Zur Bildungskinetik der F-Folgezentren in KCl

Following the same procedure as in part I the formation of Z₁-centers under Flight irradiation was investigated in additively colored KCl crystals doped with Ca⁺⁺ and Sr⁺⁺ ions. The measurements show that again F′-centers and empty anion vacancies are the first reaction product and determine the rate of Z₁-center formation. The temperature dependence and rate of the Z₁-center formation is in agreement with the corresponding results on F _A -center formation, demonstrating that Z₁-centers are formed as the consequence of an ionic process and not a mere electronic transfer. It is concluded that again empty anion vacancies or F′ centers diffuse randomly in the lattice (activation energy 0.6 eV) until they are captured at an impurity site. Arguments are presented that these impurities are divalent cation/vacancy complexes, so that the model of the Z₁-center should be a combination of the F-center with this complex. The independence of the Z₁-band of the nature of the divalent cation indicates the assoziation of the F-center to the vacancy-side of the complex. A characteristic delay period in the Z₁-center formation can be accounted for by a non-statistical distribution of F-centers and divalent cations to each other. This is a necessary consequence of the high temperature dynamical equilibrium between these imperfections which is frozen in by the quenching of additively colored crystals. A direct proof for this interpretation is the absence of the delay period in crystals where the F-centers are formed by x-irradiation at room temperature.     

Total Synthesis of (+)-Erogorgiaene and the Pseudopterosin A−F Aglycone via Enantioselective Cobalt-Catalyzed Hydrovinylation

Due to their pronounced bioactivity and limited availability from natural resources, metabolites of the soft coral Pseudopterogorgia elisabethae, such as erogorgiaene and the pseudopterosines, represent important target molecules for chemical synthesis. We have now developed a particularly short and efficient route towards these marine diterpenes exploiting an operationally convenient enantioselective cobalt-catalyzed hydrovinylation as the chirogenic step. Other noteworthy C−C bond forming transformations include diastereoselective Lewis acid-mediated cyclizations, a Suzuki coupling and a carbonyl ene reaction. Starting from 4-methyl-styrene the anti-tubercular agent (+)-erogorgiaene (>98 % ee) was prepared in only 7 steps with 46 % overall yield. In addition, the synthesis of the pseudopterosin A aglycone was achieved in 12 steps with 30 % overall yield and, surprisingly, was found to exhibit a similar anti-inflammatory activity (inhibition of LPS-induced NF-κB activation) as a natural mixture of pseudopterosins A−D or iso-pseudopterosin A, prepared by β-D-xylosylation of the synthetic aglycone.     

The structure and lattice dynamics of RbBr(1 0 0) and RbI(1 0 0) single crystal surfaces: A tensor low energy electron diffraction analysis

The structure and lattice dynamics of RbBr(1 0 0) and RbI(1 0 0) single crystal surfaces cleaved under UHV conditions were investigated by means of low energy electron diffraction (LEED) at temperatures of 156 K and 183 K, respectively. Since RbBr and RbI are insulators the experiments were carried out with a microchannel plate LEED system at very low primary currents (5 nA). For both materials four different diffraction orders could be observed. Diffraction patterns were recorded over an energy range from 30 eV to 220 eV in increments of 2 eV and I(V) curves for each spot were extracted. The I(V) curves were analyzed using the tensor LEED approach. For both alkali halide substrates surface structures of (1 × 1) periodicity close to the truncated bulk structure were found. For RbBr, the first interlayer distance is reduced by about 2.2%, where the Rb⁺ cations in the topmost layer are shifted inwards by 0.06(3) Å, and the anions also exhibit an inward shift which is however smaller (0.04(3) Å). The root mean square vibrational amplitudes are enlarged by a factor of 1.3 for Rb⁺ and 1.25 for Br⁻, respectively. For RbI(1 0 0) the cations of the topmost layer are shifted inwards by 0.07(3) Å and the anions outwards by 0.02(1) Å. The vibrational amplitudes of the ions are not enlarged as for RbBr but close to the corresponding bulk values.     

Strongly non-linear transverse envelope solitons

Solitary wave solutions of the coupled equations for transverse high frequency waves and the low frequency ion motion (equations of continuity and momentum) are investigated.     

Die Photoionenspektren von SCl2, S2Cl2 und S2Br2

Photoionization Mass Spectra of SCl₂, S₂Cl₂, and S₂Br₂ Photoionization mass spectra of SCl₂, S₂Cl₂, and S₂Br₂ have been measured. Heats of formation, bond energies, and ionization potentials of fragments have been calculated from appearance potentials.     

Photoionization mass spectrometry of molecular clusters using synchrotron radiation

The photoionization and dissociative ionization of molecular aggregates using synchrotron radiation is reported. The main objective of the review is to consider the intracluster relaxation processes after ionization. For hydrogen-bonded systems proton transfer is dominant. For small clusters (n<4) appearance potentials, ionization potentials, absolute proton affinities, proton solvation energies and intermolecular bond energies in the ionic clusters are deduced. For van der Waals aggregates proton transfer can also be used to characterize the intermolecular bond in the ionic cluster. Aggregates of CH₄, SiH₄, CH₃F show proton transfer in contrast to simple aromatic compounds, which reveal no proton transfer. From the fragmentation pattern and appearance potentials relaxation by intracluster ion molecule reactions is discussed. In heterogeneous clusters intracluster Penning ionization is observed. The shift of the charge transfer resonances depends on the π-electron density in the aromatic system. The width and spectral position of these resonances are influenced by the cluster size.     

Spurenelementbestimmung in Luftstaubproben mittels Neutronenaktivierung

Zusammenfassung Die Neutronenaktivierungsanalyse kann zur Bestimmung von Spurenelementen in Luftstaubproben auch bei Sammelzeiten von nur wenigen Stunden vorteilhaft eingesetzt werden. Für die Sammeltechnik haben sich Cellulose-Papierfilter als besonders spurenarm erwiesen. Für die meisten Elemente sind die Abscheidegrade befriedigend. In einer Reaktor-Kurzzeitbestrahlung von ca. 1 min können die Elemente Se, V, Al, Mg, Br, Cl, In, Mn, in einer nachgeschalteten Langzeitbestrahlung von ca. 1 Tag die Elemente Na, K, Cu, As, W, La, Cd, Au, Sb, Sm, Ca, Fe, Co, Zn, Cr, Sc quantitativ analysiert werden. Im Kernforschungszentrum Karlsruhe und an der Autobahn Karlsruhe—Bruchsal wurden Luftstaubkonzentrationen für die Elemente Se, V, Br, Mn, Cu, As, Zn, Fe, Co ermittelt. Erhöhte Werte an der Autobahn wurden lediglich für Brom gefunden. Blei, mit Atomabsorption bestimmt, verhält sich analog wie Brom.Zu danken ist Herrn Prof. C. Keller, der die Durchführung der Bleianalysen mittels Atomabsorption im Institut für Radiochemie der GfK Karlsruhe ermöglicht hat.     

Decoupling by a projection

The asymptotic behaviour for μ→∞ of the family H+μP is investigated, where H is a semi-bounded but not bounded selfadjoint operator, P is an orthoprojection, H is local with respect to $\text{P}\text{?}\text{=1?P}$. A characterization of the Friedrichs extension of

by the strong resolvent convergence limit of the family H+μP (which exists) is given. Applications to differential operators and strengthening of the main result (as to convergence with respect to the trace norm for some power of the resolvent) are discussed. Also an application to certain two space scattering systems is given.