High-resolution small-angle x-ray investigations on poly-o-bromostyrene in benzene solutions

Small-angle x-ray investigations on poly-o-bromostyrene in benzene solution at extremely high resolution (corresponding to a Bragg's value of 3200 Å) proved to be able to link together the ranges covered by small-angle x-ray scattering and light scattering. On the other hand, there are problems encountered in molecular weight determination of chain molecules, since both methods at extremely small angles and at finite concentrations reach the limits of particle scattering. The differing results obtained by means of the two methods for the molecular weight of a rather high molecular weight sample of poly-o-bromostyrene are ascribed to entangelements stabilized by dipole–dipole interactions. These, due to the differing Bragg's angles and concentration ranges in the two methods, affect the experimental results to a different degree.     

Zur hochspannungselektrophoretischen Trennung anorganischer Ionen unter besonderer Berücksichtigung der Platmmetalle

Zusammenfassung Die hochspannungselektrophoretische Wanderung der Halogenokomplexe der Platinmetalle und einer Reihe weiterer anorganischer Ionen wird mit Nitrilotriessigsäure und Äthylendiamintetraessigsäure als Elektrolyt in Abhängigkeit von verschiedenen Versuchsparametern (Elektrolytkonzentration,ph-Wert und Substanzmenge) untersucht. Die Wanderungsgeschwindigkeiten der verschiedenen Metallionen bzw.-komplexe zeigen charakteristische Abstufungen, die sich mit den für die hochspannungselektrophoretische Wanderung gültigen Gesetzmäßigkeiten erklären lassen. Beispielsweise beobachtet man eine Abnahme der Beweglichkeit bei Ersatz von Chlorid- durch Bromidionen (Masseneinfluß), Auswirkungen der vomph bzw. der Elektrolytkonzentration abhängigen unterschiedlichen Komplexierungen zwei- und dreiwertiger Ionen, Einflüsse der auf Hydrolyse zurückgehenden Änderungen der Ligandenzusammensetzung sowie Unterschiede der Wanderungsgeschwindigkeiten als Folge der Komplexierung mit NTE oder AeDTE.Durch die unter bestimmten Bedingungen erreichbare Abstufung der Beweglichkeiten können verschiedene Gemische, unter anderem auch die Chlorokomplexe der meisten Platinmetalle in der Reihenfolge Ir > Os Pt > Rh Pd > Ru (> Rh), getrennt werden. NTE ist dabei für Trennungen besser als AeDTE geeignet.

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The high tension electrophoretic separation of inorganic ions with special reference to the platinum metals. I

Summary The high tension electrophoretic migration of the halogeno complexes of the platinum metals and several other inorganic ions was investigated with nitrilotriacetic acid and ethylenediaminetetraacetic acid as electrolytes in relation to the various experimental parameters (electrolyte concentration,ph-value, and amount of substance). The migration velocities of the various metal ions or complexes exhibit characteristic gradations that may be explained on the basis of the regularities that are valid for the high tension electrophoretic migration. Instances are: a decrease was observed in the mobility when chloride was replaced by bromide ions (mass effect), influence of different complexing of di- and trivalent ions that are related to changes in theph or electrolyte concentration, or influences of the changes due to hydrolysis in the composition of the ligands or alterations in the migration rates resulting from complexing with nitrolotriacetic acid or EDTA.The gradation of the mobility obtained under certain conditions are employed as the basis of a procedure for separating various mixtures, including also the chloro complexes of most of the platinum metals in the succession Ir > Os Pt > Rh Pd > Ru (> Rh). It has been found that NTE is better for separations than EDTA.

     

Boron-boron bonding in pentaborane-9

Calculations of the electronic structure of pentaborane-9 have been carried out using MO, VB, three-centre bond, and NPSO wavefunctions, in order to determine the approximation most suitable for this type of molecule. The best of these wavefunctions as determined by comparison with a tenparameter CI function, was one of the NPSO functions.

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Zusammenfassung Die Elektronenstruktur von Pentaboran-9 wurde unter Verwendung von MO-, VB-, NPSO- und Dreizentrenbindungs-Wellenfunktionen berechnet. Die am besten geeignete unter diesen ist nach einem Vergleich mit einer zehnparametrigen CI-Funktion die NPSO-Funktion.

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Résumé Des calculs de la structure électronique du 9-pentaborane ont été effectués en utilisant des fonctions d'onde M.O., V.B., liaisons à trois centres et NPSO, afin de déterminer l'approximation qui convient le mieux à ce genre de molécule. La meilleure de ces fonctions d'onde, en comparaison d'une fonction d'I.C. à dix paramètres, s'avère l'une des fonctions NPSO.

     

Analytische Probleme der Darstellung radioaktiven Schwefelwasserstoffs mit hoher spezifischer Aktivit?t

Zusammenfassung Es wird ein Verfahren im Mikromaßstab zur Darstellung und Analyse von höchstreinem Schwefelwasserstoff von hoher bis sehr hoher spezifischer Aktivität beschrieben. Durch Anwendung der Adsorptions-Chromatographie und isothermer Destillation konnte bei hohen Ausbeuten der Gehalt an Verunreinigungen unter 10^–2 Molprozent gesenkt werden. Die massenspektrometrische H₂S-Analyse und ihre Problematik wurden ausführlich behandelt. Durch geeignete Versuche und ihre theoretische Interpretation konnte eindeutig nachgewiesen werden, daß im Massenspektrometer durch Nebenreaktionen des H₂S sowohl CS₂ als auch H₂O sekundär gebildet werden, wodurch eine Verfälschung des Analysenergebnisses eintritt.Als Kontrollmethode für die Reinheit des H₂S während des Ablaufes der Sulfidierungsreaktionen im Innern der geschlossenen Apparatur erwies sich die Messung des Tripelpunktdruckes als besonders geeignet. Sie wurde dafür zu einer Mikromethode für nur wenige Milliliter radioaktiven Gases modifiziert, die noch ca. 7 ppm Verunreinigungen zu erfassen erlaubt.

