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31.
A limited quantum chemistry approach has been used to examine changes to the electric-field gradient at oxygen sites in rare-earth barium copper oxides (RBCO) due to a bonded muon (or hydrogen). Results are reported for an all electron, extended basis set calculation for an OMu– molecule which is embedded in various point charge clusters to simulate the RBCO crystal environment. Differences between the gradients for O2– and OMu– are examined for five likely muon bond sites. In each case the muon significantly modifies the calculated gradient.This work was supported by the Robert A. Welch Foundation (Grant D-1053). We also wish to thank Carel Boekema for numerous discussions during the course of this project. 相似文献
32.
Experimental confirmation of the predicted shallow donor hydrogen state in zinc oxide 总被引:3,自引:0,他引:3
Cox SF Davis EA Cottrell SP King PJ Lord JS Gil JM Alberto HV Vilão RC Piroto Duarte J Ayres de Campos N Weidinger A Lichti RL Irvine SJ 《Physical review letters》2001,86(12):2601-2604
We confirm the recent prediction that interstitial protium may act as a shallow donor in zinc oxide, by direct spectroscopic observation of its muonium counterpart. On implantation into ZnO, positive muons--chemically analogous to protons in this context--form paramagnetic centers below about 40 K. The muon-electron contact hyperfine interaction, as well as the temperature and activation energy for ionization, imply a shallow level. Similar results for the cadmium chalcogenides suggest that such shallow donor states are generic to the II-VI compounds. The donor level depths should serve as a guide for the electrical activity of interstitial hydrogen. 相似文献
33.
R. L. Lichti T. R. Adams D. W. Cooke R. S. Kwok C. Boekema J. C. Lam D. E. Farrell N. Bansal 《Hyperfine Interactions》1991,63(1-4):73-79
Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa2Cu3O7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration
depth anisotropy are observed forB‖c andB
c. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux
pinning characteristics are suggested as the fundamental cause of the additional effects. 相似文献
34.
Hans Peter Hrter Heinz Lichti Urs Stauss Othmar Schindler 《Helvetica chimica acta》1976,59(4):1203-1212
Comparison of reaction products afforded by phenylguanidine derivatives with β-ketoesters or propiolic esters, respectively (synthesis of pyrimidones). 2-Anilino-imidazolines, when treated with either β-ketoesters or propiolic esters, yield two isomeric groups of pyrimidones. The isomerism is based on different positions of the carbonyl group in the pyrimidone ring. The mass spectra permit an unequivocal assignment of constitution I to the product formed with β-ketoesters and of constitution V to that formed with propiolic esters. Additionally, 2-(2-amino-anilino)-2-imidazoline (XII) when treated with methyl phenylpropiolate yields IX; while treatment with ethyl benzoylacetate yields XIII as an intermediate, which eliminates spontaneously one molecule of water to give the benzimidazole derivative XIV. Phenylguanidines (XV) add propiolic esters in the same way as do imidazoline derivatives. Photochemical cleavage of two carbon atoms with their adherent hydrogen atoms from the imidazole ring of the pyrimidones (V) leads to aminopyrimidine derivatives, e.g. XVI. 相似文献
35.
T. L. Duty J. H. Brewer K. Chow R. F. Kiefl A. W. MacFarlane G. D. Morris J. W. Schneider B. Hitti R. Lichti L. Brard J. E. Fischer A. B. Smith Jr R. M. Strongin 《Hyperfine Interactions》1994,86(1):789-795
The Co60Mu radical in polycrystalline C60 has been studied in zero magnetic field between 9 K and 200 K, and at room temperature. At low temperatures, we observe three low-frequency oscillations which correspond to the intra-triplet transitions of a completely anisotropic muon-electron hyperfine interaction. These signals exhibit a strongly temperature-dependent T1, attributed to thermally-activated jump rotational diffusion of the C60Mu radical. A fit to an Arhenius law yields an activation energy of 200(20) meV for temperatures below the fcc-sc structural phase transition. At room temperature only the motionally-narrowed 325 MHz singlet-triplet transition is observed. 相似文献
36.
S. F. J. Cox G. H. Eaton D. S. Sivia M. S. Watt D. W. Cooke M. Leon M. A. Paciotti J. L. Smith W. L. Hults T. L. Estle B. Hitti C. Boekema J. Lam A. Morrobel-Sosa R. L. Lichti J. Oostens C. Schwab E. A. Davis A. Singh N. Ayres De Campos J. Ayres De Campos P. J. Mendes J. M. Gil K. Chow R. Duvarney P. F. Meier 《Hyperfine Interactions》1994,85(1):59-65
Cross relaxation between implanted positive muons and27Al nuclei in Al metal, lightly doped with Cu to impede the muon diffusion, shows weak resonances at 2.3 and 4.0 mT. Assignment of these to polarization transfervia the 1/2 3/2 and 3/2 5/2 transitions of the (J=5/2) spins leads to a quadrupole coupling constante
2qQ/h=1.8(1) MHz,i.e. an electric field gradient on Al nuclei immediately adjacent to the muon siteq=0.048(3) a.u., with a small departure from axial symmetry. 相似文献
37.
S. R. Kreitzman T. L. Estle B. Hitti J. W. Schneider K. H. Chow R. L. Lichti 《Hyperfine Interactions》1994,87(1):1063-1068
A microwave-SR (WSR) spectrometer has been developed which operates in the frequency region of 1–2 GHz. The spectrometer geometry is that of longitudinal field (LF)SR and is typically used in time integral measurements. The high frequency of this instrument distinguishes it from the currently used RFSR spectrometers and allows high field measurements to be made for normal Mu type systems. This allows one to avoid low field broadening mechanisms that may be present, either from electronic spin-lattice relaxation or nuclear hyperfine interactions.Technical details of the tunable microwave cavity and the RF coupling scheme are presented. Experimental spectra of Mu lines in SiO2 and GaAs are displayed. 相似文献
38.
39.
The structure of scilliglaucoside, a cardiac active squill glycoside, is revised. The assignment of the new structural formula 1 is made on the basis of NMR. spectral data. 相似文献
40.
D. W. Cooke M. S. Jahan R. S. Kwok R. L. Lichti T. R. Adams C. Boekema W. K. Dawson A. Kebede J. Schwegler J. E. Crow T. Mihalisin 《Hyperfine Interactions》1991,63(1-4):213-218
Zero-field muon-spin-rotation (μSR) measurements on (Y1? x Pr x )Ba2Cu3O7 [x=1.0, 0.8, 0.6, and 0.54] show evidence for antiferromagnetic ordering of the Cu moments within the Cu?O planes, with Néel temperatures 285, 220, 35. 30 and 20 K, respectively. Forx=1.0 the local muon magnetic field is ≈16 mT, but decreases to ≈12 mT at 17K, due to additional magnetic ordering. The zero-field data, in conjunction with transport data, allow construction of a complete phase diagram for this system. Transverse-field (1 kOe) μSR data forx=0.2 (T c =75 K) show that the muon depolarization is determined primarily by the Cu nuclear moments forT>T c , and by the vortex state forT c . Fitting the superconducting-state data to a BCS model yields an extrapolated zero-temperature magnetic penetration depth of 2170 Å. 相似文献