Extended Hückel molecular orbital calculations on some titanium–oxygen systems

1968 ◽  
Vol 46 (16) ◽  
pp. 2667-2674 ◽  
Author(s):  
Yu-Ping Hsia
Keyword(s):  
Molecular Orbital ◽  
Energy Levels ◽  
Molecular Orbital Calculations ◽  
X Ray ◽  
Near Ultraviolet ◽  
Extended Hückel ◽  
Self Consistent ◽  
X Ray Absorption ◽  
Tetragonal Batio ◽  
Absorption Edges

Extended Hückel molecular orbital calculations have been performed on localized TiO68− units with the precise geometry of such a unit in solid rutile, anatase, and brookite TiO2 and tetragonal BaTiO3. The relative values of one-electron energy levels in these compounds are obtained in terms of a "self-consistent" charge and population calculation. Examination of the resulting energy levels and charge distributions has led to reasonable explanations of previously unexplained data on (1) the visible and near-ultraviolet absorption spectra of these compounds, (2) the low energy X-ray absorption edges of rutile, anatase, and brookite TiO2, and (3) the pressure dependence of the absorption edges of rutile TiO2 and tetragonal BaTiO3.

ENERGY LEVELS OF TRIARYLMETHYL CARBONIUM IONS

1964 ◽  
Vol 42 (4) ◽  
pp. 810-817 ◽  
Author(s):  
E. K. Ng ◽  
F. C. Adam
Keyword(s):  
Molecular Orbital ◽  
Energy Levels ◽  
Fluorescence Band ◽  
Molecular Orbital Calculations ◽  
Structure Representation ◽  
Near Ultraviolet ◽  
Carbonium Ions ◽  
Visible Spectra ◽  
Made In

The near ultraviolet and visible spectra of the various phenyl-, p-biphenyl methyl carbonium ions have been investigated and the polarization of the absorptions relative to the fluorescence band have been determined. An assignment of the transitions is made, using as a basis simple molecular orbital calculations and the expectations based on the structure representation. These are compared to the assignments made in earlier researches. The calculated intensities are found to agree favorably with the observed values.

Molecular Orbital Interpretation of X‐Ray Absorption Edges

1969 ◽  
Vol 50 (1) ◽  
pp. 344-350 ◽  
Author(s):  
Wolf Seka ◽  
Harold P. Hanson
Keyword(s):  
Molecular Orbital ◽  
X Ray ◽  
X Ray Absorption ◽  
Absorption Edges

Solvation Structure of Solvated Cu(I) Ions in Non-Aqueous Solvents as Studied by EXAFS and ab initio Molecular Orbital Methods

1999 ◽  
Vol 54 (2) ◽  
pp. 193-199 ◽  
Author(s):  
Y. Inada ◽  
Y. Tsutsui ◽  
H. Wasada ◽  
S. Funahashi
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Steric Effect ◽  
Molecular Orbital Calculations ◽  
Enthalpy Of Solvation ◽  
Octahedral Structure ◽  
X Ray ◽  
Solvation Structure ◽  
Solvent Molecules ◽  
X Ray Absorption

The structure parameters around the Cu(I) ion in pyridine (PY), 4-methylpyridine (4MPY), 2-methylpyridine (2MPY), 2,6-dimethylpyridine (26DMPY), and acetonitrile (AN) were determined by the extended X-ray absorption fine structure (EXAFS) method. The solvation structures of the Cu(I) ion in PY, 4MPY, and AN are 4-coordinate tetrahedral with Cu-N bond lengths of 205, 205, and 200 pm, respectively. In the case of 2MPY and 26DMPY, the Cu(I) ion has a 3-coordinate triangular structure with a Cu-N bond length of 201 pm. Such a decrease in the coordination number was interpreted in terms of the bulkiness of the solvent molecules. In order to clarify the most stable solvation structure of the Cu(I) ion, we carried out ab initio molecular orbital calculations for the solvation system of [Cu(NCH)n]+ (n = 1 - 6 ) where the steric effect is negligible. The Gibbs free energy of solvation was the smallest in the case of n = 4 and the 4-coordinate tetrahedral solvation of the Cu(I) ion was theoretically evaluated as most stable. The enthalpy of solvation monotonously decreases with increasing n, while the entropy of solvation proportionally increases. Although a larger gain of enthalpy is observed for the octahedral structure rather than the tetrahedral one, the entropic loss for the former overcomes the enthalpic gain.

scholarly journals Al-driven peculiarities of local coordination and magnetic properties in single-phase Alx-CrFeCoNi high-entropy alloys

Nano Research ◽  
2021 ◽  
Author(s):  
Alevtina Smekhova ◽  
Alexei Kuzmin ◽  
Konrad Siemensmeyer ◽  
Chen Luo ◽  
Kai Chen ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Single Phase ◽  
Magnetic Circular Dichroism ◽  
Surface Region ◽  
Face Centered Cubic ◽  
X Rays ◽  
X Ray ◽  
High Entropy ◽  
X Ray Absorption ◽  
Absorption Edges

AbstractModern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties. Herein, peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic (fcc)- and body-centered cubic (bcc)-structured high-entropy Alx-CrFeCoNi alloys (x = 0.3 and 3, respectively) are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges. Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision. The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry. A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account. X-ray magnetic circular dichroism technique employed at L2.3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values. Extended to nanostructured versions of multicomponent alloys, such studies would bring new insights related to effects of high entropy mixing on low dimensions.

X-RAY ABSORPTION EDGES OF TRANSITION- METAL-DOPED Y1Ba2Cu3−xMxO7−∂

1988 ◽  
Vol 02 (05) ◽  
pp. 1153-1156 ◽  
Author(s):  
J. B. BOYCE ◽  
F. BRIDGES ◽  
T. CLAESON ◽  
T. H. GEBALLE ◽  
M. NYGREN ◽  
...  
Keyword(s):  
Transition Metal ◽  
X Ray ◽  
Metal Doped ◽  
X Ray Absorption ◽  
Absorption Edges

scholarly journals Anisotropy of X-ray Absorption Cross Section in CeCoGe3 Single Crystal

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 544
Author(s):  
Andrei Rogalev ◽  
Fabrice Wilhelm ◽  
Elena Ovchinnikova ◽  
Aydar Enikeev ◽  
Roman Bakonin ◽  
...  
Keyword(s):  
Cross Section ◽  
Absorption Cross Section ◽  
Linear Dichroism ◽  
X Rays ◽  
Absorption Cross ◽  
X Ray ◽  
Measured Absorption ◽  
Linearly Polarized ◽  
X Ray Absorption ◽  
Absorption Edges

Absorption spectra of two orthogonal linearly polarized x-rays in a single CeCoGe3 crystal were measured at the ID12 beamline of the ESRF for the energies near the K-edges of Ge, Co and near the L23 edges of Ce. The X-ray natural linear dichroism (XNLD) was revealed in the vicinity of all the absorption edges, which indicates a splitting of electronic states in a crystalline field. Mathematical modelling in comparison with experimental data allowed the isotropic and anisotropic parts of atomic absorption cross section in CeCoGe3 to be determined near all measured absorption edges. The calculations also show that the “average” anisotropy of the cross section close to the Ge K-edge revealed in the experiment is less than the partial anisotropic contributions corresponding to Ge atoms in two different Wyckoff positions.

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