The structure of hyperalkaline aqueous solutions containing high concentrations of gallium--a solution X-ray diffraction and computational study.

Highly concentrated alkaline NaOH-Ga(OH)3 solutions with 1.18 M ≤ [Ga(III)]T ≤ 2.32 M and 2.4 M ≤ [NaOH]T ≤ 4.9 M (where the subscript T denotes total or analytical concentrations) have been prepared and investigated by solution X-ray diffraction and also by ab initio quantum chemical calculations. The data obtained are consistent with the presence of only one predominant Ga(III)-bearing species in these solutions, which is the tetrahedral hydroxo complex Ga(OH)4(-). This finding is in stark contrast to that found for Al(III)-containing solutions of similar concentrations, in which, besides the monomeric complex, an oxo-bridged dimer was also found to form. From the solution X-ray diffraction measurements, the formation of the dimeric (OH)3Ga-O-Ga(OH)3(2-) could not unambiguously be shown, however, from the comparison of experimental IR, Raman and (71)Ga NMR spectra with calculated ones, its formation can be safely excluded. Moreover, higher mononuclear stepwise hydroxo complexes, like Ga(OH)6(3-), which have been claimed to exist by others in the literature, were not possible to experimentally detect in these solutions with any of the spectroscopic techniques used.

Are there atomic orbitals in a molecule?

Effective atomic orbitals (AOs) have been calculated by the method of the "fuzzy atoms" analysis by using the numerical molecular orbitals (MOs) obtained from plane-wave DFT calculation, i.e., without introducing any atom-centered functions. The results show that in the case of nonhypervalent atoms there are as many effective AOs with non-negligible occupation numbers, as many orbitals are in the classical minimal basis set of the given atom. This means that, for nonhypervalent systems, it is possible to present the MOs as sums of effective atomic orbitals that resemble very much the atomic minimal basis orbitals of the individual atoms (or their hybrids). For hypervalent atoms some additional orbitals basically of d-type are also of some importance; they are necessary to describe the back-donation to these positive atoms. It appears that the d-type orbitals play a similar role also for strongly positive carbon atoms. The method employed here is also useful to decide whether the use of polarization functions of a given type is a matter of conceptual importance or has only a numerical effect.

Structural studies of water in hydrophilic and hydrophobic mesoporous silicas: an x-ray and neutron diffraction study at 297 K.

Water confined in a sol-gel network has been characterized by x-ray and neutron diffraction for two samples of mesoporous silica: one with a hydrophilic character (a nonmodified one) and another with a hydrophobic character (a modified one with a methylated internal pore surface). The pore size has been previously characterized [J. Jelassi et al., Phys. Chem. Chem. Phys. 134, 1039 (2010)] to have a mean pore diameter of approximately 55 Å. The diffraction measurements presented in this paper have been made at room temperature [293 K] for a filling factor of 0.45, giving a mean thickness of 8-9 Å for the water layer. The results show that the local order of the confined water molecules in the intermediate region of 3-6 Å is significantly different from that of the bulk water and also for the two different environments. For the hydrophilic sample, the siloxyl groups at the surface modify the water structure through the effects of interfacial hydrogen-bonding, which influences the orientational configuration of local water molecules and creates a modified spatial arrangement in the pore. In the case of the hydrophobic sample, there is no specific interaction with the pore wall, which is primarily van der Waals type, and the water molecules at the interface are differently oriented to create a hydrogen-bonded network linked more directly to the rest of the water volume. In the present circumstances, the thickness of the water layer has a relatively small dimension so that the interpretation of the measured diffraction pattern is not as straightforward as for the bulk liquids, and it is necessary to consider the effects of diffraction-broadening from a distributed sample volume and also the contribution from cross-terms that remain after conducting a "wet-minus-dry" analysis procedure. These analytic difficulties are discussed in the context of the present measurements and compared with the work of other groups engaged in the study of water confined in different environments. The present results, again, emphasize the complexity influencing the properties of water in a confined geometry and the strong influence of surface interactions on its behavior.

[Penetrating neck and facialinjury : arrow, an rare but still current etiology]. / Plaie cervico faciale : la fleche , une etiologie tres rare, encore d'actualite.

