction Approximations For (N,Γ) Cross Sections, N. D. Scielzo

Physics Faculty Publications

The surrogate nuclear reaction method can be used to determine neutron-induced reaction cross sections from measured decay properties of a compound nucleus created using a different reaction and calculated formation cross sections. The reliability of (n,γ) cross sections determined using the Weisskopf-Ewing and ratio approximations are explored for the ^{155, 157}Gd(n,γ) reactions. Enriched gadolinium targets were bombarded with 22-MeV protons and γ rays were detected in coincidence with scattered protons using the Silicon Telescope Array for Reaction Studies/Livermore-Berkeley Array for Collaborative Experiments (STARS/LiBerACE) silicon and germanium detector arrays. The γ-emission probabilities for the ^{154, 156, …}

Sulfur K-Edge Photo-Fragmentation Of Ethylene Sulfide, Wayne C. Stolte, Gunnar Ohrwall

Chemistry and Biochemistry Faculty Research

We have investigated the photofragmentation properties of the three-membered ring heterocyclic molecule ethylene sulfide or thiirane, C₂H₄S, by time-of-flight mass spectroscopy. Positive ions have been collected as a function of photon energy around the S K ionization threshold. Branching ratios were derived for all detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. We present a new assignment of the spectral features around the S K-edge.

Fragmentation Properties Of Three-Membered Ring Heterocyclic Molecules By Partial Ion Yield Spectroscopy: C2h4o And C2h4s, Wayne C. Stolte, I. Dumitriu, S-W Yu, Gunnar Ohrwall, Maria Novella Piancastelli, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We investigated the photofragmentation properties of two three-membered ring heterocyclic molecules, C₂H₄O and C₂H₄S, by total and partial ion yield spectroscopy. Positive and negative ions have been collected as a function of photon energy around the C 1s and O 1s ionization thresholds in C₂H₄O, and around the S 2p and C 1s thresholds in C₂H₄S. We underline similarities and differences between these two analogous systems. We present a new assignment of the spectral features around the C K-edge and the sulfur L_{2 …}

Experimental And Theoretical Investigation Of Molecular Field Effects By Polarization-Resolved Resonant Inelastic X-Ray Scattering, Stephane Carniato, Renaud Guillemin, Wayne C. Stolte, Loic Journel, Richard Taieb, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

We present a combined theoretical and experimental study of molecular field effects on molecular core levels. Polarization-dependent resonant inelastic x-ray scattering is observed experimentally after resonant K-shell excitation of CF₃Cl and HCl. We explain the linear dichroism observed in spin-orbit level intensities as due to molecular field effects, including singlet-triplet exchange, and interpret this behavior in terms of population differences in the 2p_x,y,z inner-shell orbitals. We investigate theoretically the different factors that can affect the electronic populations and the dynamical R dependence of the spin-orbit ratio. Finally, the results obtained are used to interpret the L-shell …

Partial Ion Yield Sspectroscopy Around The Cl 2p And C 1s Ionization Thresholds In Cf3cl, D. Ceolin, Maria Novella Piancastelli, Wayne C. Stolte, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We present a partial ion yield experiment on freon 13, CF₃Cl, excited in the vicinity of the C 1s and Cl 2p ionization thresholds. We have collected a large amount of cationic fragments and a few anionic fragments at both edges. We have observed a strong intensity dependence of Rydberg transitions with ion fragment size for the CF_nCl⁺ and CF_n⁺/F⁺ (n=0–3) series at both the Cl 2p and C 1s ionization edges. Selectivity in the fragmentation processes involving the C–Cl and C–F bonds are highlighted by the intensities of the C …

Yttrium And Hydrogen Superstructure And Correlation Of Lattice Expansion And Proton Conductivity In The Bazr0.9y0.1o2.95 Proton Conductor, A. Braun, A. Ovalle, V. Pomjakushin, A. Cervellino, S. Erat, Wayne C. Stolte, T. Graule

Chemistry and Biochemistry Faculty Research

Bragg reflections in Y-resonant x-ray diffractograms of BaZr_0.9Y_0.1O_2.95 (BZY10) reveal that Y is organized in a superstructure. Comparison with neutron diffraction superstructure reflections in protonated/deuterated BZY10 suggests that both superstructures are linked, and that protons move in the landscape imposed by the Y. The thermal lattice expansion decreases abruptly for protonated BZY10 at T≥648±20 K, coinciding with the onset of lateral proton diffusion and suggesting a correlation of structural changes and proton conductivity. The chemical shift in the Y L₁-shell x-ray absorption spectra reveals a reduction from Y³⁺ toward Y²⁺ upon …

Reconstructing Three-Dimensional Shape Envelopes From Time-Resolved Small-Angle X-Ray Scattering Data, Jessica Lamb, Lisa W. Kwok, Xiangyun Qiu, Kurt Andresen, Hye Yoon Park, Lois Pollack

Physics and Astronomy Faculty Publications

Modern computing power has made it possible to reconstruct low-resolution, three-dimensional shapes from solution small-angle X-ray scattering (SAXS) data on biomolecules without a priori knowledge of the structure. In conjunction with rapid mixing techniques, SAXS has been applied to time resolve conformational changes accompanying important biological processes, such as biomolecular folding. In response to the widespread interest in SAXS reconstructions, their value in conjunction with such time-resolved data has been examined. The group I intron from Tetrahymena thermophila and its P4–P6 subdomain are ideal model systems for investigation owing to extensive previous studies, including crystal structures. The goal of this …

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.

