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141.
J. Hladký S. NĚmeček M. Novák A. Prokeš J. Votruba K. -F. Albrecht A. Meyer M. Sachwitz B. N. Guskov V. G. Krivokhizhin M. F. Likhachev I. A. Savin G. Vesztergombi 《Czechoslovak Journal of Physics》1977,27(11):1210-1218
Results of the first elastic K
S
o
regeneration experiment on carbon, using magnetic spark chamber spectrometer, are presented in the beam momentum interval 10p50 GeV/c. The d ifferentia cross section d/dt is reconstructed in the range 0·0025–t0·02 (GeV/c)2 and its slopeB is found to be momentum independent with an average valueB=(65±11) (GeV/c)–2. The results are in agreement with the calculations using the coherent production model. 相似文献
142.
Conversion electrons following the Mössbauer absorption of the 6.2 keV -rays of181Ta were observed in backscattering geometry. Mössbauer spectra for tantalum single crystal and foil surfaces (mean-depth 330 Å) are compared with normal transmission spectra for tantalum foils (bulk). While no broadening of lines is observed for carefully polished single crystal furfaces, foil surfaces show considerably broader lines than bulk spectra. The linewidth and isomer shift indicate an increase of the concentration of absorbed residual gases at the foil surfaces. The observed dispersion term arising from the interference between photo- and conversion electrons for this E1-transition, depends only on the absorber thickness. 相似文献
143.
M. W. Müller A. Merz M. -W. Ruf H. Hotop W. Meyer M. Movre 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,21(2):89-112
We have carried out a comprehensive experimental and theoretical investigation of the autoionizing collision systems He*(23 S, 21 S) + He*(23 S). We present high resolution electron energy spectra, obtained with a single He* beam (average relative collision energy 〈E rel〉=1.6 meV) and with crossed He* beams (〈E rel〉> =61 meV). The spectra show substantial structure, and under single beam conditions fast oscillations due to the interference of incoming and outgoing heavy particle waves in the entrance channels are observed. Accurate ab initio potential curves for the seven lowest He*—He*(Σ) molecular states have been obtained from a Feshbach projection scheme, and width functions for He*(23 S) + He*(23 S) have been derived by Stieltjes imaging. Based on these ab initio data, detailed quantum mechanical calculations of the electron spectra have been carried out and provide a thorough understanding of the experimentally observed spectral features. Good overall agreement of the calculated spectra with the experimental data is observed. The close coincidence in the positions of the experimental and theoretical peaks, especially for He*(23 S) + He*(23 S), underlines the reliability of the ab initio potentials. In the He*(21 S) + He*(23 S) electron spectrum, the dominant peak is traced to be due to autoionization from the 23Σ+ g molecular state accessed via an avoided crossing. We also present a detailed discussion of the total ionization cross sections σtot and of the fraction σAI/σtot for associative ionization together with a critical comparison with previous work. The ionization probabilities for close collisions in entrance channels, from which autoionization is spin-allowed, are near unity, and therefore the absolute values and the collision energy dependence of the total cross sections simply reflect the long-range behaviour of the excited state potentials. 相似文献
144.
La2O(CN2)2 was synthesized from a 1:1:2 molar reaction mixture of LaCl3, LaOCl, and Li2(CN2) at 650 °C. Well developed single crystals were grown from a LiCl‐KCl flux. The crystal structure was refined as monoclinic (space group C2/c, Z = 2, a = 13.530(2) Å, b = 6.250(1) Å, c = 6.1017(9) Å, β = 104.81(2)°) from single crystal X‐ray diffraction data. The La3+ and (CN2)2— ions in the crystal structure of La2O(CN2)2 can be compared to Fe3+ and S22— ions in the cubic pyrite structure, being arranged like in a distorted NaCl type structure with their centers of gravity. In addition, the O2— ions in La2O(CN2)2 are occupying 1/4 of the tetrahedral voids formed by the arrangement of metal ions. 相似文献
145.
There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols. 相似文献
146.
