On the Reliability of the Structures of Lead(II) Hydroxo Complexes Obtained by MNDO Method

1999 ◽  
Vol 64 (8) ◽  
pp. 1269-1273 ◽  
Author(s):  
Martin Breza ◽  
Alena Manová
Keyword(s):  
Reasonable Agreement ◽  
Mndo Method ◽  
X Ray ◽  
Hydroxo Complexes ◽  
Optimum Geometry ◽  
Semiempirical Mndo

Optimum geometry of tetrahedro-Pb4[(μ3-OH)4]4+ cluster obtained by the semiempirical MNDO method corresponds to Td symmetry. The calculated Pb-Pb (3.70 · 10-10 m) and Pb-O (2.33 · 10-10 m) distances are in reasonable agreement with experimental X-ray data. Additional H2O inclusion makes the agreement worse.

On the Structure of Lead(II) Complexes in Aqueous Solutions. I. Trinuclear Clusters

1995 ◽  
Vol 60 (4) ◽  
pp. 527-536 ◽  
Author(s):  
Martin Breza ◽  
Alena Manová
Keyword(s):  
Quantum Chemistry ◽  
Aqueous Solutions ◽  
Electronic Structures ◽  
Mndo Method ◽  
Model Systems ◽  
Trinuclear Clusters ◽  
The Stability ◽  
Semiempirical Mndo

Using semiempirical MNDO method of quantum chemistry the optimal geometries and corresponding electronic structures of [Pb3(OH)n]6-n model systems as well as of their hydrated [Pb3(OH)n(H2O)8-n]6-n analogues (n = 4, 5) are investigated. The most stable trinuclear lead(II) complexes present in aqueous solutions correspond to cyclo-(μ3-OH)(μ2-OH)3Pb32+, Pb(μ-OH)2Pb(μ-OH)2Pb2+, cyclo-(μ3-OH)2(μ2-OH)3Pb3+, Pb(OH)(μ-OH)2Pb(μ-OH)Pb(OH)+ and Pb(OH)(μ-OH)2Pb(μ-OH)2Pb+ systems. The key role of OH bridges (by vanishing direct Pb-Pb bonds) on the stability of individual isomers is discussed.

Dynamical Theory for Simultaneous X-Ray Diffraction

1966 ◽  
Vol 10 ◽  
pp. 67-79
Author(s):  
P. Penning
Keyword(s):  
Experimental Data ◽  
Plane Wave ◽  
Quantitative Data ◽  
Reasonable Agreement ◽  
Dynamical Theory ◽  
Inversion Symmetry ◽  
Surprising Result ◽  
X Ray Diffraction ◽  
Wave Fields ◽  
X Ray

AbstractComplete dynamical solutions for three coupled plane-wave components in crystal structures with inversion symmetry have been found. After reviewing briefly the dynamical solutions for wave fields with two coupled plane-wave components, the results for the three-beam case are discussed in qualitative terms. Attention is paid to singular points and lines on the ω-surface, and to the attenuation of the mode-intensity because of absorption. The most surprising result is that in the case one of the reflections is forbidden (Umweganregung) the absorption is reduced in comparison with the adjoining two-beam cases. Experimental data are in reasonable agreement with the theory. Quantitative data are presented for a few three-beam cases of simultaneous diffraction of Cu Kα. radiation in germanium.

On the Structure of Lead(II) Complexes in Aqueous Solutions. III. Hexanuclear Clusters

2002 ◽  
Vol 67 (2) ◽  
pp. 219-227 ◽  
Author(s):  
Martin Breza ◽  
Alena Manová
Keyword(s):  
Quantum Chemistry ◽  
Aqueous Solutions ◽  
Electronic Structures ◽  
Mndo Method ◽  
Experimental Techniques ◽  
Hexanuclear Clusters ◽  
Semiempirical Mndo

Optimum geometries based on experimental structures and corresponding electronic structures of [Pb6(μ3-OH)8]4+ and [Pb6O(μ3-OH)6]4+ clusters as well as of their hydrated [Pb6(μ3-OH)8(H2O)6]4+ and [Pb6O(μ3-OH)6(H2O)6]4+ analogues are investigated using the semiempirical MNDO method of quantum chemistry. Direct Pb-Pb and O-O bonds are vanishing in the systems under study. Small differences in interatomic Pb-Pb and Pb-O distances between these clusters indicate that they cannot be distinguished by recent experimental techniques in solution. Both the mentioned structures are stable and might coexist in solution.