Penetrating neck and facial injuries are rare withonly a few cases reported in literature. Indeed, they are extremely rare in developed countries but remain relevant in our rural areas that are characterized by the recurrence of intertribal clashes. It was in thiscontextthatwereceivedtwo patients in the department of ENT of Niamey National Hospital. They presented with head and neck trauma. The middle stage of the neck in the first case and, in the left lateral face of the nasal pyramid in the second. Surgical management, under general anesthesia, enabled the removal of an arrow in both cases.

Les plaies pénétrantes cervico-faciales par flèche ont fait l'objet de très peu de publications dans la littérature. En effet, elles sont d'une extrême rareté dans les pays développés mais restent encore d'actualité dans nos régions à communautés majoritairement rurales, caractérisées par la récurrence des affrontements intertribaux. C'est dans un tel contexte que nous avons reçu deux patients au service d'ORL et CCF de l'hôpital national de Niamey. Ils présentaient un traumatisme cervico facial. L'agent vulnérant, une tige métallique, était enfoncé dans l'étage moyen du cou chez le premier et, dans la face latérale gauche de la pyramide nasale chez le second. Une prise en charge chirurgicale, sous anesthésie générale, a permis l'extraction d'une flèche dans les deux cas.

Car-parrinello molecular dynamics simulation of liquid formic acid.

First-principles molecular dynamics has been used to investigate the structural, vibrational, and energetic properties of formic acid, formic acid-formate anion dimers, and liquid formic acid in a periodically repeated box with 32 formic acid molecules. We found that in liquid formic acid the hydrogen-bonded clusters mainly consist of linear branching chains. From our simulation, we got good agreement with the available structural and dynamical data. We also studied the proton transfer in the cis-formic acid-formate anion dimer, and we showed that this proton transfer does not have any potential barrier. The hydrogen bonding statistics as well as the mean lifetime of the hydrogen bonds are analyzed.

CO adsorption and CO and O coadsorption on Rh(111) studied by reflection absorption infrared spectroscopy and density functional theory.

The adsorption of carbon monoxide on Rh(111) and on oxygen modified Rh(111) was investigated using thermal desorption spectroscopy, reflection absorption infrared spectroscopy (RAIRS), and density functional theory. The results show that CO adsorbs on Rh(111) in on top sites at low coverages. With increasing coverage hollow sites and bridge sites get occupied according to the RAIRS results. A new vibrational feature at high wave numbers was found in the on top region of the CO stretching frequency. This feature can be explained by a local high density CO structure where two CO molecules are adsorbed in the ( radical3x radical3)R30 degrees structure. The coadsorption of oxygen and carbon monoxide leads to a shift of the CO stretching frequency to higher wave numbers with increasing O to CO ratio. CO adsorption on a (2x1) oxygen layer is possible and RAIRS shows that the CO adsorbs in on top and most likely in bridge sites in this case.

A reflection absorption infrared spectroscopy and density-functional theory investigation of methanol dehydrogenation on Rh(111)V alloy surfaces.

The dehydrogenation reaction of methanol on a Rh(111) surface, a Rh(111)V subsurface alloy, and on a Rh(111)V islands surface has been studied by thermal-desorption spectroscopy, reflection absorption infrared spectroscopy, and density-functional theory calculations. The full monolayer of methanol forms a structure with a special geometry with methanol rows, where two neighboring molecules have different oxygen-rhodium distances. They are close enough to form a H-bonded bilayer structure, with such a configuration, where every second methanol C-O bond is perpendicular to the surface on both Rh(111) and on the Rh(111)V subsurface alloy. The Rh(111)V subsurface alloy is slightly more reactive than the Rh(111) surface which is due to the changes in the electronic structure of the surface leading to slightly different methanol species on the surface. The Rh(111)V islands surface is the most reactive surface which is due to a new reaction mechanism that involves a methanol species stabilized up to about 245 K, partial opening of the methanol C-O bond, and dissociation of the product carbon monoxide. The latter two reactions also lead to a deactivation of the Rh(111)V islands surface.