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BEAM EXPOSURE DEPENDENCE AND MECHANISMS OF PHOTON-STIMULATED DESORPTION FROM ALKALI FLUORIDES

Description: Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F{sup +} yield above the F(2s) edge which are absent in the Li{sup +} spectrum, differences in detail in the Li{sup +} and F{sup +} yields near the Li(1s) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.
Date: November 1, 1983
Creator: Parks, C.C.; Shirley, D.A. & Loubriel, G.
Partner: UNT Libraries Government Documents Department

BEAM PIPE DESORPTION RATE IN RHIC.

Description: In the past, an increase of beam intensity in RHIC has caused several decades of pressure rises in the warm sections during operation. This has been a major factor limiting the RHIC luminosity. About 430 meters of NEG coated beam pipes have been installed in the warm sections to ameliorate this problem. Beam ion induced desorption is one possible cause of pressure rises. A series beam studies in RHIC has been dedicated to estimate the desorption rate of various beam pipes (regular and NEG coated) at various warm sections. Correctors were used to generate local beam losses and consequently local pressure rises. The experimental results are presented and analyzed in this paper.
Date: June 23, 2006
Creator: HUANG, H.; FISCHER, W.; HE, P.; HSEUH, H.C.; IRISO, U.; PTITSYN, V. et al.
Partner: UNT Libraries Government Documents Department

Revisiting the total ion yield x-ray absorption spectra of liquid water microjets

Description: Measurements of the total ion yield (TIY) x-ray absorption spectrum (XAS) of liquid water by Wilson et al. (2002 J. Phys.: Condens. Matter 14 L221 and 2001 J. Phys. Chem. B 105 3346) have been revisited in light of new experimental and theoretical efforts by our group. Previously, the TIY spectrum was interpreted as a distinct measure of the electronic structure of the liquid water surface. However, our new results indicate that the previously obtained spectrum may have suffered from as yet unidentified experimental artifacts. Although computational results indicate that the liquid water surface should exhibit a TIY-XAS that is fundamentally distinguishable from the bulk liquid XAS, the new experimental results suggest that the observable TIY-XAS is actually nearly identical in appearance to the total electron yield (TEY-)XAS, which is a bulk probe. This surprising similarity between the observed TIY-XAS and TEY-XAS likely results from large contributions from x-ray induced electron stimulated desorption of ions, and does not necessarily indicate that the electronic structure of the bulk liquid and liquid surface are identical.
Date: February 16, 2008
Creator: Saykally, Richard J; Cappa, Chris D.; Smith, Jared D.; Wilson, Kevin R. & Saykally, Richard J.
Partner: UNT Libraries Government Documents Department

TEMPERATURE-PROGRAMMED DESORPTION: PRINCIPLES, INSTRUMENT DESIGN, AND DEMONSTRATION WITH NAALH4

Description: This article is a brief introduction to temperature-programmed desorption (TPD), an analytical technique devised to analyze, in this case, materials for their potential as hydrogen storage materials. The principles and requirements of TPD are explained and the different components of a generic TPD apparatus are described. The construction of a modified TPD instrument from commercially available components is reported together with the control and acquisition technique used to create a TPD spectrum. The chemical and instrumental parameters to be considered in a typical TPD experiment and the analytical utility of the technique are demonstrated by the dehydrogenation of titanium-doped NaAlH{sub 4} by means of thermally programmed desorption.
Date: November 7, 2006
Creator: Stowe, A & Ragaiy Zidan, R
Partner: UNT Libraries Government Documents Department

Desorption Kinetics of H2O from Cab-O-Sil-M-7D and Hi-Sil-233 Silica Particles

Description: Temperature programmed desorption (TPD) was performed at temperatures up to 850K on Cab-O-Sil-M-7D and Hi-Sil-233 silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 9-14.5 kcal/mol. However, the activation energies of desorption for chemisorbed water varied from {approx} 19 kcal/mol to > 59 kcal/mol for Cab-O-Sil-M-7D, and {approx} 23-37 kcal/mol for Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>30 kcal/mol) will not escape the silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (19-26 kcal/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies < 30 kcal/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1-0.4 wt. % of water in M9787 polysiloxane formulations containing {approx} 21% Cab-O-Sil-M-7D and {approx} 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that absorbed H{sub 2}O and Si-OH bonds on the silica surfaces are the major contributors to water outgassing from M97 series silicones.
Date: January 26, 2000
Creator: Dinh, L.; Balooch, M. & LeMay, J.D.
Partner: UNT Libraries Government Documents Department