Molecular electronic structure of subphthalocyanine macrocycles

2000 ◽  
Vol 04 (06) ◽  
pp. 611-620 ◽  
Author(s):  
V. R. FERRO ◽  
L. A. POVEDA ◽  
R. H. GONZÁLEZ-JONTE ◽  
J. M. GARCIA DE LA VEGA ◽  
T. TORRES ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Central Region ◽  
Quantum Chemical ◽  
Theoretical Calculations ◽  
Molecular Electronic ◽  
X Ray ◽  
Compositional Changes ◽  
Molecular Electronic Structure ◽  
Semiempirical Mndo

Quantum chemical calculations at semiempirical (MNDO methods) and ab initio (6-31G and STO-3G basis ses) levels have been performed on boron(III) subphthalocyanines 1-10. Theoretical calculations predict a cone-shaped structure for these compounds independently of the kind of peripheral substitution and even of compositional changes in the central region of the macrocycle (for example, substitution of the boron atom by two hydrogens). The theoretical calculations are in excellent agreement with previous X-ray determinations.

scholarly journals Investigation of the EXAFS Cumulants of Silicon and Germanium Semiconductors by Statistical Moment Method: Pressure Dependence

2011 ◽  
Vol 21 (3) ◽  
pp. 245
Author(s):  
Ho Khac Hieu ◽  
Vu Van Hung ◽  
Nguyen Van Hung
Keyword(s):  
Pressure Dependence ◽  
Moment Method ◽  
Reasonable Agreement ◽  
Statistical Moment ◽  
X Ray ◽  
Lattice Constants ◽  
Silicon And Germanium ◽  
X Ray Absorption ◽  
Analytical Expressions ◽  
Statistical Moment Method

Pressure dependence of Extended X-ray Absorption Fine Structure (EXAFS) cumulants of silicon and germanium have been investigated using the statistical moment method (SMM). Analytical expressions of the first and second cumulants of silicon and germanium have been derived. The equations of states for silicon and germanium semiconductors have been also obtained using which the pressure dependence of lattice constants and volume of these semiconductors have been estimated. Numerical results using the developed theories for these semiconductors are found to be in good and reasonable agreement with those of the other theories and with experiment.

scholarly journals Light Curve Models for SN 1987A and Diagnosis of Supernova Interior

1988 ◽  
Vol 108 ◽  
pp. 319-334
Author(s):  
Ken’ichi Nomoto ◽  
Toshikazu Shigeyama ◽  
Masa-aki Hashimoto
Keyword(s):  
Light Curve ◽  
Reasonable Agreement ◽  
Light Curves ◽  
Shock Propagation ◽  
Helium Abundance ◽  
X Ray ◽  
Sn 1987A ◽  
Shock Heating ◽  
Helium Stars ◽  
Optical Light Curve

AbstractPresupernova evolution of the progenitor of SN 1987A, hydrodynamics of explosion (shock propagation, explosive nucleosynthesis), optical light curve due to shock heating and 56Co decay, and X-ray and γ-ray light curves are calculated and compared with the observations of SN 1987A. Constraints on the mass of the hydrogen-rich envelope Menv (i.e., mass loss history) and the helium abundance in the envelope are obtained from the progenitor’s blue-red-blue evolution as well as from the light curve. The explosion energy E and the mass and distribution of 56Ni are inferred from the light curves. Models and observations are in reasonable agreement for E/Menv = 1.5 ± 0.5 × 1050 erg/M⊙, Menv = 5 - 10 M⊙, and MNi ∼ 0.07 M⊙. Mixing of 56Ni into the envelope is indicated.Light curves of exploding bare helium stars are also calculated to see whether the observed Type Ib supernova light curves can be accounted for.

