Band 44, Heft 1

The locked-dipole model for reactions between ions and polar molecules is modified by introducing the moment of inertia into the centrifugal term of the interaction potential. The resulting rate coefficients are compared with other models and experimental data.

Small angle neutron scattering (SANS) was done with meltspun amorphous Ni 32 Pd 52 P 16 in the as-quenched state as well as after annealing at 533 K, 570 K. and 607 K, 20 h each. The double logarithmic plot of the structure factor versus the momentum transfer shows linear behaviour with noninteger Porod-slopes. The results are interpreted with the scattering from fractally rough inner surfaces. The as-quenched state contains fluctuations of the scattering length density associated with smooth boundary interfaces. Annealing yields rough boundary interfaces, the roughness being largest after the 570 K annealing. Annealing at the higher temperature of 607 K yields less rough boundary interfaces.

It is shown that it is possible to set up a structural model for the amorphous Fe 90 Zr 10 -aIloy which is in agreement both with diffraction and XANES data, the latter being sensitive to higher than binary correlations.

The maximum entropy method (MEM) is applied to the analysis of the closely spaced nuclear quadrupole resonance spectra of 35 Cl in hexachlorobenzene and 14 N in trarts-azobenzene. The superiority of the MEM to usual FFT spectra is discussed with respect to the precision of frequency measurements and the noise characteristics in broad and noisy NQR spectra.

The optical absorption spectrum of Mn 2+ ions doped in zinc thallium sulphate hexahydrate has been studied at room and liquid nitrogen temperatures. The observed bands are assigned as transitions from the 6 A 1g (S) ground state to various excited quartet levels of Mn 2+ ion in octahedral symmetry. The fine structure observed in the 4 T 2g (D) band is explained as due to spin-orbit interaction. All the observed band positions have been fitted with the parameters B, C, Dq and α .

The temperature dependence of the density of N(p-n-nonyloxy benzylidene)p-n-butylaniline (90.4) is studied. The compound exhibits smectic A, smectic F and smetic G phases. The isotropicsmectic A (IA) and smetic A-smectic F phase transitions are found to be first order. The calculated thermal expansion coefficient and differential scanning calorimetry support the density results. The density jumps, associated enthalpies and the estimated pressure dependence of the transition temperatures for IA transitions in other compounds are also presented.

The electrical behaviour of La 2-x Sr x CuO 4-y solid solutions (with x = 0, x = 0.025, x = 0.05, and x = 0.15) at temperatures between 10 and 900 K and under different oxygen partial pressure p O2 = 1 ÷ 10 -6 atm) has been investigated. The samples prepared and measured under an O 2 flux (i.e., with y = 0) show a superconducting transition with T c = 46, 29. 37 K for x = 0. 0.05 and 0.15, respectively. The samples with x = 0.025, y = 0, and x = 0, y ≠ 0 exhibit no sign of superconductivity. In the temperature range 100-900 K. La 2 CuO 4 is semiconducting, whereas the electrical resistivity is independent of temperature for the x =0.025 sample, and the x = 0.05 and x = 0.15 are metallic.

Double Resonance Modulation (DRM) microwave spectroscopy has allowed the determination of the complete substitution structure of normal, mono-deuterated and perdeuterated 1,3.4-thiadiazole (N 2 C 2 H 2 S). The shift of the centre of gravity between the normal and the d 2 -form and the swing of inertia! axes relative to the C 2v symmetrical forms in the 2-d 1 -species have been used to revise the small coordinates of hydrogen and deuterium atoms. Bond lengths (in Å) and bond angles (in degrees), with uncertainties covering all three molecular forms, are found as follows: The results suggest that the shift and the swing of inertial axes between different ‘parent’ forms, which can both be determined from the moments of multiply substituted molecular isotopes, may be used with advantage to refine the position of near-axis atoms.

