Band 49, Heft 12

In a previous paper a general group theoretical discussion of effective boson-fermion coupling theories (with com posite two-fermion bosons) resulting by weak mapping of nonlinear spinor-isospinor field models was given. In the present work these considerations are extended to the case of broken isospin symmetry and applied to a microscopic subfermion-description of phenomenolog­ical gauge theories with Higgs symmetry breaking.

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.

The mm-wave spectra of 15 N 18 O and 14 N 17 O in both X 2 Π 1/2 and X 2 Π 3/2 states have been measured and assigned for the first time. Improved rotational and, for the first time, 17 O hyperfine coupling constants have been derived from the analysis. The 14 N 17 O data yield parameters of the unpaired electron spatial distribution near both nuclei. Furthermore, the deviation from the Born-Oppenheimer approximation is confirmed on the basis of the rotational constants of five isotopomers. Finally, when comparing the nuclear spin-rotation constants to the ones of other molecules containing 14 N or 17 O nuclei, a roughly linear proportionality with the rotational constant B is found.

The structure of zinc(II) bromo complexes in methanol and N,N-dimethylformamide (DMF) (molar ratio [solvent]/[ZnBr 2 ] = 10, temperature range 77 -333 K) has been investigated by Raman scattering and X-ray diffraction. In the methanol solution symmetric Zn - Br vibrations (γ 1 ) of the dibromo- and tribromozinc(II) complexes were observed at 209 and 184 cm -1 , respectively. With decreasing temperature the intensity of the γ 1 band decreased for the dibromo and increased for the tribromo complex. In addition, the γ 1 band for the tetrabromo complex appeared in the supercooled and glassy methanol solutions. In the DMF solution only one band, assigned to both the dibromo-and tribromozinc(II) complexes, was observed. Its intensity did not change with temper­ature. The X-ray diffraction data revealed that the average number of Z n -Br interactions within the zinc (II) bromo complexes does not change with temperature while the number of nonbonding Br ··· Br interactions within the complexes increases from 1.5 at 298 K to 1.9 at 243 K for the methanol solution and from 1.3 at 298 K to 1.8 at 243 K for the DMF solution. These Raman and X-ray results have confirmed that in both methanol and DMF solutions at high temperatures the dibromo species is predominantly formed, whereas at low temperatures the tribromo complex is favored, the tetrabromo species being formed only in the supercooled and glassy methanol solutions. The temperature dependent equilibrium shifts of the zinc(II) bromo complexes in the methanol and DMF solutions are discussed together with previously reported results for the aqueous phase.

NMR proton relaxation rates of normal and oxygen-17 enriched m ethanol-d 3 in a mixture of 71 mol% methanol and 29 mol% dimethylsulphoxide-d 6 (DMSO) were measured as a function of temperature between 298 and 158 K. From these data rotational correlation times of the methanol molecule in the mixture and the oxygen-proton dipolar spin-lattice coupling parameter were ob­tained. The latter parameter is considerably smaller than the one obtained from neutron diffraction studies of the molecular geometry of methanol. Additionally, deuteron and oxygen-17 relaxation rates were measured over the same temperature range. Using the rotational correlation times obtained from the oxygen-17 induced proton relaxation rates, the quadrupole coupling constant for deuterium was derived; it shows a temperature dependence. Application of the Poplett relation yielded the oxygen-17 quadrupole coupling constants, so that oxygen correlation times could be obtained. Comparison of deuteron and oxygen correlation times indicates that the reorientation of the methanol molecule in the methanol/DMSO mixture is anisotropic.