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 L_2,3-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 …

Focusing Capillary Optics For Use In Solution Small-Angle X-Ray Scattering, Jessica S. Lamb, Sterling Cornaby, Kurt Andresen, Lisa W. Kwok, Hye Yoon Park, Xiangyun Qiu, Detlef-M. Smilgies, Donald H. Bilderback, Lois Pollack

Physics and Astronomy Faculty Publications

Measurements of the global conformation of macromolecules can be carried out using small-angle X-ray scattering (SAXS). Glass focusing capillaries, manufactured at the Cornell High Energy Synchrotron Source (CHESS), have been successfully employed for SAXS measurements on the heme protein cytochrome c. These capillaries provide high X-ray flux into a spot size of tens of micrometres, permitting short exposures of small-volume samples. Such a capability is ideal for use in conjunction with microfluidic mixers, where time resolution may be determined by beam size and sample volumes are kept small to facilitate mixing and conserve material.

Design And Performance Of A Curved-Crystal X-Ray Emission Spectrometer, A. C. Hudson, Wayne C. Stolte, Dennis W. Lindle, Renaud Guillemin

Chemistry and Biochemistry Faculty Research

A curved-crystal x-ray emission spectrometer has been designed and built to measure 2–5 keV x-ray fluorescence resulting from a core-level excitation of gas phase species. The spectrometer can rotate 180°, allowing detection of emitted x rays with variable polarization angles, and is capable of collecting spectra over a wide energy range (20 eV wide with 0.5 eV resolution at the Cl K edge) simultaneously. In addition, the entire experimental chamber can be rotated about the incident-radiation axis by nearly 360° while maintaining vacuum, permitting measurements of angular distributions of emitted x rays.

Femtosecond Nuclear Motion Of Hcl Probed By Resonant X-Ray Raman Scattering In The Cl 1s Region, Marc Simon, Loic Journel, Stephane Carniato, Richard Taieb, I. Minkov, Faris Gel'mukhanov, P. Salek, H. Agren, Renaud Guillemin, Wayne C. Stolte, A. C. Hudson, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Femtosecond dynamics are observed by resonant x-ray Raman scattering (RXS) after excitation along the dissociative Cl 1s→6ơ* resonance of gas-phase HCl. The short core-hole lifetime results in a complete breakdown of the common nondispersive behavior of soft-x-ray transitions between parallel potentials. We evidence a general phenomenon of RXS in the hard-x-ray region: a complete quenching of vibrational broadening. This opens up a unique opportunity for superhigh resolution x-ray spectroscopy beyond vibrational and lifetime limitations.

Photo-Induced Current Measurements In Chlamydomonas Cell Suspensions, Collin D. Capano

Renée Crown University Honors Thesis Projects - All

In order to fully understand the principles behind phototaxis in flagellate algae, it is necessary to measure the electric currents these cells create when processing light stimuli. Many different techniques have been developed to do this. One of these techniques, measuring from cell suspensions, has a number of advantages over the others that makes it highly desirable. However, the lab that first developed this method of recording did not describe the setup very well. The result is that in the thirteen years since it was first reported, only one other independent lab has been able to reproduce the results despite …

Detection Of Bacillus Spores By Aptamer Selectivity Using Atomic Force Microscopy, Nina M. Houtkooper

Theses and Dissertations

The anthrax attack of Oct 2001 demonstrates the need for a rapid detector for spores of Bacillus anthracis (BA). Current technology requires cultures of BA to be grown for 24 hours. Using aptamers, a type of nucleic acid ligand selective for a target molecule, to select BA spores for measurement without culturing is a possible solution for quicker detection. An aptamer having a specially selected structure is expected to selectively bind to the surface of its target spore, separating it from other material. An atomic force microscopy (AFM) method was developed to test this selectivity. Aptamers having structure selected to …

Near-Edge X-Ray Absorption Fine Structure Study Of Ion-Beam-Induced Phase Transformation In Gd2(Ti1-Yzry)2o7, Ponnusamy Nachimuthu, S. Thevuthasan, V. Shutthanandan, E. M. Adams, W. J. Weber, B. D. Begg, D. K. Shuh, Dennis W. Lindle, Eric M. Gullikson, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

The structural and electronic properties of Gd₂(Ti_1−yZr_y)₂O₇ (y=0–1) pyrochlores following a 2.0-MeV Au²⁺ ion-beam irradiation (~5.0 X 10¹⁴ Au²⁺/cm²) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd₂(Ti_1−yZr_y)₂O₇ leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd₂(Ti_{1−y …}

Fragmentation Dynamics Of H2s Following S 2p Photoexcitation, Renaud Guillemin, S-W Yu, Wayne C. Stolte, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

The fragmentation dynamics of core-excited H₂S has been studied by means of partial anion and cation yield measurements around the S L_2,3-subshell ionization thresholds. All detectable ionic fragments are reported, and significant differences between partial ion yields are observed. Possible dissociation pathways are discussed by comparison to previous studies of electron spectra.

