bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissolution of Alkali Fluoride and Chloride Crystals in Water Studied by Molecular Dynamics Simulations
Authors: Fukushima N. , Tamura Y. , Ohtaki H.
Published: February 2015

The dissolution of cubic crystals of NaF, KF, CsF, LiCl, NaCl, and KCl consisting of 32 cations and 32 anions in an isolated box containing 216 water molecules was studied at 298 K by molecular dynamics simulations. The ion-ion, ion-water and water-water interactions were described in terms of the Tosi-Fumi, Kistenmacher-Popkie-Clementi, and Matsuoka-Clementi-Yoshimine potentials, respectively. During the simulation periods of 12 ps for NaF, CsF and LiCl and 20 ps for KF, NaCl and KCl cations did not dissolve, while anions dissolved from the CsF, LiCl and NaCl crystals but not from the NaF, KF and KCl crystals. The mass effect in the dissolution of CsF was examined by giving the ceasium ions the atomic weight of the fluoride ion (18.998). In case of the "light" caesium ions in the crystal fluctuated less far and again fluoride ions but no caesium ions were dissolved.
The Sites of Premelting in Organic Compounds
Authors: Dosseh Gilberte , Fuchs Alain H.
Published: February 2015

Bartis recently proposed a theory which should allow to determine whether impurities or defects are responsible for the premelting phenomena in crystalline solids. We have tested this model on several orientationally disordered molecular crystals studied by proton NMR spectroscopy. This showed that extended defects, and more likely grain boundaries are at the origin of the premelting phenomena in these crystals.
Hyperfine Structure and Relaxation Times of 4-Oxo-TEMPO/Methyl Alcohol Solutions in Weak and Strong Fields
Authors: Sünnetçioğlu M. , Bingöl G. , Sungur R.
Published: February 2015

The hyperfine structure of the 4-Oxo-TEMPO (2,2,6,6-tetramethyl-4-oxopiperidin-oxyl-l) free radical was investigated. Theoretical investigation includes four methyl groups protons close to the unpaired electron. Energy levels and transition probabilities were found by using second order and first order perturbation theory, respectively, and from these data theoretical spectra of the free radical were obtained. Diluted solutions in CH3-OH were prepared and the spectra were recorded with a double resonance spectrometer (1.53 mT) and Varian E-9X-band ESR spectrometer (~0.3 T). In order to understand the influence of time dependent phenomena on the linewidths, electronic relaxation times of 4-Oxo-TEMPO and its perdeuterated form (PDT) were measured at two different fields by using cw saturation method.
Anomalous Behaviour of the Mean Dipole Polarizability α of Neopentane C(CH3)4 in the Temperature Range between 250 K and 360 K
Authors: Hohm Uwe , Kerl Klaus
Published: February 2015

The temperature dependence of the dynamic dipole polarizability α(λ) of gaseous neopentane has been re-examined in the temperature range between T = 250 K and T - 360 K at the four HeNelaser wavelengths λ = 543.51 nm, 594.11 nm, 611.97 nm, and 632.99 nm. These interferometric measurements are compared with former determinations of the dynamic as well as the static dipole polarizability in the solid, liquid and gaseous state. In all cases, a shape of α(T) in the range between 290 K and 310 K has been observed which is similar to the shape of α (λ) in an absorption band. This observation is connected with other physico-chemical quantities of neopentane.
Influence of Hydrogen on the Structure of Amorphous Sputtered Fe-Co-Tb Films by Means of Wide- and Small Angle Neutron Scattering
Authors: Heckele M. , Bellissent R. , Brunseh A. , Lamparter P. , Steeb S.
Published: February 2015

Sputtered amorphous Fe-Co Tb-films with perpendicular and in-plane magnetic anisotropy were investigated by wide- and small angle neutron scattering. By combination with X-ray data the maxima in the pair correlation function could be attributed to the individual atomic pairs. Thus also partial coordination numbers and a short range order parameter could be determined.

