bluuebunny/crossref_metadata_2025 huggingface dataset:
New Opportunities for Charge Density Studies Using the FAST Area Detector
Authors: Lehmann Christian W. , Karaulov Alexander , Hursthouse Michael B.
Published: February 2015

The requirements for charge density studies of more complex molecules have been realized by use of the FAST area-detector diffractometer in conjunction with a rotating-anode generator, which allows to collect large quantities of diffraction data within less than two days, independent of unit cell size. Oxalic acid dihydrate has been chosen for test experiments. Data collection strategies are described and preliminary results are presented. These show that data of sufficiently high quality for charge density studies can be collected.
Use of Symmetry in Coupled Hartree-Fock Calculations of Non-linear Response Tensors in Molecules
Authors: Lazzeretti P. , Malagoli M. , Zanasi R.
Published: February 2015

A new computational scheme for electric dipole hyperpolarizabilities has been devised within the coupled Hartree-Fock method. Only the projection of second-order perturbed orbitals onto the subspace spanned by unperturbed virtual orbitals is computed. The entire molecular symmetry is exploited to reduce computational effort: a reduced two-electron integral file containing only symmetry-distinct matrix elements over the atomic basis functions is processed at each iteration. In addition, only symmetry-independent first-and second-order perturbed density matrices need to be calculated. An efficient computer program implementing the present approach has been developed.
Electron Density Distributions and Atomic Charges
Authors: Hess B. , Lin H. L. , Niu J. E. , Schwarz W. H. E.
Published: February 2015

Accurate electron densities and X-ray form factors of Li, Be, F and their ions have been calculated. Electron correlation, crystal fields and ionic charge transfer change the form factors by up to a few percent, mainly in the range of sin θ/ λ < 1/3 Â -1 . Although electron correlation and crystal fields are small perturbations, their effects on the density and form factor are not additive. Densities or form factors of atomic and ionic systems are very similar; [Li0F0] and [Li+F-] procrystals differ by an effective charge transfer of not more than 0.4 e. Charge transfer and charge overlap in crystals cannot be distinguished uniquely. When the experimental data on Li2BeF4 (approximately reproduced by 3/4 atomic plus 1/4 ionic procrystal) are interpreted from the atomic partial charges are as low as 0.1 e (Li+ 0.1
2Be+ 0.2F- 0.1
4); when interpreted from the ionic viewpoint,

the charges are much higher, namely 0.7 e. Intermediate viewpoints are also possible.
Calculation of Compton Profiles Using a Multipole Expansion of the Momentum Density
Authors: Blaas Claudia , Redinger Josef , Podloucky Raimund , Jonas
Published: February 2015

A practical method for the calculation of Compton profiles for cubic systems with O and Oh symmetry is presented that is based on a multipole expansion of the electron momentum density (EMD) in terms of cubic harmonics. The central quantities, the expansion coefficients, are deter-mined by a Gaussian-type integration (special directions) over the angular coordinates. From these coefficients the coefficients of an analogous expansion of the Compton profile can be directly calculated, establishing a transparent relationship between the electron momentum density and the Compton profile. This direct relationship offers the possibility of tracing back Compton-profile anisotropics to EMD anisotropics more easily, as demonstrated for MgO and FeAl.
Atomic Orbitals from Compton Profiles
Authors: Schmider Hartmut , Smith, Jr. Vedene H.
Published: February 2015

A recently developed method for the least-squares reconstruction of one-particle reduced density matrices from one-particle expectation values has been applied to isotropic Compton profiles of neon from the literature. The resulting densities in momentum and position space are compared with the ones obtained from ab-initio calculations.
Dynamic Structure Factor: An Introduction
Authors: Sturm K.
Published: February 2015

The doubly differential cross-section for weak inelastic scattering of waves or particles by manybody systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system.

The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-particle response function in self-consistent field approximations, such as the random-phase approximation or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function.
Theories of Compton Scattering by Magnetic Materials
Authors: Lovesey Stephen W.
Published: February 2015

Theoretical work on the cross-section for Compton scattering by magnetic materials is surveyed. Exact results for scattering by a free polarized electron are contrasted with corresponding results obtained perturbatively for a model of bound electrons with a finite width to the momentum distribution.
Momentum-Density Studies of Some Compounds with Triatomic Linear Anions
Authors: Horenian R. O. , Weyrich W.
Published: February 2015

High-purity powder samples of lithium and sodium azide (LiN3 , NaN3), cyanate (LiOCN, NaOCN) and hydrogen fluoride (LiFHF, NaFHF) were studied by means of 59.54 keV Compton spectroscopy. The measured isotropic Compton profiles were corrected for multiple scattering and transformed to spherically averaged reciprocal form factors Ba(s).

The experimental results are compared with theoretical reciprocal form factors obtained from Hartree-Fock calculations with different types of basis sets (Gaussian-and Slater-type orbitals, with and without polarisation functions) both for the free ions and for several kinds of clusters. The importance of intraionic and interionic interaction for the description of chemical bonding in these compounds is pointed out and discussed.
Compton Scattering from Heavier Metals
Authors: Sharma B. K
Published: February 2015

The use of Compton scattering in the determination of electronic structure has grown considerably in the last two decades. With the advent of synchrotron radiation it has become possible, even with good resolution, to measure several single-crystal orientations to determine three-dimensional electron momentum distributions. Although most of the earlier work has been directed to low-Z materials, in the last few years medium and high-Z metals have also been investigated with this technique. In this paper we present a review of these studies on heavier metals with particular attention to the difficulties encountered. Compton profile measurements from techniques based on energetic ion beams are also considered briefly.
Compton Scattering Experiments with Polychromatic Radiation
Authors: Schütz Wolfgang , Waldeck Beate , Flösch Dietmar , Weyrich Wolf
Published: February 2015