Anion And Cation-Yield Spectroscopy Of Core-Excited Sf6, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, M. M. Sant'anna, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF₆. All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we …

Probing Cation Antisite Disorder In Gd2ti2o7 Pyrochlore By Site-Specific Nexafs And Xps, Ponnusamy Nachimuthu, S. Thevuthasan, Mark H. Engelhard, W. J. Weber, D. K. Shuh, N. M. Hamdan, B. S. Mun, E. M. Adams, D. E. Mccready, V. Shutthanandan, Dennis W. Lindle, G. Balakrishnan, R. C. Ewing

Chemistry and Biochemistry Faculty Research

Disorder in Gd₂Ti₂O₇ is investigated by near-edge x-ray-absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS). NEXAFS shows Ti⁴⁺ ions occupy octahedral sites with a tetragonal distortion induced by vacant oxygen sites. O 1s XPS spectra obtained with a charge neutralization system from Gd₂Ti₂O₇(100) and the Gd₂Ti₂O₇ pyrochlore used by Chen et al. [Phys. Rev. Lett. 88, 105901 (2002)], both yielded a single peak, unlike the previous result on the latter that found two peaks. The current results give no evidence for …

Performance Characteristics Of Beamline 6.3.1 From 200 Ev To 2000 Ev At The Advanced Light Source, Ponnusamy Nachimuthu, J. H. Underwood, C. D. Kemp, Eric M. Gullikson, Dennis W. Lindle, David K. Shuh, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

Bend magnet beamline 6.3.1 at the Advanced Light Source operates from 200 eV to 2000 eV, primarily used for x-ray absorption fine structure investigations. The beamline optics consist of a compact, entrance-slitless, Hettrick-Underwood type variable-line-spacing plane-grating monochromator and refocusing mirrors to provide a 25 μm × 500 μm spot at the focal point in the reflectometer end station. Wavelength is scanned by the simple rotation of the grating and illuminates a fixed exit slit. The LabView based beamline control and data acquisition computer code has been implemented to provide a convenient interface to the user. The dedicated end station is …

Photofragmentation Dynamics Of Core-Excited Water By Anion-Yield Spectroscopy, Wayne C. Stolte, M. M. Sant'anna, Gunnar Ohrwall, Maria Novella Piancastelli, I. Dominguez-Lopez, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Partial-anion and- cation yields from H₂O are presented for photon energies near the oxygen K edge. The O^- yield exhibits a feature above threshold attributed to doubly excited states, in contrast to the H^- and cation yields, which are nearly featureless above threshold. Additionally, the lack of the OH^- fragment indicates radiative decay and provides a negligible amount of anion formation.

Development Of A Portable Carbon Monoxide Sensor Based On An External Cavity Diode Laser At 1565 Nm, Eva Shirley Norris

Theses

Carbon monoxide is a major trace gas pollutant with road traffic being responsible for most emissions. Work has been done on the development of a carbon monoxide sensor, which is potentially capable of measuring the gas in vehicle exhaust emissions. This is based on tunable diode laser absorption spectroscopy The device must distinguish carbon monoxide from other gas species and from particulate matter. The device should also operate with a response time of the order of one second, have the potential for portability and a capacity for remote operation. Experimental work presented compares and contrasts the characteristics of the free-running …

Fragmentation Processes Following Core Excitation In Acetylene And Ethylene By Partial Ion Yield Spectroscopy, Maria Novella Piancastelli, Wayne C. Stolte, Gunnar Ohrwall, S-W Yu, D. Bull, K. Lantz, Alfred S. Schlachter, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Partial ion yield spectroscopy provides a very detailed picture of fragmentation processes following core excitation in isolated molecules. We exploit this potential in the analysis of decay processes following C1s→π and C1s→Rydberg excitations in ethylene and acetylene. We show that the relative intensity of spectral features related to the excitation to empty molecular orbitals or to Rydberg states is a function of the time variation of the fragmentation process. Namely, we see an intensity increase in the Rydberg states compared to the molecular orbitals as the fragmentation process becomes more extensive, a result attributable to the diffuse nature of the …

Holographic Analysis Of Diffraction Structure Factors, S. Marchesini, N. Mannella, C. S. Fadley, M. A. Van Hove, J. J. Bucher, D. K. Shuh, L. Fabris, M. J. Press, M. W. West, Wayne C. Stolte, Z. Hussain

Chemistry and Biochemistry Faculty Research

We combine the theory of inside-source/inside-detector x-ray fluorescence holography and Kossel lines/x ray standing waves in kinematic approximation to directly obtain the phases of the diffraction structure factors. The influence of Kossel lines and standing waves on holography is also discussed. We obtain partial phase determination from experimental data obtaining the sign of the real part of the structure factor for several reciprocal lattice vectors of a vanadium crystal.