bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bending Energy Minimisation Criterion for Molecular Geometry in XY3 Pyramidal Systems
Authors: Indira K. , Rudra Warier M. K. , Ananthakrishnan T. R. 
Published: February 2015

Abstract
A study of the variation of the vibrational potential energy contribution with interbond angles in XY3 pyramidal molecules confirms the observation previously made for XY2 bend symmetric systems that the actual equilibrium
y
configuration lies in the premises of minimum A study of the variation of the vibrational potential energy contribution with interbond angles
in XY3 pyramidal molecules confirms the observation previously made for XY2 bend symmetric
systems that the actual equilibrium configuration lies in the premises of minimum Vbend and zero Vstretch-bend *
Interrelation Between Molecular Motions and Structure in Solid Trimethylamine-boron-trichloride as Studied by NMR
Authors: Głowinkowski S. , Jurga , S. , Szcześniak E. 
Published: February 2015

Abstract
The temperature dependences of proton second-moment and spin-lattice relaxation times (T1 and T1ρ) have been measured in solid (CH3)3NBCl3. The nature of reorientation processes occurring in the complex has been established and the activation parameters determined. The motions are discussed in relation to the molecular structure of the complex
An Electron Paramagnetic Resonance Study of Mn2+ Ions Doped in Langbeinites
Authors: Böttjer T. , Lehmann G. , Stockhausen M. 
Published: February 2015

Abstract
The cubic (high temperature) phase of some langbeinites, A+
2 B2
2+(SO4)3 with 11 different combinations of A and B type cations, doped with Mn2+, is investigated by EPR. Powder or single crystal spectra are measured at X-band. They indicate centers of axial symmetry in all cases. In 6 of the langbeinites two centers are found which differ considerably in intensity. Both centers are substitutional defects (Mn in the crystallographically nonequivalent divalent B ion sites). For the more intense one the zero field splitting parameter is proved to be negative in all cases. That center is assigned to the more spacious site which, depending on the cation size, allows for local relaxation. It is shown by comparison with predictions of the superposition model that relaxation appears to be effective
Determination of Partial Structure Factors of Molten Eutectic Ni33Ge67
Authors: Halm Th. , Hoyer W. , Neumann H. , Bellissent R. 
Published: February 2015

Abstract
Using isotopic substitution and X-ray scattering, different weighted structure factors were measured and combined in order to calculate partial structure factors. Although we got an overdetermined system of equations, the solution of this problem was difficult due to the small value of the determinant. From the partial pair correlation functions and the radial concentration correlation function a splitting of the first coordination shell is obvious. The dip in SNi-Ge and the corresponding peak in SNi-Ni indicate some degree of charge transfer in the melt.
A Study of the Motion of High-Energy Electrons in a Helium Hollow Cathode Discharge
Authors: Donkó Z. 
Published: February 2015

Abstract
The motion of high-energy electrons was studied in a helium hollow cathode discharge using Monte Carlo simulation. The calculations were carried out in the pressure range of 2-10 mbar. The length of the cathode dark space (CDS) was determined by simulation in an iterative way using experimental voltage-current density characteristics of the discharge. At the lowest helium pressure (2 mbar) the concentration of high-energy electrons was found to be the same at the CDS-negative glow boundary and at the midplane of the discharge while at 8 mbars it was found to be by 1-2 orders of magnitude smaller. The results of our calculations support the existence of "oscillating" electrons. The probability of 1, 2 and 3 transfers through the negative glow (NG) for primary electrons was found to be 37%, 11 % and 2%, respectively, at 2 mbar pressure. The spatial distribution of ionizations and the angular distribution of electron velocity at the CDS-NG boundary were also investigated. The pressure dependence of the current balance at the cathode was obtained, and the results indicate that with decreasing pressure other secondary emission processes than ion impact become important in the maintenance of the discharge.
Approaches to the Study of van der Waals Interactions in Solids
Authors: Weiss Alarich 
Published: February 2015

