Showing papers in "Zeitschrift für Naturforschung A in 1986"
TL;DR: In this article, the development of the theory of shielding and antishielding of nuclear quadrupole moments is reported and various contributions to the Sternheimer shielding and Antishielding factors are discussed.
Abstract: The development of the theory of shielding and antishielding of nuclear quadrupole moments is reported. The various contributions to the Sternheimer shielding and antishielding factors are discussed. Also the history of the different calculational techniques is outlined.
51 citations
TL;DR: In this article, the rotational spectra of pyridine and [4-D]-pyridine were reanalysed and the D quadrupole coupling was determined.
Abstract: We reanalysed the 14N hyperfine structure in the rotational spectra of pyridine and [4-D]- pyridine with higher precision and determined the D quadrupole coupling. It is intended to provide a reference for comparison with substituted pyridines.
45 citations
TL;DR: In this paper, the torsion of the local flow around closed orbits and its relation to the superstructure in the bifurcation set of strictly dissipative nonlinear oscillators is investigated.
Abstract: The torsion of the local flow around closed orbits and its relation to the superstructure in the bifurcation set of strictly dissipative nonlinear oscillators is investigated. The torsion number describing the twisting behaviour of the flow turns out to be a suitable invariant for the classification of local bifurcations and resonances in those systems. Furthermore, the notions of winding number and resonance are generalized to arbitrary one-dimensional dissipative oscillators.
42 citations
TL;DR: In this article, the authors discuss the current status of understanding of the factors that determine the origin of nuclear quadrupole interactions in metallic systems, and the nature of agreement between theory and experiment by considering hexagonal close packed metals beryllium, magnesium, zinc and cadmium.
Abstract: This paper deals with the current status of understanding of the factors that determine the origin of nuclear quadrupole interactions in metallic systems. The major emphasis is on pure metals in which there is currently better understanding of the origin of the electric field gradient (EFG) at the nuclear sites. The procedures for the determination of the electron densities that lead to the electronic contributions to the EFG’s is discussed as well as the quantitative procedures for incorporation of antishielding effects. The nature of agreement between theory and experiment is examined by considering the hexagonal close packed metals beryllium, magnesium, zinc and cadmium. The sensitiveness of the calculated EFG to the procedure used for obtaining electron densities is discussed in beryllium using orthogonalized plane wave and augmented plane wave procedures. The nature of agreement between theory and experiment currently attainable for semi-metals and semiconductors is discussed. The bearing of some of the results in these latter systems by procedures dealing with clusters of atoms to simulate the infinite solid on the future of such procedures for imperfect systems and surfaces is commented upon. A brief discussion is presented about the various possible contributors to the temperature dependence of EFG’s in pure metals and comparison is made between theory and experiment for zinc and cadmium. The factors that can contribute to the EFG’s in imperfect metallic systems, including alloys, at both host and impurity nuclei are discussed, and some of these factors are illustrated by considering two examples of these systems, EFG ’s at host Al and Cu nuclei due to mu mesons introduced in the metal and at impurity nuclei in alloys involving cadmium metal host. The concluding section discusses directions in which further efforts are needed to improve our theoretical understanding of both pure metals and imperfect metallic systems.
38 citations
TL;DR: In this paper, the temperature dependence of the molecular twisting power was determined in the nematic wide range mixture RO-TN 404 in the presence of 1-phenyl-1,2-ethandiol.
Abstract: Mesogenic chiral esters of 1-phenyl-1,2-ethandiol, 1-cyclohexyl-1,2-ethanediol, 1,2-diphenyl- 1,2-ethanediol, 1,1´-bi-2-naphthol, 1-phenylethanol, 1-phenyl-2,2,2-trifluorethanol and 1-(9- anthryl)-2,2,2-trifluorethanol were synthesized. The temperature dependence of the molecular twisting power was determined in the nematic wide range mixture RO-TN 404. All compounds show good solubility and unusual high values of the molecular twisting power.
38 citations
TL;DR: In this article, the deuteron (2H) solid state NMR spectra of benzene-d6 adsorbed on microcrystalline boron nitride and on two graphitized carbon blacks (G raphon and Sterling MT) were measured at temperatures between 75 and 120 K.
