Surface termination, composition and reconstruction of Fe3O4(001) and γ-Fe2O3(001)

We address a current controversy concerning the nature of the surfaces of Fe₃O₄(001) and γ-Fe₂O₃(001) grown on MgO(001) by molecular beam epitaxy. Despite recent claims to the contrary, we show that γ-Fe₂O₃(001) unambiguously exhibits a (1×1) surface net, in contrast to Fe₃O₄(001), which assumes a R45 reconstruction. In addition, we present high-energy-resolution Fe 2p and O 1s core-level photoelectron spectra obtained at both normal and grazing emission for γ-Fe₂O₃(001) and Fe₃O₄(001). These spectra show that the Fe₃O₄(001) surface has a higher Fe(III)/Fe(II) ratio than the bulk, and that the asymmetry in the O 1s line shape for Fe₃O₄(001) is due to final state effects rather than the presence of a surface oxygen or hydroxyl species.     

Are C-H groups significant hydrogen bonding sites in anion receptors? Benzene complexes with Cl-, NO3-, and ClO4-

Theoretical calculations,examination of crystallographic data, and experimental binding energies suggest that even in the absence of electron-withdrawing substituents, simple arenes such as benzene form hydrogen bonds with anions that can exceed 50% of the strength of those formed by O-H and N-H groups. Thus, when present in a receptor, even moderately acidic C-H groups can significantly enhance the anion binding affinity and they should be considered as additional binding sites within the host cavity.     

Novel hybrid materials with high stability for electrically switched ion exchange: carbon nanotube-polyaniline-nickel hexacyanoferrate nanocomposites

A novel and stable carbon nanotube-polyaniline-nickel hexacyanoferrate nanocomposite film has been synthesized by the electrodeposition method, and the feasibility for removing radioactive caesium through an electrically switched ion exchange process using the nanocomposite film has been evaluated in a mixture containing NaNO3 and CsNO3.     

Measurement of viscosity and shear wave velocity of a liquid or slurry for on-line process control

An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid-fluid interface, has been developed by the staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear wave reflection at the solid-fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were conducted for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick-similar to pipe wall thickness) we increased the sensitivity of the measurement. At the sixth echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silicone oils). The results show that, for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silicone oils are very small and range from 315 to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated. These results show that, depending on the fluid characteristics, either the viscosity or the shear wave velocity can be used for process control. There are several novel features of this sensor: (1) The sensor can be mounted as part of the wall of a pipeline or tank or submerged in a tank. (2) The sensor is very compact and can be located within the process stream. (3) The sensor can interrogate and characterize very attenuative liquids or slurries because the sensor operation depends upon reflection at the interface between the solid and the fluid, rather than on transmission through a liquid. (4) The sensor performance is not affected by fluid flow rate, entrained air, or vibration.     

Investigation of a hybrid TCSCF-DFT procedure

In this work a family of hybrid TCSCF-DFT procedures for treating inherently two-configurational species is introduced and applied to the low-lying singlet and triplet states of B₂ and C₂H₄. The hybrid procedures permit self-consistent determination of the orbitals in both the TCSCF and Kohn-Sham subspaces. Received: 15 October 1997 / Accepted: 13 January 1998     

The electronic structure and conformation of dimethylaminobenzonitrile

Ab initio molecular orbital (MO) computations on the closed shell singlet ground state ofN, N-dimethylaminobenzonitrile (DMABN) are reported. Fully optimized structures of several conformers of DMABN were calculated at the HF/6-31G level of theory. Our results indicate that for each of these conformations the minimum energy structure has a trigonal (sp² hybridized] amino nitrogen. The most stable DMABN conformer was found to be planar with its methyl groups eclipsed. The Koopmans ionization potentials and dipole moments of the various ground state conformers are compared. The implications for dynamical models of twisted-intramolecular charge transfer (TICT) are discussed. Moreover, the use of qualitative MO theory arguments provides an interpretation of the computational results in a simple orbital interaction framework.A. Mellon Foundation Fellow (1989–1992).Operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Beam induced reduction of U(VI) during X-ray photoelectron spectroscopy: The utility of the U4f satellite structure for identifying uranium oxidation states in mixed valence uranium oxides

Reduction of U^VI by the beam during X-ray photoelectron spectroscopy (XPS) is a commonly observed phenomenon. This can affect the determination of the U oxidation state, or states, in U oxides (or U compounds in general) and compromise the validity of peak parameters derived from U^VI oxide standards. However, there is little quantitative information on the reduction kinetics and species produced. The objective of this contribution is to investigate and quantify the effects of X-ray beam reduction of U^VI during XPS analysis. Successive U4f XPS spectra were taken over a 26 h period during the X-ray induced reduction of U^VI oxy-hydroxide that was precipitated onto the basal plane of mica. In addition, valence band XPS spectra, including the U5f region, were recorded. Factor analysis identified three dominant and, by definition, linearly independent components. Consequently, we fit the U4f level, including the satellite structure, with three components that represented U^VI, U^V, and U^IV. Peak parameters were remarkably stable and consistent with U^VI, U^V, and U^IV over the entire reduction sequence despite the likely formation of a partially covalent mixed-valence U oxide. Although the satellite features for U^IV and U^V were modified by their bonding environment, they still served well as diagnostic tools for identifying U oxidation states. In particular, the 8 eV satellite appears to be a robust indicator of U^V over a range of bonding environments. This is important because the presence of U^V might not be necessarily obvious in the primary peak envelope if XPS energy resolution is low and/or U^IV-U^V binding energy separations are appreciably less than 1 eV. We also discuss insights obtained from modeling the kinetic data for the time evolution of U^VI, U^V, and U^IV.