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951.
Joachim Bollmann Heinz A. Klose Jörg Röhrich Winfried Frentrup Axel Mertens 《Mikrochimica acta》1992,107(3-6):179-187
Using high-sensitive deep level transient spectroscopy (DLTS), we have determined ion-related defects in monocrystalline silicon in the asimplanted state. In comparison with secondary ion mass spectrometry (SIMS) data and neutron depth profiling (NDP) results it is demonstrated that the defect profiles and the chemical distributions have nearly identical shape. From these experimental facts it can be concluded that this electrical spectroscopy can be applied for the detection of very low concentrations (down to 1010 cm–3) of implanted ion species. 相似文献
952.
Joachim G. Liehr A. Gareth Brenton John H. Beynon Wilhelm J. Richter 《Journal of mass spectrometry : JMS》1981,16(3):139-143
Mass spectra of 2-hydroxydiphenylmethane and its derivatives are characterized in the upper mass region by an abundant ion m/z 165. Metastable ion measurements reveal that this ion is formed from the molecular ion of the parent compound by elimination of H2O and hydrogen. A fluorenyl cation structure is proposed for this ion on the basis of identity of collision induced mass analyzed ion kinetic energy spectra of ion m/z 165 generated from 2-hydroxydiphenylmethane and from fluorene. Four different pathways of formation of a fluorenyl cation are discussed. The contribution of each of these to the genesis of fragment m/z 165 was monitored in a reversed geometry instrument by measuring the first fragmentation in the first field free region and the second fragmentation in the second field free region. 相似文献
953.
Upon reaction with NaBH4 the carbene chelates [C5H5(CO)xMC(C6H5N(CH3)C(C6H5)N(CH3)]PF6 (I,M = Mo, x = 2; II,M = Fe, x = 1) are reduced at the carbene carbon with formation of the neutral compounds C5H5(CO)xMC(H)(C6H5)N(CH3)C(C6H5)N(CH3) (III and IV). Depending on the orientation of the incoming H substituent with respect to the C5H5 ligand two different isomers A and B are obtained which can be separated by column chromatography. Whereas the H? addition to the Fe compound II is almost stereospecific (formation of 95% IVB), the stereoselectivity of the H? addition to the Mo compound I is influenced by a competitive metal centered rearrangement of III in opposite direction. The approach to the equilibrium IIIA/IIIB 85/15 can be measured by 1H NMR spectroscopy (ΔG3328 26.6 kcal/mol). 相似文献
954.
For Co2(CO)8, the representative of a whole class of bridged cobalt complexes, the 18-electron rule predicts a direct metal-metal bond in addition to the metal-bridge bonds. By intuition, this bond should have bent-bond character. However, it is well-known from charge density analyses that no bond critical point exists in the corresponding spatial region. Otherwise, the energy density distribution points to a certain stabilizing contribution of this local area to the total molecular energy. It is shown that a partitioning of the total charge and energy densities into orbital contributions can lead to a deeper insight into complex bonding properties. 相似文献
955.
The growing capabilities of FTIR spectrometers and computers have opened the use of new sample preparation techniques in infrared spectroscopy. In addition to the established KBr pellet technique and ATR spectroscopy, diffuse reflectance and photoacoustic spectroscopy are increasing in importance. A systematic experimental comparison of these techniques has been made in order to make proper use of their mutual advantages. 相似文献
956.
957.
Polymeric Thiolato Complexes [M(SPh)3]∞ of the Metals Mo, W, Fe, and Ru with Linear Metal Chains. Synthesis and Crystal Structure of (OC)3Fe(SPh)3Fe(SPh)3Fe(CO)3 · 2(CH3)2CO At high temperature the reaction of the metal carbonyls Mo(CO)6, W(CO)6 and Fe(CO)5 with S2Ph2 (Ph = C6H5) yields the polymeric complexes [M(SPh)3]∞. Similarly [Ru(SPh)3]∞ can be obtained from ruthenium(III) acetylacetonate and HSPh. At room temperature under UV-irradiation Fe(CO)5 reacts with S2Ph2 to form the oligomeric complex (OC)3Fe(SPh)3Fe(SPh)3Fe(CO)3. The polymeric complexes [M(SPh)3]∞ (M = Mo, W, Fe, Ru) are composed of linear chains with bridging SPh-ligands between the metal atoms. Of these complexes [Fe(SPh)3]∞ is paramagnetic, whereas the others exhibit antiferromagnetic behaviour. The spin coupling is presumably connected with the formation of metal pairs, resulting in alternating shortened and extended distances in the metal chain. The oligomeric complex (OC)3Fe(SPh)3Fe(SPh)3Fe(CO)3 crystallizes triclinic in the space group P1 with z = 2. It has almost the symmetry D3d with a linear arrangement of the Fe atoms. The paramagnetism of Fe3(CO)6(SPh)6 can be explained by a d6 high spin configuration of the central atom and low spin behaviour of the two other Fe atoms, which are bonded to CO. 相似文献
958.
