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Bonding Properties (bonding + property)
Selected AbstractsA Combined Gas-Phase Electron Diffraction/Mass Spectrometric Study of the Sublimation Processes of TeBr4 and TeI4: The Molecular Structure of Tellurium Dibromide and Tellurium DiiodideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008Sergey A. Shlykov Abstract The sublimation processes of TeBr4 at 471(5) K and TeI4 at 373(5) K were studied with a combined gas-phase electron diffraction and mass spectrometric technique (GED/MS). The mass spectra and the analysis of the GED intensities showed that a contribution of 40(3) mol-% TeBr2, 59(3) mol-% Br2, and 1 mol-% TeBr4 was formed in the vapor over TeBr4(s). Solid tellurium tetraiodide decomposes to form I2(g) and Te(s). A very small contribution of 3.3,±,2.1 mol-% of gaseous TeI2 was also determined by both GED and MS. The "metallic" Te accumulated in the solid phase vaporizes at above ca. 670 K as the predominately Te2 molcular species. Refinement of the GED intensities resulted in rg(Te,Br) = 2.480(5) Å and ,gBr,Te,Br = 99.0(6)° for TeBr2 and rg(Te,I) = 2.693(9) Å and ,g(I,Te,I) = 103.1(22)° for TeI2. The small contribution of TeBr4 observed in the mass spectra of the vapor over TeBr4 could not be observed in the GED data. Geometric parameters and vibrational frequencies for the tellurium dihalides TeX2 with X = F, Cl, Br, and I were calculated with B3LYP, MP2, CCSD, and CCSD(T) methods by using aug-cc-pVTZ basis sets and various core potentials for the tellurium atom. Bonding properties in tellurium dihalides are discussed on the basis of natural bond orbital analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Assignments and hydrogen bond sensitivities of UV resonance Raman bands of the C8-deuterated guanine ringJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2002Akira Toyama Isotope-edited Raman spectroscopy, a combination of site-selective isotopic labeling and Raman difference spectroscopy, is a useful method for studying the structure and interaction of individual nucleic acid residues in oligonucleotides. To obtain basic data for applying isotope-edited Raman spectroscopy to guanine residues, we studied the vibrational modes of UV resonance Raman bands of the C8-deuterated guanine ring by examining the wavenumber shifts upon seven isotopic substitutions (2- 13C, 2- 15N, 6- 18O, 7- 15N, 8- 13C, 9- 15N and 1,- 13C). The hydrogen bond sensitivities of the Raman bands were also investigated by comparing the Raman spectra recorded in several solvents of different hydrogen bonding properties. Some of the Raman bands were found to be markers of hydrogen bonding at specific donor or acceptor sites on the guanine ring. The Raman bands, which shift on C8-deuteration, remain in the difference spectrum between the unlabeled and C8-deuterated guanine rings. Among them, a negative peak around 1525 cm,1 and a strong positive/negative peak pair around 1485/1465 cm,1 serve as markers of hydrogen bonding at N7 and C6O, respectively. Another weak positive/negative peak pair around 1025/1040 cm,1 is sensitive to hydrogen bonding at the proton donor sites (N1,H and N2,H2). The applicability of the hydrogen bond markers has been tested by using a 22-mer oligonucleotide duplex containing eight guanine residues and its analog in which a single guanine residue is C8-deuterated. The difference spectrum shows that the hydrogen bonding state of the guanine residue at the labeled position is consistent with the Watson,Crick base pair structure of DNA. Isotope-edited Raman spectroscopy is a useful tool for studying the hydrogen bonding state of selected guanine residues in oligonucleotides. Copyright © 2002 John Wiley & Sons, Ltd. [source] Electronic Structure and Bonding of All Crystalline Phases in the Silica,Yttria,Silicon Nitride Phase Equilibrium DiagramJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Wai-Yim Ching This paper reviews the structures and properties of 10 binary, ternary, and quaternary crystals within the equilibrium phase diagram of the SiO2,Y2O3,Si3N4 system. They are binary compounds SiO2, Y2O3, Si3N4; ternary compounds Si2N2O, Y2Si2O7, and YSi2O5; and quaternary crystals Y2Si3N4O3 (M-melilite), Y4Si2O7N2, (N-YAM), YSiO2N (wallastonite), and Y10(SiO4)6N2 (N-apatite, N-APT). Although the binary compounds are well-known and extensively studied, the ternary and the quaternary crystals are not. Most of the ternary and the quaternary crystals simply have been referenced as secondary phases in the processing of nitrogen ceramics. Their crystal structures are complex and not precisely determined. In the quaternary crystals, there exists O/N disorder in that the exact atomic positions of the anions cannot be uniquely determined. It is envisioned that a variety of cation,anion bonding configurations exist in these