Wide angle diffraction revealed that the film with magnetic in-plane anisotropy contained 13 atomic percent hydrogen. The hydrogen incorporation causes substantial changes in the short range order, associated with enhanced formation of Tb-rich clusters, and the in-plane anisotropy. The clustering effect was confirmed by results from small angle scattering with polarized neutrons
Transit Times in Lltra-Relativistic Heavy-Ion Collisions
Authors: Wolschin G.
Published: February 2015

Mean transit times in heavy-ion collisions are calculated as functions of the relativistic incident energy and the impact parameter. As a consequence of special relativity, they become constant in a central collision of O with Pb at T~0.15TeV. Together with a geometrical estimate of the maximum energy densities in the interaction region, it is argued that heavy ions in a large hadron collider may produce a quark-gluon plasma due to the plateau in the transit times at ultra-relativistic energies
An MD Simulation of Concentrated Aqueous Solutions of Caesium Iodide
Authors: Tamura Y. , Ohtaki H. , Okada I.
Published: February 2015

Molecular dynamics simulations of concentrated aqueous Csl solutions have been performed for Csl: H2O = 1:20 (2.78 molal) at 298 K and 341 K and 1:10 (5.56 molal) at 349 K. Effects of temperature and concentration on the structures of the hydrated ions, the ion pairs, and ionic aggregates are discussed by comparing the results with X-ray diffraction data obtained under similar conditions [1]
Bromine Spin-Rotation Coupling Constants of Cyclopropylbromide-79Br and -81Br
Authors: Heineking N. , Gripp J. , Dreizler H
Published: February 2015

We reinvestigated the microwave spectrum of cyclopropylbromide with the increased resolution of pulsed microwave Fourier transform spectroscopy. Because of the higher frequency precision, it was possible to determine the spin-rotation coupling constants of bromine. Global fits of rotational constants, quartic centrifugal distortion constants, quadrupole coupling constants including the off-diagonal component χac , and spin-rotation coupling constants simultaneously to almost one hundred hyperfine components for each of the two bromine isotopomers resulted in overall standard deviations of well below 5 kHz
Nuclear Quadrupole Hyperfine Structure in the Rotational 2Q1-Subbranch of Deuteroisothiocyanic Acid, DNCS
Authors: Heineking N. , Dreizler H.
Published: February 2015

The two-nuclei quadrupole hyperfine structure of four 2Q1-subbranch transitions of deuteroisothiocyanic acid, DNCS, has been resolved and analyzed by use of a waveguide microwave Fourier transform spectrometer. The analysis yielded one previously unknown quadrupole coupling constant ( χ- ≡ χbb-χcc) for both nitrogen ( χ-
N = +27.6(11) kHz) and deuterium X-
D = +175.8(11) kHz). Taking into account the results from earlier work on HNCS, DNCS, HNCO, and DNCO, the orientations of the principal axis systems of the two quadrupole coupling tensors could be calculated. It appears that while the deuterium tensor is aligned to the D-N internuclear axis as expected, the nitrogen tensor is tilted away from the bisector of the DNC angle by 13° towards the NCS chain
Static and Dynamic Properties of Ferroelectric Liquid Crystals in the Vicinity of a First-Order SmA-SmC* Phase Transition
Authors: Netz Roland R. , Hess Siegfried
Published: February 2015

A unified theoretical description of static and dynamic properties of ferroelectric liquid crystals in terms of a Landau free energy is presented. The shear deformation tensor is used as principal order parameter. Results for the stationary case for tilt angle variation and dielectric properties are compared with experiments on a compound with a pronounced first-order SmA-SmC* phase transition for various strengths of the applied electric field
Solvation Structure of the Ti(III) Ion in Methanol Solutions and in Perfluorinated Ionomers Swollen by Water and Methanol. A Study by ESR and ENDOR
Authors: Schlick Shulamith , Myers Brian E. , Sjöqvist Lars , Lund Anders
Published: February 2015