Abstract: The 52.7 MHz deuteron (2H) solid state NMR spectra of benzene-d6 adsorbed on microcrystalline boron nitride and on two graphitized carbon blacks (G raphon and Sterling MT) were measured at temperatures between 75 and 120 K. Both on boron nitride and on the graphitized carbons the benzene molecules exhibit hexad axis rotation which is fast on the NMR time scale. From the spectra of benzene on the graphitized carbon blacks it is deduced that the molecules are oriented with their planes parallel to the graphite basal planes exposed. At the deuteron sites the shielding tensor which is set up by the action of the static field on the susceptibility tensor of the graphite microcrystallites possesses a shielding anisotropy of + 150 ppm and + 200 ppm for the Graphon and Sterling MT blacks, respectively.
35 citations
TL;DR: Laser a impulsions et faisceaux de particules permettent de produire un rayonnement de corps noir intense dans une cavite as discussed by the authors.
Abstract: Laser a impulsions et faisceaux de particules permettent de produire un rayonnement de corps noir intense dans une cavite
32 citations
TL;DR: In this paper, Strutinsky-type calculations indicate that the potential energy favors four channels in the nuclear fission of 252Cf, and the connection of this finding with experimental results on the distribution of fragment mass, total kinetic energy, neutron multiplicities, and relative abundances is discussed.
Abstract: Strutinsky-type calculations indicate that the potential energy favors four channels in the nuclear fission of 252Cf. The connection of this finding with experimental results on the distribution of fragment mass, total kinetic energy, neutron multiplicities, and relative abundances is discussed. Similar calculations for 227Ac, 236U, and 258Fm show that the changing preponderance of the four channels seems to describe striking trends in the fission of the actinides, in particular the dip in the total kinetic energy at symmetrical fission of 236U and the enormously high average kinetic energy of the 258Fm fragments.
29 citations
TL;DR: The structure of single crystals of the organic metals α- and β-(BEDT-TTF) was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis as discussed by the authors.
Abstract: The structure of single crystals of the organic metals α- and β-(BEDT-TTF) was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the α-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization in one of the two donor stacks have been found. The β-phase develops a superstructure with a unit cell volume three times as large as that at room temperature and with pronounced distortions of the I3--ions.
27 citations
TL;DR: In this article, the triple zeta + polarisation quality of a number of N-F, N-Cl and N-O bonded molecules is reported for the first time.
Abstract: Ab initio calculations, generally of triple zeta + polarisation quality, and sometimes with configuration interaction and iterative natural orbitals, are reported for a number of N-F, N-Cl and N-O bonded molecules. Evaluation of the electric field gradients (EFG) generally gives a good account of microwave inertial axis data, which can then be extended to the EFG principal axis data.
25 citations
TL;DR: Meclure et Choi as discussed by the authors propose an expression for la masse effective electronique le long de la direction d'un champ magnetique dans Bi sous quantification magnetique en utilisant la relation de dispersion generalisee des electrons de conduction.
Abstract: On propose une expression pour la masse effective electronique le long de la direction d'un champ magnetique dans Bi sous quantification magnetique en utilisant la relation de dispersion generalisee des electrons de conduction proposee par Meclure et Choi
TL;DR: In this paper, the self-diffusion coefficients of n-butane, n-pentane and 2-butyne were determined in the liquid state by NM R-techniques at pressure up to 200 MPa and temperatures up to 450 K.
Abstract: The pressure and temperature dependence o f the self-diffusion coefficients D of n-butane, n-pentane, n-hexane, n-decane, trans-2-butene, cis-2-butene and 2-butyne were determined in the liquid state by NM R-techniques at pressure up to 200 MPa and temperatures up to 450 K. The results are taken as tests for the various dynamical models and compared to results obtained by M D calculations. The activation parameters for translational transport and the parameters for the RHS-m odel are derived and discussed.
TL;DR: In this paper, the optical anisotropy of tribenzocyclononene derivatives with R = -OC(O)C6H4CnH2n+i and R = O(O)-C 6H4OCnH 2n+1 possess enantiotropic pyramidic mesophases, and it is suggested that this effect reflects conformational changes involving the side chain benzene ring.
Abstract: Hexasubstituted tribenzocyclononene derivatives with R = -OC(O)C6H4CnH2n+i and R = -OC(O)C6H4OCnH2n+1 possess enantiotropic pyramidic mesophases. These mesophases exhibit an uncommon feature in that their optical anisotropy changes sign as function of temperature within the mesophase region. It is suggested that this effect reflects conformational changes involving the side chain benzene ring.
TL;DR: In this article, the self-diffusion coefficients of sodium, chloride and iodide ions in water-methanol mixtures and the ion-solvent interactions were determined.
