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1.
2.
Frank Abild-Pedersen Ole Lytken Jakob Engbk Gunver Nielsen Ib Chorkendorff Jens K. Nrskov 《Surface science》2005,590(2-3):127-137
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. 相似文献
3.
4.
Jakob Oren Michaela Vardi Rossana Viskin Sarah Abramson Benzion Fuchs 《Helvetica chimica acta》1993,76(3):1182-1193
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. 相似文献
5.
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) 相似文献
6.
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. 相似文献
7.
Jakob Wirz 《Helvetica chimica acta》1976,59(5):1647-1655
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. 相似文献
8.
The ESCA spectrum of protonated 1,8-bis-(dimethylamino) naphthalene (“proton sponge”) (I) has been recorded in the region of N1s binding energies. The results indicate that IH+ possesses an unsymmetrical N? H…?N hydrogen bridge. 相似文献
9.
Wolfgang Marterer Horst Prinzbach Grety Rihs Jakob Wirz Jaques Lecoultre Edgar Heilbronner 《Helvetica chimica acta》1988,71(8):1937-1965
The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I1 = 8.00, I2 = 9.05 eV; 2 ; I1 = 8.00, I2 = 9.25eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond. 相似文献
10.
Robert Fugmann Herbert Nickelsen Ingeborg Nickelsen Jakob H. Winter 《Angewandte Chemie (International ed. in English)》1970,9(8):589-595
In mechanized systems used for searching in literature stores there is a steadily growing necessity not only to be able to formulate concepts as a search condition but also the characteristic connections under which these concepts appear in the inquiry. In this way the precision of the mechanized literature search is considerably increased. TOSAR has been developed in order to improve computerized literature searching in this respect. 相似文献