Spectrophotometric and spectrofluorometric determination of zinc and cadmium with 2,2'-pyridil bis(2-quinolylhydrazone)

The chelating ligand, 2,2'-pyridil bis(2-quinolylhydrazone), has been used for the spectrophotometric determination of zinc and cadmium in synthetic samples. The molar absorptivities of these metal complexes in 80% ethanol-water solution at pH 8 were found to be 4.60 x 10(4) and 5.10 x 10(4) 1.mole(-1).cm(-1) for zinc and cadmium respectively. Beer's law was obeyed for metal-ion concentrations between 1.0 x 10(-6) and 2.5 x 10(-5)M. The limits of detection were found to be 52 and 79 ng ml for zinc and cadmium respectively. The complexes fluoresced in 80% ethanol-water at pH 8 for zinc and at pH 10 for cadmium. The linear range for fluorescence as a function of metal-ion concentration was found to be 5 x 10(-7)-5 x 10(-6)M for both zinc and cadmium. Transition-metal ions interfere severely with both the spectrophotometric and fluorimetric determinations, and must be removed beforehand. An ion-exchange procedure is suitable for this.     

Massenspektrometrische Untersuchung der Gaszusammensetzung w?hrend der Bildung von Pyrokohlenstoff aus Methan

Zusammenfassung Die Änderung der Gaszusammensetzung während der Bildung und Abscheidung von Pyrokohlenstoff auf einer heißen Wolframdrahtoberfläche wurde mit Hilfe massenspektrometrischer Analyse verfolgt sowie die auf und in dem Draht stattfindenden Prozesse anhand seines elektrischen Widerstandes und der aufgenommenen Heizleistung registriert. Das Reaktionsgefäß war ein Quarzglaskolben, der Methan als Pyrolysegas enthielt (100 Torr) und in dessen Mitte der Wolframdraht gespannt war. Die Versuche wurden im Temperaturbereich von etwa 1650–2400° C durchgeführt, wobei die Oberflächentemperatur des Drahtes während eines Versuches konstant gehalten wurde.Wie die Korrelation der massenspektrometrischen Ergebnisse mit dem Verlauf des elektrischen Widerstandes ergab, läßt sich der Pyrolysevorgang in eine Anlaufphase und eine Beschichtungsphase unterteilen. Die Länge der Anlaufphase ändert sich exponentiell mit dem reziproken Wert der Temperatur. Während dieses Abschnittes werden in der Gasphase hauptsächlich Wasserstoff, Äthan und Äthen gebildet. In der Beschichtungsphase werden im wesentlichen Äthin und Wasserstoff erzeugt, Äthan und Äthen dagegen werden wieder abgebaut. Es zeigte sich, daß die Reihenfolge, in der die einzelnen Pyrolyseprodukte ihre Maximalmengen im Kolben erreichen, einem abnehmenden H/C-Verhältnis entspricht. Die Äthinmenge erreichte erst nach dem Abschalten der Drahtheizung ihren Maximalwert. Überhaupt wurden die Reaktionen in der Gasphase durch das Abschalten der Drahtheizung nicht beendet, sondern liefen noch lange Zeit weiter.

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Mass-spectrometric analysis of gas-composition during the formation of pyrolytic carbon from methane

The change of gas composition during formation and deposition of pyrolytic carbon on the surface of hot tungsten wires was measured by mass-spectrometric analysis. Processes affecting the wire were observed by measuring its electrical resistance and the take-up of power. The reaction vessel was a quartz glass bulb filled with 100 Torr methane gas. In the middle of this bulb the tungsten wire was fastened. The experiments were made within a temperature range of approximately 1650 to 2400° C. However, during any experiment the temperature of the surface of the wire was kept constant. The correlation between the mass-spectrometric results and the behaviour of the electrical resistance shows that the dynamics of pyrolysis can be separated into two periods: a starting period and a deposition period. The duration of the starting period depends exponentially upon the reciprocal value of temperature. During this period mainly hydrogen, ethane and ethylene are produced in the gas phase. During the deposition period, however, mainly acetylene and hydrogen are produced, but the amounts of ethane and ethylene were diminished.From the results it can be seen that the specific gaseous products reach their maximum quantities in the bulb with a decreasing H/C-ratio. Furthermore, the chemical reactions in the gas phase were not stopped by switching off the current, but continued for a long time afterwards. Acetylene reached its maximum quantity in the bulb after switching off the current.

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Herrn Prof. Dr. H. Specker zum 60. Geburtstag gewidmet.     

