Recent Submissions

  • Nuclear Magnetic Resonance Evidence of Disorder and Motion in Yttrium Trideuteride

    Balbach, John L.; Conradi, Mark S.; Hoffmann, Markus M.; Udovic, Terrence J.; Adolphi, Natalie L.; Knox College; National Institutes of Health; NIST Center for Neutron Research; The College at Brockport; Washington University in St Louis (12/1/1998)
    Three samples of YDx, with x ranging from 2.9 to nearly 3.0, were studied with deuterium nuclear magnetic resonance to gain insight into the locations of the D atoms in the lattice and their motions. Line shapes at low temperatures (200–330 K) show substantial disorder at some of the deuterium sites. Near 355 K, the spectrum sharpens to yield three uniaxial Pake patterns, reflecting a motional averaging process. However, the three measured intensities do not match the ratios expected from the neutron-determined, HoD3-like structure. This is strong evidence that the structure and space group of YD3 are different than reported, or that the current model needs adjustment. At still higher temperatures near 400 K, the Pake doublet features broaden, and a single sharp resonance develops, signalling a diffusive motion that carries all D atoms over all sites. The temperature at which line shape changes occur depends on the number of deuterium vacancies, 3-x. The changes occur at lower temperatures in the most defective sample, indicating the role of D-atom vacancies in the motional processes. The longitudinal relaxation rate T1-1 displays two regimes, being nearly temperature independent below 300 K and strongly thermally activated above. The relaxation rate depends on the number of deuterium vacancies, 3-x, varying an order of magnitude over the range of stoichiometries studied and suggesting that D-atom diffusion is involved. Also, the activation energy describing T1-1?(kB×5500?K) approximately matches that for diffusion. An unusual ?0-0.7 frequency dependence of T1-1 is observed. A relaxation mechanism is proposed in which diffusion is the rate-determining step and in which frequency dependence arises from a field-dependent radius of the relaxation zones.
  • New Approach to Silver Halide Photography Using Radical Cation Chemistry

    Gould, I.; Lenhard, J. R.; Muenter, A. A.; Godleski, Stephen A.; Farid, S.; Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ; Research Laboratories, Eastman Kodak Company, Rochester, NY; The College at Brockport (1/1/2001)
    A new mechanism for spectral sensitization of silver halide is described, which can potentially double the sensitivity of photographic emulsions. The photooxidized sensitizing dye is trapped using an organic donor molecule, which fragments to form a cation and a reducing radical, which injects an electron into the conduction band of the silver halide. In this way, two conduction-band electrons can be produced for each absorbed photon.
  • X-Ray Absorption Spectroscopy and Imaging of Heterogeneous Hydrothermal Mixtures Using a Diamond Microreactor Cell

    Fulton, John L.; Darab, John G.; Hoffmann, Markus M.; Pacific Northwest National Laboratory; The College at Brockport (4/1/2001)
    Hydrothermal synthesis is an important route to novel materials. Hydrothermal chemistry is also an important aspect of geochemistry and a variety of waste remediation technologies. There is a significant lack of information about the speciation of inorganic compounds under hydrothermal conditions. For these reasons we describe a high-temperature, high-pressure cell that allows one to acquire both x-ray absorption fine structure (XAFS) spectra and x-ray transmission and absorption images of heterogeneous hydrothermal mixtures. We demonstrate the utility of the method by measuring the Cu(I) speciation in a solution containing both solid and dissolved Cu phases at temperatures up to 325?°C. X-ray imaging of the various hydrothermal phases allows micro-XAFS to be collected from different phases within the heterogeneous mixture. The complete structural characterization of a soluble bichloro-cuprous species was determined. In situ XAFS measurements were used to define the oxidation state and the first-shell coordination structure. The Cu–Cl distance was determined to be 2.12 Å for the CuCl2? species and the complete loss of tightly bound waters of hydration in the first shell was observed. The microreactor cell described here can be used to test thermodynamic models of solubility and redox chemistry of a variety of different hydrothermal mixtures.
  • Studying in situ Hydrothermal Reactions with X-ray Absorption Spectroscopy

    Hoffmann, Markus M.; The College at Brockport (1/1/1998)
  • Short-Pathlength, High-Pressure Flow Cell for Static and Time-Resolved Infrared Spectroscopy Suitable for Supercritical Fluid Solutions Including Hydrothermal Systems

    Hoffmann, Markus M.; Addleman, R. Shane; Fulton, John L.; Pacific Northwest National Laboratory; The College at Brockport (3/1/2000)
    An optical flow cell for high pressures and temperatures is described. The use of a novel window design allows for a precise, fixed optical pathlength that can be varied by use of spacers that range from a few micrometers to several millimeters. The cell pathlength is not affected by changes in pressure or temperature. The novel window design may be applicable to other high-pressure spectroscopic cells. The flow-cell design has a minimal sample dead volume, which is important for kinetic studies. The design eliminates the need for brazing or for a soft-sealing material for the optical windows, thereby minimizing the number of materials in contact with the sample. Using only diamond and platinum or platinum alloys as the corrosion resistant materials, the design is optimized for the study of aqueous solutions at high temperatures. Infrared spectra of an aqueous sodium tungstate solution up to 400?°C and 380 bar pressure are presented. Time-resolved infrared data are also presented for the ultraviolet photolysis reaction of ?-naphthoyl azide in supercritical carbon dioxide.
  • Nuclear Magnetic Resonance Probe for Supercritical Water and Aqueous Solutions

    Hoffmann, Markus M.; Conradi, Mark S.; The College at Brockport; Washington University in St Louis (1/1/1997)
    A nuclear magnetic resonance (NMR) probe for high pressure, high temperature studies is presented. While applicable to many physical systems, the device is optimized for the study of the physics and chemistry of supercritical water and its solutions. The design is modular and is particularly simple, using readily available parts and materials. A new approach is presented for elimination of the magnetic field from the heater currents. The probe has been used to 600?°C and 400 bar. The rf performance is quite good; the NMR linewidth is about 0.1 ppm full width at half-height at any pressure and temperature.
  • Ion Man

    Hoffmann, Markus M.; The College at Brockport (11/1/2012)
    This is an interview with Professor Markus Hoffmann of The College at Brockport. He is Principal Investigator for a research project studying the ion pairing and aggregation behaviour of ionic liquids, the description of which is becoming increasingly important due to their growing use within science and industry.