The local environment of Ti3+ cations in methanol solutions and in Nafion perfluorinated ionomers swollen by water and methanol has been studied by electron spin resonance (ESR) and by 1H and 2H electron nuclear double resonance (ENDOR) spectroscopies. The two major sites reflecting the ligation of the cations as a function of solvent structure and cation concentration have been analyzed, using whenever possible the method of orientation selection for the ENDOR transitions. The distance RN of the protons from the central cation, and the angle ΘN between the symmetry axis of Ti3+ and the Ti3+ -proton vector have been deduced by evaluating the dipolar interaction tensor and by simulating the orientation dependence of the ENDOR signal. For site 1 of Ti3+ in methanol (g॥
= 1.986 and g⊥
= 1.894) no orientation selection was possible, and RN
values in the range 4.1 to 4.6 Å are suggested from the ENDOR splittings. For site 2 of Ti3+ in methanol (g॥ = 1.943 and g⊥
= 1.960) equatorial and axial methyl protons have been detected; the RN values deduced from the simulations are 3.95 and 4.35 Å, respectively. For Ti3+ in Nafion swollen by water (g
|| = 1.997 and g⊥
= 1.907), equatorial and axial protons from OH groups have been detected, and the ENDOR spectra were simulated with RN values of 2.60 and 3.10 Å respectively for these protons
Dependence of Potential Energy on Inter-bond Angles in Simple Molecules
Authors: Indira K. , Warier M. K. Rudra , Ananthakrishnan T. R. , Paul C. M.
Published: February 2015

A method is developed to investigate the variation of potential energy contributions (Vstretch, Vbend, Vstretch-bend and Vstretch-stretch) in simple molecules when their inter-bond angles θ are varied arbitrarily. Applied to XY2 bend symmetric systems, the V - θ plots suggest that the actual equilibrium configuration in these molecules lies in the premises of minimum Vbend and zero Vstretch-bend.
An NQR Study of Tetrachloride Complexes of Group IVA Elements
Authors: Feshin Valentin P. , Voronkov Mikhail G.
Published: February 2015

The results of an NQR study on the MCl4 complexes (M = Si, Ge, Sn) with organic heteroatom ligands (including those containing several coordination centers) are summarized: chloroanhydrides of unsaturated, aromatic and heteroaromatic carboxylic acids; alkylarylethers, ketones, aryldichlorophosphates, nitrogen-containing compounds, etc. The octahedral or trigonal-bipyramidal structure of these complexes has been established, and the factors influencing the formation and structure of such complexes (component ratio, character of ligand and M atom) have been analyzed. The structure of several complexes may vary with time or depend on the crystallization condition of the system. Some of these results indicate coordination isomerism. The quantitative ratios between the 35Cl NQR frequency shifts of ligand and axial Sn-Cl bonds in trigonal-bipyramidal RCOCl • SnCl4 complexes relative to the initial component frequencies have been found
NQR Studies of Organic Compounds Containing Tetra- or Pentacoordinated Atoms of Elements of Groups IVA and VIA
Authors: Feshin Valentin P.
Published: February 2015

The 35Cl and 79Br NQR spectra of halogen-containing organic compounds of Si, Ge, Sn and Te, in which these atoms may be tetra- or pentacoordinated, have been compared to the results of their X-ray diffraction analysis. The NQR technique was also used to study a large number of such compounds for which X-ray investigations were found to be impossible. It has been shown that the NQR technique may be considered as a rapid method for the determination of the electronic and spatial structure of these compounds. The conditions for pentacoordination of atoms of IVA group elements have been also formulated.
Theoretical Study of the Electric Field Gradient in Silver Iodide
Authors: Frantz G. , Leiberich R. , Schmidt P. C.
Published: February 2015

