Single d-metal atoms on F(s) and F(s+) defects of MgO(001): a theoretical study across the periodic table

Single d-metal atoms on oxygen defects F(s) and F(s+) of the MgO(001) surface were studied theoretically. We employed an accurate density functional method combined with cluster models, embedded in an elastic polarizable environment, and we applied two gradient-corrected exchange-correlation functionals. In this way, we quantified how 17 metal atoms from groups 6-11 of the periodic table (Cu, Ag, Au; Ni, Pd, Pt; Co, Rh, Ir; Fe, Ru, Os; Mn, Re; and Cr, Mo, W) interact with terrace sites of MgO. We found bonding with F(s) and F(s+) defects to be in general stronger than that with O2- sites, except for Mn-, Re-, and Fe/F(s) complexes. In M/F(s) systems, electron density is accumulated on the metal center in a notable fashion. The binding energy on both kinds of O defects increases from 3d- to 4d- to 5d-atoms of a given group, at variance with the binding energy trend established earlier for the M/O2- complexes, 4d < 3d < 5d. Regarding the evolution of the binding energy along a period, group 7 atoms are slightly destabilized compared to their group 6 congeners in both the F(s) and F(s+) complexes; for later transition elements, the binding energy increases gradually up to group 10 and finally decreases again in group 11, most strongly on the F(s) site. This trend is governed by the negative charge on the adsorbed atoms. We discuss implications for an experimental detection of metal atoms on oxide supports based on computed core-level energies.     

Oligosaccharide Analogues of Polysaccharides. Part 9. Synthesis and Thermolysis of Acetylenosaccharide-Derived 1,2-Dialkynylbenzenes

Thermolysis of the 1,2-bis(glucosylalkynyl)benzenes 6 and 16 was studied to evaluate the effects of intramolecular H-bonding on the activation energy of the Bergman-Masamune-Sondheimer cycloaromatization, and to evaluate the use of the cycloaromatization for the synthesis of di-glycosylated naphthalenes. The dialkynes were prepared by cross-coupling of the O-benzylated or O-silylated glucosylalkynes 1 and 4 (Scheme 1). Thiolysis of the known 1 , or acetolysis of 1 , followed by deacetylation ( →2→3 ) and silylation gave 4 . Cross-coupling of 1 or 4 with iodo- or 1,2-diiodobezene depended upon the nature of the added amine and on the protecting group, and led to the mono- and dialkynylbenzenes 5 and 6 , or 12, 13 , and 15 , respectively. The benzyl ethers 5 and 6 gave poor yields upon acetolysis catalyzed by BF₃ · OEt₂, while Ac₂O/CoCl₂ · 6 H₂O transformed 6 in good yields into the regioselectively debenzylated 10 . Desilylation of 7 and 13 gave the alcohols 8 and 14 , respectively. Thermolysis of 6 in PhCl gave 22 and 23 , independently of the presence or absence of 1,4-cyclohexadiene; 23 was formed from 22 (Scheme 2). Acetolysis of 22 gave the hexaacetate 24 that was completely debenzylated by thiolysis, yielding the diol 26 and trans-stilbene, evidencing the nature and position of the bridge between the glucosyl moieties (Scheme 3). Thiolysis of 22 yielded the unprotected 2,3-diglucosylnaphthalene 28 , a new type of C-glycosides. Depending upon conditions, hydrogenation of 22 led to 29 (after acetylation), 30 , or 32 . NMR and particularly NOE data evidence the threo-configuration of the bridge. The structure of 23 was confirmed by hydrolysis to the diol 34 and diphenylacetaldehyde, and by correlation of 23 with 22 via the common product 31 . Formation of 22 is rationalized by a Bergman cyclization to a diradical, followed by regioselective abstraction of a H-atom from the BnO? C(2) group, and diastereoselective combination of the doubly benzylic diradical (Scheme 4). While thermolysis of 3 in EtOH sets in around 140°, 16 did not react at 160° and decomposed at 180–220°. No evidence for intramolecular H-bonds of 16 , as compared to 14 , were found.     