We show an iterative algorithm that allows to obtain accurate Compton profiles J(q) from Compton scattering spectra I2 (ω2), if the excitation radiation is not strictly monochromatic. It requires knowledge of the spectral distribution of the primary radiation I1(ω1), validity of the impulse approximation and dominance of a monochromatic part in I1(ω1) over the polychromatic rest. Conversely, the primary spectrum is often experimentally not directly accessible. In such a situation it is possible to evaluate the primary spectrum I1(ω1) from the spectrum of scattered photons, I2(ω2), with a similar iterative algorithm. We use a scattering target of high atomic number in order to ensure that the elastically scattered photons dominate the inelastically scattered ones. From the scattered spectrum we get a model for the Compton profile that allows us to separate the inelastic part of the scattered spectrum from the elastic part, which, in turn, is proportional to the spectral distribution of the primary radiation.
Deep Inelastic Neutron Scattering in the Study of Atomic Momentum Distributions
Authors: Evans Alan C. , Mayers Jerry , Timms David N. , Cooper Malcolm J.
Published: February 2015

The electron-volt spectrometer (EVS) at the pulsed neutron source facility (ISIS) is being developed for the study of atomic momentum distributions. Neutrons with energies in the range 1 to 100 eV are incident on the sample, and the time-of-flight (TOF) spectrum of the scattered beam is measured by an array of fixed detectors. A resonant foil difference technique is used to yield a set of TOF spectra for those neutrons scattered into a fixed energy and through fixed angles. Information on the momentum distribution of the target nuclei can be deduced within an impulse approximation in a procedure analogous to that in Compton scattering of electrons by photons.

Crystalline compounds containing aligned hydrogen bonds and other hydrogenous compounds are of particular interest owing to the high cross-section of the proton at these neutron energies. With improved statistical accuracy of the data it is anticipated that deviations of the proton's potential from a harmonic potential may be determined. Non-hydrogenous systems have also been investigated. A description is given of the basic theory and interpretive method. Data obtained on numerous systems are presented and discussed.
On Spanning Trees in Catacondensed Molecules
Authors: Gutman I. , Mallion R. B.
Published: February 2015

Among all catacondensed benzenoid molecules the unbranched systems possess the largest number of spanning trees. Some other relations for the spanning-tree count of catacondensed benzenoids are also reported. The results obtained continue to hold for catacondensed molecules composed of rings the size of which differ from six. The propositions reported do, however, depend for their validity on there being rings of only one size in the catacondensed system under study.
Thermodynamics of the HSO4
– Formation in Aqueous Solutions up to 473 K and 975 bar
Authors: Bilal B. A. , Müller E.
Published: February 2015

The equilibrium constant, partial molal volume, entropy and enthalpy of the formation of HSO4
- ion in aqueous solutions have been determined up to 473 K and 975 bar at the ionic strengths 1 = 0 as well as in NaCl solutions having I = 1, 0.5 and 0.1 mol kg-1 At 473 K, for instance, the thermodynamic formation constant K0 decreases by ≈ 0.75 log units from saturation pressure to 975 bar. The corresponding decrease of the apparent formation constant Q at I = 1 m is ≈ 0.6 log units. The increased dissociation at higher pressure leads to a decrease of the partial molal volume and entropy due to the resulting higher electrostriction in the system.
Inner Bremsstrahlung Accompanying the Non-Unique First Forbidden β-Decay of 141Ce
Authors: Khalil E. I.
Published: February 2015

The inner Bremsstrahlung (I.B.) spectrum accompanying the β-decay of 141Ce (non-unique first forbidden β-transition) was measured using a single channel scintillation spectrometer. The measured I.B. was analyzed by the variable width peeling-off method. This analyzed and corrected I.B. was compared with those calculated according to the original theories of Knipp and Uhlenbeck as well as of Bloch (KUB), the coulomb corrected theories of Lewis and Ford and of Nilsson, and according to detour-transition calculations of the Ford and Martin theory. Ths shape correction factor suggested by Konopinski and Uhlenbeck on the Fermi β-decay theory was applied to the calculated I.B. based on Nilsson's theory (modified KUB theory). The experimental results are in better agreement with the modified KUB theory than the other theories.
Is the Gravitational Force Elementary?
Authors: Stumpf H. , Borne Th. , Kaus H. J.
Published: February 2015

The gravitational force is assumed to be mediated by spin 2 gravitons which are composed of four spin 1/2 (sub-) fermions. The dynamics is governed by a nonlinear spinorfield equation with nonperturbative Pauli-Villars regularization and canonical quantization. On the quantum level the fermion dynamics is expressed by a functional equation for algebraic state functionals, and the "graviton" (functional) states are defined to be solutions of the diagonal part of this equation. The effective interaction between such graviton states and fermions is studied by means of a weak mapping between the original functional equation and an effective functional equation for gravitons and fermions. In the low energy limit this mapping produces for the effective fermion dynamics (apart from selfinteractions) a Dirac equation in anholonomic coordinates coupled to the anholonomic connections of a gravitational field, i.e. the usual phenomenological expression for a gravitational force acting on spin 1 /2 fermions.
Monomer and Excimer Fluorescence of 2-Phenylindole in p-Xylene at 20 °C Studied by Frequency-Domain Fluorometry
Authors: Kawski A. , Gryczyński I. , Maliwal B. P. , Piszczek G.
Published: February 2015

