Band 53, Heft 10-11

The pure 1-alkanols C 4 to C 12 and seven of their short/long chain binary equimolar mixtures are in-vestigated by static and dynamic dielectric measurements up to 36 GHz at 20, 30 and 40 °C. The apparent dipole moment and the relaxation parameters from a three Debye term analysis of the spectra are discussed. The mixtures are found to behave like a one component alcohol of mean chain length. An odd-even effect is revealed by comparison of mixtures containing C 11 with those containing C 12 as long chain mixture component.

The influence of the dichroic azo dye on the phase transition temperatures of the mesogenic homolo-gous series of 1-[4-n-alkyl-biphenyl]-2-[4-isothio-cyanatophenyl] ethane (nTPEB) for n = 2 -10 has been examined. For the dye-nTPEB mixtures the polarized absorption spectra as a function of tem-perature have been recorded. From these spectra the order parameter of the dye dissolved in the liquid crystalline hosts in the whole region of the nematic phase has been determined. The order parameter has revealed the odd-even alternation, similarly as the clearing temperature. In the smectic B phase the mosaic texture has been observed and conclusions concerning structural form of this phase have been drawn.

We analyse linear networks of impedances in the case when the impedances at every level differ by a factor of b from those at the previous level. Such networks can be used as models for rough surfaces, in which case there will exist a level of finest detail which must be taken into account in any calculation. We obtain an exact expression for the ratio of the impedance of the network to the outer impedance for an arbitrary number of elements in the network. We show that this class of networks shows a transition from a fractal geometric structure to a non-fractal structure according to the value of b. However, their effective impedance is never fractal.

In this paper we report the first molecular dynamics study combining fast field-cycling and conven-tional NMR techniques in a thermotropic liquid crystal of discotic molecules exhibiting an ordered columnar hexagonal mesophase. Using the association of these techniques we obtained proton T 1 data over a very large domain of Larmor frequencies (ω/2π from 500 Hz to 85 MHz). The proton spin-lattice relaxation results were analysed considering the structure of the mesophase and the types of movements which are expected to influence significantly the relaxation rate, namely local molecu-lar rotational reorientations, inter-columnar self-diffusion and collective movements corresponding to bending and compression of the columns. We verified that these mechanisms dominate the relaxation respectively for high, medium and low Larmor frequencies.

The log-compound-Poisson distribution for the breakdown coefficients of turbulent energy dissipation is proposed, and the scaling exponents for the velocity difference moments in fully developed turbulence are obtained, which agree well with experimental values up to measurable orders. The under-lying physics of this model is directly related to the burst phenomenon in turbulence, and a detailed discussion is given in the last section.

The TV-particle quantum mechanical system in an external field is considered on the basis of two-particle density functions. The main point of the presented work is to reveal the advantages of the two-particle density formalism as compared to the common one-particle density formalism applied to a simple example. The two-particle density formalism permits us to take into account the exact two-particle interaction without additional models. The exchange and correlation effects can be considered by a proper choice of the trial function. By using the presented formalism we calculate the density of the electron gas on different metal surfaces. A simple trial function allowing for correlations gives us a more correct fit to the experimental data on the metal dipol barriers than corresponding calculations with the one-particle density formalism. It is also shown that a Pertubation of the external potential can be effectively taken into account by a Pertubation calculation for the trial function.

Amorphous Co-P alloys with different phosphorous concentrations were produced by meltspinning, sputtering, and electrodeposition. From the combination of X-ray and neutron diffraction the atomic distances and coordination numbers for the Co-Co- and the Co-P correlations were determined. The short range structure, in dependence of the P-concentration, 9 at% P ≤ c p ≤ 26 at% P, exhibits rather abrupt changes at the eutectic composition, c pe = 19.9 at% P. It is suggested that at P-contents above c p,e the short range order is more pronounced than at lower P-contents. The coordination of nine Co atoms around P, as established previously for many transition metal-metalloid glasses, is found only at the eutectic composition. There is almost no dependence of the structure of the amorphous alloys on the specific production method. It is indicated that the melt-spun and the sputtered glasses are in a slightly more relaxed state than the electrodeposited glasses.

