Density functional theory study of nine-atom germanium clusters: effect of electron count on cluster geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(9)(z) clusters (z = -6, -4, -3, -2, 0, +2, and +4) starting from three different initial configurations. Double-zeta quality LANL2DZ basis functions extended by adding one set of polarization (d) and one set of diffuse (p) functions were used. The global minimum for Ge(9)(2)(-) is the tricapped trigonal prism expected by Wade's rules for a 2n + 2 skeletal electron structure. An elongated tricapped trigonal prism is the global minimum for Ge(9)(4)(-) similar to the experimentally found structure for the isoelectronic Bi(9)(5+). However, the capped square antiprism predicted by Wade's rules for a 2n + 4 skeletal electron structure is only 0.21 kcal/mol above this global minimum indicating that these two nine-vertex polyhedra have very similar energies in this system. Tricapped trigonal prismatic structures are found for both singlet and triplet Ge(9)(6)(-), with the latter being lower in energy by 3.66 kcal/mol and far less distorted. The global minimum for the hypoelectronic Ge(9) is a bicapped pentagonal bipyramid. However, a second structure for Ge(9) only 4.54 kcal/mol above this global minimum is the C(2)(v)() flattened tricapped trigonal prism structure found experimentally for the isoelectronic Tl(9)(9)(-). For the even more hypoelectronic Ge(9)(2+), the lowest energy structure consists of an octahedron fused to two trigonal bipyramids. For Ge(9)(4+), the global minimum is an oblate (squashed) pentagonal bipyramid with two pendant Ge vertices.     

Polarity effects on wavelength dependence of the fluorescence quantum yield for indole

The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process.     

Infrared laser induced energy transfer studies in S18O2

Vibrational energy transfer has been studied in S¹⁸O₂, following pumping of the symmetric stretch (ν₁) by a Q-switched CO₂ laser. Fluorescence from the asymmetric stretch (ν₃) is monitored as a function of time following the laser pulse. This fluorescence rises with a rate constant of 74 ± 10 ms^?1 torr^?1, and then decays with a rate constant of 3.6 ± 0.1 ms^?1 torr^?1 for the S¹⁸O₂ itself. The effect of rare gases on the rise and fall rates was also studied. The results agree well with those on S¹⁶O₂ and are consistent with a double V-V picture in which the excitation is distributed rapidly between the stretches, but is shared with the bend much more slowly. This produces molecules in which the stretches are much “hotter” than the bend, giving rise to possibilities of laser action on the stretch-to-bend transitions and mode-selective vibrational enhancement of chemical reactions. Also, new results have been derived on the kinetics of V-V processes in mixtures. V-V transfer in various isotopic mixtures of SO₂ has been studied and the kinetic analysis indicates that S¹⁸O₂ and S¹⁶O₂ exhibit the same V-V rates.     

Modified Potentiometric Sensors for the Separate Determination of Cationic Surfactants

The main electrochemical and performance characteristics of solid-contact sensors for cationic surfactants based on an organic cetylpyridinium–tetraphenylborate ion exchanger were determined. It was found that the surface of the sensors for cationic surfactants can be modified with poly(vinyl chloride) molecular sieves. The modified electrodes can separately determine alkylpyridinium homologues with different lengths of hydrocarbon radicals (C₁₀–C₁₈).     

Complex activators in analytical catalytic reactions

Summary The influence of pairs of carboxylic acids on the oxidation ofp-phenetidine hydrochloride by chlorate and traces of vanadium(V) as catalyst is studied. The activator systems used are sulphosalicylic acid + tartaric acid, sulphosalicylic acid + citric acid, tartaric acid + citric acid. It is shown that in some cases the joint activating effect is much higher than that of either activator alone. The kinetic data obtained with complex activator systems confirm the concept of different types of activating action in the two stages of the catalytic reaction. Some combinations of activators could be used in catalytic analysis.