complex crystals. The electronic structure and bonding in these crystals are, therefore, of great interest and are indispensable for a fundamental understanding of structural ceramics. We have used ab initio methods to study the structure and bonding properties of these 10 crystals. For crystals with unknown or incomplete structural information, we use an accurate total energy relaxation scheme to obtain the most likely atomic positions. Based on the theoretically modeled structures, the electronic structure and bonding in these crystals are investigated and related to various local cation,anion bonding configurations. These results are presented in the form of atom-resolved partial density of states, Mulliken effective charges, and bond order values. It is shown that Y,O and Y,N bonding are not negligible and should be a part of the discussion of the overall bonding schemes in these crystals. Spectroscopic properties in the form of complex, frequency-dependent dielectric functions, X-ray absorption near-edge structure (XANES), and the electron energy-loss near-edge structure (ELNES) spectra in these crystals also are calculated and compared. These results are discussed in the context of specific bonding configurations between cations (silicon and yttrium) and anions (oxygen and nitrogen) and their implications on intergranular thin films in polycrystalline Si3N4 containing rare-earth elements. [source] Mit Schrauben Bewehren , Neue ErgebnisseBAUTECHNIK, Issue 4 2009Martin Trautz Univ.-Prof. Holzbau; Baumechanik; Timber Construction; Structural Mechanics Abstract Selbstbohrende Vollgewindeschrauben ermöglichen wirkungsvolle Verstärkungen und Versteifungen sowie leistungsfähige Fügungen von Holzbauteilen. Dabei werden gezielt die hohe axiale Zugfestigkeit und Dehnsteifigkeit sowie der kontinuierliche Verbund der Schrauben genutzt, um ähnlich einer Bewehrung im Stahlbetonbau die schwachen Tragrichtungen des Holzes senkrecht und schräg zur Faserrichtung zu ertüchtigen. Die Bemessung der verschiedenen Schraubenkonfigurationen kann mit Hilfe der aus dem Stahlbetonbau bekannten Stabwerkmodelle erfolgen, die den inneren Kraftfluss im Bauteil bzw. im Anschluss nachbilden und eine einfache Dimensionierung der Schrauben ermöglichen. In mehreren Versuchsreihen mit Bauteilverstärkungen und -fügungen im Jahr 2007 an der RWTH Aachen konnte die erfolgreiche Anwendung dieses Konstruktionsprinzips gezeigt werden. Darauf aufbauend wurden in einem Fortsetzungsprojekt im Jahr 2008 veränderte und verfeinerte Schraubenkonfigurationen konstruiert und auf ihr Festigkeitsverhalten hin untersucht. Versuche an stahllamellenverstärkten Brettschichtholz-Trägern und biegesteifen Rahmenecken unter positiver und negativer Momentenbelastung zeigten eine hohe Leistungsfähigkeit, die das Potential der Methode nachdrücklich untermauert. Self-tapping screws as reinforcement , new results. Self-tapping continuously threaded screws can be used as elements for reinforcement or joints in timber construction because of their high axial strength and excellent bonding properties. The layout of the reinforcing or joining screws can be derived from strut-and-tiemodels which are common in concrete design and follow the internal flow of forces. Several series of tests in 2007 already showed the high potential of this construction method on various joint details and reinforced timber elements. Based on this success in 2008 further tests were taken out on joints and timber beams with altered and more sophisticated screw configurations. Hereby the load-bearing capacity of timber beams reinforced with steel lamellas and rigid frame corners connected with self-tapping screws was extraordinary and demonstrated once more the high potential of this design method. [source] Structural, Electronic, and Bonding Properties of Zeolite Sn-Beta: A Periodic Density Functional Theory StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Sharan Shetty Abstract The structural, electronic, and the bonding properties of the zeolite Sn-beta (Sn-BEA) have been investigated by using the periodic density functional theory. Each of the nine different T-sites in BEA were substituted by Sn atoms and all the nine geometries were completely optimized by using the plane-wave basis set in conjunction with the ultra-soft pseudopotential. On the basis of the structural and the electronic properties, it has been demonstrated that the substitution of Sn atoms in the BEA framework is an endothermic process and hence the incorporation of Sn in the BEA is limited. The lowest unoccupied molecular orbitals (LUMO) energies have been used to characterize the Lewis acidity of each T-site. On the basis of the relative cohesive energy and the LUMO energy, the T2 site is shown to be the most favorable site for the substitution Sn atoms in the BEA framework. [source] | ||||||||||