Band 218, Heft 1

EXAFS spectroscopy is a useful method for determining the local structure around a specific atom in disordered systems. This technique provides information about the coordination number, the nature of the scattering atoms surrounding a particular absorbing atom, the interatomic distance between the absorbing atom and the backscattering atoms, and Debye–Waller factor. The measurements are done with high energy X-rays, which are normally generated by synchrotron radiation sources. The data analysis is facilitated by specially developed program packages suitable for evaluation purposes. EXAFS spectroscopy is employed in several fields for a variety of applications. Here the structural characterization of a series of amorphous μ -oxo-bridged metallophthalocyanine dimers is presented. It is found that the phthalocyanine macrocycle has significant influence in the spectra and the results obtained are in agreement with the well-known structure of phthalocyanine complexes.

In this paper, a description of multiple kinetic isotope effects (MKIE) of degenerate double, triple and quadruple proton transfer reactions in terms of formal kinetics is developped. Both single and multiple barrier processes are considered, corresponding to so-called “concerted” and “stepwise” reaction pathways. Each step is characterized by a rate constant and the transfer of a given H isotopes or ensemble of H isotopes. The MKIE are expanded in terms of kinetic H/D isotope effects P contributed by single sites in which a proton is transferred in the rate limiting steps. By combination with a modified Bell tunneling model the formalism developed can be used in order to take into account tunneling effects of both concerted and stepwise multiple proton transfers at low temperatures.

From a physical point of view powders represent an intermediary state between solids and fluids. This holds especially with respect to their flow properties. Gravitational forces as well as interparticle forces are acting on particles in bulk powders. As long as the gravitational forces are prevailing the powder is able to flow. However as soon as the interparticle forces dominate the powder becomes cohesive. It does not flow any longer. Based on empirical observations highly dispersed Silicone dioxide is added to powders to improve their flowability. In the present paper we will present some findings obtained from studies on binary mixtures consisting of 0.2(m/m) of a nanoscaled material and corn starch. They give some insight into the mechanism of action of flow regulators. In addition they allow to classify flow regulators with respect to their efficiency as well as to their effectiveness. Furthermore the findings give hints on how to optimize existing flow regulators or to develop new improved ones.

Micromodification of surfaces is the introduction of well-defined, directly local changes in the chemical or physical properties of such surfaces. This includes etching processes, deposition of materials and chemical modification of the surface material. As a scanning probe technique, the scanning electrochemical microscope (SECM) is predestined to generate chemical changes locally. Our intention is to demonstrate the effect of local chemical changes on a surface. For this purpose, we first recapitulate the work of our group on micromodification and then deal with galvanic deposition of metals, electroless deposition of conducting polymers and the use of etching to introduce organic features onto an inorganic surface.

The S 1 ( 1 B 2 ) ← S 0 ( 1 A 1 ) electronic transition of anisole and the anisole/CO 2 aggregate cooled in a supersonic free jet has been investigated in detail using REMPI spectroscopy and quantumchemical model calculations. The 42 intramolecular modes of anisole in the 1 S 1 state are assigned. Some previous assignments of modes of anisole in the 1 S 1 state have been improved, some of the assignments are still tentative. The origin of the corresponding electronic transition in the 1:1-aggregate is blueshifted by 117cm −1 versus the 0-0 transition of anisole, the origine in the 1:2-agreggate is redshifted by 216cm −1 . Probably a second conformer of the 1:1-aggregate is formed in the molecular beam. 36 fundamental modes of the anisole/CO 2 1:1-cluster out of possible 46 intramolecular modes are assigned. Spectral shifts of the fundamental modes in the 1 S 1 state of anisole/CO 2 due to the aggregation have been observed. The intermolecular modes and their binary combinations with intramolecular modes have been analyzed.

It is known that the intramolecular rearrangement of the ligands in trigonal-bipyramidal (TBP) molecules ( e.g. PF 5 ) follows a scheme first proposed by Berry and termed the Berry pseudorotation (BPR). There are 20 isomers, which are interconnected by 30 BPR reaction paths. In this paper, the time evolution of a given initial state is treated based on a set of first-order kinetic equations as well as on the basis of state-to-state tunneling processes. The dynamic equations are solved analytically using the eigenvalues and eigenvectors of the reaction-path connectivity matrix. It is shown that in the kinetic case the populations of all isomers approach an equilibrium value p i (∞) = 1/20 while in the quantum case the individual isomers are never equivalent neither in time nor as time average. This fact is related to the strong regularity of the eigenvalue spectrum of the connectivity matrix for the reaction graph network. Consequently, pure quantum effects cannot be the basis for the occurrence of five equivalent ligands in PF 5 (as was found experimentally).

The primary steps of photosynthesis proceed via light-induced radical pairs as short-lived intermediates. In this paper we discuss novel coherence phenomena which can be observed for these species. It is demonstrated that the analysis of quantum beat oscillations in combination with multifrequency EPR and a magnetically oriented sample represents a powerful structural tool. We expect that this is of general interest, since the detailed structure of radical pair intermediates can be determined on a nanosecond time scale.