Abstract
Van der Waals forces are of short range. In molecular crystals the interacting atoms or groups of atoms of a molecule are fixed in their position with respect to the atoms of the neighboring molecules. From measurements of the intermolecular interactions via properties which can be assigned to the individual atoms (groups), such as hyperfine interactions or vibrational frequencies, as a function of the intermolecular distances, the van der Waals (vdW) potentials may be evaluated.
We propose the use of discrete changes of intermolecular distances for studying vdW-interactions, the method of “Several Solid States”,
a) by combining a molecule A with different moleculs Bi, in stoichiometric proportions and in a crystallographically ordered way to molecular solid complexes;
b) by investigating the changes of atomic (group) properties in systems with two ore more solid phases appearing in the phase diagram as a function of temperature (pressure). This way of using several solid states is offered only by chance;
c) by using the fact that in many molecular solids there is more than one molecule in the asymmetric unit of the elementary cell in the crystal structure, and therefore several vdW-potentials for chemically identical intermolecular neighbors;
d) by the synthesis of compounds containing the atoms (groups), the vdW-interactions of which one wants to study, with one or more centers of chirality. With one center of asymmetry in the molecule one finds the molecule considered in two different situations of vdW-contacts at least, and, in first approximation, one can assume identical intramolecular interactions (besides the optical activity). Two chirality centers within the molecule lead to three (at least) different crystal fields: a) (±); b) (− −) respectively (+ +); c) (− −, + +).
Examples of hyperfine interaction studies, based on this "Several Solid States" concept are discussed.
Crystal Structure and 35Cl NQR of ( — ) β-(trichloromethyl)- β-propiolactone. Comparison with (±) β-(trichloromethyl)-β-propiolactone
Authors: Dou Shi-qi , Basaran Reha , Paulus Helmut , Weiss Alarich 
Published: February 2015

Abstract
The crystal structure of(-)β-(trichloromethyl)-β-propiolactone at room temperature is reported, as is the 35Cl NQR spectrum in the range 77 ≦ T/K ≦ 323.5. The compound crystallizes with the space group D2
4-212121, Z = 8, a = 2416.0 (10) pm, b = 975.6 (4) pm, c = 595.0 (2) pm. The intramolecular distances and angles of the two crystallographically independent (-) molecules in the unit cell are equal within the limits of error. The spread of the 35Cl NQR spectrum is within 600 kHz, not changing in the temperature range covered. The crystal structure and 35Cl NQR spectrum are discussed.
The results found for the (-) compound are compared with the corresponding ones reported for the (±) compound [1], and the influence of the different intramolecular interactions in the two solid states of the chemically identical compounds on the NQR spectrum is discussed.
ESR of Gamma Irradiation Damage Centers in Single Crystals of Some Phenol Derivatives
Authors: Köksal F. , Osmanoğlu Ş. , Tapramaz R. 
Published: February 2015

Abstract
Phenoxy radicals have been observed and identified in gamma irradiated 2-t-bu-4-methylphenol, 2,6-di-t-bu-4-methylphenol and 2-amino-4-methylphenol single crystals.
Lithium Isotope Effects in Cation Exchange Chromatography of Lithium Lactate in Water-Dimethyl Sulfoxide and Water-Acetone Mixed Solvent Media
Authors: Oi Takao , Kondoh Akiko , Ohno Etsuko , Hosoe Morikazu 
Published: February 2015

Abstract
Lithium isotope separation by ion exchange displacement chromatography of lithium lactate in water-dimethyl sulfoxide (DMSO) and water-acetone mixed solvent media at 25 °C was explored. In both the water-DMSO and water-acetone system, the single stage isotope separation factor (S) was a convex function of the mixing ratio of the solvents in the external solution phase; S had its maximum value of 1.00254 at water: DMSO = 25:75 v/v and 1.00182 at water: acetone = 75:25 v/v. Strong correlations of S with solvent partitions between the solution and the exchanger phases were found in both systems, which was qualitatively explainable by considering the lithium isotope distributions between the two phases based on the fundamental lithium isotope effects and the relative affinities of water, DMSO and acetone towards the lithium ion.
Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. I. Method
Authors: Koch Wolfhard 
Published: February 2015

Abstract
Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.
X-Ray Diffraction Study of the Electron Density and Anharmonicity in K2PtCl6
Authors: Restori Renzo , Schwarzenbach Dieter 
Published: February 2015