Abstract: In spite of the great interest in the porperties of water-organic solvent electrolyte solutions, data on the ionic mobilities in such systems are scarce. Usually the ionic mobility is calculated from the equivalent conductance and the transference num ber. Ionic transference numbers have been reported for water and 17 organic solvents [1], but only for a few water-organic solvents mixtures. Similar information can be obtained from the ionic self-diffusion coefficients, which have been reported for a few water-organic solvent systems [2-5], The aim of the present work was to determine the self-diffusion coefficients of sodium, chloride and iodide ions in water-methanol mixtures and to study the ion-solvent interactions.
TL;DR: The possible values of the number of Kekulé structures (K) of a benzenoid hydrocarbon with h hexagons are examined in this article, where the lowest possible value of K is h + 1.
Abstract: The possible values of the number of Kekulé structures ( K) of a benzenoid hydrocarbon with h hexagons are examined. For normal benzenoids the lowest possible value of K is h + 1. Based on this result the benzenoid systems which have K up to 24 are determined. A number of results concerning enumeration and classification of benzenoid systems is reported.
TL;DR: In this article, a three-center four-electron bond of the X-Sb-X group and cation-anion interaction was found to be responsible for wide spaced halogen resonance lines and unusual temperature dependences of the NQR frequencies.
Abstract: C1, 3581Br, and 121Sb N Q R spectra were observed in com plexes o f the type RxSbyX z with anionstoichiometries SbCl4 , SbClg- , SbBr4 , SbBr^~, SbBr^- , and Sb2Br^~. Several complexes showwidely spaced halogen resonance lines and unusual temperature dependences o f the NQ Rfrequencies. These findings are accounted for 35Cl, 81Br, and 121Sb NQR spectra were observed in complexes of the type RxSbyXz with anion stoichiometries SbCl4- , SbCl63- , SbBr4- , SbBr52-, SbBr63- , and Sb2Br93-. Several complexes show widely spaced halogen resonance lines and unusual temperature dependences of the NQR frequencies. These findings are accounted for in terms of a three-center four-electron bond of the X-Sb-X group and cation-anion interaction.
TL;DR: In the case of more than one escape route, this set becomes a "fuzzy boundary" (Mira) and its projection as the map becomes noninvertible (1-D ) is a "Julia set in 1 D ".
Abstract: Julia sets are self-similar separatrices of the coast-line type found in noninvertible 2-D maps. The same class of maps also generates hyperchaos (chaos with two mixing directions). Smale’s notion of a “nontrivial basic set” provides a connection. These sets arise when a chaotic (or hyperchaotic) attractor “explodes”. In the case of more than one escape route, this set becomes a “fuzzy boundary” (Mira). Its projection as the map becomes noninvertible (1-D ) is a “Julia set in 1 D ”. In the analogous hyperchaos case the 2-D limiting map contains a classical Julia set of the continuous type. An identically looking set can also be obtained within a non-exploded hyperchaotic attractor, however, as a “cloud”. Julia-like attractors therefore exist. The theory also predicts Mandelbrot sets for 4-D flows. Julia-like behavior is a new, numerically easy-to-test for property o f most nontrivial dynamical systems.
TL;DR: Etude de la structure electronique de Li 2, cristallin par une approche par amas finis dans le cadre d'un modele semiempirique d'orbitale moleculaire du type INDO as discussed by the authors.
Abstract: Etude de la structure electronique de Li 2 , cristallin par une approche par amas finis dans le cadre d'un modele semiempirique d'orbitale moleculaire du type INDO
TL;DR: In this paper, the anomalous behavior of NQR parameters is analyzed in terms of ordering processes of the ammonium ions and the intermolecular potential energy is used to evaluate the potential barrier to molecular rotation in C6Cl6 and sym-C6Cl3F3.
Abstract: Simple methods to analyze the anomalous behavior of NQR parameters are presented. Unusual positive temperature coefficients of antimony resonance frequencies in (NH4)2SbF5 below the phase transition at 169 K were interpreted in terms of ordering processes of the ammonium ions. Calculation of the EFG in LaF3 revealed that the translational diffusion of Li ions brings about an anomalous decrease in η of the 139La NQR at high temperatures. The same kind of an EFG calculation was made to predict the 14N NQR frequency in Li3N . The calculation of the intermolecular potential energy was used to evaluate the potential barrier to molecular rotation in C6Cl6 and sym-C6Cl3F3. It was shown in the latter that the quadrupolar relaxation, due to a reorientational jump to a metastable site, works in the low temperature phase below 296 K. while the molecular three-fold reorientation is the dominant relaxation mechanism in the high temperature phase.
TL;DR: In this article, the authors used differential scanning calorimetry to identify the phase transitions of metal hydrogen double-salts at ambient temperature, using the enthalpy and temperature of the endothermic phase transitions.