The effect of 2-phenylindole (2PI) concentration in p-xylene upon the fluorescence decay time was investigated by frequency-domain fluorometry. The fluorescence decay of a dilute (10~ 5 M) 2PI solution in p-xylene at 20 °C is single exponential with the mean decay time t = 1.87 ns and practically independent of the observation wavelength (A obs) in the fluorescence band. The fluores-cence decay in a highly concentrated solution (6 x 10" 3 M) is heterogenic and depends on A obs . For a given modulation frequency (~ 200 Hz), the fluorescence phase shifts at the longwave observation (440-480 nm) distinctly exceed 90°, thus clearly indicating that the observed (excimer) fluorescence results from a process taking place in the excited state. The fluorescence decays were measured at seven values of A obs (360-480 nm), and all the results were analyzed comprehensively (tj and t 2 are equal for all A obs ; the amplitudes are different). The lifetimes of the excimer state is relatively short (~3.5 ns). Radiative (r e) and non-radiative (t,) rate constants for monomer fluorescence of 2PI in p-xylene were determined using appropriate data from photo-and radioluminescence measure-ments.
Comment on "Surrealistic Bohm Trajectories"
Authors: Dürr Detlef , Fusseder  , Goldstein Sheldon , Zanghi Nino
Published: February 2015

From the perspective of orthodox quantum theory, no meaning can be assigned to the notion of the "slit" through which the atom passed in the experiments under discussion in this paper. From a Bohmian perspective this notion does have meaning. Moreover, when we compare the answer provided by BM with the answer provided, not by orthodox quantum theory, but by a naive, largely incoherent operationalism, we obtain different answers. So what?
Stochastic Resonance in Experiment
Authors: Kittel A. , Richter R. , Hirsch M. , Flätgen G. , Peinke J. , Parisi J.
Published: February 2015

We observe the phenomenon of stochastic resonance in a semiconductor experiment. Originally, such an effect was predicted for bistable dynamical systems that are influenced by a periodic modulation as well as a random perturbation. In that case, a "resonance" peak can be observed in the power spectrum. The phenomenon investigated is the low-temperature impact ionization breakdown. There, bistability results from the competing states of low and high conductance.
On the Scaling Function of Lyapunov Exponents for Intermittent Maps
Authors: Stoop R. , Parisi J.
Published: February 2015

The scaling function of Lyapunov exponents for intermittent systems is full of particularities if compared with hyperbolic cases or the usual, nonhyperbolic, parabola. One particularity arises when this function is calculated from finite-time Lyapunov exponents: Different scaling properties with respect to the length of the finite-time chains emerge. As expected from random walk models, the scaling of an ensemble with non-Gaussian fluctuations evolves for certain values of the external parameter.
A "Superfat" Attractor with a Singular-Continuous 2-D Weierstrass Function in a Cross Section
Authors: Rössler O. E. , Hudson J. L.
Published: February 2015

A 3-D invertible map generating a 4-loop solenoid attractor is presented. The attractor of the "standard" 4-solenoid turns out to be "fat" - that is, fractal dimensionality exceeds topological dimensionality by more than unity. If a fourth variable that is weakly damped is added to this 3-variable map, a new type of attractor is generated. In a cross section it is a continuous nowhere-differentiable function over a 2-D domain which is a 2-D Cantor set. Such an object can be called a "singular-continuous 2-D Weierstrass function". The latter can be "superfat" (dimension gap larger than 2). Realistic systems possessing attractors of this new type are possible.
Differential Thermal Analysis under Pressure on Cyanocyclohexane, 1,2,3,4-Tetrahydro-5,6-dimethyl-1,4-methanonaphthalene, and 2-Methyl-2-propanol
Authors: Reuter J. , Brückert T. , Würflinger A.
Published: February 2015

Differential thermal analysis has been performed on cyanocyclohexane (CCH), 1,2,3,4-tetrahydro-5,6-dimethyl-1,4-methanonaphthalene (TDMN), and 2-methyl-2-propanol (t-butanol) up to 300 MPa. The latter compound was also investigated dielectrically. CCH displays an ODIC phase that transforms only reluctantly to the low-temperature stable phase II. Annealing under pressure can appreciably accelerate this transformation. For all three compounds the phase diagrams were established. For CCH and TDMN also the pressure dependence of the glass transition has been determined.
A Broadband Microwave Fourier Transform Spectrometer, Especially Designed for Stark Effect Investigations of Almost Nonpolar Molecules; the Electric Dipole Moment and the Anisotropy in the Static Electric Polarizability Tensor of 1,1-Dideuteroallene, D2C = C = CH2
Authors: Meyer V. , Sutter D. H.
Published: February 2015

A bridge type microwave Fourier transform spectrometer, equipped with flat oversized Stark cells and an operational range from 8 GHz to 40 GHz is described. As application we report the experimental determination of the vibronic ground state dipole moment and of the anisotropy in the static polarizability of 1,1-dideuteroallene. Our experimental values are: μa = 0.0053(2) D for the dipole moment, and (α∥ - α⊥) = 4.26(6) • 10-24 cm3 , for the polarizability anisotropy.
Theoretical Study of the C3II-X3II Transition in CSi
Authors: Trinder W. , Reinsch E. A. , Rosmus P.
Published: February 2015

The radiative lifetimes of the C3Il-X3II transition of the CSi radical have been calculated from highly correlated electronic wavefunctions and compared with available experimental data. For this transition, the Franck-Condon approximation fails due to the strong R-dependency of the transition moment function.
Crystal Structure of Trimethylammonium Perchlorate in Three Solid Phases Including the Ionic Plastic Phase Obtainable above 480 K
Authors: Ishida Hiroyuki , Kubozono Yoshihiro , Kashino Setsuo , Ikeda Ryuichi
Published: February 2015