Study of the Electronic Structure of Ni(eta(5)-C(5)H(5))(NO) by Variable-Photon-Energy Photoelectron Spectroscopy and Density Functional Calculations

Photoelectron spectra, with photon energies varying from 18 to 120 eV, have been measured for Ni(eta(5)-C(5)H(5))(NO). Relative partial photoelectron cross sections and branching ratios have been evaluated for the first three valence ionization bands. He I and He II photoelectron spectra have been remeasured for Ni(eta(5)-C(5)H(5))(NO) and Ni(eta(5)-C(5)H(4)CH(3))(NO). In the latter case, the fine structure on the first band differs from that in the previously published spectrum. Density functional calculations have been carried out to determine the ionization potentials of the lowest lying states of Ni(eta(5)-C(5)H(5))(NO) as well as the corresponding photoionization cross sections and the resulting branching ratios using the LCGTO-DF and LDKL-DF methods, respectively. Both experimental and theoretical investigations lead to an ion state ordering (2)E(1) < (2)E(2) approximately (2)A(1)< (2)E(1) and an assignment of (2)E(1) states to the first and third bands with the (2)A(1) and (2)E(2) states comprising the second band. This differs from the original assignment in the literature, where the (2)A(1) ionization was assigned to a high-energy shoulder on the first band. The separation of this shoulder from the main band maximum of 0.23 eV (1850 +/- 81 cm(-)(1)) suggests that it may be caused by excitation of the NO stretching vibration in the ion. The neutral molecule has a NO stretch of 1832 cm(-)(1); the calculated energies for the neutral molecule and the cation are 1845 and 1911 cm(-)(1), respectively. Agreement between calculated and experimental ionization energies and good matching of the theoretical and measured branching ratios support the new assignment of the photoelectron spectrum.     

Relativistic effects on geometry and electronic structure of small Pdn species (n=1, 2, 4)

Relativistic effects on the properties of small neutral Pd_n species (n=1, 2, 4) and Pd₂⁻ have been examined for the first time at the all‐electron level by performing scalar‐relativistic and nonrelativistic density functional calculations using a gradient‐corrected density functional. Relativistic effects are found to be important: They lead to a contraction of bond lengths, increase of vibrational frequencies, and a significant enhancement of binding energies. While relativistic effects are quite uniform for several states of Pd₄, they vary for the states examined for Pd₂, leading to a change of ground state due to relativity. The calculated relativistic properties of Pd₂ and Pd₂⁻ are in good agreement with available experimental data from mass spectrometry and photoelectron spectroscopy. For Pd₄ three‐dimensional structures are found to be preferred to planar ones and many nearly isoenergetic isomers exist. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 405–416, 1999     

Positron lifetime and microstructural characterisation of a-Si:H deposited by low temperature HW-CVD on paper substrates

In thin film electronic applications, the limiting factor, in terms of cost and usability, is generally the substrate material. As a consequence, different materials are being investigated as potential lightweight, inexpensive and flexible substrates. In this respect, we have been the first research collaboration to produce silicon-based electronics on paper substrates. Here we present structural characterisation of hydrogenated amorphous silicon (a-Si:H) layers deposited on 80 g m⁻² wood-free paper, with and without an intermediate metallic interlayer, using low temperature hot wire chemical vapour deposition (HW-CVD). Both pulsed positron beam profiling and X-ray diffraction studies indicate that the growth rate on the uncoated substrate is slightly higher than with prior metallization. There is no evidence of a crystalline phase or voids in the a-Si:H layers. The internal defect structure is similar, with a dominant dangling bond complex of similar size, which has a slightly longer lifetime than in layers grown at higher temperatures on conventional substrates.     