The crystal structures of C 6 H 5 NClCOCH 2 Cl (1), C 6 H 5 NClCOCHCl 2 (2), C 6 H 5 NClCOCCl 3 (3), and C 6 H 5 NHCOCCl 3 (4) have been determined at room temperature (lattice constants, d in pm).(1): P2 1 /c, Z = 4, a = 738, b = 645, c = 1891, β = 90.41°, d (N -C l) = 171, d (C = O ) = 121; (2): P2 1 /c, Z = 4, a = 820, b = 1495, c = 905, β = 114.78°, d (N -Cl) = 171, d (C = O ) = 120; (3): P 21/c, Z = 4, a = 819, b = 1853, c = 718, β = 103.64°, d (N -Cl) = 172, d (C = O ) = 120; (4): P2 1 /c, Z = 4, a = 551, b = 1704, c = 1035, β = 93.08°, d (C = O) = 121. For (2), (3), and (4) the 35 Cl NQR frequencies have been determined in the range 77 ≤ T /K ≤ 300. At 77 K (γ in MHz): (2): γ (w,1) = 37.600, γ (w,2) = 38.188, γ (N) = 51.858; (3): γ (w,1) = 39.944, γ (w,2) = 40.512, γ (w,3) = 40.739, γ (N) = 52.791; (4): γ (w,1) = 39.428, γ (w,2) = 39.452, γ (w,3) = 39.986. For the compound C 6 H 5 NHCOCHCl 2 (5) the 35 Cl NQ R measured at 77 K is: γ (w,1) = 37.195 MHz, γ (w,2) = 37.596 MHz. The relation, γ( 35 Cl) = d (N -Cl) is discussed.

The phase diagram and the 35 Cl NQR spectrum of (ClH 2 C) 2 (CH 3 )C -COOH have been studied in the temperature range 77 ≤ T/K ≤ melting point (343.8 K). On heating no phase transition appears. The cooling cycle shows strong undercooling of the melt, a phase transition at T m → I = 319.9 K and a transition from the orientationally disordered phase I to the ordered phase II at T I → II = 297.2 K. The 35 Cl NQR spectrum is a doublet with negative temperature coefficients within the temperature range covered, showing no phase transition in the heating cycle. At 77 K (298 K) the frequencies are in MHz: γ 1 = 34.830 (34.140); γ 2 = 34.018 (33.258). The ordered solid crystallizes in the space group Pbca, Z = 8, a = 1019.7 (3) pm, b = 1146.3 (3) pm, c = 1293.8 (3) pm. Phase I (plastic phase) is cubic face centered, a = 911 pm, Z = 4.

125 Te nuclear spin relaxation (NSR) and electrical conductivity measurements were performed on ultrapure single-crystalline paratellurite (α -TeO 2 ) between about 50 K and the melting point (1007 K) at various oxygen partial pressures (1 bar -10 -4 bar). At elevated temperatures the NSR rate 1 / T 1 and conductivity σ are caused by the diffusive motion of point defects. From the observed p 02 -dependence of 1/T 1 and σ a defect model is developed which is shown to be consistent with the experimental data. The model involves ionic oxygen interstitials (O″ i ), doubly charged oxygen vacancies (Vö) and charge-compensating electron holes (h • ). The observed pressure dependence suggests that the NSR rate is induced by the motion of Vö while the conductivity is due to the mobility of h • . Evaluation of the data leads to 3.3 eV for the incorporation enthalpy of oxygen on interstitial sites and to 4.5 eV for the formation enthalpy of oxygen Frenkel pairs (O″ i - Vö). Further, the chemical diffusion coefficient D c is found to be caused by the ambipolar diffusion of O″ i and h • . At 950 K we obtained from both the NSR and conductivity experiments D c = (1 ± 0.3) • 10 -5 cm 2 /s.

Gamma irradiation damage centres in (NH 4 ) 2 SiF 6 , (NH 4 ) 2 SnCl 6 , (NH 4 ) 2 PtCl 6 , [(CH 3 ) 2 NH 2 ] 2 SnCl 6 , (NH 4 ) 2 PdCl 6 and ultraviolet irradiation damage centres in (CH 3 ) 4 NCH 3 COO and (CH 3 ) 4 NBr have been investigated by electron paramagnetic resonance spectroscopy. It has been found that the radicals produced in (NH 4 ) 2 SiF 6 and (NH 4 ) 2 SnCl 6 is N 2 H 4 + , and those in (NH 4 ) 2 PtCl 6 are NH 3 + and (PtCl 6 ) 3- . In [(CH 3 ) 2 NH 2 ] 2 SnCl 6 the species is (CH 3 ) 2 NH + , and in (NH 4 ) 2 PdCl 6 the species is (PdCl 6 ) 3 - . Furthermore, it has been shown that the ultraviolet irradia­ tion produces ĊH 3 and CO 2 - radicals in (CH 3 ) 4 NCH 3 COO and ĊH 3 radical in (CH 3 ) 4 NBr. The EPR parameters of the observed radicals have been determined.

