Hyperfeinstruktur-Untersuchungen im Rhenium-I-Spektrum

By optical means (i.e. hollow cathode, Fabry-Perot-interferometer and spectrograph) the hyperfine structure of 15 transitions in the Re-I spectrum was investigated. This permits to state the hfs coupling constantsA, B for 15 levels belonging to the configurations (5d ⁵) 6s ², (5d ⁵) 6s 6p, (5d ⁵) 6s 7s, (5d ⁶) 6s, (5d ⁶) 6p and (5d ⁴) 6s ² 6p. It was found that the (5d ⁵) 6s ^{2 6} S _5/2 ground state, too, shows a small hfs. Of its magnetic splitting both size and sign could be determined (A _0,185,187=?2,2±0,4 mK); for a possible quadrupole splitting upper limits were obtained. Estimates of the quadrupole moments resulted inQ _185,187?2,9b. — In the case of two levels (x ⁶ P _7/2 andy ⁶ F _11/2) the hfs analysis raises doubts as to their classification.     

On the addressing problem for directed graphs

The “distance” from vertexu to vertexv in a strongly connected digraph is the number of arcs in a shortest directed path fromu tov. The addressing problem, first formulated in the undirected case by Graham and Pollak, entails the assignment of a string of symbols to each vertex in such a way that the distances between vertices are equal to modified Hamming distances between corresponding strings. A scheme for addressing digraphs is proposed, and the minimum address length is studied both in general and in certain special cases. The problem has some interesting reformulations in terms of matrix factorization and extremal set theory. Supported by NSF grant MCS 84-02054.     

Theg-factor of the 181 keV level of99Tc and hyperfine fields of Tc in Fe,Co, Ni

Theg-factor of the 181 keV-level of⁹⁹Tc has been redetermined by the spin rotation method. Measurements with polycrystalline sources of Tc in Fe, Co, and Ni yielded values of the hyperfine fields at the Tc nucleus. $$\begin{gathered} g = + 1.310(25) \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Fe) = ( - )290(15)kOe \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Co) = ( - )170(5)kOe \hfill \\ H_{hf} (Tc{\mathbf{ }}in{\mathbf{ }}Ni) = - 47.8(1.5)kOe. \hfill \\ \end{gathered} $$      

Schnelle Reaktionen organischer Verbindungen in L?sung

Zusammenfassung Es wird eine einfache Apparatur beschrieben, die die Bestimmung der Geschwindigkeit schneller Reaktionen in Lösung und die Aufnahme der Spektren von instabilen Zwischenprodukten hierbei gestattet.

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Summary A simple apparatus is described for determining the kinetics of fast solution reactions and for measuring the spectra of unstable intermediates.

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Der Deutschen Forschungsgemeinschaft danken wir sehr für die Mittel zum Bau der beschriebenen Apparatur.     

Die gas-chromatographische Untersuchung der Pyrolyseprodukte von Kautschuken

Ohne Zusammenfassung     

Lösungsmitteleffekte in Kernresonanzspektren gesättigter Kohlenwasserstoffe

Proton NMR solvent effects ν(CCl₄) – ν(C₆H₆) have been measured for the methyl groups in 25 saturated cycloalkanes. Magnitude and sign of the Δ values are correlated with the molecular shape. The results are discussed with particular respect to stereochemistry, and they provide a new method for distinguishing between geometrical isomers.     

The high-pressure <Emphasis Type="Bold">α/β</Emphasis> phase transition in lead sulphide (PbS)

The high-pressure behaviour of PbS was investigated by angular dispersive X-ray powder diffraction up to pressures of 6.8 GPa. Experiments were accompanied by first principles calculations at the density functional theory level. By combining both methods reliable data for the elastic properties of rock-salt type α- and high-pressure β-PbS could be obtained. β-PbS could be determined to crystallise in the CrB-type (B33), with space group Cmcm. The reversible ferro-elastic α/β transition is of first order. It is accompanied by a large volume discontinuity of about 5% and a coexistence region of the two phases. A gliding mechanism of {001} bilayers along one of the cubic 〈110〉 directions governs the phase transition which can be described in terms of group/subgroup relationships via a common subgroup, despite its reconstructive character. The quadrupling of the primitive unit cell indicates a wave vector (0, 0,π/ a ) on the Δ-line of the Brillouin zone. Received 11 October 2002 Published online 14 February 2003 RID="a" ID="a"Also at: Institute of Physics of the Czech Academy of Sciences, Cukrovarnicka 10, 16253 Praha 6, Czech Republic e-mail: knorr@min.uni-kiel.de RID="b" ID="b"Present address: University of Cambridge, Cavendish Laboratory (TCM), Madingley Road, Cambridge CB3 0HE, UK RID="c" ID="c"Present address: Johann-Wolfgang Goethe Universit?t, Mineralogisches Institut, Kristallographie, Senckenberganlage 30, D 60054 Frankfurt a.M., Germany     

Present and future experiments with stored exotic nuclei at the FRS-ESR facility

High accuracy mass and lifetime measurements are performed with the combination of the in-flight separator FRS and the cooler-storage ring ESR at GSI. Exotic nuclei are produced via projectile fragmentation and fission at (400–900) MeV/u. This energy range is the basis for unique experimental conditions with bare and few-electron fragments and allows for the first time investigations for decay channels which are rare or strictly forbidden in neutral atoms. New experimental developments and data including the discovery of new isotopes are presented. The comparison of the experimental results with theoretical predictions indicates the potential for improvements of nuclear models. A new generation of experiments will be possible with the advent of the proposed international Facility for Antiproton and Ion Research (FAIR).