The electric field gradient (EFG) in hexagonal Agl at the iodine site is studied theoretically by three different procedures, namely the point charge model, the Hartree-Fock cluster approach, and the augmented plane wave band structure procedure. A comparison is made for the electronic charge distribution and the sizes of the various contributions to the EFG obtained by the different procedures. From the point charge model and the Hartree-Fock cluster approach one gets almost the same result for the EFG, q = +0.743 • 1021 V/m2 and +0.816 • 1021 V/m2 respectively. Only a rather preliminary result of q = +0.393 • 1021 V/m2 is found by the band structure calculation to be compared with the experimental value of qexp= ±0.415 • 1021 V/m2 .

The confidence limits of the theoretical results are discussed, including possible ways to bridge the gap between the theoretical results by different methods and experiment. Both the cluster and the band structure calculations are shown to support an ionic model for hexagonal Agl with some overlap between the charge distributions on neighboring ions.
14N NQR and the Molecular Charge Topology in Coordinated Ammonia
Authors: Murgich Juan , Aray Yosslen , Ospina Edgar
Published: February 2015

14N NQR spectra of [Co(NH3 ) 6 ] • 3Cl, [Co(NH3 ) 5CO3 ] • NO 3 , [Zn(NH3 ) 4 ] • 2Cl, [Zn(NH3 ) 4 ] •(BF4)2, and [Ag(NH3) 4 ] • NO 3 were obtained at 77 K. The results, analyzed by means of the topology of the charge distribution obtained from ab-initio MO calculations of free and of a model of coordinated NH3 , showed that bonding to the metal-ion produces a strong decrease (Co ≫ Zn ≈Ag) in the N nonbonded density ("lone pair") and an increase in the bonded maxima found in the N - H bond direction of the N valence shell.
Chlorine-NQR Relaxation Near the Structural Transitions of Natural and Deuterated (NH4)2TeCl6
Authors: Dimitropoulos C. , Borsa F. , Pelzl J.
Published: February 2015

The temperature and isotope dependence of the 35,37Cl-NQR spin-lattice relaxation rate near the cubic to trigonal phase transition at Tc1 ≌ 87 K has been investigated in both (NH4) 2TeCl6 and (ND4)2TeCl6 salts. In the temperature range of ~ 20 K above and ~ 10 K below TCl, the relaxation obeys the relation (T1 • T)2 ∞(T-TCl). This behaviour corresponds to a direct relaxation mechanism in presence of a strongly damped rotational soft mode of the TeCl2
6- tetrahedra and is discussed on the basis of cation-anion coupling near the critical region. Below TCl we observe an extra contribution to the 35,37Cl relaxation rate which is tentatively ascribed to the dynamics of the NH4+ tetrahedra.
Chlorine Nuclear Quadrupole Relaxation and Cationic Motion in Trimethylsulfonium Hexachloroselenate(IV): [(CH3)3S]2SeCl6
Authors: Kaga Makoto , Asaji Tetsuo , Ikeda Ryuichi , Nakamurab Daiyu
Published: February 2015

The 35Cl NQR spin-lattice and spin-spin relaxation times, T1Q and T2Q, respectively, and the 1HNMR spin-lattice relaxation time T1H at 32 and 60 MHz were determined for [(CH3)3S]2SeCl6 as functions of temperature. The rapid decrease of observed above ca. 250 K with increasing temperature was attributed to the onset of reorientation of the [SeCl6 ]2- complex anion with the activation energy Ea = 42 + 5 kJ mol -1 . When cooled from ca. 250 K, T1Q showed an anomalous decrease. This T1Q decrease was explained by electric field gradient modulation related to some cationic motion. Possible origins of the cationic motion are discussed
35Cl NQR Relaxation in Chloral Cyclohexylhemiacetal
Authors: Niki Haruo , Igei Ryokan , Kyan Hiroshi , Hamagawa Takeshi , Isono Takahiro , Hashimoto Masao
Published: February 2015