Abstract
X-ray diffraction data in heavy-atom compounds may be sensitive to anharmonic atomic displacements, since the large core electron densities result in appreciable scattering amplitudes at large reciprocal distances. Since bonding electron densities may also exhibit sharp features affecting high-order reflections, they may be difficult to distinguish from anharmonic effects. We have analyzed an accurate room-temperature single-crystal X-ray data set of K2 PtCl6 using least-squares anharmonic displacement and charge density formalisms. The Hirshfeld charge density formalism, which has successfully been applied to many light-atom structures, fails to parametrize satisfactorily the data, whereas the electron densities at K and CI are easily accounted for by an anharmonic Gram-Charlier expansion to 4th order. Densities around Pt are parametrized only by a combination of anharmonicity and charge density formalisms. If economical parametrizations of the experimental data are preferred to more complicated ones, anharmonicity may be conjectured to play an important rôle while the main bonding feature consists of a preferential occupation of the 5d-orbitals of Pt with t2g symmetry.
Static and Dynamical Valence-Charge-Density Properties of GaAs
Authors: Pietsch Ullrich 
Published: February 2015

Abstract
Owing to the close neighbourhood of Ga and As in Mendeleev's table, GaAs shows two fundamental classes of X-ray structure amplitudes distinguished by their extremely different scattering power. They are differently sensitive to the valence electron density (VED) redistribution caused by the chemical bond and must be measured by different experimental methods. Using such data, both the VED and the difference electron densities (DED) are calculated here. Comparison with theoret-ical densities shows that the VED is characterized by covalent, ionic and metallic contributions. The DED constructed from GaAs and Ge data demonstrates the electronic response caused by a "protonic" charge transfer between both f.c.c. sublattices as well as the transition from a purely covalent to a mixed covalent-ionic bond. Especially the charge-density accumulation between nearest neighbours (bond charge (BC)) depends on the distance between the bonding atoms and changes under the influence of any lattice deformation. This phenomenon is described by a BC-transfer model. Its direct experimental proof is given by measuring the variation of the scattering power of weak reflections under the influence of an external electric field. This experiment demonstrates that the ionicity of the bond changes in addition to the BC variation.
Electron Density and Bonding in Ring Silicates: Beryl, Cordierite, Dioptase
Authors: Belokoneva Elena L. , Tsirel'son Vladimir G. 
Published: February 2015

Abstract
The electron density and bonding in the silicates beryl, cordierite and dioptase has been investigated. The replacement of Be, Si and Al atoms in the identical structural fragments leads to a (δr-redistribution and changes the σ-bond character from slightly polar to strongly polar. The condensation of [SiO4]-tetrahedra in the rings leads to the accumulation of electron density near bridge oxygens. This phenomenon is expressed especially in dioptase (pure ring silicate). Therefore, the electron density picture may be considered as a supplementary independent criterion for classi-fication of crystal structures. The experimental (δr-maps for H20 molecules in dioptase are in good agreement with theoretical ones. The δr distribution of 3 d-electrons and bonding in the Jahn-Teller distorted Cu-octahedron can be interpreted from crystal-field-theory point of view.
Estimation of Charge Density on Nitrogen in Amides by Measurement of One-Bond Carbon-Hydrogen Nuclear Coupling Constants in N-CH3 Group
Authors: Haake Paul , Tyssee Donald A. 
Published: February 2015

Abstract
One-bond, 13C-1H coupling constants, J1(C-H), 'in amines, ammonium ions, and carboxylic amides correlate with structure and support the concept that the value of J1(C-H) is related to the charge density on the nitrogen atom; for example, amine oxides have nearly the same charge density at nitrogen as does the tetramethylammonium ion. The J1(C-H) values for methyls bonded to nitrogen in various amides then give an experimental estimate of the charge density at the nitrogen atom that enables an estimate of the bond order in the C-N amide-bond; the data suggest that carboxylic amides have a C-N bond order of about 1.35, that sulfonamides have an S-N bond order of about 1.45, and that phosphinamides, R2 P(O)N(CH3)2 , have a P-N bond order of about 1.3. In contrast, aminephosphines have a P-N single bond. The value for carboxylic amides is in reasonable agreement with bond distances in amides.
The Electron Density Distribution in Be Metal Obtained from Synchrotron-Radiation Powder Data by the Maximum-Entropy Method
Authors: Takata Masaki , Kubota Yoshiki , Sakata Makoto 
Published: February 2015