The crystal structures of (CH3)3NHClO4 in three solid phases were studied by X-ray diffraction techniques. X-ray powder patterns taken at ca. 500 and 445 K revealed that the plastic phase (Phase I) attainable above 480 K crystallizes in a CsCl-type cubic structure with a = 5.845 (1) Å, Z = 1, V = 199.7 (2) Å3, and Dx = 1.327 g cm -3, while Phase II, stable between 480 and 396 K, forms a tetragonal structure with a = 9.912 (4), c = 7.01 (2) Å, Z = 4, V = 689 (3) Å3, and Dx = 1.54 gem -3. The room temperature phase (Phase III) was studied by single crystal X-ray diffraction and found to form a monoclinic lattice with space group P21 , a = 5.749(1), b = 8.670(1), c = 7.5585 (9) Å, ß = 102.66 (1)°, Z = 2, V = 367.6 (2) Å3 , and Dx= 1.441 g cm -3. Thermal measurements, differential thermal analysis and differential scanning calorimetry, were carried out on these solid phases, and the obtained results were compared with those observed for (CH3)3NHBF4.
Search for an Admixture of a 17 keV Neutrino in the β Decay of 35S
Authors: Müller S. , Shiping Chen , Daniel H. , Dragoun O. , Dragounová N. , Hagn H. , Hechtl E. , Hiddemann K.-H. , Špalek A.
Published: February 2015

The β spectrum of a mass-separated thin 35S source has been measured with a small-volume Si photodiode. The energy-dependent response function of the total experimental set-up was calculated by the Monte Carlo method without any adjustable parameter. For an admixture of the hypothetical 17 keV neutrino, an upper limit of 0.59% (95% CL) was determined. Neglecting electron scattering on the spectrometer diaphragm was shown to generate a false 17 keV neutrino admixture of 0.3%.
Low Frequency Nuclear Quadrupole Resonance with SQUID Amplifiers
Authors: Clarke John
Published: February 2015

The dc SQUID (Superconducting QUantum Interference Device) can be configured as an ampli­fier of spin-echos with a noise temperature of approximately 10 mK (f/1 M Hz) at an operating temperature of 1.5 K. A Fourier transform spectrometer based on a SQUID with a superconducting input circuit and operated in a flux-locked loop is used to obtain nuclear quadrupole resonance (NQR) spectra in a broadband m ode over the bandwith 0 -1 M Hz. Spin-echo spectra of 14N in NH4ClO4 reveal sharp NQR resonances, obtained simultaneously, at 17.4, 38.8 and 56.2 kHz. At 1.5 K, the measured longitudinal and transverse relaxation times T1 and T2 for the 38.8 kHz transition are 63 ± 3 ms and 22±2 ms, respectively.
Nitrogen-14 NQR Multiple-Pulse Spin-locking in the Axial Electric Field Gradient
Authors: Furman G . B.
Published: February 2015

The behavior of a nuclear spin-1 system with the Hamiltonian including: a) the interaction of the electric quadrupole moment of nuclei with the axial gradient of the crystal electric field; b) a homonuclear and heteronuclear dipole-dipole coupling; and c) the interaction with a multiple pulse radiofrequency field of arbitrary orientation was considered. The effective Hamiltonian is con­structed by using the Floquet theory. The secular parts of the homonuclear and heteronuclear dipole-dipole interaction was found and the quasi-equilibrium magnetization was calculated.
Theoretical Investigation on the Nuclear Quadrupole Interaction of CH3Cl, CH2Cl2 and CHCl3
Authors: Frantz Gerald , Dufner Hagen , Schmidt P.C.
Published: February 2015

The nuclear quadrupole interaction of 35Cl in CH3Cl, CH2Cl2 and CHCl3 has been studied theoretically by the Hartree-Fock-Roothaan procedure. The influence of the crystal field on the nuclear quadrupole coupling constant is incorporated by the cluster approach and by using point charges that are consistent with the external potential.
Quadrupole Coupling Assignments in Inorganic Periodic Systems by ab initio Calculation of Electric Field Gradients
Authors: Palmer Michael H. , Blair-Fish John A.
Published: February 2015

Ab initio SCF calculations were performed in the unit cell environment, making use of the periodic behaviour to compute a wave-function for the bulk material. Electric field gradient (EFG) calcula­tions were performed on the resulting wave-functions, and these are compared with experimental quadrupole coupling parameters. Examples of inorganic molecular and ionic crystals (nitrogen, chlorine and lithium nitride) and minerals or partially covalent lattice structures (alumina, petalite, α-quartz, boron oxide, boron nitride and sulphur nitride) are described. The effects of the basis set in these calculations are considered, and the limitations imposed by the nature of the calculation are described.
A 35Cl NQR and MNDO study of 3,5-dichloro-1,2,4-triazole and its ionic forms
Authors: Dolgushin G.V. , Lazarev I.M . , Larina L.I. , Lopyrev V.A. , Voronkov M .G .
Published: February 2015

The 35Cl NQR spectra of 3,5-dichloro-1,2,4-triazole derivatives have been examined. MNDO calculations of chloroazoles (imidazole, triazole) including their ionic forms have been carried out. In 3,5-dichloro-l,2,4-triazole complexation and protonation occur of position 4 at the triazole ring.
35Cl NQR of 1,5,2-Diazaphosphorine Derivatives
Authors: Dolgushin G. V. , Nikitin P. A. , Sapozhnikov Yu. E. , Dmitrichenko M. Yu. , Rozinov V. G. , Voronkov M. G.
Published: February 2015