X-Ray Topographic Analysis of Strain Fields Associated with Micron-Sized Gratings on Si(100) Surfaces

1989 ◽  
Vol 160 ◽  
Author(s):  
A.P. Jardine ◽  
M. Dudley ◽  
G. Tolis ◽  
G-D. Yao ◽  
S.M. Durbin
Keyword(s):  
Single Crystals ◽  
Plane Strain ◽  
Strain Field ◽  
Reasonable Agreement ◽  
Zone Model ◽  
Ion Etching ◽  
Strain Fields ◽  
Topographic Analysis ◽  
X Ray ◽  
Beam Reflection

AbstractSi(100) single crystals containing circular gratings etched into the surface using reactive ion etching were analysed using both monochromatic and white beam reflection X-ray topography. Some features of observed X-ray topographic contrast associated with the gratings were modelled using a diffracting zone model, based on a simple radial in-plane strain field. Reasonable agreement was obtained between this model and observations.

The Chemisorption of C on Al(111)

1998 ◽  
Vol 05 (02) ◽  
pp. 537-543
Author(s):  
E. E. Mola ◽  
G. A. Appignanesi ◽  
J. L. Vicente
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Interaction Energy ◽  
Adsorption Site ◽  
Mndo Method ◽  
Scanning Tunneling ◽  
Surface Site ◽  
Tunneling Microscopy ◽  
Semiempirical Mndo

The chemisorption of C atoms on Al(111) was studied by means of the semiempirical MNDO method. The incorporation of the C adatom into the clusters was considered and the most favorable chemisorption site was evaluated. The hcp in-surface site was identified as the most stable adsorption site, in agreement with recent scanning tunneling microscopy (STM) experiments. This fact allowed us to use the MNDO method to evaluate the interaction energy of two chemisorbed C atoms in order to understand the observed formation of an ordered carbon underlayer. The low mobility of single isolated C adatoms revealed in STM experiments is also discussed.

Analysis of Functional Scoliosis by Means of an Anisotropic Beam Model of the Human Spine

1985 ◽  
Vol 107 (3) ◽  
pp. 281-285 ◽  
Author(s):  
L. Lindbeck
Keyword(s):  
Reasonable Agreement ◽  
Small Difference ◽  
Frontal Plane ◽  
Elastic Beam ◽  
Beam Model ◽  
Leg Length ◽  
X Ray ◽  
Human Spine ◽  
Anisotropic Elastic ◽  
Experimental Findings

An upright, muscle-relaxed human spine, suffering from a mild functional scoliosis, caused by a small difference in leg length, is modeled as an anisotropic, elastic beam. The lower end of the beam is built-in in a fixed body, i.e., the laterally tilted pelvis. The upper end is rigidly attached to a rigid body, i.e., the supported upper part of the trunk, which is supposed to move freely in the frontal plane. It is shown that the characteristic scoliotic curvature of the spine, observed on an X-ray picture, can be reproduced by means of buckling analysis of the beam model, using realistic values of geometric and loading parameters and a properly chosen bending stiffness, which is found to be in reasonable agreement with earlier experimental findings. The analysis also shows that the muscle-relaxed upright equilibrium position of the spine is mechanically unstable.

scholarly journals An X-ray study of the dissociation of an alloy of copper, iron and nickel

1943 ◽  
Vol 181 (987) ◽  
pp. 368-378 ◽  
Keyword(s):  
Quantitative Data ◽  
Reasonable Agreement ◽  
Wave Length ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cubic Lattice ◽  
Cubic Structure ◽  
Average Wave ◽  
Diffraction Effects ◽  
The Way

A description is given of the unusual X-ray diffraction effects shown by the alloy Cu 4 FeNi 3 while it is in the process of splitting up from one face-centred cubic structure into two. Before the formation of the tetragonal structures described by Bradley a state is formed in which each line of a powder photograph is accompanied by quite strong side-bands. An explanation of this is given and is shown to be in reasonable agreement with most of the quantitative data from the X-ray photographs. This explanation is that the original cubic lattice is regularly deformed by the segregation of the different atoms. From the positions of the side-bands the directions of the deformations and their average wave-length can be estimated. The intensities, however, do not fit in with the theory; they do not vary exactly in the way predicted. It is shown, however, that the variation is in closer agreement with this sort of modulation of the structure than with any other, but it has not, so far, been found possible to find any factor that will modify the intensities of the side-bands in the way required.

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