The complex permittivity ε* has been measured non-invasively in the cornea of two types of animal eyes and in erythrocyte suspensions in the frequency domain 1 ... 18,000 MHz. These measurements shall help to distinguish between eye diseases in a very early stage and to track the possible effect of “microthermics”, respectively. The analysis of the miniaturised probe used for the reflection method and the experimental set-up with its automatic scanning facility are presened.

The hydrothermal formation of sodium hydroxyborate enclathrated sodalite synthesized from an initial ternary mixture of mullite, cristobalite and corundum has been investigated. Depending on temperature and pressure the compound Na 7.5 [AlSiO 4 ] 6 [B(OH) 4 ] 1.5 · 2H 2 O could be synthesized in form of polycrystalline powder as well as in form of single crystals. The kinetics of the sodalite growth could be determined at 423 K and 473 K. 29 Si-and 27 Al MAS NMR was shown to be the preferred method to describe the conversion into sodalite quantitatively. Evidence for the first formation of polycrystalline sodalite has been found after the total dissolution of mullite and cristobalite. Single crystal X-ray diffraction data were used for the structure determination and refinement. The position and orientation of the hydroxyborate anions within the sodalite's /β-cages could only be found in the course of a "rigid body" refinement with constraints for the B(OH) 4 tetrahedron. The boron atoms are located in an off-centre position within the sodalite cages. One out of the four oxygen atoms of the hydroxyborate group is positioned near the centre of a face of the sodium tetrahedron, whereas the three remaining oxygen atoms are near to the middle of its edges.

A proton NMR method is described which enables rotational flow and viscosity measurements of low molecular weight ṉematic ḻiquid c̱rystals (NLC's). This is achieved by an extension of the common NMR field-cycling technique, namely by fast electronic switching of both the external magnetic field direction and strength. In thermodynamic equilibrium, the director of an NLC with positive diamagnetic anisotropy (Δ χ > 0) orients parallel to the external magnetic field. Thus a change of this direction causes a reorientation process of the molecules to align to the new equilib­rium, which in low viscous systems in contrast to polymer liquid crystals is rather fast and hence requires fast field switching. We have studied systematically this response as a function of the initial field rotation angle 90 relative to the director for some homologous NLC's of the n-alkyl-cyano-biphenyl (nCB) series. It is shown that there exists a critical angle θ cr in such a way that for θ o < θ cr , however (e.g. in the case of 5 CB θ cr is ≈ 85 degrees) the viscoelastic behaviour is more complicated because of a coupling between flow and director gradients. The analysis of the alignment process by the changes of the proton line spectra also allows to determine the Leslie viscosities α 1 , α 2 , α 3 , α 4 + α 5 , and the average Frank elastic constant K̄ by a single measurement.

14 N nuclear quadrupole resonance spectroscopy, detected with a Superconducting Quantum Interference Device, makes possible the study of nitrogen environments in amino acids and small peptides. The present experiments characterize: 1) the effects of intermolecular interactions upon the amino nitrogen of serine upon cocrystallization of the stereoisomers in a range of concentrations; 2) the changes of the amino and imidazole nitrogen environments brought about by combining L-Alanine and L-Histidine into the dipeptide L-Ala-L-His.

The quantum-classical transition of methyl rotation highlights conflicting assumptions of quan­tum and classical mechanics, the first assuming that identical fermions are indistinguishable while the second recognises they are distinguishable through their histories. When this is introduced into quantum mechanics, the two are compatible and there is a smooth transition of the methyl rotational spectrum with increasing temperature through the merger of three broadening peaks. The changing character of methyl dynamics through this transition is discussed.

Hydrotalcite-like Fe-Ni-hydroxides [Ni 2/3 II Fe 1/3 III (OH) 2 ](CO 3 ) 1/6 (H 2 O) y , [Ni 3/4 II Fe 1/4 III (OH) 2 ]-(CO 3 ) 1/8 (H 2 O) y and [Ni 3/4 II/III Fe 1/4 III (OH) 2 ](CO 3 ) 0.14 (H 2 0) y as well as the ternary oxide NaNi 2/3 Fe 1/3 O 2 have been studied by 57 Fe-Mössbauer spectroscopy. All samples contain Fe 3+ in a high spin state. The quadrupole interaction is smaller if a magnetic splitting is present, which may indicate a non-parallel arrangement of the principal axis of the EFG and the hyperfine field. The temperature dependence of the spectra has been understood in terms of collective cluster excitations. In this model the magnetic energy of a single domain depends on the direction of the total magnetic moment and on magnetic interaction with the neighbourhood. The spectral lineshape could be fitted assum­ing uniaxial relaxation.