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Zusammenfassung Der Einfluß von Carbonsäurepaaren auf die Oxydation von p-Phenetidin-hydrochlorid durch Chlorat und Spuren von Vanadin(V) als Katalysator wurde untersucht. Als Aktivierungssysteme wurden Sulfosalicylsäure und Weinsäure, Sulfosalicylsäure und Zitronensäure, Weinsäure und Zitronensäure verwendet. In manchen Fällen ist der gemeinsame Aktivierungseffekt größer als der eines der jeweiligen Aktivatoren allein. Die kinetischen Daten der komplexen Systeme bestätigen die Annahme einer verschiedenartigen Aktivierung der zwei Stufen der katalytischen Reaktion. Manche Aktivatorkombinationen könnten für die katalytische Analyse von Wert sein.

     

Spectrophotometric determination of ruthenium(III) using diphenylcarbazone

Summary The purple violet ruthenium(III)-diphenylcarbazone complex which is formed at p _h 5–7, and has an absorption maximum at 530 nm with molar absorption coefficient 16.2·10⁴l.cm^–1.mole^–1 is suggested for the estimation of 20–125g ruthenium(III) spectrophotometrically in 30–60% ethanol. The complex is stable over p _h range 3.2–8.4. The limits of interference due to foreign ions have been studied.

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Zusammenfassung Der bei p _h 5 bis7 entstehende Ruthenium(III)-Diphenylcarbazon-Komplex hat ein Absorptionsmaximum bei 530 nm und einen Absorptionskoeffizienten von 16,2·10⁴ l.cm^–1.Mol^–1. Die spektrophotometrische Bestimmung von 20 bis 125g Ruthenium(III) in 30 bis 60%igem Äthanol mit Hilfe dieses zwischen p _h 3,2 und 8,4 beständigen Komplexes wurde vorgeschlagen. Die Störung durch Fremdionen wurde geprüft.

     

Zur Existenz von zwei Kristallmodifikationen der Mellitsäure

Zusammenfassung Es wurde röntgenorgraphisch und mit Hilfe derDTA, festgestellt, daß die Mellitsäure nur in einer Modifikation, der orthorhombischen¹, vorliegt. Die Darstellung der Mellitsäure^2,3 wurde in Einzelheiten modifiziert. Die Reinheit der Präparate wurde spektroskopisch, im IR- bzw. UV-Gebiet, und mit Hilfe der Papierchromatographie geprüft.

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by means of X-ray analysis and DTA it was found that mellitic acid exists only in the orthorhombic modification. The preparation of mellitic acid was modified in part. The purity ot the samples obtained was checked by IR-and UV-spectroscopy and by paper chromatography.

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Zur Kenntnis von Salzen einiger aromatischer Polycarbonsäuren, 3. Mitt.; 2. Mitt.:B. Hájek, E. Kálalová undF. Petr, Z. Chem.5, 230 (1965).

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Gewidmet dem Andenken an Professor Dr.Hans Meyer meinen Lehrer an der ehemaligen Deutschen Universität in Prag. Prof.Meyer geboren am 31. März 1871 in Wien, gestorben am 28. November 1942 in Theresienstadt, beschäftigte sich eingehend (mitH. Raudnitz u. a.) mit der Darstellung und Untersuchung der Mellitsäure und ihrer Derivate.     

Production of oxygen enriched air by rapid pressure swing adsorption

A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.It is demonstrated by a simple mathematical model of isothermal single adsorbate pressure swing ad(de)sorption concept on a single adsorbent particle that the specific production rate of a PSA process cannot be indefinitely increased by reducing the cycle time of operation when adsorbate mass transfer resistances are finite.     

Determination of the quaternary compound ciclotropium in human biological material after hydrolysis and derivatization with the fluorophor flunoxaprofen chloride

The quantitative determination of the quaternary spasmolytic compound ciclotropium and its metabolite N-isopropyltropinium is described for human plasma and urine. The analytical procedure consists of ion-pair extraction from biological material, alkaline hydrolysis, subsequent derivatization with the fluorophor flunoxaprofen chloride and separation by high-performance liquid chromatography on a reversed-phase column with fluorimetric monitoring. The detection limits of 0.5 ng/ml in plasma and 10 ng/ml in urine at signal-to-noise ratios higher than 3 permit the determination of pharmacokinetic parameters after therapeutic doses.