Thiemann J Jankowski J Rykl J Kurzawski S Pohl T Wittmann-Liebold B Schlüter H 《Journal of chromatography. A》2004,1043(1):73-80
For the purification of a target protein, liquid chromatography is the method of choice, if its activity has to be maintained. The selection of optimum parameters will improve in proportion to the number of individual parameters varied in initial experiments. Here a fast screening method is described, which utilizes automated parallel chromatographic experiments in the batch mode in 96-well plates. The principle of this protein-purification-parameter screening (PPS) system is demonstrated with a mixture of four proteins. An application of PPS for the determination of a purification step of an angiotensin-II-generating enzyme from a crude tissue extract is shown. 相似文献
959.
Werner M. Dÿck Kurt Dehnicke Gisela Beyendorff-Gulba Joachim Strhle 《无机化学与普通化学杂志》1981,482(11):113-120
Azido Complexes of Zirconium: ZrCl3N3, [ZrCl4N3]22?, [ZrCl4(N3)2]2?; Crystal Structure of (PPh4)2 [ZrCl4N3]2 Highly explosive ZrCl3N3 is formed by the reaction of ZrCl4 with iodine azide in dichloromethane suspension. According to the i.r. spectra, the compound is polymeric by azide and chlorine bridges. Zirconium tetrachloride reacts with one and two moles of tetraphenylphosphonium azide respectively, forming the thermally and mechanically stable complexes (PPh4)2[ZrCl4N3]2 and (PPh4)2[ZrCl4(N3)2]. The crystal structure of (PPh4)2[ZrCl4N3]2 was determined by X-ray methods (1942 reflexions, R = 6.5%). The complex crystallizes in the monoclinic space group P21/n with two formula units per unit cell. The structure consists of tetraphenylphosphonium cations and dimeric anions [ZrCl4N3]22?, in which the Zr atoms are linked by the α-N atoms of the azide groups, forming a centrosymmetric Zr2N2 ring with symmetry D2h. According to the i.r. spectra, the azide groups in the complex (PPh4)2[ZrCl4(N3)2] are covalently bonded at the Zr atom in trans positions. 相似文献
960.
Brázdová V Ganduglia-Pirovano MV Sauer J 《The journal of physical chemistry. B》2005,109(49):23532-23542
The structure, stability, and vibrational properties of isolated V2O5 clusters on the Al2O3(0001) surface have been studied by density functional theory and statistical thermodynamics. The most stable structure does not possess vanadyl oxygen atoms. The positions of the oxygen atoms are in registry with those of the alumina support, and both vanadium atoms occupy octahedral sites. Another structure with one vanadyl oxygen atom is only 0.12 eV less stable. Infrared spectra are calculated for the two structures. The highest frequency at 922 cm(-1) belongs to a V-O stretch in the V-O-Al interface bonds, which supports the assignment of such a mode to the band observed around 941 cm(-1) for vanadia particles on alumina. Removal of a bridging oxygen atom from the most stable cluster at the V-O-Al interface bond costs 2.79 eV. Removal of a (vanadyl) oxygen atom from a thin vanadia film on alpha-Al2O3 costs 1.3 eV more, but removal from a V2O5(001) single-crystal surface costs 0.9 eV less. Similar to the V2O5(001) surface, the facile reduction is due to substantial structure relaxations that involve formation of an additional V-O-V bond and yield a pair of V(IV)(d1) sites instead of a V(III)(d2)/V(V)(d0) pair. 相似文献