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101.
At least three different types of oxygen atoms may be present in the surface region of Pd(111) which may be distinguished by their thermal, chemical, structural and electronic properties. Exposure to O2 at low temperatures causes the formation of 2 × 2 and structures from chemisorbed oxygen, the latter being probably stabilized by small amounts of Hab or COab on the surface. The initial sticking coefficient was estimated to be about s0 ≈ 0.3, the adsorption energy ~55 kcal/mole. The photoelectron spectrum exhibits an additional maximum at 5 eV below EF. During thermal desorption dissolution of oxygen in the bulk strongly competes; on the other hand absorbed oxygen may diffuse to the surface giving rise to high temperature peaks in the flash desorption spectra. High temperature (~1000 K) treatment of the sample with O2 causes the formation of a more tightly bound surface species also characterized by a 2 × 2 LEED pattern which is chemically rather stable and which is considered to be a transition state to PdO. The latter compound is only formed by interaction with NO at about 1000 K via the reaction which offers a rather high “virtual” oxygen pressure. This reaction leads to drastic changes of the photoelectron spectrum and is also identified within the LEED pattern. 相似文献
102.
K.H. Althoff H. Beckschulze R. Conrad J. DeWire H. Herr E. Hilger V. Kadansky O. Kaul D. Menze W. Meyer 《Nuclear Physics B》1975,96(3):497-508
At the Bonn 2.5 GeV electron synchrotron the first measurements of the target asymmetry for the reaction γ + n ↑ → π? + p have been performed. The negative pions were detected in a magnetic spectrometer at a constant pion c.m. angle of 40° and photon energies between 0.45 GeV and 2.0 GeV. Deuterated butanol was used as target material. The polarization of the deuterons was about 16%. The results show a significant difference from the previously measured π+ asymmetry. 相似文献
103.
A. Renouprez P. Fouilloux R. Stockmeyer H. M. Conrad und G. Goeltz 《Colloid and polymer science》1978,256(8):829
Ohne Zusammenfassung 相似文献
104.
3,4-Dimethoxyfuran: Properties, Calculations and some Substitution Reactions 3,4-Dimethoxyfuran (3,4-DF) is much more reactive than furan itself. We present experimental details for the synthesis of this useful compound in 50–100 g batches. 3-4-Dibenzyloxyfuran has also been prepared. Quantum mechanical calculations by PPP-and CNDO-methods analogous to furan itself gave the following information (compared with furan): enhanced negative partial charge at C(2) and C(5), higher acidity at α-position, a stronger and at the same time inverted dipol moment. In accordance with the calculations, 3,4-DF can easily be substituted by weak electrophilic reagents, e.g. in a typical Mannich reaction. The bis-amino compound 8 is produced in good yields. Lithiation by butyl-Li leads to mono- or di-substituted products. The mono- and di-Li-3,4-DF have been used for the preparation of various acylated and alkylated 3,4-DF derivatives. By acid hydrolysis of 3,4-DF crystalline 4-methoxy-3 (2H)-furanone has been prepared. 相似文献
105.
Horminone, taxoquinone and other royleanones, obtained from two Abyssinian Plectranthus species (Labiatae). From the coloured glands on the leaves of two botanically unclassified Plectranthus sp. from Abyssinia, a series of royleanones has been isolated, namely royleanone ( 1 ) and 6,7-dehydroroyleanone ( 2 ) from one species, and 6,7-dehydroroyleanone, horminone ( 3 ), taxoquinone ( 4 ), 6β, 7α-dihydroxyroyleanone ( 5 ), 7α-acetoxy-6β-hydroxyroyleanone ( 6 ) and 7-oxoroyleanone ( 7 ) respectively, from the other. 相似文献
106.
107.
The hierarchy of kinetic equations for diffusion-reaction processes are rederived using a Fock space formalism for the Master equation. In the diffusion dominated case the reactive part can be analyzed perturbationally. In according to the experimental situation the behaviour of the system is governed by one space dimension. The summation of a whole class of terms in a perturbative serie yields the scaling behaviour of the production rate of the C particle. The solution depends on the ratio of the diffusion constantsD=D
A
/D
B
and the ratio of the characteristic time scales for reaction and diffusion, respectively. Various special cases and approximations are discussed in terms ofD. The analytical results can be supported by numerical simulations. 相似文献
108.
Hans Peter Weber Trevor J. Petcher Marcel Hensch Conrad Hans Eugster 《Helvetica chimica acta》1975,58(7):2009-2018
The structures of two acid catalysed rearrangement products of taxochinone ( 1 ) have been determined by X-ray analysis. One of the products turned out to be a 20 (10→9) abeo-abietane ( 2 ), the other an optically inactive phenalenone ( 3 ). Crystals of the former compound, C20H26O3, belong to space group P212121 with four molecules per cell and the structure was refined with 879 significant reflexions to R = 0.032. Crystals of the latter compound, C20H22O2, belong to space group P21/c with 12 molecules per cell and the structure was refined with 1823 significant reflexions to R = 0.058. 相似文献
109.
Karpoxanthin and 6-Epikarpoxanthin A tetrahydroxy-β,β-carotene previously isolated in minute amounts from ripe hips of Rosa pomifera was now identified as (3S,5R,6R,3′R)-5,6-dihydro-β,β-carotene-3,5,6,3′-tetrol ( 2 ). Acid hydrolysis of (9Z)-antheraxanthin ( 3 ) gave 2 and its C(6)-epimer 4 . Tetrol 2 is named karpoxanthin. 相似文献
110.
He II-ultraviolet photoelectron spectra (hv = 40.8 eV) from a carbon monoxide layer adsorbed on a Cu(111) surface exhibit two peaks at 8.5 and 11.6 eV below the Fermi level and a weaker maximum centered at about 13.5 eV. The emission from the Cu d-band is markedly suppressed after adsorption. The results are discussed in terms of the recent models for assigning the UPS peaks observed after adsorption of CO on transtion metals 相似文献