Hydroxylation and dehydroxylation at Cu(III) surfaces

X-ray photoelectron spectroscopy has shown how both chemisorbed oxygen present at a Cu(III) surface and nitric oxide introduced into the gas phase can induce hydroxylation of the surface from an adlayer of molecularly adsorbed water at 80 K. The interaction of water vapour with a clean Cu(III) surface is also reported.     

Prime and principal ideals in the algebraN +

Archiv der Mathematik -     

Determination of therapeutic plasma concentrations of tetrabenazine and an active metabolite by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method for the determination of tetrabenazine and a hydroxy metabolite in plasma is described. Tetrabenazine and the hydroxy metabolite are quantified as their dehydro derivatives using fluorescence detection. This method has been applied to the analysis of plasma samples from patients with Huntington's chorea and has been found to be sensitive, reliable and specific for tetrabenazine and the hydroxy metabolite. The plasma concentrations of tetrabenazine found in patients were lower than could be detected using previously published methods.     

Some studies of lead and iron adsorption on the W(100) surface by field emission microscopy

The behaviour of lead and iron adsorbed on the W(100) surface has been studied by probe hole field emission microscopy, field desorption, and by measurement of the total energy distribution (TED) of field-emitted electrons. Lead adsorbed at 300 K which reduces the work function of W(100) can be completely removed at 78 K by field desorption below 3.2 V Å^?1 and the resulting surface has both the work function and TED, which are characteristic of the clean plane. Condensation at 800 K followed by field desorption, results in a plane surface of work function 4.17 eV and an altered TED. This effect is attributed to the microfacetting, which is observed by LEED. The Swanson peak in the W(100) TED which is removed by submonolayer amounts of lead re-emerges at monolayer coverage when lead adopts the (1 × 1) structure. Such behaviour is consistent with the model proposed by Kar and Soven. A spectral peak observed when lead is adsorbed on the reconstructed W(100) surface is thought to derive from the atomic ¹D state. Adsorption of iron on a W(100) surface reduces φ considerably due to dipole formation and efficiently quenches the Swanson peak. Higher coverages introduce other peaks in the TED enhancement curve, and by adopting an energy scale based on the work of Hagstrum, an attempt is made to interpret the observed peaks in terms of the known energy structure of the free iron atom. One of the three spectral peaks is assigned to the 4s² ground state of the iron atom, and the remaining two peaks are tentatively attributed to atomic p-states. It is concluded that while the excited state structure of the iron atom is too complex to permit complete interpretation of the spectra, this approach offers the hope that, for simpler atoms, such features may be interpreted in this way.     

Adsorption of copper on single crystal planes of tungsten

Properties of copper condensed on selected areas of a thermally cleaned tungsten surface have been studied by probe hole field emission microscopy. Interpretation of the φ_hkl?$\text{}\text{?}$gq relationship observed on (211), (111) and (310) for adsorption at T > 300 K is based on hardsphere models of the plane surfaces upon which the first monolayer of copper raises φ_ithkl, the second reduces it to a minimum value, and the third achieves $\text{}\text{?}$gf_sat on each plane. At T > 300 K the relatively low binding energy of copper on (110) prevents is population below ～2$\text{}\text{?}$gq as previously observed for lead, and the plateaux in the φ₁₁₀?$\text{}\text{?}$gq curves are thought to result from the difficulty of nucleating the first and second monolayers of copper on (110). Comparison of our observations with those made by LEED/Auger techniques emphasise significant differences between the substrates used, in that, on field emitters (110) is step-free and surrounded by a sink/ source of adatoms, while the LEED specimen is stepped but has no comparable local sink/ source. The initial changes in φ are ascribed to formation of an adsorbate-substrate dipole whose sign and magnitude is controlled by electron equilibration between the substrate metal and a broadened and partly-filled resonance level lying approximately 5.2 eV below the vacuum level. Measurement of the total energy distribution of electrons field emitted from (110) and (132) supports this picture which contrasts with that of Polanski and Sidorski who consider the dipole sign and strength to be controlled principally by adsite geometry. Low activation energies characterise surface transport which is controlled by one-plane processes, and in some cases transport across the probed area is controlled by processes of relatively high activation energy which take place outside the examined plane.     

Spin-trapping of ligated boryl radicals

Amine- and phosphine-boryl radicals add to 2-methyl-2-nitrosopropane, 2,4,6-tri-t-butylnitrosobenzene, and phenyl-N-t-butylnitrone to give nitroxide spin-adducts and the application of these spin-trapping reactions as mechanistic probes is described.     

Migdal-Kadanoff study of Z4 symmetric systems with generalized action

For the Z₄ lattice gauge theory in four dimensions or the related spin system in two dimensions, we consider real space renormalization group transformations on the most general single plaquette or nearest neighbor action. The Migdal-Kadanoff recursion relations in differential form have several fixed points and predict a rich phase structure.     

Some results on Ramsey numbers using sumfree sets

Maximal sumfree sets chosen from the non-zero elements of galois group of order 2⁶ (i.e. GF(2⁶)?{0}) are found to be of size 13, 17, 18, 20 and 32 only. This gives a negative result to an investigation which would otherwise have delivered an exact value of the Ramsey number R(3,3,3,3;2).