Abstract: Alkali metal hydrogen double salts can have more than one stable phase at ambient temperature. These phases can be identified by the enthalpy and temperature o f the endothermic phase transitions they undergo when heated. Transitions to these phases at ambient temperature depend on mechanical treatment (grinding, one-dimensional pressure) as well as on the water vapour pressure above a sample. Eight phase transitions (o f which five were not known before) have been studied by means o f differential scanning calorimetry.
TL;DR: In this paper, the authors outline roughly the "normal" dielectric relaxation behavior of polar liquids as a reference for the investigation of more complex (e.g. associating) systems, some theoretical considerations and experimental results (mainly on two component mixtures) are presented.
Abstract: In an attempt to outline roughly the \"normal” dielectric relaxation behaviour of polar liquids as a reference for the investigation of more complex (e.g. associating) systems, some theoretical considerations and experimental results (mainly on two component mixtures) are presented. They show that for a distinct spectral component a simple equation can be used which approximately relates the relaxation strength to the moment of the relaxing moiety. The rotational relaxation time is practically not affected by the static permittivity but is correlated to the molecular size and the macroscopic viscosity, thus allowing for conclusions on the effective radius of the tumbling moieties.
TL;DR: In this paper, the potential energy, dipole moment, and electronic transition moment functions for the A 3Π and X 3Σ- states of PH have been calculated from highly correlated electronic wavefunctions.
Abstract: Potential energy, dipole moment, and electronic transition moment functions for the A 3Πand X3Σ- states of PH have been calculated from highly correlated electronic wavefunctions. The electric dipole moments in the vibrational ground state of PH are calculated to be 0.637 Debye (A 3Π) and 0.403 Debye (X3Σ-). The predicted rates of spontaneous emission between low lying vibrational states of the X state lie in the range of 46 to 109 sec-1 (PH) and 12 to 30 sec-1 (PD). The calculated radiative lifetime of the v' = 0 level in the A 3Π state of 400 ns is lower by about 10 percent than the most recent experimental value. The classical intersection of the 5Σ- and the A 3Πstate has been calculated to lie between v' = 2 and 3 with an expected uncertainty of about 500 cm−1, whereas the onset of the rotationally dependent predissociation lies at v' = 0, J' = 11.
TL;DR: Based on the calculated electric field gradient (q) from ab initio Cl wavefunctions with large basis set (including ƒ functions on N and d functions on H) and the experimental nuclear quadrurupole coupling constant (e Q q) for nitrogen in NH3, an improved value o f the quadrupole moment of 14N was proposed as Q (14N ) = 2.08 x 10-26cm2 as mentioned in this paper.
Abstract: Based on the calculated electric field gradient (q) from ab initio Cl wavefunctions with large basis set (including ƒ functions on N and d functions on H) and the experimental nuclearquadrupole coupling constant (e Q q) for nitrogen in NH3, an improved value o f the quadrupole moment of 14N is proposed as Q (14N ) = 2.08 x 10-26cm2. The value calculated using a wavefunctionnear the Hartree-Fock limit enlarged ≈ 10% by the Cl treatment.
TL;DR: In this article, the components of the coupling tensor in the principal inertia axis system and the n a components of dipole moments have been determined by high-resolution microwave Fourier transform spectroscopy.
Abstract: The nitrogen 14N quadrupole hyperfine structure and the Stark effect in the rotational spectra of methyl isocyanate and methyl isothiocyanate were investigated by high resolution microwave Fourier transform spectroscopy. The components of the coupling tensor in the principal inertia axis system and the n a components of the dipole moments have been determined.
TL;DR: In this article, the 3v3 band shape, at moderate compression up to 0.1 g · cm-3, is adequately represented by summing over individual rotation-vibration lines with halfwidths proportional to the density.
Abstract: Near infrared absorption of pure CO2 in the 3v1 + v3, 2v1 + 2v20 + v3, v1 + 4v20 + v3, 6v20 + v3 Fermi tetrad region around 6300 cm-1 and in the 3v3 second overtone region around 6970 cm-1 was measured at temperatures between 298 K and 500 K to a maximum pressure of 3100 bar. The 3v3 bandshape, at moderate compression up to 0.1 g · cm-3, is adequately represented by summing over individual rotation-vibration lines with half-widths proportional to the density. Band maximum positions and vibrational intensities between gaseous and liquid-like states are reported and discussed. Promising applications of high-pressure high-temperature near infrared spectroscopy to the quantitative analysis of CO2 are illustrated for the 3200 cm-1 to 7400 cm-1 region. The technique can be used for CO2 concentrations or at optical path lengths differing by several orders of magnitude.
