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241.
242.
Wolfgang Schattke 《Progress in Surface Science》1997,54(3-4):211-227
Photoemission in the vacuum ultraviolet photon regime has proved to be an effective tool for the investigation of valence band surface electronic structure. The interpretation cannot be exclusively confined to the valence bands but has to consider cross sections with realistic final states consistently designed within the one-step model. Therefore especially in the surface sensitive photoemission, several effects hide the final goal of deducing the energetic and wavefunction structure together with microscopic potential parameters through a convincing agreement of calculated with measured spectra. The final states band structure is much less well understood than the valence band structure under consideration. The optical potential, which controls the surface sensitivity through the underlying damping mechanisms, widely relies on empirical assumptions. Furthermore, the photon field is not only strongly influenced but in the vicinity of the plasma frequency also deteriorated by the electronic response. In view of high resolution spectroscopy the accuracy of the data interpretation is affected, and in fact, band-mapping methods are no longer valid. Examples of recent calculations to account for these effects are reviewed. 相似文献
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Phosphate protection in the phosphotriester approach is improved by the new, versatile p-nitrophenylethyl group due to its stability in the condensation step and its clean removal by DBU and DBN respectively. 相似文献
247.
Automatic titrators are designed to do exactly what a lab-technician used to do. Much more sophisticated automation of volumetry is possible. Omegaphoresis [3] in buffer-free [2] sample solutions automatically creates a stationary multiple component titration curve or zoned pattern with normalized concentrations of each separated species. An automatic measurement of each zone length yields their quantity. Simultaneous automatic detection of all the zones in a 10–20 component solution in less than 2 minutes, with a precision of ±2%, a required amount of the order of less than one nanomol and a resolution of ±pK < 0.01 replaces acid-base, complexometric, and certain types of redox-titrimetry. An option of the method allows identification of the components as well. 相似文献
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(PPh4)2[WO2Cl3]2 · 2 CH2Cl2. Synthesis, Vibrational Spectrum, and Crystal Structure Depending on the stoichiometry and the solvent, dichloromethane or 1.2-dichloroethane, WO2Cl2 reacts with tetraphenylphosphonium chloride affording (PPh4)2[WO2Cl4] or (PPh4)2[WO2Cl3]2, respectively. Both compounds are easily soluble in dichloromethane, from which they can be crystallized under incorporation of two molecules CH2Cl2 per formula unit. The crystalline compounds have been characterized by their IR and Raman spectra. According to the X-ray crystal structure analysis, (PPh4)2[WO2Cl3]2 · 2 CH2Cl2 crystallizes in the triclinic space group P1 with one formula unit per unit cell (986 independent observed reflexions, R = 0.061). Lattice constants: a = 1100.2, b = 1116.9, c = 1238.4 pm, = 69.40, = 80.46 and = 85.62°. The crystals consist of PPh4⊕ ions, centrosymmetric [WO2Cl3]22? anions and CH2Cl2 molecules. In the anions, the tungsten atoms are linked via two oxo bridges with WO distances of 184 and 252 pm. The distorted octahedral coordination around each tungsten atom is completed by three terminal chloro and one terminal oxo ligand (WO bond length 166 pm), the latter being in trans position to the longer WO bridging bond. (PPh4)2[WO2Cl4] · 2 CH2Cl2 also forms triclinic crystals that are isotypic with (PPh4)2[WOCl5] · 2 CH2Cl2 and in which the anions must have orientational disorder. 相似文献
250.
The title compound was prepared by annealing molybdenum powder with an excess of tin. Single-crystals were obtained by dissolving the tin-rich matrix in hydrochloric acid. They are Pauli paramagnetic. The crystal structure was determined from single-crystal X-ray diffractometer data: P6222, a = 548.8(1) pm, c = 1417.1(2) pm, Z = 6, R = 0.036 for 18 variable parameters and 389 structure factors. MoSn2 is only the second representative of the hexagonal Mg2Ni-type structure. The relation of the structure to the CuAl2-type is discussed. 相似文献