The 79 Br and 127 I NQR spectra were investigated for 1,2-diammoniumethane dibromide, -diiodide, 1,3-diammoniumpropane dibromide, -diiodide, piperazinium dibromide monohydrate, and piperazinium monoiodide in the temperature range 77 ≦ T/K ≦ 420. Phase transitions could be observed for the three iodides. The temperatures for the phase transitions are: 400 K and 404 K for 1,2-diammoniumethane diiodide, 366 K for 1,3-diammoniumpropane diiodide, and 196 K for piperazinium monoiodide. The crystal structures were determined for the piperazinium compounds. Piperazinium dibromide monohydrate crystallizes monoclinic, space group C2/c, with a= 1148.7 pm, 0 = 590.5 pm, c= 1501.6pm, β = 118.18°, and Z = 4. For piperazinium monoiodide the orthorhombic space group Pmn 2 1 was found with a = 958.1 pm, b = 776.9 pm, c = 989.3 pm, Z = 4. Hydrogen bonds N - H ... X with X = Br, I were compared with literature data.

The dynamic dielectric properties of diluted aqueous solutions of propylene carbonate, ethylene carbonate (EC). 4-butyrolactone and cyclohexanone (CH) have been measured at 20 °C. On assuming normal solute relaxation, the water relaxation can be described by two superimposed Debye type contributions, which may be interpreted in terms of a hydration model. Qualitatively, the influence on the water relaxation increases from EC to CH.

Synthetic pyrite crystals doped with halogen (CI, Br) or manganese (Mn) were investigated by ESR at 78 K with an X-band spectrometer and a TE 102 cavity with 100 kc field modulation. The crystals were preferably measured with the directions 〈100〉, 〈110〉, and 〈111〉 parallel to the static magnetic field H O . The ESR spectrum of Mn-doped crystals showed a sextet which can be explained by a spin-Hamiltonian for an electron spin S = 1/2 in interaction with the nuclear spin I = 5/2 of the Mn nucleus for axial symmetry. Due to the observed spin and due to the orientation of the paramagnetic centers the spectra were assigned to Mn 2+ in the low spin state which resides on cation site in the FeS 2 , lattice. In halogen-doped crystals four pairs of lines can be interpreted by the interaction of the two isotopes of I = 3/2, 79 Br, 81 Br and 35 Cl, 37 Cl, respectively, with an electron spin S = 1/2. According to the observed symmetry of the ESR signals the paramagnetic centers can be explained as (S-X) 2- radicals (X = CI, Br) which substitute for the (S 2 ) 2- dumb-bells of pyrite. All crystals evoked extremely narrow ESR lines, especially the halogen-doped crystals with linewidths down to 0.03 mT. Excellent agreement between measured and calculated spectra up to the finest details has been obtained.

We have resolved and analysed the nuclear quadrupole hyperfine structure in the rotational spectra of 4-pyridinecarbaldehyde and 3-pyridinecarbaldehyde, C 5 H 4 NCHO. The results are discussed and compared to those of previously measured pyridine compounds. The electron withdrawing effect of the aldehyde-function, in the 3- and 4-position at the ring system, has been calculated, and the differences in the results are discussed.

Seven solid phases including three metastable phases of (CH 3 ) 3 CNH 3 NO 3 were revealed by differential thermal analysis in the temperature range between 80 K and the melting point (418 K), and cationic dynamics in each phase was studied by use of 1 H-NMR techniques. The highesttemperature solid phase obtainable above 412 K was found to be an ionic plastic phase, where the cations perform rapid translational self-diffusion and overall rotation about their center of gravity.

The higher order mode distortion in measuring dielectric constants on high lossy, high permittivity liquids in the GHz range is investigated by a simulation procedure as well as by experiment. For this, a homodyne method for measuring ε* is introduced in analogy to precision EPR-work.

It is shown that a ZnS:Eu phosphor with line emission spectrum can be prepared without coactivator introduction, contrary to previous results. The broad-band emission established in ZnS: Eu, Li is ascribed to the formation of Eu 2+ centres due to the removal of lattice stress by lithium incorporation.

We present an investigation and interpretation of the 11 B-quadrupole hyperfine structure (hfs) in the rotational spectrum of phenyldifluoroborane in the torsional ground state of the BF 2 group. The measurements were made with a microwave Fourier transform (MWFT) spectrometer in the frequency range between 5 and 8 GHz.

The work functions and thermionic constants of the hexagonal tungsten bronzes K 0.30 WO 3 (φ = 1.76 eV, A = 3 A/ cm 2 K 2 ) and Rb 0.30 WO 3 (φ = 1.88 eV, A = 10 A/cm 2 K 2 ) are determined and compared with those of the corresponding alkaline metals and hexagonal Cs 0.305 WO 3 .