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Analytical problems of the preparation of radioactive hydrogen sulphide of high specific activity

A procedure in micro scale is described for the preparation and analysis of hydrogen sulphide of maximum purity with high to very high specific activity. High yield and impurity contents of less than 10^–2 Mol-% could be achieved by the use of adsorption chromatography and isothermal distillation.The mass-spectrometric H₂S analysis and its problems are discussed in detail. By suitable experiments and their theoretical interpretation it could clearly be shown that CS₂ and H₂O are formed secondarily by side-reactions of hydrogen sulphide in the mass spectrometer, thus causing erroneous results. Measurement of the triple-point pressure proved to be particularly suitable for checking the purity of H₂S during the course of the sulphurizing reactions within the closed apparatus. It has been modified to a micro method for only a few ml of radioactive gases, permitting the determination of about 7 ppm of impurities.

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Der Deutschen Forschungsgemeinschaft und dem Fonds der Chem. Industrie gebührt Dank für die Förderung dieser Untersuchungen.

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Herrn Prof. Dr. E. Asmus zum 60. Geburtstag gewidmet.     

Über das «pK» elektronisch angeregter Azulenium-Kationen

It is shown that azulenium cations in the first electronically excited state S₁ are stronger acids than in the ground state S₀. Their apparent pK″*, obtained from the H₀-dependence of the quenching of the azulenium cation S₁ → S₀ fluorescence does not correspond to a true acid-base equilibrium in the electronically excited state S₁. The pK″* values are kinetically controlled, the rate of reprotonation of azulene in the S₁ state being too low to compete with the internal conversion to S₀.     

Magnetic correlations in Eu x Sr1−x S and the ferromagnet-spin glass transition

Neutron (Bragg and small angle) scattering and susceptibility measurements are used to study magnetic ordering in Eu _x Sr_1–x S with ferromagnetic nearest neighbor exchangeJ ₁ and antiferromagnetic next-nearest neighbor exchangeJ ₂. We present data for 0.50x0.70 which cannot be analyzed within the merely geometrical treatments of percolation theory. Breakdown of ferromagnetism occurs atx _c =0.51, far above the percolation thresholdx _p =0.136, and a spin-glass phase is observed in the intermediate concentration regime. Close tox _c , the ferromagnetic state is also displaced by the spinglass phase at lower temperatures. Both properties are a general characteristic of diluted systems with competing interactions. An effective decoupling of finite magnetic clusters from the ferromagnetic net arises from frustration, which enhances the ground-state entropy. Anomalous properties below the Curie temperatureT _c as well as atT _c support this microscopic picture.     

Defect structures of ion-implanted α-tin

Single crystalline and polycrystalline -tin has been implanted at room temperature with 80-keV ions of radioactive^119m Sn,¹¹⁹Sb, and^119m Te. The radioactive nuclei decay to the Mössbauer level of¹¹⁹Sn. Mössbauer spectra of the emitted 24-keV radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic¹¹⁹Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s ² configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s ² 5p ² configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO₂ molecules are formed in the bulk. The interstitial¹¹⁹Sn and the¹¹⁹Sn-vacancy pairs are proposed to represent elementary point defects in -tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes.     

Mössbauer spectroscopy with the 93 keV-resonance in67Zn

The procedures and results of high resolution Mössbauer experiments performed with the 93.3 keV resonance in absorbers of⁶⁷ZnO,⁶⁷ZnS (both wurtzite and sphalerite structures),⁶⁷ZnSe,⁶⁷ZnTe and⁶⁷ZnF₂ are reported. An essentially linear dependence between the isomer shift and the Pauling electronegativity of the ligands was found. A value of r ²=+11×10^–3 fm² is estimated. The Mössbauer parameters for both ZnS structures are equal within present limits of error. In particular, no quadrupole interaction was observed in the wurtzite modification. This indicates a nearly identical local symmetry at the Zn site in the two ZnS structures.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany and the Kernfor-schungszentrum Karlsruhe     

Effect of elastic strain and stress on the superconducting transition temperature of quench-condensed films

The volume dependence of the superconducting transition temperatureT _c of amorphous and highly disordered films is investigated by bending the film substrate. The volume coefficientd InT _c /d InV of annealed Sn and Pb films agrees with the volume coefficient known from hydrostatic pressure experiments. This bending technique is applied to superconducting modifications which can be produced only by quench condensation onto a substrate at liquid helium temperature. Amorphous films such as Bi, Ga, Sn₉₀Cu₁₀ and Pb_xBi_1–x, as well as highly disordered Sn and Pb films, are investigated. The relations found between the volume coefficient, the electron-phonon coupling constant and the Grüneisen parameter _G are in reasonable agreement with the volume dependence ofT _c for non-transition metals, obtained on the basis of the McMillan equation. In particular, the results represent an expansion of this kind of investigation to very strong-coupling superconductors.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthdayPaper based in part on a Habilitationsschrift submitted to the Fakultät für Physik, Universität Karlsruhe (TH)