Multielementanalyse von Schwebst?uben der Stadt Ulm und Vergleich der Luftbelastung mit anderen Regionen

Zusammenfassung Es wurden die Konzentrationen von 54 Elementen in der Luft der Stadt Ulm, die als Beispiel für eine mittelgroße Industriestadt angesehen werden kann, bestimmt. Hierfür wurden die auf Celluloseacetatmembranfiltern mit durchflußgeeichten Geräten gesammelten Schwebstäube von zwei Probenahmeorten in der Innenstadt (Stadtzentrum/Münster und Ehinger Tor — ein stark frequentierter Verkehrsknotenpunkt) mittels INAA, ETAAS und Mikrotitrimetrie analysiert.Im Vergleich mit dem Stadtzentrum wurde in der Luft des Standortes Ehinger Tor für fast alle Elemente eine deutlich höhere Konzentration gemessen, die im allgemeinen auf eine höhere Gesamtstaubkonzentration zurückzuführen ist. Lediglich die Elemente Br, Cr, Cu, Mo, Pb und Sb sind auch im Luftstaub dieses Sammelortes erheblich angereichert. Dies kann durch den Straßenverkehr als Emissionsquelle an diesem stark frequentierten Verkehrsknotenpunkt erklärt werden. Im Stadtzentrum wurden die Elementhöhenprofile durch Probenahme in 2, 16 und 70 m über dem Boden ermittelt. Für die meisten Elemente konnte dabei kein wesentlicher Einfluß dieses Probenahmeparameters auf die Konzentration festgestellt werden.Allgemein liegen die ermittelten Konzentrationen im Rahmen der wenigen anderen bisher untersuchten mittelgroßen Städte.

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Multielement analysis of airborne dust of the city of ulm and comparison with other regions

Summary The concentrations of 54 elements were determined in the air of the city of Ulm, which can serve as an example for a well industrialized city of medium size. The airborne dust samples were collected at two places (city center/Münster and Ehinger Tor — a center of traffic) with flow calibrated samplers on cellulose acetate membrane filters, and analyzed by INAA, ETAAS and micro titration.The higher concentrations of nearly all elements in the air of the sampling place Ehinger Tor in comparison with that of the city center is approximately proportional to the increased concentration of the whole dust at this sampling place. Only the Elements Br, Cr, Cu, Mo, Pb and Sb are enriched in the airborne dust, which can be explained by the heavy street traffic at this sampling place. In the city center, samples were collected in the height of 2, 16 and 70 m and, for most elements, only a slight effect of the height on the concentration was found.The element concentrations determined in the air of the city of Ulm are generally at similar level as available results for some few other medium large cities.

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Herrn Prof. Dr. Hartkamp zum 60. Geburtstag gewidmet     

Exact results for one-dimensional disordered bosons with strong repulsion

We study one-dimensional disordered bosons with strong repulsive interactions. A Bose-Fermi mapping expresses this problem in terms of noninteracting Anderson-localized fermions, whereby known results for the distribution function of the local density of states, the spectral statistics, and density-density correlations can be transferred to this new domain of applicability. We show that disorder destroys bosonic quasi-long-range order by calculating the momentum distribution, and comment on the experimental observability of these predictions in ultracold atomic gases.     

Improved limit on the rate of the decay K+ --> pi(+)&mgr;(+)e(-)

We report results of a search for the lepton-family number violating decay K+-->pi(+)&mgr;(+)e(-) from data collected by experiment E865 in 1996 at the Alternating Gradient Synchroton of Brookhaven National Laboratory. We place an upper limit on the branching ratio at 3.9x10(-11) ( 90% C.L.). Together with results based on data collected in 1995 and an earlier experiment, E777, this result establishes a combined 90% confidence level upper limit on the branching ratio at 2.8x10(-11). We also report a new upper limit on the branching ratio for pi(0)-->&mgr;(+)e(-) of 3.8x10(-10) ( 90% C. L.).     

Strong interaction shifts and widths in light kaonic atoms

Energy shifts and line widths of X-ray transitions in kaonic atoms have been measured with an accuracy of about 10%. These data have been interpreted in terms of an optical potential. Whereas earlier approaches based on the free K⁻N scattering lengths fail to reproduce the data, a set of effective parameters consistant with all now available experiments could be derived.