Physical Sciences and Mathematics Commons^™

Properties Of New York/New Jersey Harbor Sediments, K. W. Jones, Huan Feng, E. A. Stren, U. Neuhäusler, J. Osán, N. Marinkovic, Z. Song

Huan Feng

Sediments found in waterways around the world may contain toxic compounds of anthropogeilic origin that can harm the environment and human health. As a result, it is often necessary to remove them and find disposal methods that are environmentally and economically acceptable. Here, we report on results obtained in an experimental program to characterize the nature of the sediment contamination. The objective was to gain a better understanding of the properties of the sediments to develop better methods for understanding the fate and transport of the contaminants and for improving methods for their removal from the sediments. Our investigations made …

Circular Dichroism Spectroscopy In The Undergraduate Curriculum, Adam Urbach

Adam R Urbach

Circular dichroism spectropolarimetry (CD) is a method of optical spectroscopy that seems in most practical ways like UV−visible spectroscopy. The main difference between the two methods is that CD, instead of measuring the absorbance of light as a function of wavelength, measures the difference in absorbance of left versus right circularly polarized light as a function of wavelength. A CD spectrum is an observation of the structure of a chiral compound; it often serves as a “fingerprint” of the structure of biological molecules such as proteins and nucleic acids. For this reason, CD has been broadly applied in biochemistry and …

Identification Of An Active Site-Bound Nitrile Hydratase Intermediate Through Single Turnover Stopped-Flow Spectroscopy, Natalie Gumataotao, Misty L. Kuhn, Natalia Hajnas, Richard C. Holz

Richard C. Holz

Stopped-flow kinetic data were obtained for the iron-type nitrile hydratase from Rhodococcus equi TG328-2 (ReNHase) using methacrylonitrile as the substrate. Multiple turnover experiments suggest a three-step kinetic model that allows for the reversible binding of substrate, the presence of an intermediate, and the formation of product. Microscopic rate constants determined from these data are in good agreement with steady state data confirming that the stopped-flow method used was appropriate for the reaction. Single turnover stopped-flow experiments were used to identify catalytic intermediates. These data were globally fit confirming a three-step kinetic model. Independent absorption spectra acquired between 0.005 …

The Rhizosphere: A Synchrotron- Based View Of Nutrient Flow In The Root Zone, Theodore K. Raab, David A. Lipson

Ted K. Raab

At two energy “endpoints” of the EM spectrum accessible to synchrotron biologists (IR radiation and soft X-rays), we have found experimental methods providing unique opportunities to observe processes and test hypotheses essential to understanding plantsoil- microbe interactions. Availability of IR synchrotron beamlines will continue to expand worldwide, and we hope that plant and microbial biologists will incorporate the type of spectral data presented in this chapter as just one of a legion of “-omics” methods. Considering the shear flux of C through belowground ecosystems annually (and how poorly constrained they are in many regions), synchrotrons must continue to demand the …

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

Robert Hinde

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 …

Investigation Of New Chelation Ion Chromatography Procedure To Determine The Surface Composition Of Powdered Metal Oxide Samples In The Solid State., B. Peebles, Michael Setter

Michael P. Setter

Numerous tests have been conducted on the feasibility of characterizing the surfaces of metal oxide powders using HPLC. An in-line filter housing was modified to serve as a sample chamber to replace the sample loop. A gradient pump was used to gradually increase eluent acidity to find the conditions at which the surface of a metal oxide powder began to dissolve. The theoretical masses of surface monolayers of metal oxide powders were compared with the experimentally determined masses of dissolved material thought to be from the surface to test whether surface and bulk dissolution phenomena in acidic conditions are separable …

Raman Spectroscopy Of Rhombohedral P4o10, Sean J. Gilliam, Scott Kirkby, Clifton N. Merrow, Daniel Zeroka, Ajit Banerjee, James O. Jensen

Scott J. Kirkby

Infrared-Active Vibron Bands Associated With Substitutional Impurities In Solid Parahydrogen, Robert Hinde

Robert Hinde

We present a model for the line shapes of infrared-active Q₁(0) vibron bands observed in solid parahydrogen doped with low concentrations of spherical substitutional impurities. The line shapes are highly sensitive to the H₂ vibrational dependence of the dopant–H₂ interaction. When this vibrational dependence is strong, the dopant can trap the infrared-active vibron in its first solvation shell; in this case, the trapped vibron manifests itself in the absorption spectrum as a narrow feature to the red of the pure solid’s vibron band.

