CPT-symmetry studies with antihydrogen

Various approaches to physics beyond the Standard Model can lead to small violations of CPT invariance. Since CPT symmetry can be measured with ultra-high precision, CPT tests offer an interesting phenomenological avenue to search for underlying physics. We discuss this reasoning in more detail, comment on the connection between CPT and Lorentz invariance, and review how CPT breaking would affect the (anti)hydrogen spectrum.     

Exploring between the extremes: conversion-dependent kinetics of phosphite-modified hydroformylation catalysis

The kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a rhodium monophosphite catalyst has been studied in detail. Time-dependent concentration profiles covering the entire olefin conversion range were derived from in situ high-pressure FTIR spectroscopic data for both, pure organic components and catalytic intermediates. These profiles fit to Michaelis-Menten-type kinetics with competitive and uncompetitive side reactions involved. The characteristics found for the influence of the hydrogen concentration verify that the pre-equilibrium towards the catalyst substrate complex is not established. It has been proven experimentally that the hydrogenolysis of the intermediate acyl complex remains rate limiting even at high conversions when the rhodium hydride is the predominant resting state and the reaction is nearly of first order with respect to the olefin. Results from in situ FTIR and high-pressure (HP) NMR spectroscopy and from DFT calculations support the coordination of only one phosphite ligand in the dominating intermediates and a preferred axial position of the phosphite in the electronically saturated, trigonal bipyramidal (tbp)-structured acyl rhodium complex.     

Temperature analysis of laser heated polymers on microsecond time scales

To investigate the temperature profiles on laser heated polymer films, we track the thermal radiation with 1 μs time and 1 μm spatial resolution. The resulting two-dimensional temperature graphs are compared to finite element simulations in order to understand the heat conversion and flow. The temperature measurement setup consists of a NIR laser and an optical detection system, which includes high performance optics and a microsecond gated camera, equipped with several interference filters. In this way the thermal radiation is detected in the visible range with spectral resolution. Fitting the spectrum with Planck’s law, two-dimensional micrographs of the temperature distribution are obtained. For polystyrene surfaces we were able to analyze the heating and the ablation behavior. Good agreement was found between experimental results and finite element simulations, when ablation is limited to a few tens of nanometers of the film thickness. Ablation of polystyrene starts at 150°C, 50 K above the glass transition temperature. We suggest a photomechanical ablation mechanism at that threshold fluence. For ablation at higher fluence and peak temperature, experiments indicate a thermal decomposition reaction. The temperature range of spinodal decomposition is not reached and can in our case be ruled out as ablation mechanism.     

Microscale investigation of surface contaminations during silicon epitaxial growth

Microchimica Acta - Epitaxial (epi) stacking faults on silicon wafers with <100>- and <111>-orientation were induced by intentional contamination with substances...     

Electronic Structure and Absorption Spectra of Biferrocenyl and Bisfulvalenide Diiron Radical Cations: Detection and Assignment of New Low‐Energy Transitions

New transitions : Low‐energy electronic transitions have been detected spectroscopically in the Fe^II–Fe^III mixed‐valent biferrocenyl radical cation, but are absent in the spectra of the neutral analogue. They have been assigned by time‐dependent DFT calculations (squares in figure). Analogous investigations were performed for the bisfulvalenide Fe^II–Fe^III radical cation.

     

On the Galois coverings of a cluster-tilted algebra

We study the module category of a certain Galois covering of a cluster-tilted algebra which we call the cluster repetitive algebra. Our main result compares the module categories of the cluster repetitive algebra of a tilted algebra C and the repetitive algebra of C, in the sense of Hughes and Waschbüsch.     

1,1′ Ferrocenylenediol as chelating ligand for cobalt in fivefold and sixfold coordination geometry: Synthesis,Electrochemistry and X-ray crystal structure of [{((1,1′ O2(η5-C5H5)2Fe)2}Co(OEt2){(η5-Me5C5)Co}2] and [{((1,1′ O2(η5-C5H5)2Fe)3}Co((η5-EtMe4C5)Co)2]

The title compounds 3 and 4 were synthesized by reaction of 1,1′ ferrocenylenediol with the Co triple decker compounds [{(η⁵-Me₅C₅)Co}₂(η⁶:η⁶-toluene)] and [{(η⁵-EtMe₄C₅)Co}₂(η⁶:η⁶-toluene)], respectively. The central Co atom of 3 is coordinated by five O atoms in a square-pyramidal manner. The remaining two Co atoms of 3 are coordinated to a Me₅C₅ ligand in a η⁵-fashion and by the two O atoms of two 1,1′ ferrocenylenediolato ligands which serve as chelating ligands. In 4, the central Co atom is coordinated to all six O atoms of three ferrocenylenediolato ligands in a trigonal-prismatic manner, whereas the two other Co atoms are coordinated by an EtMe₄C₅ ligand in a η⁵-fashion and by three O atoms of three ferrocenylenediolato ligands resulting in an overall tripoidal structure for 4.