Engineered Natural Geosorbents for In-Situ Immobilization of DNAPLs and Heavy Metals

Description: The report summarizes work progress from 9/15/02-12/31/2003 for the project. Progresses in these five specific areas of investigation are summarized: (1) Production of engineered natural geosorbents (ENGs); (2) Characterization of the physicochemical properties of ENGs; (3) Characterization of the sorption and desorption properties of ENGs for TCE, PCE; (4) Characterization of the sorption and desorption properties of ENGs for heavy metals 4a; and (5) Characterization of the competitive sorption and desorption properties of ENGs for DNAPL and heavy metals.
Date: June 1, 2003
Creator: Weber, Walter J.
Partner: UNT Libraries Government Documents Department

Femtosecond laser postionization of sputtered and laser desorbed atoms

Description: This paper examines the photoionization efficiency of a femtosecond laser ionization source on several atomic species. Use of femtosecond laser ionization pulses to photoionize the desorbing flux from a sample surface is examined. Example of mass spectra produced is given using 248 nm pulse on sputtered Au. Al and Mo have widely different ionization potentials and show that 248 nm pulses are more efficient at photoionization than longer wavelengths; this is enhanced for Mo with high ionization potential. It is concluded that efficient photoionization occurs for atoms with ionization potentials low enough for two-photon ionization to occur.
Date: June 1, 1995
Creator: Pellin, M.J.; Lykke, K.R. & Calaway, W.F.
Partner: UNT Libraries Government Documents Department

PREPARATION OF OXOPORPHINATOMANGANESE (IV) COMPLEX

Description: Oxo-manganese-tetraphenylporphyrin (O=Mn{sup IV}-TPP) has been prepared by an oxygen-transfer reaction from iodosylbenzene to MnIITPP and characterized by its i.r. and field desorption mass spectra, which are identical to those of the product obtained by direct oxidation of Mn{sup III}(TPP) in an aqueous medium; it transfers oxygen to triphenylphosphine to produce triphenylphosphine oxide, and it is suggested that similar intermediates are important in oxygen activation by cytochrome P-450 as well as in the photosynthetic evolution of oxygen.
Date: July 1, 1980
Creator: Willner, I.; Otvos, J. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Brominated Tyrosine and Polyelectrolyte Multilayer Analysis by Laser Desorption VUV Postionization and Secondary Ion Mass Spectrometry

Description: The small molecular analyte 3,5-dibromotyrosine (Br2Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br2Y were analyzed by laser desorption postionization mass spectrometry (LDPI-MS). LDPI-MS using 7.87 eV laser and tunable 8 ? 12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br2Y films allowed detection by≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br2Y to be ~;;8.3?0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at≤8 eV photon energies. However, single photon ionization could only detect Br2Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi3 + secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. The negative ion SIMS depended strongly on the high electron affinity of this specific analyte and the analyte?s condensed phase environment.
Date: March 14, 2011
Creator: Chicago, University of Illinois at; Blaze, Melvin M. T.; Takahashi, Lynelle; Zhou, Jia; Ahmed, Musahid; Gasper, Gerald et al.
Partner: UNT Libraries Government Documents Department

Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling

Description: The objectives of the overall collaborative EMSP effort (with which this project is associated) were to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties and to relate such characterization both to fundamental molecular-scale understanding and field-scale models of geochemistry and mass transfer. The research was intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to allow the development of approaches by which laboratory-developed geochemical models could be upscaled for defensible field-scale predictions of uranium transport in the environment. Within this broader context, objectives of the JHU-based project were to test hypotheses regarding the coupled roles of adsorption and impermeable-zone diffusion in controlling the fate and transport of U(VI) species under conditions of comparatively short-term exposure. In particular, this work tested the following hypotheses: (1) the primary adsorption processes in the Hanford sediment over the pH range of 7 to 10 are surface complexation reactions of aqueous U(VI) hydroxycarbonate and carbonate complexes with amphoteric edge sites on detrital phyllosilicates in the silt/clay size fraction; (2) macroscopic adsorption intensity (at given aqueous conditions) is a function of mineral composition and aquatic chemistry; and (3) equilibrium sorption and desorption to apply in short-term, laboratory-spiked pristine sediments; and (4) interparticle diffusion can be fully understood in terms of a model that couples molecular diffusion of uranium species in the porewater with equilibrium sorption under the relevant aqueous conditions. The primary focus of the work was on developing and applying both models and experiments to test the applicability of "local equilibrium" assumptions in the modeling interpretation of sorption retarded interparticle diffusion, as relevant to processes of U(VI) diffusion in silt/clay layers. Batch isotherm experiments were first used to confirm sorption isotherms under the intended test conditions ...
Date: October 12, 2006
Creator: Bai, Jing; Dong, Wenming & Ball, William P.
Partner: UNT Libraries Government Documents Department

