Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2)

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.     

Über die in einem einfachen Verlustsystem induzierten stochastischen Prozesse

Zusammenfassung Zweck dieser Untersuchungen ist es, für einGI|G|1) — Servicesystem ohne Warteplätze die Prozesse der von diesem System abgewiesenen Kunden bzw. nach erfolgtem Service ausgeschiedenen Kunden im Hinblick auf ihre Verwendung als Eingangsprozesse für weitere Servicesysteme zu charakterisieren.Für beide Prozesse ist es gelungen, die Anzahl der in einem beliebigen Zeitintervall abgewiesenen bzw. ausgeschiedenen Kunden durch Wahrscheinlichkeitsgesetze zu beschreiben. Darüber hinaus konnten notwendige und hinreichende Bedingungen angegeben werden, wann der Prozeß der ausgeschiedenen Kunden wieder die EigenschaftGI besitzt.

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Summary The purpose of this investigation is, to describe in case of aGI |G|1) — servicesystem without waiting-room the processes of clients refused by this system respectively cast out after having finished service with regard to their applying as input-processes of any other servicesystem.It has been achieved for both processes to set up the probability laws of the number of clients refused respectively cast out during any interval of time.Beyond these results the author has quoted necessary and sufficient conditions for the process of clients cast out to possess the propertyGI.

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Diese Untersuchung wurde im Rahmen eines von Herrn Prof. Dr.H. Söhngen geleiteten Forschungsauftrags des BMVtdg durchgeführt.

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Vorgel. v.:H. Söhngen.     

Direct observation of key reaction intermediates on gold clusters

Using ultraviolet photoelectron spectroscopy, we provide direct experimental evidence that di-oxygen species are stable on anionic gold dimer and tetramer clusters at room temperature. The stabilization of molecular oxygen is crucial for the high activities of the low-temperature reactions on gold catalysts.     

Short range order in the isotropic phase of antiferroelectric liquid crystals

Optical activity measurements in the isotropic phase of two antiferroelectric liquid crystal systems in which the chirality can be varied reveal unusual behaviour of the short range order. In one system the phase sequence as the chirality is increased is smectic A, smectic C^*_A, and smectic Q. In the other system the phase sequence is smectic C^*, smectic C^*_A, and smectic Q as the chirality is increased. The short range order of the isotropic phase behaves similarly for these systems, showing mean field behaviour at low chirality and far above the phase transition, but deviating from this behaviour significantly as the chirality is increased and the phase transition is approached. These optical activity results indicate how different is the short range order in the isotropic phase for these antiferroelectric liquid crystal systems and demonstrates the crucial role played by chirality. Past theoretical work that includes smecticlike fluctuations in the calculation of short range order in the isotropic phase is capable of qualitatively explaining these results.