Ternary Rare-Earth Halides of the A2MX5 Type (A = K, In, NH4, Rb, Cs; X = Cl, Br, I) Ternary rare-earth (=M) chlorides, bromides, and iodides In2MCl5, (NH4)2MCl5, Rb2MCl5, Cs2MCl5, CsRbMCl5, K2MBr5, Rb2MBr5, K2MI5, and Rb2MI5 have been synthesized. Single crystals of In2PrCl5, Rb2PrCl5, K2PrBr5, and K2PrI5 were grown and the structures refined. The other halides were characterized by x-ray powder patterns. They are isotypic either with K2PrCl5(orthorhombic, Pnma, Z = 4, hexagonal arrangement of chains of edge-connected polyhedra [PrX7]) or with Cs2DyCl5 (orthorhombic, Pbnm, Z = 4, hexagonal arrangement of cis-corner-connected octahedra [DyCl6]) which may be discriminated in structure field diagrams. The thermal expansion was investigated für Cs2LuCl5 and Rb2PrX5 (X = Cl, Br, I). 相似文献
147.
[reaction: see text]. A convergent total synthesis of the methyl ester of zincophorin, an ionophore antibiotic, has been realized relying on a diastereoselective titanium-mediated aldol coupling between the C1-C12 and C13-C25 subunits. The latter fragment was prepared by using a Carroll-Claisen rearrangement. 相似文献
148.
J. Meyer 《Fresenius' Journal of Analytical Chemistry》1967,231(4):241-252
Zusammenfassung Es wird ein Verfahren zur Spurenbestimmung in Reinstsilber und Reinstsilberverbindungen beschrieben, das besonders für Routineanalysen geeignet ist. Das Verfahren beruht auf der hochselektiven Abtrennung des Matrixelementes von sämtlichen elektropositiveren Begleitspuren durch Reduktion mit Ameisensäure aus salpetersaurer Lösung, wobei das Silber als Amalgam abgeschieden wird. In der Spurenanreicherungslösung werden die für die Reinheitskontrolle von Silber und dessen Verbindungen wichtigsten Begleitelemente Pb, Cu, Cd, Zn amalgamvoltammetrisch, Tl, Ga, In, Fe, Ni, Mn flammenspektrometrisch und As photometrisch bestimmt. Die relativen Standardabweichungen liegen zwischen 2 und 13%, die Nachweisgrenzen zwischen 10–6 und 10–5%. Die prinzipiellen Möglichkeiten der Bestimmung weiterer Elemente sowie der Anwendung anderer Bestimmungsmethoden werden erörtert.über bisher bekannte Verfahren zur Spurenbestimmung in Silber wird berichtet.
Summary A method for the determination of trace amounts of metallic impurities in high-purity silver and silver salts is described. The procedure is based on an extremely selective separation of the silver matrix from all accompanying trace elements more electropositive than silver. The silver is separated by reducing a nitric acid solution of the sample with formic acid and depositing the silver as an amalgam. In the solution containing the enriched traces the elements being most important for the purity control of silver and its salts are detected voltammetrically (Pb, Cu, Cd, Zn), flame-spectrometrically (Tl, Ga, In, Fe, Ni, Mn) and photometrically (As). The relative standard deviations for the different elements were found to be between 0.02 and 0.13, the limits of detection between 10–6 and 10–5%. The possibilities to detect further elements and to apply other determination methods are pointed out.Previously known procedures for detecting trace amounts of impurities in silver are reported.相似文献
149.
150.
The reactions between trans-[Os(IV)(tpy)(Cl)(2)(NCN)] (1) and PPh(3) and between trans-[Os(IV)(tpy)(Cl)(2)(NPPh(3))](+) (2) and CN(-) provide new examples of double derivatization of the nitrido ligand in an Os(VI)-nitrido complex (Os(VI)N). The nitrilic N-bound product from the first reaction, trans-[Os(II)(tpy)(Cl)(2)(NCNPPh(3))] (3), is the coordination isomer of the first iminic N-bound product from the second reaction, trans-[Os(II)(tpy)(Cl)(2)(N(CN)(PPh(3)))] (4). In CH(3)CN at 45 degrees C, 4 undergoes isomerrization to 3 followed by solvolysis and release of (N-cyano)iminophosphorane, NCNPPh(3). These reactions demonstrate new double derivatization reactions of the nitrido ligand in Os(VI)N with its implied synthetic utility. 相似文献