NQR frequencies and asymmetry parameters (η) of 35Cl chlorine-containing 1,5,2-diazaphosphorine derivatives are reported and discussed. NMDO calculations with total optimization of geometry have been carried out. The νcal and ηcal values, calculated by means of the Townes and Dailey theory, correlate well with the experimenal data.
Bromine NQR and Crystal Structures of Tetraanilinium Decabromotricadmate and 4-Methylpyridinium Tribromocadmate
Authors: Ishihara Hideta , Krishnan V. G. , Dou Shi-qi , Paulus Helmut , Weiss Alarich
Published: February 2015

The 79,81Br NQR spectra of tetraanilinium decabromotricadmate (1) and 4-methylpyridinium tribromocadmate (2 ) were studied as function of temperature and their crystal structures were determined. (C6H5NH3)4Cd3Br10 (1): Space group D1 5
2h - Pbca , Z = 4, a = 2507.8(7) pm, b = 1985.4(5)pm, c = 763.0(2)pm. Characteristic for the structure are trioctahedral units [Cd3Br10] condensed to planes. Within the units the octahedra are face connected and further condensed to planes via common corners. Two types of hydrogen bonds are observed. The 81Br NQR lines with frequencies (MHz, 298 K) of 62.98, 52.59, 43.39, 41.82, and 40.71 are little temperature dependent with positive and negative coefficients. The wide frequency range of the NQR lines is reflected by the wide range of the intraionic distances, 263 ≤ d(Br-Cd)/pm ≤300.

(4-(CH3)C5H4NH)CdBr3 (2): C5
2h - P21/n, Z = 4, a = 1228.8(5}pm, b= 1168.5(5)pm, c = 758.3(3)pm, β = 95.30(1)°; the CdBr⊖
3 ions are condensed to chains. The 81Br NQR spectrum is a triplet with frequencies (MHz, 298 K) of 66.01, 55.39, and 50.75. The temperature dependence is small, with positive and negative temperature coefficients. The distances d(Cd-Br) are 256 pm (Cd-Br(2)), 261 pm (Cd -Br(1)), and 284 pm (Cd-Br(3)) and in the chain [CdBr3]Br(1) and Br(3) are bridging atoms.

The relations between Br-NQR and crystal structures are discussed.
Effect of Deuteration on the Phase Transitions and on the Critical Dynamics in Ammonium Hexachlorometallates
Authors: Pelzl J. , Dimitropoulos C.
Published: February 2015

Recent and novel data obtained from chlorine NQR measurements on natural and deuterated (NH4)2MCl6 compounds are discussed with special regard to the influence of the ammonium-ion dynamics on the structural stability of these crystals. The temperature dependence (4.2 K to 350 K) of the chlorine NOR frequency vQ and relaxation rates T1
-1 , T2
-1 obtained from the natural ammonium salts of Sn, Pd, Os, Pb, Te, Se and from the deuterated salts of Sn, Te and Se are analysed. Slight deviations from the normal temperature behaviour of vQ and T1
-1 are found in Sn, Pd and Os compounds which stay cubic in the whole temperature range. The ammonium compounds of Pb and Te undergo a structural transformation between 80 K and 90 K from the cubic to a trigonal phase which is distinguished by the preservation of the single line spectrum of the chlorine NQR below rel. The observed divergence of T1
-1 at the transition point can be described in terms of a spin-phonon process in the presence of an overdamped soft mode. Deuteration of (NH4)2TeCl6 only slightly affects the transition of Tc2 but leads to new structural changes at lower temperatures. Whereas the natural compound stays trigonal down to 4.2 K the deuterated crystal undergoes two additional structural transformations at Tc2 = 48 K and Tc3 = 28 K which are correlated with a slowing down of the deuteron motion. Approaching Tc2 from above, the spin-lattice relaxation rate and the spin-spin relaxation rate of the chlorine NQR exhibit distinct anomalies which are attributed to limited jumps of the octahedron in a shallow potential. The barrier height of this potential deduced from the chlorine NQR spin-lattice relaxation rate is 400 K. The transition at Tc2 is explained by the condensation in one minimum of this potential. At Tc3 a long range correlation is formed which is accompanied by a rotation of the octahedron about its fourfold axis. A similar mechanism is adopted for the transitions observed in (NH4)2SeCl6 at Tc= 24 K and in (ND4)2 SeCl6 at Tc = 48 K.
Study of the Molecular Dynamics from Deuterium Zeeman and Quadrupolar NMR Relaxation of 4,4´-di-n-Heptylazoxybenzene in the Nematic and Smectic A Phases
Authors: Forte C. , Geppi M. , Veracini C. A.
Published: February 2015

The deuterium spin-lattice (T1Z) and quadrupolar (R1Q) relaxation times of the liquid crystal 4,4´-Heptyl-azoxybenzene (HAB), deuterated on the aromatic rings and the first methylene group of the chains, have been measured by means of the Jeener-Broekaert pulse sequence at two different frequencies (10 and 46.04 M Hz) and throughout the nematic and the smectic A phase. By applying suitable models, we have determined rotational and reorientational diffusion coefficients and evalu­ated the contribution of the different motions (internal, molecular and collective) to the relaxation. In particular we have found a non negligible contribution from order director fluctuations.