A global scaling property for bifurcation diagrams of periodic orbits of smooth scalar maps with both one and two dimensional parameter spaces is examined. It is argued that for both parameter spaces bifurcations within a periodic window of a given scalar map are well approximated by a linear transformation of the bifurcation diagram of a canonical map.

Ising chains characterized by smoothly varying two-body potentials, including a generalized version of the Kac model, are studied. As a novel aspect we show that one-dimensional maps associated with such chains in the spirit of the thermodynamical formalism possess fractal deriva­tives. We discuss how long-range potentials lead to intermittent-like behavior in the associated one-dimensional map.

The thermodynamic approach is applied for the description of normal and anomalous diffusion of one-dimensional maps on a grid of unit cells. The characteristic entropy functions are calculated. For the anomalous cases, the locations of the critical lines are determined.

Multifractal properties of the invariant densities of correlated random maps are analyzed. It is proven that within the thermodynamical formalism phase transitions for finite correlations may be due to transients. For systems with infinite correlations we show analytically that phase transitions can occur as a consequence of localization-delocalization transitions of relevant eigenfunctions.

In this contribution we propose a technique to analyse arbitrary invariant subsets of chaotic dynamical systems. For this purpose we introduce the constrained Frobenius-Perron operator. We demonstrate the use of this operator by determining the geometrical multifractal spectrum of invariant chaotic subsets of one-dimensional maps which are either coexisting side by side indepen­dently or are embedded in a larger set close to a crisis configuration.

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.

A map lattice of globally coupled shift maps is investigated by analytical methods. The breakdown of the well known space time mixing regime at weak coupling strength is accompanied by a global synchronization of the maps. Furthermore a Cantor set like repeller survives which produces chaotic transients.

Here we illustrate the effectiveness of the thermodynamical formalism applied to a well known chaotic phenomenon, the intermittency. This leads us to a new classification for intermittent phe­nomena from the point of view of the generated chaotic phases in the spectrum of the generalized entropies K (q). New types of intermittencies are found related to the absence or presence of phase transitions with infinite jump in K (q). This is underlined with examples. It is also shown via examples that the existence of a marginally stable fixed point in the system is neither necessary nor sufficient for intermittency.

The weak-noise asymptotics of the blurring effect of noise on fractals can be described by scaling laws. It does not only depend on the geometric properties of the fractals but also on their generating dynamics. This is illustrated with the example of the Feigenbaum attractor.

We study transport in dynamical systems characterized by intermittent chaotic behavior with coexistence of dispersive motion due to periods of localization, and of enhanced diffusion due to periods of laminar motion. This transport is discussed within the continuous-time random walk approach which applies to both dispersive and enhanced motions. We analyze the coexistence for the standard map and for a one-dimensional map.

We address the escape rate for single-humped maps near a boundary crisis multiplicatively coupled to weak uncorrelated noise. A scaling law for the rate is derived predicting a stabilization of deterministic transient chaos by noise. Generalizations to maps near interior crises and band merging points are given.

Expressions in terms of group-velocity time-correlation functions for the ionic mobilities of molten 6 LiCl, 7 LiCl and ( 6 Li, 7 Li)Cl are derived, taking the time-averaged zero momentum of inertia of each of the three groups of ions into account. MD-simulations have been performed for 6 LiCl and 7 LiCl, yielding agreement between the simulated and the published experimental reduced isotope effect, although the temperature -volume conditions of the simulations did not conform with natural LiCl.

Zero-kinetic-energy (ZEKE) photoelectron spectra of metalcarbide anions are presented, allowing a high resolu­tion spectroscopic access to intermediates in catalytic reac­tions of hydrocarbons on metal surfaces. As a first compound, FeC 2 (an intermediate of the iron/acetylene system) has been chosen. Important for successful ZEKE spectroscopy was a special anion source and the selection by time-of-flight mass spectrometry. In addition, conventional laser induced photo­ detachment photoelectron spectroscopy in combination with our anion source and mass analyzer delivered valuable new information.

Experimental results on the interaction of tritium with fine particles of titanium, published in Phys. Lett. A and attributed to decelerated β-decay of tritium solved in titanium, are instead explained by adsorption of tritium on the surface of the particles, formation of tritium oxide when oxygen is present, and normal β-decay.