Chemical Analysis By X-Ray Spectroscopy Near Phase Transitions In The Solid State, Juana Vivó Acrivos, L. Nguyen, T. Norman, C. T. Lin, W. Y. Liang, J. M. Honig, P Somasundaran

Juana Vivó Acrivos

The methods discussed in this work show that the types of changes which may be observed, by precise XAS measurements of Absorbance A versus temperature, across a phase transition are: the changes in the relaxation time of the final states  due to fluctuations near a phase transition; the detection of the anomalous Bragg condition coupled to phonon modes XAS enhancement that identifies the temperature interval where the phonon modes are active, the symmetry changes which introduce new allowed transitions to finite states below an element edge, near Tc indicate what symmetry changes occur, and the method of XTDAFST0 = …

Diffraction Effects In Single‐ And Two‐Laser Photothermal Lens Spectroscopy, Stephen E. Bialkowski, Agnes Chartier

Stephen E. Bialkowski

A simple method for calculating the effects of optical geometry on photothermal lens signals is shown. This method is based on calculating cumulative electric-field phase shifts produced by a series of Gaussian refractive-index perturbations produced by the photothermal effect. Theoretical results are found for both pulsed-laser and continuous Gaussian laser excitation sources and both single- and two-laser apparatuses commonly employed in photothermal lens spectroscopy. The effects of apparatus geometry on the resulting signal are shown. Analytical time-dependent signal results are found for small signals. Analytical pump–probe focus geometry results allow direct optimization for certain conditions. The calculations indicate that the …

Accounting For Saturation Effects In Pulsed Infrared Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski

Stephen E. Bialkowski

Equations that relate photothermal lens focal lengths and photothermal deflection angles to saturation absorption coefficients are derived. These equations are derived for two-level absorbers with both homogeneously and inhomogeneously broadened transitions. Initial and time-dependent photothermal lens signals are calculated. Equations describing the zero-time signals are exact to within the simplifying assumptions of the derivation, while the time-dependent signals are approximate. The approximation is performed by the use of a finite series of Gaussian functions to model the temperature change profile distorted by nonlinear absorption. The excitation irradiance-dependent signal behavior for rectangular and exponential excitation pulse time profiles for homogeneously and …

Application Of The Batio3 Beam Fanning Limiter As An Adaptive Spatial Filter For Signal Enhancementin Pulsed Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski

Stephen E. Bialkowski

A method for obtaining a high-contrast visible-light signal from infrared absorption in low-absorbance samples is described. This method is based on a beam-fanning optical limiter in photorefractive BaTiO₃. The resulting signal is not linear but does exhibit an enhanced signal-to-background ratio that is 4 to 6 orders of magnitude better than that of conventional infrared absorption spectrophotometry in the shot-noise limit. A simple model for the beam-fanning, optical-limiter-based, pulsed-laser-excited photothermal spectroscopy detector is found to describe the experimental data adequately. This technique using photothermal spectroscopy detection may have advantages for rapid signal analysis and for two-dimensional visible imaging …

Conduction Band Symmetry In Ta Chalcogenides From Ta L Edge X-Ray Absorption Spectroscopy (Xas), Juana Vivó Acrivos, S.S. P. Parkin, J. Code, J. Reynolds, K. Hathaway, H. Kurasaki, E. Marseglia

Juana Vivó Acrivos

No abstract provided.