A comparison between the T1Z and T1Q measurements performed by means of Jeener-Broekaert and Wimperis pulse sequences is also shown.
X-Ray Diffraction Study of Methanol-Water Mixtures
Authors: Bakó I. , Pálinkás G. , Heinzinger K.
Published: February 2015

X-ray diffraction patterns o f m ethanol-water mixtures with mole fractions of methanol molecules o f 0.1, 0.25 and 0.9 have been measured. The experimental structure functions of mixtures are compared with those of pure solvents and with recent Molecular Dynamics results. Difference structure functions similar to thermodynamic excess functions are introduced for the analysis of methanol-water interactions. The comparison of the total and the difference structure functions from experiments and simulations shows an overall good agreement.
Scalar Potentials and the Dirac Equation
Authors: Bergerhoff Bastian , Soff Gerhard
Published: February 2015

The Dirac equation is solved for various types of scalar potentials. Energy eigenvalues and normalized bound-state wave functions are calculated analytically for a scalar 1 / r-potential as well as for a mixed scalar and Coulomb 1 / r-potential. Also continuum wave functions for positive and negative energies are derived. Similarly, we investigate the solutions of the Dirac equation for a scalar square-well potential. Relativistic wave functions for scalar Yukawa and exponential potentials are determined numerically. Finally, we also discuss solutions of the Dirac equation for scalar linear and quadratic potentials which are frequently used to simulate quark confinement.
The Structure of Amorphous Platinum Disulfide as Studied by Anomalous X-ray Scattering
Authors: Saito Masatoshi , Wakeshima Makoto , Sato Nobuaki , Fujino Takeo , Waseda Yoshio , Matsubara Eiichiro , Jacob K. Thomas
Published: February 2015

Anomalous X-ray scattering (AXS) has been applied to study the structure of amorphous plati­ num disulfide, Pt1-xS2, prepared by the precipitation process. The local atomic arrangement in amorphous Pt1-xS2 was determined by the least-squares variational method so as to reproduce the experimental differential interference function at the Pt Lm absorption edge by the AXS method as well as the ordinary interference function by Mo K α. The structural unit in amorphous Pt1-xS2 is found to be a PtS6 octahedron, similar to that in crystalline PtS2. These octahedra share both their corners and edges, while only edge-sharing linkages occur in crystalline PtS2
Polymer Crystallization as the Self-Organization of Chain Macromolecules
Authors: Melker A. I. , Vorobyeva T. V.
Published: February 2015

MD simulation is used to investigate ther self-organization exhibited by a chain o f atom s with strong interaction between nearest neighbours and weak interaction between more distant atoms. It is shown that the supermolecular structure is formed in several steps: at first, an initially straight chain becom es zigzag-shaped, then the zigzag ribbon folds, producing regions of crystalline and amorphous structure; after that the system contracts into a globe, the amorphous-structure regions transforming into crystalline ones by a reptile like motion. A simple analytical description of such polymer structuring is also given.
The 33S Nuclear Hyperfine Structure in the Rotational Spectrum of Isothiazole
Authors: Gripp J. , Kretschmer U. , Dreizler H.
Published: February 2015

We investigated the 33S nuclear quadrupole coupling in the rotational spectrum of isothiazole in natural abundance by molecular beam Fourier transform microwave spectroscopy. In addition the 14N nuclear quadrupole coupling could be analyzed with high precision. We derived the rotational constants A = 8275.51880(80) MHz, B = 5767.06181 (40) MHz, and C = 3396.85702(36) MHz, quartic centrifugal distortion constants, and the quadrupole coupling constants χaa (33S) = 8.7015 (57) MHz, χbb(33S) = -32.9696(60) MHz, χaa(14N) = 1.0732(47) MHz and χbb(14N) = -2.4753(46) MHz.
Some Algebraic Properties of Maxwell-Dirac Isomorphism
Authors: Simulik Vladimir
Published: February 2015

A new derivation of the Maxwell-Dirac isomorphism is presented. A complete set of transformations connecting Maxwell's electrodynamics and wave mechanics is obtained.
The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals
Authors: Dierking I. , Gießelmann F. , Zugenmaier P. , Mohr K. , Zaschke H. , Kuczynski W.
Published: February 2015

The cholesteric twist inversion by temperature variation o f a single component thermotropic liquid crystalline system was experimentally investigated and is explained by the partial twisting power model, evaluating the temperature dependent pitch o f five different configurations of a benzoic acid biphenyl ester with two chiral centers. The temperature dependence o f the twisting power and the cholesteric pitch for several stereoisomeric compounds can in first approximation be predicted by the partial twisting powers of the individual chiral centers determined from the partially racemic configurations.
Fluorescence of 8-(Phenylamino)-1-naphthalene-ammonium- sulfonate in Solvents of Different Polarity
Authors: Hüttenhain S. H. , Balzer W. , Feldmann R.
Published: February 2015

The solvatochromic fluorescence properties of 8-(phenylamino)-1-naphthalene-ammoniumsulfonate (1) were investigated in 22 pure solvents of rising polarity. The measurements of both Stokes' shifts and intensities discriminated between protic and aprotic solvents. Fairly good linear correlation plots of the dependence could be obtained on neglection of the values of tert.-butanol, DMF and DMSO.
Hydromagnetic Kelvin-Heimholtz Instability in the Presence of Suspended Particles and Finite Larmor Radius Effect
Authors: Sanghvi R. K. , Chhajlani R. K.
Published: February 2015