Amorphous Co 100-x P x foils in the concentration range 13.4 ≤ x ≤ 26 were produced by electrodeposition. The extended X-ray absorption fine structure (EXAFS) at the phosphorous K-edge was measured in transmission mode. The phase shift was determined from the EXAFS spectrum of a crystalline Co 2 P reference sample. The EXAFS spectra of the amorphous Co-P alloys are characterized mainly by one single contribution from a shell of Co-atoms at a distance of 2.3 Å around the P-atoms. A small additional contribution at a shorter distance of 2.0 Å may be a hint on some direct P-P neighbours. The evaluation of reliable coordination numbers from the EXAFS spectra of the amorphous alloys is not possible.

Systematic calculations of the neutron-nucleus scattering parameters at several neutron energies Ei < 2 keV have been performed for 37 isotopes ( 6 Li,... 59 Co) in the mass region of 6 ≤ A ≤ 60, using the large compilation of experimental neutron-nucleus scattering data obtained in Garching. In the first stage of these calculations, the s-wave potential scattering radius R’, the scattering lengths b coh , b ± , and the bound state parameters (E b , Γ γ , gΓ 0 n ) have been calculated for each isotope, employing the general least squares fit (GLSQF) for the experimental and the corresponding theoretical values of the total neutron-nucleus cross sections σ exp tot (E i ) at several energies E i , absorption cross sections σ abs (E o ) and of the coherent scattering lengths b coh . The theoretical expressions for these parameters were deduced on the basis of the usual S-matrix formalism with no assumption about the particular shape of the optical model potential. In the second stage of our calculations, the spherical Fiedeldey- Frahn optical potential was employed for the pure theoretical description or the above mentioned neutron-nucleus scattering characteristics. The results obtained have been analyzed and compared with the values deduced from measurements.

The temperature evolution of the 7 Li NMR spectra and relaxation rates in many investigated solid lithium conductors shows more or less the same behavior. These compounds are characterized by a disordered lithium sublattice with a surplus of cation sites in cavities and channels of the anionic network. At low temperature, the spectra consist of a central line and a distributed satellite base structure. Upon increasing temperature, both components narrow until a reduced constant width with a well resolved quadrupole structure is reached. The mean nuclear quadrupole coupling parameters reduce by either about 5 or by a factor of 15 in all the compounds. The spin-lattice relaxation rates 1/T 1 are asymmetric as a function of reciprocal temperature and of quadrupolar origin. The activation energy of the main process of ionic motion may best be obtained from the temperature dependence of the dipolar spin-spin-relaxation rate 1/T 2 . The spectral densities of the relaxation dependences correspond to those for inhomogeneous motions; they may be described by modification of the BPP equation, a Cole-Davidson distribution or a Kohlrausch-Williams-Watts function. Within this study three LISICON systems, Li 4-3x Ga x GeO 4 , and two phosphates Li 3 M 2 (PO 4 ) 3 (M = Sc, In) were investigated or re-investigated which fit well into this scheme. Activation energies of 39-43 kJ/mol (Li 4-3x Ga x GeO 4 with x = 0.06,0.14, 0.24), 53 kJ/mol (Li 3 Sc 2 (PO 4 ) 3 ) and 75 kJ/mol (Li 3 In 2 (PO 4 ) 3 ) were obtained.

X-ray diffraction experiments of molten oxide glasses, which give new insights into the structure of melts, were carried out. Using modern means (synchrotron radiation, image plates, container-less high-temperature technique) it could be shown that the short range order of melt and solid glass is often qualitatively different. If vitreous B 2 O 3 or binary borate glasses with low content of network modifier are heated up above Tg , the network topology begins to alter. With rising temperature more and more of the boroxol groups are replaced by independent B0 3 groups. While melting a metaphosphate glass, how-ever, structural changes of another kind take place. In solid glass the environment of the network modifier ions is similar to the one found in crystalline modifications, and their distances to the surrounding PO 4 tetrahedra have narrow distributions. In the melt, however, these distances scarcely become evident, probably owing to the increased thermal motion of the modifier ions.

