The use of direct recoil spectrometry (DRS) for the study of water vapor interactions on polycrystalline metallic surfaces—the H2O/U and H2O/Ti systems

Using direct recoil spectrometry (DRS), the shadowing of surface H atoms by neighboring O atoms can differentiate between full and partial dissociation routes of water molecules on the surface as well as point to the geometrical arrangements of hydroxyl surface groups. The H₂O/U and H₂O/Ti systems were compared. It has been found that different mechanisms control the water-surface interactions in these systems.For the H₂O/U system, a simple direct-collision (Langmuir-type) dissociative chemisorption controls the process. Two consecutive stages were identified: (i) below ∼70% monolayer coverage, a complete dissociation of water into oxygen ion and two H atoms, which chemisorb on the remaining unreacted metallic surface and (ii) above about 70% of a full layer coverage, three dimensional oxide islands start to form, causing partial dissociation of water and the formation of surface hydroxyls.For the H₂O/Ti system, a more complicated mechanism, which involves a precursor state, seems to control the process. In that case, two concurrent routes act simultaneously. In addition to the simple direct-collision mechanism, water precursor clusters (bound by hydrogen bonds), which partly dissociate, result in chemisorbed tilted hydroxyl clusters (even at low-coverage). The relative contributions of the precursor route and the direct-collision route are pressure dependent, with the former being dominant at higher exposure pressures.     

Zum Nachweis freier S?ure im Magensaft

Ohne Zusammenfassung     

Comments on "solvation parameters. 2. A simplified molecular topology to generate easily optimized values"

A polemic is presented in regards to a recent paper by Laffort and Héricourt [J. Chem. Inf. Model. 2006, 46, 1723-1734].     

The weak electroproduction of Σ in electron–proton scattering

We obtain differential cross sections for the reaction e⁻+p→Σ⁰+ν_e, for incident electron energies from 0.5 GeV to 6.0 GeV. This calculation is phenomenologically based and makes use of SU(3) and SU(2) relations. We obtain contributions of the individual form factors to the differential cross section and show that the vector current form factor dominates in the region of observability. We also obtain reaction rates for a standard set of conditions. Finally we compare this case with that for Λ production and discuss what might be learned from this reaction concerning the structure of the weak, strangeness changing, hadronic current.     

Ueber Nachweis und Bestimmung der Salzs?ure des Magensafts

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Time differential perturbed angular correlation studies of hafnium hydrides

The dependence of the electric field gradients (EFG) in Hafnium-Hydride systems as a function of the composition H/Hf in the cubic δ and tetragonal ε phases were investigated using the time-dependent perturbed angular correlation (TDPAC) technique, with¹⁸¹Ta as the nuclear probe. Two EFGs were found in the ε phase, indicating the existence of two major symmetries surrounding the Ta probe. The results indicate that the trend of the EFGs, in the ε phase, are due to the changes in the lattice parametersa _o,c _o as hydrogen is added to the Hf-H system. In the δ phase, only one major symmetry was found. Both phases are characterized by broad frequency distributions and large anisotropies.     

Morphology changes due to AC induced electromigration in Gd islands on W(1 1 0)

Gd islands were grown on W(1 1 0) surface by evaporating Gd on the substrate at room temperature and subsequent annealing. STM images reveal in many cases islands which have a deep hole inside them. The appearance of the hole is associated with the application of an AC field. No such holes appear when the sample is heated by a DC current. We show that this can be explained by the combined affect of the AC field and the barrier to diffusion introduced by steps that can create a nucleus for further growth of an island which includes a hole in the middle. This may be generalized to a technique of tailoring the size, shape and distances of islands by, for example, two orthogonal AC fields with a phase delay of 90° between them.     

Evaluation of the kinetics and mechanisms of hybriding reactions

A scheme for a kinetic study of the hydriding reactions of metals is presented. This scheme is based on a combined kinetic and metallographic study of hydride formation in metallic samples with well defined geometrical shapes.Since the directly measured kinetic quantity (which is the overall reaction rate) depends also on parameters which are not related to the intrinsic nature of the reaction (i.e., on the geometrical shape of the sample and on the topochemistry of the product development) an intrinsic kinetic parameter IKP, should be evaluated in order to characterize uniquely a given reacting system. The choices for these intrinsic parameters and the methods for their evaluation are presented.Different theoretical models for the hydriding reactions are summarized and the predicted pressure-temperature dependence of the IKP's are discussed in light of these models. In some cases the comparison between the experimental and theoretical pressure-temperature behavior may elucidate the mechanisms controlling the respective reactions.     

Superconductivity of palladium tritide

The superconductivity and reverse isotope effect have been measured in high pressure tritium gas loaded palladium tritide (PdT_x) for x values from 0.72 to 0.81.