A linear analysis of the combined influence of a finite ion Larmor radius and suspended particles on Kelvin-Helmholtz instability in the presence of a uniform magnetic field is carried out. The magnetic field is assumed to be uniform and transverse to the direction of streaming. The medium is assumed to be incompressible. Certain simplifying assumptions are made for the motion of the suspended particles. A dispersion relation for such a medium has been obtained using appropriate boundary conditions. The stabilizing effect of a finite Larmor radius has been reasserted in the absence of the suspended particles. A stability criterion for the medium is derived, which is found to be independent of the presence of the suspended particles. Similarly a condition of instability of the system is also derived. Numerical analysis is presented in a few limiting cases of interest. Furthermore, growth rates of unstable modes of the configuration with increasing relaxation fre­quency of the particles and finite Larmor radius have been evaluated analytically. It is shown that the finite Larmor radius in the presence of the suspended particles destabilizes a certain wave number band which is stable otherwise. Implications of the suspended particles on the growth rate of unstable modes are discussed in the limit of vanishing ion Larmor radius.
Hierarchic Analysis of Chaotic Scattering in Reactive Collisions
Authors: Kovács Zoltán , Wiesenfeld Laurent
Published: February 2015

The method of classical trajectories is applied for a double Morse potential modeling indirect reactive collisions of three collinear atoms. The system shows chaotic scattering, which is studied in details through a hierarchic analysis of the singularities of the time delay function. Tools of the thermodynamic formalism are used to extract global quantities characterizing the scattering process.
Comments on H/D Isotope Effects on Polarizabilities of Small Molecules. Correlation with Virial Coefficient, Molar Volume, and Electronic Second Moment Isotope Effects
Authors: Van Hook W. Alexander , Wolfsberg Max
Published: February 2015

Literature data on H/D isotope effects on polarizability are reviewed. An argument based on perturbation theory correlates the isotopic differences with electronic transition moments via vibrational averaging. The contribution of the second moment isotope effect is especially important. The approach is first illustrated with a calculation on H2/D2 and then employed to correlate differential refractive index data on about twenty other H/D isotopic pairs. A table of bond polarizability isotope effects is presented which permits the estimation of polarizability isotope effects for various kinds of H/D substituted compounds. Coupling these results with known isotope effects on vibrational amplitude permits calculation of vapor phase virial coefficient isotope effects, while combina­tion with refractive index data on liquids yields reasonable values for the sum of the isotope effects on molar volume and electronic second moment. However the quantitative correlation of the polarizability isotope effect with isotope effects on vapor pressure or thermodynamic activity is less direct.
Pair Formation of Free Nucleobases and Mononucleosides in the Gas Phase
Authors: Dey Michael , Grotemeyer Jürgen , Schlag Edward W.
Published: February 2015

The formation of neutral bimolecular clusters of unsubstituted nucleobases and mononucleosides in the gas phase has been studied by IR laser desorption of the neutral molecules into a supersonic beam expansion. The complementary nucleobase pairs adenine-thymine and cytosine-guanine of D N A have been found to be formed in preference to non complementary base pairs. Association constants for the formation of the dimers of free nucleobases and nucleosides in the gas phase are calculated from the experimental results. A strong influence due to side groups affecting the dimer formation of the nucleobases is shown.
Fluorescence Anisotropy Decays of 4-Cyano-N,N-dimethylaniline in Propylene Glycol Studied by Frequency-Domain Fluorometry
Authors: Kawski A. , Piszczek G. , Gryczyńskia I. , Gryczyńskia Z.
Published: February 2015

The fluorescence lifetimes of 4-cyano-N,N-dimethylaniline (CDMA), measured in propylene glycol at 293 K using frequency-domain fluorometry, in the short emission (SE) and long emission (LE) bands are 20 ps and 1.65 ns, respectively. The higher emission anisotropies in the SE band compared to that in the LE band are due to weaker rotational depolarization of fluorescence. Emission anisotropy decays imply that the initial limiting emission anisotropy, r (0), is the same in the SE and LE bands and amounts to 0.28. This reflects the fact that the directions of transition moments in these bands are parallel. In the case of CDMA in propylene and ethylene glycol at temperatures from 293 to 343 K, viscosity more strongly affects the relaxation to the TICT state than does the change in polarity of the solvents used.
Isolated versus Condensed Anion Structure IV: An NQR Study and X-ray Structure Analysis of [H3N(CH2)3NH3]CdI4 * 2H2O, [H3CNH2(CH2)3NH3]CdBr4, [(CH3)4N]2CdBr 4, and [(CH3)3S]2CdBr4*
Authors: Ishiharaa Hideta , Horiuchib Keizo , Douc Shi-qi , Gesingc Thorsten M. , Buhlc J.-Christian , Paulus Helmut , Fuessd Hartmut
Published: February 2015

The phase I of [H3N(CH2)3NH3]CdI4 • 2H2O (1) crystallizes with isolated [CdI4]2-tetrahedra; monoclinic, C2/c, Z = 8, a = 1702.6(3), b= 1459.3(3), c= 1555.5(3) pm, and ß= 120.32(3)° at 299 K. (1) shows a first-order phase transition at T1↔II = 245 K. The eight 127I(v1) NQR lines in phase II change discontinuously into four lines in phase I. The transition entropy from DSC measurements, ∆S = 5.0 J K1- mol-1 , shows that this transition is probably due to order-disorder of cations. [H3CNH2(CH2)3NH3]CdBr4 (2) crystallizes with isolated [CdBr4]2- tetrahedra; orthorhombic P212121, Z = 4,a= 1447.8(5), b = 1280.3 (4), c = 709.7(3) pm at 299 K. (2) shows four 81Br NQR lines between II and around 325 K, above which temperature the lines disappear. [(CH3)4N]2CdBr4 (3) shows a second-order phase transition at T1↔II = 271 K. Three of four 81Br NQR lines in phase II disappear below this transition point, the other line can be observed up to 315 K. The transition entropy, ∆S = 9.01 J KT-1 mol-1 , indicates that the transition is an order-disorder type of the cations. [(CH3)3S]2CdBr4 (4) shows a first-order type phase transition at T1↔II = 304 K. The four lines spectrum of 81Br NQR is observed in phase II and disappears above the transition point. The transition entropy, ∆S = 46.8 J K- 1 mol-1 is abnormally large. The role of the hydrogen bond and the bridging power between the halogen and cadmium atoms upon the formation of the condensed anion structure is discussed.
Structural Investigation of Amorphous Europium Metaphosphate by X-ray Diffraction
Authors: Cannas Mario , Manca Enrico , Pinna Gabriella , Bettinelli Marco , Speghini Adolfo
Published: February 2015

