Asynchronous sampling for ultrafast experiments with low momentum compaction at the ANKA ring

A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented.     

Novel sb induced reconstruction of the (113) surface of ge

Sb induces on Ge(113) a c(2 x 2) reconstruction in which Sb breaks one Ge-Ge bond and occupies an interstitial site, in contrast to Sb adsorption on other Si or Ge surfaces. Sb saturates the three dangling bonds per unit cell of the (113) surface inducing a large strain which is released by occupation of the interstitial site. Two neighboring Sb at interstitial sites form a dimer. The structure has been determined by x-ray diffraction, applying direct methods, and ab initio density-functional-theory calculations. The adsorption geometry and the high binding energy lead one to expect that Sb cannot be used as a surfactant for the growth of Si/Ge layers on the (113) surface.     

Membrane properties of archaeal macrocyclic diether phospholipids

Several biophysical properties of four synthetic archaeal phospholipids [one polyprenyl macrocyclic lipid A and three polyprenyl double-chain lipids (B, C, D) bearing zero, one or four double bonds in each chain] were studied using differential scanning calorimetry, electron and optical microscopies, stopped-flow/light scattering and solid-state 2H-NMR techniques. These phospholipids gave a variety of self-organized structures in water, in particular vesicles and tubules. These assemblies change in response to simple thermal convection. Some specific membrane properties of these archaeal phospholipids were observed: They are in a liquid-crystalline state over a wide temperature range; the dynamics of their polyprenyl chains is higher than that of n-acyl chains; the water permeability of the membranes is lower than that of n-acyl phospholipid membranes. It was also found that macrocyclization remarkably improves the barrier properties to water and the membrane stability. This may be related to the adaptation of Methanococcus jannaschii to the extreme conditions of the deep-sea hydrothermal vents.     

Molecular Ions of Transient Species: Vinylamine-Cation

Vinylamine 1 was prepared by thermolysis of cyclobutylamine and its photoelectron spectrum was measured. I = 8.20 eV and I = 8.65 eV were found, the dominant vibrational progression (? = 725 cm^?1) indicating that in the course of 1(X)→1 ⁺( X? ) flattening around the N-atom occurs. The Franck-Condon profile of this band, however, suggests that a skeletal mode of ? ≈ 1400 cm^?1 (observed also in the iso-π-electronic systems vinyl-alcohol-cation and allyl radical) may also be excited. Comparison with the data for the isomer acetaldehyde-imine 2 and its cation s ⁺ shows that the isomer couple 1/2 constitutes a further notable example for a relative thermochemical stability inversion on going from the neutrals to the cations.     

Quadruple correlation functions and their application in double polarization experiments and in few-body problems

We define real functions which form a complete, orthogonal and rotational invariant basis for all problems depending on four directions. Their usefulness is demonstrated for processes of the type $\text{a}\text{+}\text{b}\text{→}\text{c}\text{+}\text{d}\text{,}\text{a}\text{+}\text{b}\text{→}\text{c}\text{+}\text{d}\text{,}\text{a}\text{+}\text{b}\text{→}\text{c}{}_1\text{, +}\text{c}{}_2\text{+}\text{d}$. The special case of all four directions in one plane has many applications too, e.g. in two- and three-body problems.     

Gegenbeispiele zur Interpolationstheorie der nuklearen und absolutsummierenden Operatoren

Ohne Zusammenfassung     

Heavy-ion friction force from a gas-kinetic model

A friction force is derived from the two-body collisions of projectile nucleons with target nucleons in the overlap region of their densities. We treat the diffuse surfaces of the heavy ions as Fermi gases. A certain average of the resulting friction force turns put to be identical in structure with the phenomenological Tsang-Swiatecki linear force. In our approach, the strength coefficient of the latter force can be calculated from the free two-nucleon scattering cross section without adjustable parameters. We obtain a strength which agrees well with the value found by Siwek-Wilczyńska and Wilczyński from an empirical fit.     

Is the madison convention really convenient at low energies?: The reaction 6Li(d)4He at 400 keV

It is shown that s-wave induced reactions with polarized particles can be described much more conveniently in new coordinates. Even with higher partial waves, cross sections can be fitted with less parameters than in conventional expansions.     

Applications of NMR spectroscopy of chiral association complexes. 6. rotation about the C(sp2)—C(aryl) bond in 2,6-disubstituted pivalophenones

For the investigation of the barrier to rotation about the C(sp²)—C(aryl) bond in non-planar pivalophenones five derivatives were prepared and their ¹H and ¹³C NMR spectra assigned. Methyl and bromine groups in the 3-position have opposite substituent effects on the chemical shifts of the ¹H and ¹³C signals of Me² and Me⁴. The ΔG values were determined from the coalescence temperatures of the signal splittings generated by the addition of optically active shift reagents. The accuracy of this method was estimated by using different signals of 3-bromo-2,4,6-trimethylpivalophenone and by computer simulation of the line shape. A buttressing effect of substituents in the aromatic ring was observed. A change of the twist angle by the substitution of methyl by bromine in the tert-butyl group was suggested in order to explain the changes in ΔG and the chemical shifts.