Erbium hydride thermal desorption : controlling kinetics.

Description: Thermal desorption spectroscopy (TDS) is used to study the decomposition kinetics of erbium hydride thin films. The TDS results presented in this report show that hydride film processing parameters directly impact thermal stability. Issues to be addressed include desorption kinetics for dihydrides and trihydrides, and the effect of film growth parameters, loading parameters, and substrate selection on desorption kinetics.
Date: August 1, 2007
Creator: Ferrizz, Robert Matthew
Partner: UNT Libraries Government Documents Department

FINAL REPORT - Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

Description: A magnetically coupled microbalance system has been used to measure adsorption and desorption isotherms and rates of desorption for carbon tetrachloride on dry prepared porous silica particles with narrow pore size distributions in the mesoporous range. Pore size distributions estimated from the carbon tetrachloride isotherms were found to be in close agreement with those determined using standard low temperature nitrogen adsorption. Three different types of particles were studied, with average pore diameters of 2.7 nm, 4.6 nm, and 5.9 nm. Prior to desorption rate studies, evacuated particulate samples were charged with volatile organic vapor at pressures sufficient to fill all mesopores with condensed fluid. Desorption rates into dry flowing helium were determined at 25 °C and atmospheric pressure, using the microbalance system combined with chromatographic analysis of the exit helium stream. Initial rates were found to decrease significantly, as mass adsorbed decreased. This residual mass was desorbing at such a low rate, that it can be considered a migration resistant fraction of the original mass adsorbed. Attempts to remove this residual mass at higher temperatures were partially successful; however, differences between the microbalance and gas chromatograph responses leave open uncertainty about whether the residual mass was pure carbon tetrachloride. To date, attempts at analysis of the residual mass using solvent extraction have not removed completely this uncertainty. For particles prepared using the same template surfactant, but with different average pore sizes, desorption rates were higher for the larger-pore particles, with correspondingly lower residual mass. Particles prepared with another template surfactant did not follow this pattern, exhibiting intermediate desorption rates and slightly lower residual mass, even though these particles had the smallest pores. These particles exhibited desorption isotherm behavior characteristic of larger pores connected by smaller openings. Except for peculiar behavior in the very early part of desorption experiments for one ...
Date: December 11, 2006
Creator: Miller, Dr. Reid C. & Peyton, Dr. Brent M.
Partner: UNT Libraries Government Documents Department

Carbon-14 geochemistry at the Savannah River Site

Description: Carbon-14 is among the key radionuclides driving risk at the E-Area Low-Level Waste Disposal Facility on the Savannah River Site (SRS). Much of this calculated risk is believed to be the result of having to make conservative assumptions in risk calculations because of the lack of site-specific data. The original geochemical data package (Kaplan 2006) recommended that performance assessments and composite analyses for the SRS assume that {sup 14}C did not sorbed to sediments or cementitious materials, i.e., that C-14 K{sub d} value (solid:liquid concentration ratio) be set to 0 mL/g (Kaplan 2006). This recommendation was based primarily on the fact that no site-specific experimental work was available and the assumption that the interaction of anionic {sup 14}C as CO{sub 2}{sup 2-}) with similarly charged sediments or cementitious materials would be minimal. When used in reactive transport equations, the 0 mL/g Kd value results in {sup 14}C not interacting with the solid phase and moving quickly through the porous media at the same rate as water. The objective of this study was to quantify and understand how aqueous {sup 14}C, as dissolved carbonate, sorbs to and desorbs from SRS sediments and cementitious materials. Laboratory studies measuring the sorption of {sup 14}C, added as a carbonate, showed unequivocally that {sup 14}C-carbonate K{sub d} values were not equal to 0 mL/g for any of the solid phases tested, but they required several months to come to steady state. After six months of contact, the apparent K{sub d} values for a clayey sediment was 3,000 mL/g, for a sandy sediment was 10 mL/g, for a 36-year-old concrete was 30,000 mL/g, and for a reducing grout was 40 mL/g. Furthermore, it was demonstrated that (ad)sorption rates were appreciably faster than desorption rates, indicating that a kinetic sorption model, as opposed to the steady-state K{sub ...
Date: May 10, 2013
Creator: Roberts, Kimberly A. & Kaplan, Daniel I.
Partner: UNT Libraries Government Documents Department

