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121.
122.
123.
George Hohlneicher Harald Pulm Hans-Joachim Freund 《Journal of Electron Spectroscopy and Related Phenomena》1985,37(2):209-224
First, we show that the quantity Δβ(i) = ΔEA(kii) + 2ΔEB(i) — ΔEB(k) is directly related to the final state relaxation contribution ΔER(i) of the binding energy shift ΔEB(i). ΔEA(kii) is the kinetic energy shift of the Auger transition which corresponds to the decay of a hole state with a hole in level k into a final state with two holes in level i. The shift parameter Δβ(i), which is based on information on two binding energies, is conceptually similar to Wagner's Auger parameter. To establish the relation between Δβ(i) and ΔR(i) one needs, however, less drastic approximations than in the case of Auger parameter shifts. The only approximation necessary is the assumption that ΔR(i) is determined by coulomb contributions.Secondly, we use Δβ (i) to analyse the experimental data of eighteen gaseous phosphorus-containing compounds obtained by Sodhi and Cavell1. It is shown that ΔR(P2p) is strongly related to changes in the polarizability of the ligands. The initial state effects derived from our study deviate from those expected on the basis of simple electronegativity considerations. 相似文献
124.
H. E. Hansen R. Talja H. Rajainmäki H. K. Nielsen B. Nielsen R. M. Nieminen 《Applied Physics A: Materials Science & Processing》1985,36(2):81-92
Molybdenum single crystals are irradiated at 20 K with 6 MeV protons. The radiation damage and lattice defect annealing is studied by positron lifetime spectroscopy in the temperature range from 15 to 720 K. Loss of vacancies due to recombination with mobile interstitials is observed at 40 K (Stage I) in agreement with resistivity measurements. This is the first time Stage I is observed by positrons below 77 K. The implanted hydrogen decorates the vacancies around 100 K, which is consistent with a hydrogen migration energy in molybdenum:E
M
H
= 0.3–0.4 eV. Clustering of spatially correlated vacancies takes place in a wide temperature region below the usual vacancy clustering stage (Stage III). Stage III is observed at rather low temperatures (400–480 K) due to the very high vacancy concentration. Hydrogen bound to vacancies and vacancy clusters is released above 540 K, which puts an upper limit to the hydrogen binding energy:E
B
H
1.4 eV. The present work emphasizes the advantage of employing a vacancy sensitive technique to study hydrogen in metals, where its intrinsic solubility is low. In such metals (as molybdenum) both the effective solubility and the effective mobility of hydrogen are strongly influenced by the presence of vacancies. 相似文献
125.
126.
The acid catalysed dienone-phenol rearrangement of methyl substituted o-propargyl-cyclohexadienones (scheme 3) was investigated. The rearrangements were carried out in acetic anhydride containing about 10/00 sulfuric acid. Under these conditions acetoxy benzenium ions are formed as intermediates. These then undergo charge-controlled [3s, 4s]- and [1s, 2s]-sigmatropic rearrangements. Thus, the [3s, 4s]-process leads to the formation of the corresponding allenyl-phenol acetates ( 19 , 21 , 23 , 25 , 28 , 30 ) whereas the [1s, 2s]-process yields propargyl-phenol acetates ( 20 , 22 , 24 , 26 , 29 ), respectively (cf. scheme 4). 相似文献
127.
Sagi D Peter-Katalinic J Conradt HS Nimtz M 《Journal of the American Society for Mass Spectrometry》2002,13(9):1138-1148
Application of the negative mode electrospray ionization-quadrupole time-of-flight mass spectrometry (ESI QTOF) tandem MS for determination of substitution patterns by sialic acid and/or fucose and extention by additional LacNAc disaccharide units in single branches of multianternary N-glycans from biological samples is described. Fragmentation patterns which can be obtained by low energy collision-induced dissociation (CID) using the QTOF instrument include cleavage ions, diagnostic for determination of antennarity and for specific structural features of single antennae. Systematic fragmentation studies in the negative ion mode were focussed toward formation of the D diagnostic ion relevant for assignment of 3- and 6-antennae in complex N-glycans carrying three and four antennae in combination with epitope-relevant B- and C-type ions. For validation of this approach ESI QTOF fragmentation of the permethylated analogues was carried out in the positive ion mode. Using this strategy, products of in vitro glycosylation reactions were investigated in order to clarify some general aspects of N-glycan acceptor specificity during biosynthesis. Alpha1-3fucosylation using GDP-fucose along with a soluble form of the recombinant human alpha1-3fucosyltransferase VI was carried out on tri- and tetraantennary precursors to test structural requirements for formation of Le(x) versus sLe(x) motifs. 相似文献
128.