TL;DR: In this article, the Fourier transform infrared spectra of C1F and BrF were measured with a resolution of 0.04 cm-1 in the region of the fundamental and First overtone with an accuracy of 2 and 4 x 10-3 cm
Abstract: Fourier transform infrared spectra of C1F and BrF have been measured with a resolution of 0.04 cm-1 in the region of the fundamental and First overtone with an accuracy of 2 and 4 x 10-3 cm-1, respectively. The rotational structure was resolved up to J\" = 58/62 (ClF/BrF), and υo values have been obtained from rotational analyses o f the υ 1 ← 0, 2 ← 1, 2 ← 0 and. in part, 3 ← 1 and 3 ← 0 vibrational bands. These have been employed to obtain the hitherto most accurate ωe, ωeχe and (for C1F) ωeγe values. From the rotational analyses, Be, αe, γe, De and ße have been derived.
TL;DR: The bending fundamental bands of HCCCN, υ5 and υ6, have been recorded in the region from 470 to 700 cm-1 with a resolution of 0.04 cm using an FT spectrometer as mentioned in this paper.
Abstract: The bending fundamental bands of HCCCN, υ5 and υ6, have been recorded in the region from 470 to 700 cm-1 with a resolution of 0.04 cm \"' using an FT spectrometer. The band centers have been determined precisely; υ5 = 663.2220(10) and υ6 = 498.8022(10) cm-1 . From the obtained effective rotational constants, the sign o f the /-type doubling constants has been determined to be positive for the υ5 = 1 and υ6 = 1 vibrational states.
TL;DR: In this article, it was shown that the upper bound for the total 7r-electron energy of an arbitrary conjugated hydrocarbon is upper bounded for the case of benzenoid systems.
Abstract: It should be pointed out that E^c is an upper bound for the total 7r-electron energy o f an arbitrary conjugated hydrocarbon whereas Er and EGTD are limited to alternant hydrocarbons. The expres sion (4) is an upper bound for En only in the case o f benzenoid hydrocarbons. Since benzenoid systems are necessarily alternant, it is clear that all the formulas ( l ) - ( 4 ) provide upper bounds for their total ^-electron energy. Furthermore, for benzenoid systems,
TL;DR: In this article, the functional energy representation of two-preon composite vector bosons is studied and the weak mapping of the functional representation of the spinorfield on to the functional-energy representation for the effective vector boson dynamics (with interactions) produces a non-abelian SU (2) local gauge theory (Yang-Mills theory) for a triplet of mass-zero vector Bosons in the temporal and Coulomb gauge.
Abstract: Unified nonlinear spinorfield models are self-regularizing quantum field theories in which all observable (elementary and non-elementary) particles are assumed to be bound states of fermionic preon fields. Due to their large masses the preons themselves are confined and below the threshold of preon production the effective dynamics of the model is only concerned with bound state reactions. In preceding papers a functional energy representation, the statistical interpretation and the dynamical equations were derived and the effective dynamics for preonantipreon scalar boson states and three-preon fermion (and anti-fermion) states was studied in the low energy as well as in the high energy limit, leading to a functional energy representation of an effective Yukawa theory (with high energy form-factors). In this paper the effective dynamics of two-preon composite vector bosons is studied. The weak mapping of the functional energy representation of the spinorfield on to the functional energy representation for the effective vector boson dynamics (with interactions) produces a non-abelian SU (2) local gauge theory (Yang-Mills theory) for a triplet of mass-zero vector bosons in the temporal and Coulomb gauge. This special gauge is enforced by the use of the energy representation and is compatible with the nonlinear Yang-Mills dynamics (and quantization). Apart from the non-abelian Gauss-law all other field laws and constraints directly follow from the mapping procedure. The non-abelian Gauss-law is a consequence of the relativistic invariance of the effective dynamics. PACS 11.10 Field theory PACS 12.10 Unified field theories and models PACS 12.35 Composite models of particles
TL;DR: In this paper, an outline of 14N nuclear quadrupole, internal axis method (IAM) methyl internal rotation, and fourth order centrifugal distortion was given for extrapolating transition frequencies to higher J values.
Abstract: In the following we give an outline of 14N nuclear quadrupole, internal axis method (IAM) methyl internal rotation, and fourth order centrifugal distortion - only needed for extrapolating transition frequencies to higher J values - analyses performed for 2-, 4-, and 5-methyl oxazole. The results are discussed, the three methyl oxazoles being compared with one another and with their common parent, oxazole.