Abstract
The nature of the bonding in Be metal was studied by investigating the MEM map, which is the electron density distribution obtained by the Maximum-Entropy Method. In order to avoid extinc-tion effects, 19 Bragg reflections were measured by a new powder-diffraction experiment that utilizes Synchrotron Radiation as an incident X-ray and an Imaging Plate as detector. The experiment was carried out at the Photon Factory BL6A2. In spite of the limited number of reflections used in the MEM analysis, the electron density distribution of Be was obtained accurately and reliably. The structure factors for unmeasured reflections were calculated and compared with the values observed by Larsen and Hansen [Acta Cryst. B40, 169 (1984)]. The agreement is very good. Furthermore, the MEM map revealed that Be metal forms an electronic layer in the shape of a honeycomb that is parallel to the basal plane.
Electrostatic Properties of Ions in Crystals from X-Ray Diffraction Data
Authors: Hansen Niels K. 
Published: February 2015

Abstract
A procedure for calculating the electrostatic potential and the electrostatic energy of an ion in a crystal is presented. It is based on a mixed direct and reciprocal space approach, and it takes into account the detailed charge density distribution in the crystal which can be obtained from accurate X-ray diffraction measurements.
Momentum Distribution and Charge Density in Solid-State Theory
Authors: Calais Jean-Louis 
Published: February 2015

Abstract
We present a discussion of a number of conceptual and methodological aspects associated with the theoretical characterization and computation of charge densities and momentum distributions in solids. The main ambition has been to stress properties that both exact and approximate quantities must possess. We have also attempted to point out conceptual and computational trends which would seem to be of importance for the future of the subject.
The Generalised Oscillator-Strength Density of the Helium Atom, Calculated by a New Implementation of the Complex-Coordinate Method
Authors: Saenz Alejandro , Weyrich Wolf 
Published: February 2015

Abstract
We report a calculation of the generalised oscillator-strength density (GOSD) of the helium atom for low momentum transfer. The calculation was performed by extraction of the searched entity from the resolvent of the complex-rotated Hamiltonian. That Hamiltonian was found using a standard ab-initio program without any change in the program code. The shape of the Bethe surface is reproduced (including resonances and the absorption edge). However, with increasing momentum transfer the magnitude of the calculated values for the Bethe ridge becomes too small. This is clearly demonstrated by an evaluation of the Bethe sum as a function of the momentum transfer. A comparison with recent additional theoretical data shows that the deviations are due to the employed basis set.
(e, 2 e)-Spectroscopy and the Electronic Structure of Molecules. A Short Review with Selected Examples
Authors: Coplan M. A. , Moore J. H. , Tossell J. A. 
Published: February 2015

Abstract
The simple plane wave target Hartree-Fock impulse approximation for the (e, 2e) reaction is developed. One result of the approximation is the separation of the expression for the (e, 2e) cross-section into a kinematic factor and a structure factor that contains all of the information about the target. When the target is a molecule, the structure factor can be further separated into atomic terms and a geometric term. This is illustrated for a simple one-electron homonuclear diatomic molecule. Three examples of the application of (e, 2e) spectroscopy to systems of chemical interest are given. They are borazine (inorganic benzene), the methyl siloxanes and the inorganic complex trimethylamine boron trifluoride.
Single-Particle Momentum Distributions from Deep Inelastic Neutron Scattering (DINS)
Authors: Simmons Ralph O. 
Published: February 2015