The local coordination of europium in vitreous Eu metaphosphate has been investigated, using information obtainable from crystalline EuP3O9. One glassy sample and one crystalline sample of nominal EuP3O9 composition were examined by X-ray diffraction. The description of the close coordination of Eu, deduced from the orthorhombic structure of the crystalline sample, was used as a model for the amorphous situation. Besides, as a monoclinic form of Eu metaphosphate is also reported to exist, a second model was deduced from this structure, starting from the isomorphous monoclinic Yb metaphosphate. Best fitting calculations indicated that orthorhombic coordination is the better model for the short range order of europium in the vitreous metaphosphate.
Ionic Conduction and Molecular Structure of Molten FeCl3
Authors: Akdeniz Z. , Tosia M. P.
Published: February 2015

Former experiments on molten FeCl3 have shown that, as for AlCl3 , melting is accompanied by a transition from sixfold to essentially fourfold coordination. However, in contrast to AICI3, the FeCl3 melt near freezing has an appreciable ionic conductivity. We propose a model for the structure of FeCl3 melt as consisting of closely packed Fe2Cl6 bitetrahedral molecules in equilibrium with (Fe2Cl5) + and (Fe2Cl7)- ionised species.
The Absolute Configuration of Isoancistrocladine and 'Isohamatine' by Quantumchemical CD-Calculations
Authors: Fleischhauer J. , Koslowski A. , Repges Ch. , Gulden K.-R , Bringmann G.
Published: February 2015

The absolute configuration of the naphthylisoquinolines isoancistrocladine and isohamatine at the biaryl axis was determined by comparing the measured and the calculated CD spectra.

In order to calculate these spectra we used the CNDO/S method in combination with a Boltzmann weighting of conformers with different dihedral angles at the biaryl axis. The Boltzmann factors were obtained with the AM 1 method.
Unravelling the Internal Complexities of Molten Salts
Authors: Adya Ashok K. , Takagi Ryuzo , Gaune-Escard Marcelle
Published: February 2015

Much experimental and theoretical effort has gone into revealing the internal complexities of molten salts for the past two decades. In this paper we shall show how neutron diffraction and computer simulation techniques have helped in gaining a better understanding of these systems at the microscopic level. Firstly, a short review on the structure of molten halide systems as revealed by these techniques will be presented. Complementarity of using X-rays with neutrons and, some recent results on the structure of molten DyCl3 obtained by combining neutron and X-ray diffraction with molecular dynamic simulations will be discussed. Neutron diffraction isotopic substitution techniques have played an important role in elucidating the interatomic structure of a diversity of molten salts. Pair distribution functions (PDFs), determined for a number of 1:1 and 2 :1 halide melts, provided theorists with a critical test of their model potentials. It is now clear that for 1:1 molten systems theoretical models based on Fumi-Tosi potentials can adequately describe many of the structural features. Nevertheless, the chal-lenge is two fold: (i) to determine real interatomic potentials for 2:1 and 3 :1 molten systems capable of reproducing not only the microscopic structural details obtained at the partial PDF, gαβ (r) level, but also their macroscopic behaviour and, (ii) to characterise the structure in binary molten salt mixtures.
Development of a Field Cycling NMR System for PQR Detection in Biopolymers
Authors: Ivanov Dmitri , Redfield Alfred
Published: February 2015

Our goal is to extend the sensitivity of field cycling pure quadrupole resonance (PQR) methods to be of use in biological systems. The nuclei of interest are 25Mg, 67Zn, 43Ca, 11B and 17O. The experiment is based on a field cycling double resonance technique, in which the quadrupole resonance of a rare nucleus is found through its effect on the magnetic order of the abundant nucleus to which the rare nucleus is coupled through dipole-dipole interaction. A field-cycling NMR spectrometer has been developed, based on our existing 500 MHz high resolution spectrometer. The sample can be shuttled pneumatically from the high field of a commercial 500 MHz magnet to the magnet's top, where the residual field and its gradient is canceled out by a pair of Helmholtz coils. Low field homogeneity is within 0.5 gauss. The X H signal is observed at high field as a free induction decay (FID) after a 90° pulse. At low field the sample can be irradiated by a digitally tuned RF coil in the 300 kHz-7 MHz range. The sample has to be maintained at low temperature (~30 K) to avoid relaxation via thermal motion of methyl groups in biomolecules. For this purpose field cycling equipment is placed in a variable temperature dewar (4 - 300 K). We plan to use solutions of biomolecules in standard cryoprotective buffer, containing ~ 30% glycerol. Preliminary results on the quadrupole resonance of natural abundance 17O in the cryoprotective buffer and of natural abundance 11B in a protease inhibitor at 50 mM are presented.