The crystal structure of cyclohexylhemiacetal (cycHx-CH) was determined at 296 K : monoclinic, space group P21/c, a =1028.7 (9), b = 609.5 (1), c = 1811.9 (4) pm, and ß = 99.79 (3)°, Z = 4, R = 0.0552. The three 35Cl NQR lines in cycHx-CH, T1, T2, and T2*, were measured by a pulsed method at 80-300 K. Below 200 K T1
-1 obeyed the T law well, indicating that the spin lattice relaxation is governed by lattice vibrations. The reorientation of CCl3 seems to be responsible for the sharp T: drop observed above 250 K. Shoulders in the T1 vs. 1/T curves indicate the presence of T1 minima at about 240 K. A fluctuation of the EFG due to a dynamic disorder of hydrogen atoms in the OH groups is assumed to explain the T1 minima.
NQR and Neutron Diffraction in Scheelites
Authors: Brown R. Julian C. , Shortreed E. , Szabo Andrew J. , Powell Brian M. , Stuart Stephen N.
Published: February 2015

Measurements of the spin-lattice relaxation time for rhenium in KReO4 and NH4ReO4 are reported; relaxation rates are extremely fast due to the large quadrupole moment of Re. Calculations of the electric field gradient in KReO4 show that the EFG is a very sensitive function of the orientation of the anion in the unit cell as well as of the unit cell dimensions, and that geometrical effects make a major contribution to the temperature dependence. Neutron diffraction in these two salts has been employed to determine the temperature dependence of structural parameters over a wide range of temperature, and preliminary results are reported.
Temperature dependence of the Spin-Lattice Relaxation Time of the 23Na-NMR Line in NaNO2
Authors: Igarashi M. , Kitagawa H. , Takahashi S. , Yoshizaki R. , Abe Y.
Published: February 2015

The spin-lattice relaxation time, T1, of the 23Na-NMR line in NaNO2 is measured between 25 K and 160 K at two magnetic field strengths, 1.1 T and 6.9 T. The temperature dependence of T1 for the center line, observed on a polycrystalline sample prepared by precipitation from aqueous solution, is given by a monotonous curve. T1 increases gradually as the temperature decreases. On the other hand for a single crystal, which is made by a modified Bridgman method, the temperature dependence of T1 shows two deep dips below 150 K and a frequency dependence which cannot be explained by ordinary BPP theory.

The dominant relaxation mechanism above and below 150 K is also investigated.
Isomerization of Diphenyl Polyenes. Part II. Fluorescence Properties of 1,8-Diphenyl-1,3>5,7-octatetraene in Poly (vinyl alcohol) Film
Authors: Kawski A. , Kubicki A. , Kukliński B. , Gryczyński I. , Gryczyński Z.
Published: February 2015

The effect of temperature on the fluorescence properties of 1,8-diphenyl-1,3,5,7-octatetraene (DPO) in polyvinyl alcohol) film (PVA) was investigated in the range from 295 to 428 K. Upon heating above 353 K, the quantum yield of D PO increases rapidly. This effect is irreversible, similarly as the optical density in the long wavelength absorption band (320-440 nm). It has its origin in the cis-trans conversion of DPO molecules in PVA film at high temperatures. The behaviour of the fluorescence anisotropy in the same temperature range was also investigated. The emission anisotropy was found to be a viscosity indicator in the microenvironment of the DPO molecules in PVA film.
Principal Component Analysis of Chinese Porcelains from the Five Dynasties to the Qing Dynasty
Authors: Yap C. T. , Hua Younan
Published: February 2015

