Interatomic bonding in oxygen-stabilized Ti2 Ni-type compounds

X-ray photoelectron-spectroscopic studies of oxygen-stabilized Ti₂ Ni-type compounds Ti₄M₂O_x (M = Fe, Co and Ni;x = 0.5, 1) have revealed some charge transfer from the titanium to the oxygen atoms with no direct involvement of the second metallic constituent M. Limited partial ionicity is deduced from the measured core-electron binding energies, which are intermediate between the respective values for TiO₂ and for the pure elements (Ti⁰, O₂). In particular, approximate estimations of the partial charge residing on Ti are consistent with the charges derived for the oxygen atoms, and the results correlate with the TiO distance in Ti₄M₂O, as compared with corresponding data for other systems. The implications of the interatomic bonding for the hydrogen absorption properties of the oxygen-stabilized compounds are discussed.     

Truncation of the correlation consistent basis sets: an effective approach to the reduction of computational cost?

The systematic reduction of commonly used basis sets as a means to reduce computational cost is examined for a small test set of molecules, which includes H(2), CH(4), NH(3), H(2)O, HF, and HCN. Coupled cluster with single, double, and quasiperturbative triple excitations calculations were performed using both the correlation consistent basis sets, and a set of systematically reduced basis sets to examine both the impact of the reduction upon the accuracy of the structures and energies, and the computational cost savings achieved. The effect of several truncation scenarios upon basis set convergence is also examined. Overall, for the systems studied, a reduction can occur which preserves the well-established systematic convergence behavior of the correlation consistent basis sets.     

The interaction of O2 with the surface of polycrystalline gadolinium at the temperature range 300–670 K

Auger-Electron-Spectroscopy (AES) and Direct-Recoils-Spectrometry (DRS) were applied to study the interaction of O₂ with a polycrystalline gadolinium surface, in the temperature range 300–670 K and oxygen pressure up to 2 × 10^? 6 Torr. It has been found that initial uptake of oxygen, at coverage measurable by the techniques used here, results in rapid oxide island formation. The subsurface is believed to be a mixture of oxide particles and oxygen dissolved in the Gd metal, the latter being the mobile species, even at relatively low temperatures.Enhanced inward diffusion of oxygen starts as early as 420 K and dictates the surface oxygen concentration and effective thickness of the forming oxide. The oxygen accumulation rate at the near-surface region, as measured by the O(KLL) AES signal intensity, goes through a maximum as a function of temperature at 420 K. This is a result of the combination of still efficient oxygen chemisorption that increases surface occupation and slow inward diffusion. The thickest oxide, ~ 1.7 nm, is formed at 300 K and its effective thickness was found to decrease with increasing temperature (due to oxygen dissolution into the metal bulk).Diffusion coefficients of the oxygen dissolution into the bulk were evaluated for various temperatures utilizing models for infinitely thin oxide layer and thick oxide layer, respectively. The best fit under our experimental procedure was obtained by the thick layer model, and the coefficients that were calculated are D₀ = 2.2 × 10^? 16m²s^? 1 and E_a = 46kJ/mol.     

Die Trennung der Glukose und Fruktose

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