Laser spectroscopy of the 1s HFS of H-like ions at a bunched beam in the storage ring ESR

The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in ²⁰⁷Pb⁸¹⁺. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics from an ion beam at relativistic velocities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heptaeder aus verschiedenen Netzen

Ohne Zusammenfassung     

Lebesgue constants for periodic Hermite spline interpolation operators on uniform lattices

We derive a complex line integral representation for the ebyshev norm of periodic spline interpolation operators of odd degree on uniform lattices. Several generalizations are indicated.     

Measurement of the transverse Doppler shift using a stored relativistic7Li+ ion beam

We have performed for the first time precision spectroscopy on a coasting fast⁷Li⁺ ion beam in a storage ring. The ion beam moving with 6.4% speed of light was first electron cooled and then merged with two counterpropagating laser beams acting on two different hyperfine transitions sharing a common upper level (λ-system). One laser was frequency locked to thea ₃ ¹²⁷J₂ hfs frequency component established as a secondary frequency standard at 514 nm. The second laser was tuned over theλ-resonance, which was recorded relative to¹²⁷J₂ hfs components. This experiment is sensitive to the time dilation in fast moving frames and will lead to new limits for the verification of special relatively. The present status of the experiment and perspectives in accuracy are discussed.     

Beitrag zur Mikrobestimmung des aktiven Wasserstoffs

Zusammenfassung Es wird über eine modifizierte Methode zur mikroanalytischen Bestimmung des aktiven Wasserstoffs in organischen Substanzen berichtet. Die von Lieb und Schöniger, als Ersatz der Grignard-Reaktion in die Mikroanalyse eingeführte Umsetzung mit dem wesentlich stärker und auch rascher reagierenden Lithiumaluminiumhydrid, konnte sich trotz vieler Vorteile nicht allgemein durchsetzen. Dies lag in erster Linie daran, daß das reine Lithiumalanat nur in sehr wenigen Lösungsmitteln, die zudem wegen ihres hohen Dampfdruckes für eine exakte Mikrobestimmung ungeeignet sind, löslich ist. Ersetzt man jedoch ein oder mehrere Wasserstoffatome des Alanats durch eine Alkyl- bzw. Alkoxygruppe, so führt dies zu einer wesentlichen Löslichkeitserhöhung. Unter den mög- lichen substituierten Alanaten, die wir auf ihre Brauchbarkeit zur Bestimmung aktiver Wasserstoffatome getestet haben, entsprach insbesondere das Natriumaluminiumdiäthyldihydrid weitgehend unseren Anforderungen. Es ist in Kohlenwasserstoffen, wie auch in stark polaren Lösungsmitteln sehr gut löslich. Dadurch ist auch die Möglichkeit für vergleichende Analysen mit Methylmagnesiumjodid gegeben, wodurch in manchen Fällen auf eine bestimmte Stellung oder auch sterische Hinderung der funktionellen Gruppe in der Molekel geschlossen werden kann. Die Anwendungsbreite wie auch die Genauigkeit der Alanatmethode wird an Hand der Analysendaten zahlreicher Testsubstanzen demonstriert.     

Assessment of Semiempirical Quantum Mechanical Methods for the Evaluation of Protein Structures

The ability to discriminate native structures from computer-generated misfolded ones is key to predicting the three-dimensional structure of a protein from its amino acid sequence. Here we describe an assessment of semiempirical methods for discriminating native protein structures from decoy models. The discrimination of decoys entails an analysis of a large number of protein structures, and provides a large-scale validation of quantum mechanical methods and their ability to accurately model proteins. We combine our analysis of semiempirical methods with a comparison of an AMBER force field to discriminate decoys in conjunction with a continuum solvent model. Protein decoys provide a rigorous and reliable benchmark for the evaluation of scoring functions, not only in their ability to accurately identify native structures but also to be computationally tractable to sample a large set of non-native models.     

Cover Picture

The cover picture shows the structure, determined crystallographically, of the tetrakis(trimethylstannyl)phosphonium cation that is formed with surprising ease from the reaction of P(SnMe(3))(3) with Me(3)SnOTf (OTf=OSO(2)CF(3)) and is isolated as the OTf salt. It is the first completely substituted main group organometallic phosphonium derivative, and, in contrast to the more common tetraorganic-substituted phosphonium cations is only stable in the solid state; in solution it functions as a masked Me(3)Sn(+) reagent. More about this chameleonlike ion and the N(SnMe(3))(4) cation homologue, which is equally dynamic in solution and has unusual long Sn-N bond lengths, is reported by M. Driess et al. on p. 3684 ff.