The Maier-Saupe theory is employed in order to calculate order parameters (P 2 ) , (P 4 ) from the nematic potential q. The relation between σ=q/(RT) and S = (P 2 ) corresponds well with a recently established formula by Kalmykov. The relation between the order parameters is in accordance with the analytic expression (P 4 )=5/7 (P 2 ) 2 proposed by Zanonni, but deviates significantly from the Faber model, according to which log (P 4 )=(10/3) log (P 2 ). Experimental results for 5 CB obtained from Raman measurements, however, are in better agreement with the Faber model.

We report on the measurement of rotational transitions of monodeuterated fluorobenzene in natural abundance to show the feasibility of the investigation of monodeuterated asymmetric top molecules without the necessity of isotopic enrichment.

The absolute configuration of the conformationally flexible aldehyde ester methyl-2-formyl-2-(phe-nylsulfanyl)-3-(3,4,5-trimethoxyphenyl)-propanoate was determined by comparison of measured and calculated CD spectra. The spectra were calculated by means of the so-called matrix method assuming R configuration at the stereogenic center. Calculated and observed signs of the first three most intense CD bands agree. Therefore, it was concluded that the absolute configuration of the compound was also R, which is in perfect agreement with the results of an X-ray structure determination.

The absolute configurations of both 1,5-diaza-c/s-decalin enantiomers were determined by com-parison of measured and calculated CD spectra. CD spectra for both enantiomers were recorded. Theoretical CD spectra for one of the isomers were calculated by means of the semiempirical CNDO/2S method. Eight local minima on the energy hypersurface of the title compound were used to describe the conformer equilibrium mixture. The geometries of these conformers were calculated employing one-determinant ab initio calculations using the split valence 6-31G* basis set. Boltzmann factors were then obtained using relative energies calculated with three different basis sets and including correlation(MP2)-and zero point vibrational energy. Comparing the sign of the observed and calculated longest wavelength Cotton effect, we assign an absolute configuration to the compound. This assignment was verified by means of X-ray structure determination of one of the enantiomers’ α-methoxy-α-trifluoromethylphenyl aceticacid (MTPA, Mosher’s reagent) derivative.

We observed 1 H and 2 H NMR spectra, 1 H NMR spin-lattice relaxation times, and electrical con-ductivities of water-saturated and anhydrous tetramethylammonium(TMA)-saponites between 100 and 415 K. The very weakly bound cations produced narrow 1 H and 2 H NMR lines observed in both specimens down to 150 K. The temperature dependence of the 'H NMR spin-lattice relaxation times in the water-saturated and anhydrous samples gave asymmetric minima attributable to the heteroge-neous overall rotation and self-diffusion of the cations. The inhomogeneity of the cationic motions in the anhydrous TMA-saponite was greater than in the water-saturated one. From measurements of the electrical conductivity of anhydrous TMA-saponite a large anisotropic cation-diffusivity was concluded.

Series of polyradical systems having a preponderance of common eigenvalues (strongly sub-spectral) are identified, and their structural relationships studied. A framework for the analysis and molecular modeling of graphite-related polymers is provided by an infinite two-dimensional mapping. Some analytical expressions are derived. Aryl polyradical dendrimers form numerous strongly sub-spectral sets. Potential conductive/ferromagnetic properties are indicated. Collections of subspectral structures (molecular graphs) and their eigenvalues are tabulated for the first time.

The local coordination of europium in vitreous Eu metaphosphate has been investigated, using information obtainable from crystalline EuP 3 O 9 . One glassy sample and one crystalline sample of nominal EuP 3 O 9 composition were examined by X-ray diffraction. The description of the close coordination of Eu, deduced from the orthorhombic structure of the crystalline sample, was used as a model for the amorphous situation. Besides, as a monoclinic form of Eu metaphosphate is also reported to exist, a second model was deduced from this structure, starting from the isomorphous monoclinic Yb metaphosphate. Best fitting calculations indicated that orthorhombic coordination is the better model for the short range order of europium in the vitreous metaphosphate.

The avalanche statistics of some piles of two types of sand are studied theoretically. Both symmetrical and asymmetrical piles do not preserve the behaviour of self-organized critically. We suggest a distribution (we call it Fisher distribution) interpolating between fractal and Levy-Weibull distributions which describes these dynamics.

Mean amplitudes of vibration for the recently described planar pentagonal IF 2- 5 anion have been calculated, from vibrational spectroscopic data over a wide temperature range. The results are briefly discussed and some comparisons with related species are made.