Volume 41, Issue 9

We have investigated the optical absorption of CHCl 3 , CHBr 3 , and CHI 3 in the vacuum ultraviolet, using synchrotron radiation as the light source. A number of absorption features have been observed and are assigned to n - σ*, n - s, n - p, and n - d, one electron excitations.

An improved capillary discharge technique renders possible the production of a plasma jet representing a radially symmetric LTE light source. It shows a special capability of producing plasmas of elements or compounds which exist in the solid state under normal conditions. This plasma source is also suited for the investigation of emission lines of ionised atoms. To demonstrate a possible application, relative transition probabilities of some prominent Cullines in the visible are determined and compared with results of other authors.

In order to describe a steady-state plasma equilibrium in tokamaks, stellarators or other non-axisymmetric configurations, the model of ideal MHD with isotropic plasma pressure is widely used: 0 = - ∇p + j x B . The ideal MHD-model of a toroidal plasma equilibrium requires the existence of closed magnetic surfaces. Several numerical codes have been developed in the past to solve the three-dimensional equilibrium problem, but so far no existence theorem for a solution has been proved. Another difficulty is the formation of magnetic islands and field line ergodisation, which can only be described in terms of ideal MHD if the plasma pressure is constant in the ergodic region. In order to describe the formation of magnetic islands and ergodisation of surfaces properly, additional dissipative terms have to be incorporated to allow decoupling of the plasma and magnetic field. In a collisional plasma, viscosity and inelastic collisions introduce such dissipative processes. In the model used a friction term proportional to the velocity v of the plasma is included. Such a term originates from charge exchange interaction of the plasma with a neutral background. With these modifications, the equilibrium problem reduces to a set of quasilinear elliptic equations for the pressure, the electric potential and the magnetic field. The paper deals with an existence theorem based on the Fixed-Point method of Schauder. It can be shown that a self-consistent and unique equilibrium exists if the friction term is large and the plasma pressure is sufficiently low. The essential role of the dissipative terms is to remove the singularities of the ideal MHD model on rational magnetic surfaces. The problem has a strong similarity to Bénard cell convection, and consequently a similar behaviour such as bifurcation and exchange of stability is expected.

The average rate of entropy production in a homogenous chemical system is investigated in oscillating periodic and chaotic modes as well as in coexisting stationary states. The simulations are based on an abstract model of a chemical reaction system with three freely varying concentrations. Five concentrations are assumed to be kept constant by suitable flows across the boundary. A fixed concentration is used as a control parameter. Second order mass action kinetics with reverse reaction is used. An unexpected result is that periodic modes in some windows in the chaotic interval have higher average rate of entropy production than the surrounding chaotic modes. A chaotic mode coexists with a stable stationary state with smaller entropy production. A unique (unstable) stationary state produces more entropy than the corresponding oscillating mode.

It is shown that all the adjacency relations for the basins of attraction of stable chemical species and transition states can be derived from the topology of the pattern of intrinsic-reaction-coordinate- and-separatix trajectories in the nuclear configuration space. The results are applied to thermal [1,3] sigmatropic rearrangements and they show that even the symmetry-forbidden path proceeds concertedly. The corresponding homological formulas giving the adjacency relations are derived.

By X-Ray small angle scattering the relaxation and crystallization of amorphous Mg 76 Zn 24 was investigated in-situ. Radii of gyration of the different phases developing during the annealing of the sample were determined. By comparison of the small angle scattering results with DSC-results from the literature and the phase diagram the different phases could be identified. The crystallization of amorphous Mg 76 Zn 24 is preceded by the formation of β-phase (Mg 72 Zn 28 )-like inhomogeneities in the amorphous phase. Further annealing leads to the final crystalline phases γ-MgZn and Mg.

The specific electric conductivities of the binary molten mixtures (K,Ag)Cl, (Cs,Ag)Cl, (K,Ag)Br, (Na, Ag)I, (K, Ag)I, and (Cs, Ag)I are determined as functions of temperature and composition. For 950 K, 1000 K, 1050 K, and 1100 K the equivalent conductivities and the ionic conductivities of the cations with reference to the common anion are evaluated in dependence on the composition.

Hexasubstituted tribenzocyclononene derivatives with R = -OC(O)C 6 H 4 C n H 2n+i and R = -OC(O)C 6 H 4 OC n H 2n+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.

A simple procedure to find solutions of the hydrodynamic Stokes equations is given. The procedure is used to determine the linear modes of a newtonian fluid in a pipe of circular cross section. Compressibility, shear and bulk viscosity are included, and no restrictions on the symmetry of the modes are made. Furthermore an infinite set of exact solutions of the Navier-Stokes equations is presented.

The structural changes of (NH 4 ) 2 Pb[Cu(NO 2 ) 6 ] crystals during the phase transitions at 316, 287, and 95 K were studied by means of a single crystal ESR technique. Anisotropic g values [g ∥ > g ⊥ ) were obtained in the lowest temperature phase IV, whereas the ESR spectra recorded in the intermediate phases III and II, in which the crystal is known to be tetragonally compressed along the c axis, could be interpreted by use of effective g values [g(∥c) < g(⊥c)]. In the highest temperature phase I an isotropic g value was obtained. The phases I, II, and III o f the present complex can be assumed to be very similar to the corresponding phases observed above ~ 250 K for the compounds R 2 Pb[Cu(NO 2 ) 6 ] with R = K, Rb, Cs, and Tl. However, the lowest temperature phase transition transforms the phase III with an antiferrodistortive order of the elongated [Cu(NO 2 ) 6 ] 4- octahedra into the phase IV with a ferrodistortive one. This occurs only for the complex with R = NH 4 and is very unusual. The results of the 14 N NQR experiments already reported for the phases III and IV could be well explained by the present newly proposed model.

The mid-infrared spectrum of 15 N-labeled diazirine has been recorded using a Fourier transform spectrometer at a resolution of 0.08 cm -1 . The v 3 fundamental at 1452.49 cm -1 which essentially corresponds to a symmetric methylene deformation has been analyzed in detail. The rovibrational assignment is given and, using Watson’s A-reduced Hamiltonian, the rotational and centrifugal distortion constants for the v 3 = 1 level could be determined.

The microwave and millimeterwave spectra of CH 3 OCl and CD 3 OCl have been investigated up to 200 GHz and centrifugal distortion constants up to the sixth order have been calculated using both Watson's 5-reduction and van Eijck-Typke operators. Watson’s determinable parameters have been obtained starting from both sets of constants.

We reinvestigated the 14 N quadrupole hyperfine structure (hfs) of the J K-K+ = 1 10 - 1 01 , transition of urea by use of microwave Fourier transform spectroscopy. We resolved eight components of the hfs pattern to provide a precise laboratory experiment for possible radioastronomical searches.