Methane activation on Ni(1 1 1): Effects of poisons and step defects

We have, theoretically and experimentally, investigated the dissociation of methane on the terraces and steps of a Ni(1 1 1) surface. Using Density Functional Theory (DFT) total energy calculations combined with Ultra High Vacuum (UHV) experiments, we find that the steps exhibit a higher activity than the terraces. We have, furthermore, investigated how carbon and sulfur present on the surface will deactivate the steps, leaving only the terraces active. We find the intrinsic sticking probabilities of methane on the steps and terraces at 500 K to be 2.8 × 10⁻⁷ for the steps and 2.1 × 10⁻⁹ for the terraces, in complete agreement with our calculated difference in activation energy of 17 kJ/mol.     

Homoconjugated ketones with extended unsaturation: Wavelength-selective,regioselective, diastereoselective,and enantiospecific photochemical transformations of methyl 7-oxospiro[5.5]undeca-1,3-and -2,4,-diene-2-carboxylate

The title molecules were shown to photorearrange with remarkable selectivity. Wavelength variation steers the rearrangement modes, of which the [1,2]-acyl shift was found to be largely regioselective, diastereoselective, and enantiospecific. Chemical intercorrelation of products and mechanistic studies were carried out all along. The potential significance of these photochemical processes in selective synthetic schemes is discussed.     

New reals: Can live with them,can live without them

We give a self‐contained proof of the preservation theorem for proper countable support iterations known as “tools‐preservation”, “Case A” or “first preservation theorem” in the literature. We do not assume that the forcings add reals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microchemical characterization of paintings — A case study

Summary The fundamental importance of scientific research for the preservation and restoration of works of art is uncontestable. The methods described in this paper, such as light microscopy, microchemical tests, emission spectroscopy, chromatography, scanning electron analysis, electron microprobe analysis and infrared spectroscopy, are of special significance in this filed. Nevertheless a better understanding of the problems that arise out of new special questions of art history can be obtained only by the right interpretation of the data obtained by scientific methods.

---

Mikrochemische Charakterisierung von Gemälden

Zusammenfassung Die grundlegende Bedeutung wissenschaftlicher Forschung für die Erhaltung und Restaurierung von Kunstwerken ist unbestritten. Die hier beschriebenen Methoden (Lichtmikroskopie, mikrochemische Reaktionen, Emissionsspektroskopie, Chromatographie, Rasterelektronen-Analyse und Infrarotspektroskopie) sind hierfür von zunehmender Bedeutung. Sie ermöglichen ein besseres Verständnis neuerer kunsthistorischer Probleme nur durch die richtige Interpretation der Ergebnisse wissenschaftlicher Methoden.

     

Electronic Structure and Photophysical Properties of Isoindole and its Benzo[f]- and Dibenzo[e,g]-Derivatives

The synthesis of N-methyl-benz[f]isoindole ( 2 ) and N-methyl-dibenz[e,g]isoindole ( 3 ) is reported. The NMR. spectra of N-methyl-isoindole ( 1 ) and of 2 have been analysed and the implications concerning the alternation of bond lengths are discussed. The photophysical properties of 1 to 3 have been investigated by the following methods: HeI photoelectron (PE.) spectroscopy, UV./VIS. absorption (polarization measurements by the stretched-foil technique) and emission spectroscopy (fluorescence spectra, lifetimes and quantum yields, phosphorescence spectra), and flash spectroscopy (triplet-triplet absorption spectra). The discussion of the results is based on HMO. and PPP SCF CI. calculations and points to the relationship between the heterocycles 1 to 3 and the corresponding benzenoid hydrocarbons obtained by replacement of the ? NMe? subunit by ? CH?CH? . Some comments concerning the ground state properties of isoindole and related compounds are derived from the analysis of their electronic structure.     

Electronic Structure and Photophysical Properties of Planar Conjugated Hydrocarbons with 4n-Membered Rings. I. Photoelectron Spectra of 1,5,9-Tridehydro[12]-annulene and Related Compounds

The HeI photoelectron spectra of the title compound 1 (1,5,9-cyclododecatriene-3,7,11-triyne), 1,5-didehydro[12]annulene (1,3,5,9-cyclododecatetraene-7, 11-diyne ( 2 )), sym-tri-benzotridehydro[12]annulene (tribenzo[a,e,i]-5,6,11,12,17,18-hexadehydrocyclododecene ( 3 )), and sym-dibenzodidehydro[8]annulene (dibenzo[a,e]-5,6,11,12-tetradehydrocyclooctene ( 4 )) have been recorded and analysed on the basis of various semi-empirical model calculations. Despite the distinct bond length alternation in the parent compounds and, apparently, in the radical cations, the first ionization occurs at low energies in these compounds (7.6 ± 0.2 eV). The spectra yield little information with regard to the transannular interactions of the triple bonds.