Comparison of the electronic structure of different perylene‐based dye‐aggregates

Aggregates of functionalized polycyclic aromatic molecules like perylene derivatives differ in important optoelectronic properties such as absorption and emission spectra or exciton diffusion lengths. Although those differences are well known, it is not fully understood if they are caused by variations in the geometrical orientation of the molecules within the aggregates, variations in the electronic structures of the dye aggregates or interplay of both. As this knowledge is of interest for the development of materials with optimized functionalities, we investigate this question by comparing the electronic structures of dimer systems of representative perylene‐based chromophores. The study comprises dimers of perylene, 3,4,9,10‐perylene tetracarboxylic acid bisimide (PBI), 3,4,9,10‐perylene tetracarboxylic acid dianhydride (PTCDA), and diindeno perylene (DIP). Potential energy curves (PECs) and characters of those electronic states are investigated which determine the optoelectronic properties. The computations use the spin‐component‐scaled approximate coupled‐cluster second‐order method (SCS‐CC2), which describes electronic states of predominately neutral excited (NE) and charge transfer (CT) character equally well. Our results show that the characters of the excited states change significantly with the intermolecular orientation and often represent significant mixtures of NE and CT characters. However, PECs and electronic structures of the investigated perylene derivatives are almost independent of the substitution patterns of the perylene core indicating that the observed differences in the optoelectronic properties mainly result from the geometrical structure of the dye aggregate. It also hints at the fact that optical properties can be computed from less‐substituted model compounds if a proper aggregate geometry is chosen. © 2012 Wiley Periodicals, Inc.     

The high‐resolution diffraction beamline P08 at PETRA III

The new third‐generation synchrotron radiation source PETRA III located at the Deutsches Elektronen‐Synchrotron DESY in Hamburg, Germany, has been operational since the second half of 2009. PETRA III is designed to deliver hard X‐ray beams with very high brilliance. As one of the first beamlines of PETRA III the high‐resolution diffraction beamline P08 is fully operational. P08 is specialized in X‐ray scattering and diffraction experiments on solids and liquids where extreme high resolution in reciprocal space is required. The resolving power results in the high‐quality PETRA III beam and unique optical elements such as a large‐offset monochromator and beryllium lens changers. A high‐precision six‐circle diffractometer for solid samples and a specially designed liquid diffractometer are installed in the experimental hutch. Regular users have been accepted since summer 2010.     

Compound clusters of heavy post-transition elements

Neutral binary clusters of Pb-As, Pb-Se, Pb-Te, Bi-In and Bi-Te are generated by inert gas condensation in a double oven source and probed by electron impact. Cluster ions corresponding to the Zintl polyanions Pb ₅ ^2? and Pb ₉ ^4? with respect to atom and valence electron number, are strongly enriched by electron induced dissociation ((Pb₂As₃)⁺, (Bi₄In)⁺, (Pb₄As₅)⁺, (Bi₇In₂)⁺). For the corresponding systems, no other compound cluster ions are enriched in a comparable manner. Enhanced stability is found for (Pb_n?1As)⁺ (n=7, 10, 13) and (Bi₃Te)⁺, which are isoelectronic with neutral ‘magic’ Pb_n clusters and the very stable Bi₄ molecule, respectively.     

Superconducting lead cluster films with particle size dependent reduction ofT c

To investigate films of metal clusters, a neutral lead cluster beam, generated by inert gas aggregation, is characterized via time-of-flight mass spectroscopy and subsequently used for growing a thin film (d=100 Å) on a cold sapphire substrate. In an annealing program the temperature dependence of the electrical resistance of the film is determined by the dc 4-probe technique. Directly after deposition a superconducting transition atT _c =5.6 K is observed which is shifted to higher temperatures with increasing annealing temperature (T _c =6.5 K after annealing at room temperature).     

Convergence analysis of non-conforming Trigonometric Finite Wave Elements

Trigonometric Finite Wave Elements (TFWE) are finite elements for solving problems in computational optics. The solution of those problems consist of highly oscillatory waves. TFWE are designed for obtaining optimal approximation properties for such kinds of waves with a changing wave number k. In this article, we study the convergence properties of 2-dimensional non-conforming TFWE by applying Strang’s Lemma.     

Tetracene film morphology: Comparative atomic force microscopy, X-ray diffraction and ellipsometry investigations

X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response.     

Efficient Ritz-Galerkin Discretization of PDEs with Variable Coefficients in arbitrary Dimensions using Sparse Grids

Sparse grids can be used to discretize elliptic differential equations of second order on a d-dimensional cube. Using the Ritz-Galerkin discretization, one obtains a linear equation system with 𝒪 (N (log N)^d−1) unknowns. The corresponding discretization error is 𝒪 (N⁻¹ (log N)^d−1) in the H¹-norm. A major difficulty in using this sparse grid discretization is the complexity of the related stiffness matrix. To reduce the complexity of the sparse grid discretization matrix, we apply prewavelets and a discretization with semi-orthogonality. Furthermore, a recursive algorithm is used, which performs a matrix vector multiplication with the stiffness matrix by 𝒪 (N (log N)^d−1) operations. Simulation results up to level 10 are presented for a 6-dimensional Helmholtz problem with variable coefficients. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)