This is a study of the possibility of identifying antique Chinese porcelains according to the period or dynasty, using major and minor chemical components (SiO2 , Al2O3 , Fe2O3 , K2O, Na2O, CaO and MgO) from the body of the porcelain. Principal component analysis is applied to published data on 66 pieces of Chinese procelains made in Jingdezhen during the Five Dynasties and the Song, Yuan, Ming and Qing Dynasties. It is shown that porcelains made during the Five Dynasties and the Yuan (or Ming) and Qing Dynasties can be segregated completely without any overlap. However, there is appreciable overlap between the Five Dynasties and the Song Dynasty, some overlap between the Song and Ming Dynasties and also between the Yuan and Ming Dynasties. Interestingly, Qing procelains are well separated from all the others. The percentage of silica in the porcelain body decreases and that of alumina increases with recentness with the exception of the Yuan and Ming Dynasties, where this trend is reversed.
Potentiometrie Study of Magnesium Fluoro Complexes in Aqueous Solutions up to 473 K and 1 kbar
Authors: Bilal B. A. , Müller E.
Published: February 2015

The formation of magnesium fluoro complexes in a hydrothermal fluorite-bearing model solution has been potentiometrically studied up to 473 K and 1 kbar at the ionic strength I = 1 m (NaCl), in order to estimate the competition with the formation of the lanthanide fluoro and fluorohydroxo complexes in such systems. No evidence of difluoro complex was found at p, T, [F- ] and pH conditions which are relevant to fluorite formation. The apparent formation constant Q, as well as the apparent thermodynamic data ΔG, ΔS and ΔH of MgF+ have been determined. The effect of pressure was found to be negligible. The competition with the lanthanide complexes becomes increasingly negligible with increasing T and in particular with increasing pH.
The Phase Transition of Potassium Sulfate
Authors: Kurtz Wolfgang
Published: February 2015

The discontinuous phase transition of K2SO4 is described by a semi-empirical model that uses the elastic stiffnesses ci,i and the changes in volume and entropy associated with the order-disorder transition. Consideration of the elastic anomaly (existence of soft, damped longitudinal acoustic phonons) in K2SO4 removes the disagreement between transition enthalpies ΔHtr measured calorimetrically and ΔHtr derived from the p-T phase diagram via the Clausius-Clapeyron equation. The model used requires the knowledge of the cu (i = 1, 2, 3) which in many cases is not available in the literature. It is demonstrated that these values can be calculated with sufficient accuracy from the anisotropic displacement (Debye-Waller) factors which are routinely determined in crystal structure analyses and which, therefore, are available for many substances. There is fair agreement between the calculated strain energy and ΔHtr also for K2SeO4 . In the case of K2CrO4 , use of published expansion data resulted in disagreement between calculated strain energy values and published, measured ΔHtr data.
A Microwave Fourier Transform Spectrometer in the Frequency Range of 2 to 4 GHz and its Performance
Authors: Gerke  , Dreizler H.
Published: February 2015

We present a microwave Fourier transform spectrometer with a coaxial cell in the range from 2 to 4 GHz. The performance is demonstrated by some examples showing the sensitivity and resolution.
Methyl Internal Rotation and 14N Nuclear Quadrupole Coupling from the Rotational Spectra of Ethyl Isocyanide, iso-Propyl Isocyanide and gauche- and trans-n-Propyl Isocyanide
Authors: Krüger Michael , Dreizler Helmut
Published: February 2015

The barrier heights (V3) hindering methyl internal rotation were determined with microwave Fourier transform spectroscopy from the ground vibrational state for the title molecules and found to be V3 = 3.336(52) kcal/mol for ethyl isocyanide, V3 > 3.1 kcal/mol for iso-propyl isocyanide, V3 = 2.894(23) kcal/mol for gauche-n-propyl isocyanide and V3 = 2.954(22) kcal/mol for transn- propyl isocyanide. The quadrupole coupling constants of iso-propyl isocyanide are χaa = 179.3(31) kHz, χbb = -140(15) kHz and χcc - 39(15) kHz; the constants of trans-n-propyl isocyanide were determined to be χaa = 268.1 (71) kHz, χbb = - 108(23) kHz and χcc = - 160(23) kHz.
Rotational Spectrum of cis-HS3D
Authors: Liedtke M. , Saleck A. H. , Behrend J. , Winnewisser G. , Klünsch R. , Hahn J.
Published: February 2015