Nanostructure and irreversible colloidal behavior of Ca(OH)2: implications in cultural heritage conservation 总被引:1,自引:0,他引:1
Rodriguez-Navarro C Ruiz-Agudo E Ortega-Huertas M Hansen E 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):10948-10957
Although Ca(OH)2 is one of the oldest art and building material used by mankind, little is known about its nanostructural and colloidal characteristics that play a crucial role in its ultimate performance as a binder in lime mortars and plasters. In particular, it is unknown why hydrated lime putty behaves as an irreversible colloid once dried. Such effect dramatically affects the reactivity and rheology of hydrated lime dispersions. Here we show that the irreversible colloidal behavior of Ca(OH)2 dispersions is the result of an oriented aggregation mechanism triggered by drying. Kinetic stability and particle size distribution analysis of oven-dried slaked lime or commercial dry hydrate dispersions exhibit a significant increase in settling speed and particle (cluster) size in comparison to slaked lime putty that has never been dried. Drying-related particle aggregation also leads to a significant reduction in surface area. Electron microscopy analyses show porous, randomly oriented, micron-sized clusters that are dominant in the dispersions both before and after drying. However, oriented aggregation of the primary Ca(OH)2 nanocrystals (approximately 60 nm in size) is also observed. Oriented aggregation occurs both before and during drying, and although limited before drying, it is extensive during drying. Nanocrystals self-assemble in a crystallographically oriented manner either along the 100 or equivalent 110 directions, or along the Ca(OH)2 basal planes, i.e., along [001]. While random aggregation appears to be reversible, oriented aggregation is not. The strong coherent bonding among oriented nanoparticles prevents disaggregation upon redispersion in water. The observed irreversible colloidal behavior associated with drying of Ca(OH)2 dispersions has important implications in heritage conservation, particularly considering that nowadays hydrated lime is often the preferred alternative to portland cement in architectural heritage conservation. Finally, our study demonstrates that, fortuitously, hydrated lime could be one of the first nanomaterials used by mankind. 相似文献
129.
Yevgen Posokhov Alexander Gorski Jens Spanget-Larsen Fritz Duus Poul Erik Hansen Jacek Waluk 《Chemphyschem》2004,5(4):495-502
Thioacetylacetone and its variously deuterated isotopomers have been investigated using electronic and vibrational spectroscopy combined with quantum chemical calculations. Thioacetylacetone is known for its photochromic properties, but the structures of the initial and final forms have been the subject of a long debate. Analysis of the IR spectra recorded in low-temperature argon and xenon matrices, room-temperature solutions, and in the gas phase has allowed us to establish the nature of the photochromic species and of its precursor. Similar to the case of another beta-thioxoketone, monothiodibenzoylmethane, the photo-product has been assigned to the nonchelated SH exo-rotamer of the (Z)-enethiol tautomeric form, whereas the dominant ground-state species corresponds to the chelated (Z)-enol tautomeric form. Detailed vibrational assignments have been proposed for both forms based on quantum chemical calculations and polarization experiments. In the case of the chelated (Z)-enol species prevailing in the ground state, a second-order perturbative anharmonic analysis at the B3LYP/cc-pVTZ level indicated strong anharmonic effects associated with the intramolecular hydrogen bond, leading to a shift of more than 600 cm-1 of the wavenumber of the OH-stretching vibration. A small fraction of the SH endo-rotameric chelated (Z)-enethiol form was also detected under unperturbed conditions. The (Z)-enethiol form can be converted into the (Z)-enol form by irradiation at 290 nm. 相似文献
130.
It has been shown, that in vitro incubation of Laminaria digitata extract (containing mainly As-sugar 1 (glycerol-arsenoribose) and As-sugar 3 (sulfonate-arsenoribose)) with liver cytosol, produced the same two arsenicals, as when L. digitata extract was treated with H(2)S. By parallel use of HPLC-ICP-MS and HPLC-ES-MS the compounds displayed mainly m/z 345 and m/z 409. A pure As-sugar 1 standard was obtained, and a standard of arsinothioyl-sugar 1 (m/z 345) was produced, by purging a solution of As-sugar 1 with gaseous H(2)S. The identity of arsinothioyl-sugar 1 was characterised by ES-MS, 1D and 2D NMR. Arsinothioyl-sugar 1 showed the same chromatographic behaviour and MS characteristics as one of the two arsenic-containing compounds (m/z 345) produced by incubation of L. digitata extracts with liver cytosol, and as the product of the incubation of As-sugar 1 with liver cytosol (HPLC-ICP-MS, HPLC-ES-MS). Assuming that As-sugar 3 reacts in a similar way to As-sugar 1 with H(2)S, it is most likely that the second unknown (m/z 409) is arsinothioyl-sugar 3. The degradation of As-sugar 1 in acidic solution (100 mM HCl) was followed by (1)H-NMR, and the relative slow degradation (t(1/2)= 17 h) suggests that arsenosugars are taken up from the stomach in their original chemical form, hence the study of arsenosugar incubation in tissue is highly relevant. The arsinothioyls are a new group of organoarsenicals, which have only recently been identified in nature. Here, arsinothioyl sugars are detected for the first time. The in vitro formation of arsinothioyl-sugars in liver cytosol suggests that arsinothioyls may be of large biochemical and toxicological importance. 相似文献