Abstract
Single-particle longitudinal momentum distributions in condensed matter are now accessible to direct measurement using eV neutrons. Some systems of particular interest include a) quantum solids and fluids, formed from 3Hie, 4He, and H2 , b) prototype molecular crystals, formed from noble gases, c) fluids such as H2 and Ne, which show deviations from classical behavior and d) mixed systems, in which guest-host interactions may be important. Quantum solids can be investigated at substantially different densities, for different structures, and further, can be compared to the corresponding fluids, with which they have significant similarities in their single-particle properties such as their momentum distributions. Noble gas solids comprise a graduated family with progressively varying importance of zero-point energy, of phonon anharmonicity, and of multi-body forces. They have also been very useful for matrix isolation studies, and eV neutron scattering can yield their center-of-mass motions, not previously seen directly. Finally, noble gas fluids can be used to investigate the nature and extent of final-state effects in the neutron scatttering. Such effects are defined to be the difference between the longitudinal "neutron Compton profile" and the longitudinal momentum distribution.
Neutron and PIMC Determination of the Longitudinal Momentum Distribution of HCP, BCC and Normal Liquid 4 Het
Authors: Blasdell R. C. , Ceperley D. M. , Simmons R. O. 
Published: February 2015

Abstract
Deep inelastic neutron scattering has been used to measure the neutron Compton profile (NCP) of a series of condensed 4He samples at densities from 28.8 atoms/nm3 (essentially the minimum possible density in the solid phase) up to 39.8 atoms/nm3 using a chopper spectrometer at the Argonne National Laboratory Intense Pulsed Neutron Source. At the lowest density, the NCP was measured along an isochore through the hep, bcc, and normal liquid phases. Average atomic kinetic energies are extracted from each of the data sets and are compared to both published and new path integral Monte-Carlo (PIMC) calculations as well as other theoretical predictions. In this preliminary analysis of the data, account is taken of the effects of instrumental resolution, multiple scattering, and final-state interactions. Both our measurements and the PIMC theory show that there are only small differences in the kinetic energy and longitudinal momentum distribution of isochoric helium samples, regardless of their phase or crystal structure.
Phase Diagrams of Binary Systems of Some Alkali Propionates
Authors: Mirnaya T. A. , Yaremchuk G. G. , Volkov S. V. 
Published: February 2015

Abstract
The phase diagrams of the binary systems sodium-potassium, sodium-caesium, and potassium-caesium propionates have been investigated by differential thermal analysis and hot-stage polarization microscopy. Smectic liquid crystals in the systems with sodium propionate have been discovered. Liquid crystal formation in binaries of two non-mesomorphic components is explained by latent mesomorphism which is shown to be inherent to both sodium and potassium propionate.
Correlation of Crystal Structure and Vapor Composition of Metal Dihalides
Authors: Hargittai Magdolna , Jancsó Gábor 
Published: February 2015

Abstract
The presence of dimers in the vapor of metal dihalides, as seen in electron diffraction experiments, is found to be correlated with the crystal structure of the halide and with the difference in the heat of vaporization between monomers and dimers. If the dimeric molecule cannot be recognized as a unit in the crystal, dimers are not detected in the vapor. If dimeric molecules are discernible in the crystal, they will be observed in the vapor if their heat of vaporization is not greater than that of the monomer by more than 10 kcal/mol.
Ionic Diffusion in Cu6PS5Br Studied by 63Cu NMR
Authors: Ohki H. , Harazono K. , Erata T. , Tasaki A. , Ikeda R. 
Published: February 2015

Abstract
Applying 63Cu NMR technique, we observed exchange between the nonequivalent copper sites in crystalline Cu6PS5Br, known as a member of the mineral "argyrodite". Below 200 K, where the motion of the copper (I) ion is slow, we could distinguish several nonequivalent copper sites. On increasing the temperature, the chemical exchange between the nonequivalent cation sites was seen on the 63Cu NMR spectra. We could determine the activation energy for this motion to be 35 kJ mol-1 , in good agreement with the published ionic conductivity.
Perturbation Dynamics of the Infinite Dicke Model
Authors: Honegger Reinhard , Rieckers Alfred , Unnerstall Thomas 
Published: February 2015

Abstract
By means of operator algebraic methods the dynamics of the Dicke model is investigated in the limit where the number of the two-level atoms goes to infinity and the interaction strength remains on a finite level. The infinite atomic system is treated as a mean field quantum lattice system. It is shown that the limiting dynamics is essentially determined by the collective behaviour of the atoms. With Trotter's product formula and perturbation theoretical methods we obtain explicit expressions for the unitary time evolution operators in the uncoupled representation.