The rotational spectrum of HS3D in the vibrational ground state has been measured in the frequency range between 75 and 293 GHz. Up to now, about 180 Q-, 30 P-, and 70 R-branch c-type transitions have been identified. The preliminary rotational constants of the species observed support the cis-conformation established earlier from the H2S3 rotational spectrum.
Notizen: On some Crystals of “Lapis Lazuli”
Authors: Banerjee A. , Häger T.
Published: February 2015

Some deep blue dodecahedral crystals from Afghanistan have been investigated by UV-, VIS- and IR-spectral photometry and x-ray powder diffraction technique. Contrary to earlier identification, the crystals have been identified as hauynite.
Bending Energy Minimisation Criterion for Molecular Geometry in XY3 Pyramidal Systems
Authors: Indira K. , Rudra Warier M. K. , Ananthakrishnan T. R.
Published: February 2015

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

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
Isomerization of Diphenyl Polyenes. Part III. Absorption and Fluorescence Properties of 1,4-Diphenyl-1,3-butadiene in Poly(vinyl alcohol) Film
Authors: Kawski A. , Kukliński B. , Kubicki A. , Gryczyński I.
Published: February 2015

The effect of temperature on the absorption and fluorescence properties of 1,4-diphenyl-1,3-butadiene (DPB) in polyvinyl alcohol) film (PVA) was investigated in the range from 293 to 423 K. Upon heating above 353 K, the optical density in the long wavelength region (at 339 nm) increases five times only, whereas for 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1,8-diphenyl-1,3,5,7-octatetraene (DPO) ten and twenty times, respectively. However, the total quantum yield (ΦF = 0.68) at 293 K is greater than that for the trans-trans form (ΦF = 0.63) and decreases with growing temperature. Both this effect and broadening effect in the fluorescence band at 293 K evidence the existence of two emission centres, i.e. the trans-trans and cis-trans conformers.
An Electron Paramagnetic Resonance Study of Mn2+ Ions Doped in Langbeinites
Authors: Böttjer T. , Lehmann G. , Stockhausen M.
Published: February 2015

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
Brewster Condition for Planar Interfaces of Natural Optically Active Media
Authors: Lakhtakia Akhlesh
Published: February 2015

Reflection of planewaves at the planar interface of two natural optically active media has been examined in order to obtain the Brewster condition
Determination of Partial Structure Factors of Molten Eutectic Ni33Ge67
Authors: Halm Th. , Hoyer W. , Neumann H. , Bellissent R.
Published: February 2015

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

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

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

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

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.
Thermodynamics of the Ag-Ag2S04 Electrode up to 473 K
Authors: Bilal B. A. , Müller E.
Published: February 2015

E0(T), ΔS0{T), and ΔH0(T) of the reaction Ag2S04 + H2 ⇔ 2 Ag + H2S04 have been determined up to 473 K, using the cell Pt-H2 (p) / H2SO4(m)/Ag2S04-Ag. Constant values of the standard potential E0(T) were obtained for cH2SO4 ≤ 0.0075 m where the solubility of Ag2S04 became negligible. The potential of the Ag-Ag2S04 electrode (vs. SHE) in aqueous Na2SO4 solutions of different molalities has been calculated up to 1 m and 473 K.
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

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

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

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

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

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

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

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

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

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

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.
Double-Ionisation Processes and Electronic Structures
Authors: Tavard C.
Published: February 2015

The electron momentum distribution of a given target can be extracted, under impulsive conditions, from the simple ionisation processes relevant to Compton collisions. This document classifies and investigates the physical mechanisms of double ionisation, in connection with the target electronic structure.
(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

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

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

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

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.