Volume 41, Issue 4

The geometric properties of the di-m eron solution to the SU (2) Yang-Mills equations are studied in detail. The essential geometric structure of this solution is that of a locally symmetric space endowed with a Riemannian structure which is conformally flat. The di-meron solution is representable by an integrable 3-distribution over Euclidean 4-space. The corresponding integral surfaces are obtained in analytic form.

Experiments have been carried out on the properties of a hollow cathode as an ion-source. The measured electron density, ion and neutral temperatures and drift velocities have been compared with predictions from the conservation laws for matter, momentum and energy. Very large exit drift velocities of ions and neutrals are observed. The magnitude and direction, against the electric field, can be explained on the basis of the momentum balance. At weak magnetic field strengths even supersonic drift velocities are found. The charge flux carried by the ions is about five percent of the net arc current. For small flows, the ionized fraction of the gas supply approaches 100%. The neutral particle density outside the cathode consist of a fraction drifting with a large velocity out of the cathode and a fraction of cool background atoms. The change of the ratio of these fractions with increasing distance to the cathode causes the average neutral particle drift to decrease very rapidly. Finally, an analysis of the overall cathode power balance is given.

We have derived a modified KdV equation with x dependent term in the case of a spatially inhomogeneous plasma using the stretched co-ordinate system by Asano. Exact and perturbation solutions derived from inverse scattering method are discussed.

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.

The Keating force field of tetrahedral XY 4 molecules is defined in analogy with valence and central force fields. The applicability of the Keating coordinates versus valence and central coordinates is tested by different approaches. The general conclusion goes in favour of the Keating coordinates.

X-band EPR measurements of Ni-doped BaZnF 4 crystals revealed presence of three centers. Well-resolved hyperfine structure from 19 F nuclei at suitable orientations allowed assignment of the most intense spectrum to single ions on Ba sites. The occupation of Zn sites is considerably lower. The third spectrum is assigned to pairs of Ni 2+ ions on adjacent Ba sites. Attempts to correlate the zero-field splitting (ZFS) patterns of the single ion spectra with the distortions of the first coordination spheres of Ba and Zn resp. with a single intrinsic ZFS parameter for both bridging and nonbridging ligands were equally unsuccessful as in the case of Mn 2+ .

In the following we give an outline of 14 N 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.

The nitrogen 14 N 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.

Nine isotopic species of gauche- and seven isotopic forms of rra«.s-isobutyraldehyde, (CH 3 ) 2 CHCHO, have been studied by DRM microwave spectroscopy to determine dihedral angles within and between the two rotameric conformations. In the gauche conformation one methyl group (subscript 3) eclipses the oxygen atom exactly, and best compatibility with the isotopic data is obtained when the two carbon-to-methyl bonds are assumed to be of equal length. The isotopic data for the less stable trans rotamer do not allow unequivocal determination of the bondlengths in the isobutyl skeleton, but bond angles and dihedral angles are determined satisfactorily. For both rotamers the geometry of the methyl groups was assumed with C - H = 1.088 Å and ∠ CCH = 110.2°. The following bondlenghts (in Å) and angles (in degrees) are best compatible with the isotopic data: [xxx] The structural differences between the two rotamers are explained as due to repulsion between the bonds at either end of the rotameric axis.

N,N'-Bis-salicyloyl-hydrazine (BSH) is a very efficient copper deactivator. In this study the three dimensional structure of the copper-BSH complex was investigated with a cryotransmission- electron microscope and sterical and energetic calculations. The neat copper-BSH complex forms a nearly amorphous polymer. By absorption of e.g. gaseous ammonia a hexagonal structure shows up without fundamentally transforming the conformation of the complex. The most dominant lattice periodicities are 0.9 and 1.1 nm as obtained by electron microscopical imaging, electron diffraction and sterical calculations. The model shows that copper is very well shielded in the complex by the surrounding BSH-molecules. Due to this, copper is perfectly deactivated.

pK Spectroscopic manifestations of protonation of the trimethylated pyrichrominium ion studied previously experimentally [1] are investigated using a semiempirical INDO/S Cl method. Singlet and triplet energy levels of the free ion and several protonated species are calculated, and transition energies and oscillator strengths are compared with experimental spectra. Calculated charge densities on nitrogen atoms are correlated with experimental values for the ground and lowest excited singlet and triplet states. The possibility of the proton transfer reaction (phototautomerization) in the lowest excited singlet state of monoprotonated species is discussed on the basis of INDO/S Cl calculations, fluorescence and absorption spectroscopy.

The electrical resistivity of thin palladium films deposited on amorphous substrates is measured in dependence on film thickness. The data are interpreted with the help of a statistical model taking into account structural information obtained from AES, TEM and x-ray diffraction texture analysis. The steep decrease of resistivity in the ultra-thin thickness region can be immediately correlated with the formation of coherent areas in the films. A more flattened course is reached at about 8 nm thickness where a continuous film structure develops.

The polarizabilities of some primary, secondary, and tertiary amines have been calculated with the MINDO/3-FP-method. The calculated values are found to correlate with the experimental polarizabilities and with those determined by the method of Miller and Savchik in a satisfying manner. In addition atomic polarizabilities have been calculated according to the method of Metzger. Averaging over the calculated mean atomic polarizabilities of hydrogen, carbon, and nitrogen yields increments which, when used to recalculate molecular polarizabilities, lead to values which correlate in an excellent manner with those determined from densities and refraction indices by means of the Lorenz-Lorentz-equation. Because different nitrogen increments have been determined for primary, secondary and tertiary amines, the parameters presented here make it possible to distinguish between constitutional isomers as long as they belong to different groups (i.e. primary, secondary, and tertiary amines), something which cannot be done using the method of Miller and Savchik. The increments derived do not only allow to predict the polarizabilities of primary, secondary and tertiary amines but can be used to calculate the corresponding values for hydrazines and polyfunctional amines with equal success.

In pressure jump experiments on the phase separation of binary liquid mixtures of cyclohexane + methanol, an organisation of the finely dispersed precipitate could be observed to give a macroscopic dissipative structure during the early stages of the ageing process of the newly formed phase. Preliminary phenomenological investigations suggest a mechanism similar to the Rayleigh-Benard instability (RBI) and the Soret-driven instability (SDI).

The L series of the X-ray spectrum of technetium was measured between 400 and 600 pm using the linear spectrometer of an X-ray microanalyzer. The wavelengths and relative intensities of ten identified lines are given.