Manipulating Subsurface Colloids to Enhance Cleanup of DOE Waste Sites - Final Report

Description: Colloidal suspensions near 100 {micro}g/L can be pumped from below ground. Designing injection solutions that optimally mobilize colloids in the field also promotes desorption processes. As an example, in manipulating chromium-containing colloids, injected sorbate also served to displace the ion exchangeable chromate load in that subsurface region.
Date: March 15, 2000
Creator: Gschwend, P.M. & Johnson, C.R.
Partner: UNT Libraries Government Documents Department

Erbium hydride decomposition kinetics.

Description: Thermal desorption spectroscopy (TDS) is used to study the decomposition kinetics of erbium hydride thin films. The TDS results presented in this report are analyzed quantitatively using Redhead's method to yield kinetic parameters (E{sub A} {approx} 54.2 kcal/mol), which are then utilized to predict hydrogen outgassing in vacuum for a variety of thermal treatments. Interestingly, it was found that the activation energy for desorption can vary by more than 7 kcal/mol (0.30 eV) for seemingly similar samples. In addition, small amounts of less-stable hydrogen were observed for all erbium dihydride films. A detailed explanation of several approaches for analyzing thermal desorption spectra to obtain kinetic information is included as an appendix.
Date: November 1, 2006
Creator: Ferrizz, Robert Matthew
Partner: UNT Libraries Government Documents Department

A Study of Silver: an Alternative Maldi Matrix for Low Weight Compounds and Mass Spectrometry Imaging

Description: Soft-landing ion mobility has applicability in a variety of areas. The ability to produce material and collect a sufficient amount for further analysis and applications is the key goal of this technique. Soft-landing ion mobility has provided a way to deposit material in a controllable fashion, and can be tailored to specific applications. Changing the conditions at which soft-landing ion mobility occurs effects the characteristics of the resulting particles (size, distribution/coverage on the surface). Longer deposition times generated more material on the surface; however, higher pressures increased material loss due to diffusion. Larger particles were landed when using higher pressures, and increased laser energy at ablation. The utilization of this technique for the deposition of silver clusters has provided a solvent free matrix application technique for MALDI-MS. The low kinetic energy of incident ions along with the solvent free nature of soft-landing ion mobility lead to a technique capable of imaging sensitive samples and low mass analysis. The lack of significant interference as seen by traditional organic matrices is avoided with the use of metallic particles, providing a major enhancement in the ability to analyze low mass compounds by MALDI.
Date: May 2014
Creator: Walton, Barbara Lynn
Partner: UNT Libraries

Cesium sorption and desorption on selected Los Alamos soils

Description: Laboratory experiments were conducted to evaluate the sorptivity of cesium onto Los Alamos soils under controlled experimental conditions. Four soil profiles were collected and each soil profile which is broken into layers according to previously identified soil horizons were studied. Batch sorption isotherms were studied to quantify the chemical reactivity of each soil horizon toward cesium ion. Radioactive cesium-137 was used as sorbent and gamma counting was used to quantify the amount of sorption. Desorption experiments were conducted after the sorption experiments. Batch desorption isotherms were studied to quantify the desorption of presorbed cesium from these Los Alamos soils. This study suggests cesium may sorb strongly and irreversibly on most Los Alamos soils. The amount of cesium sorption and desorption is possibly related to the clay content of the soil sample since subsurface sample has a higher clay content than that of surface sample.
Date: August 1, 1995
Creator: Kung, K.S.; Chan, J.; Longmire, P. & Fowler, M.
Partner: UNT Libraries Government Documents Department