Structural Transitions and Global Minima of Sodium Chloride Clusters

In recent experiments on sodium chloride clusters structural transitions between nanocrystals with different cuboidal shapes were detected. Here we determine reaction pathways between the low energy isomers of one of these clusters, (NaCl)35Cl-. The key process in these structural transitions is a highly cooperative rearrangement in which two parts of the nanocrystal slip past one another on a {110} plane in a direction. In this way the nanocrystals can plastically deform, in contrast to the brittle behaviour of bulk sodium chloride crystals at the same temperatures; the nanocrystals have mechanical properties which are a unique feature of their finite size. We also report and compare the global potential energy minima for (NaCl)NCl- using two empirical potentials, and comment on the effect of polarization.Comment: extended version, 13 pages, 8 figures, revte

Titanium Dioxide Nanoparticles: Synthesis, X-Ray Line Analysis and Chemical Composition Study

TiO2 nanoparticleshave been synthesized by the sol-gel method using titanium alkoxide and isopropanolas a precursor. The structural properties and chemical composition of the TiO2 nanoparticles were studied usingX-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy.The X-ray powder diffraction pattern confirms that the particles are mainly composed of the anatase phase with the preferential orientation along [101] direction.The physical parameters such as strain, stress and energy density were investigated from the Williamson- Hall (W-H) plot assuming a uniform deformation model (UDM), and uniform deformation energy density model (UDEDM). The W-H analysis shows an anisotropic nature of the strain in nanopowders. The scanning electron microscopy image shows clear TiO2 nanoparticles with particle sizes varying from 60 to 80nm. The results of mean particle size of TiO2 nanoparticles show an inter correlation with the W-H analysis and SEM results. Our X-ray photoelectron spectroscopy spectra show that nearly a complete amount of titanium has reacted to TiO2

ON THE "HIDDEN" MICROWAVE SPECTRUM OF THE ArCl2ArCl_{2} LINEAR CONFORMER

Author Institution: Department of Chemistry, University of WaterlooA new procedure has been developed to construct potential energy surfaces (PES) for atom-diatom interactions in terms of atom-atom pair potentials perturbed by intramolecular forces in the diatom, and applied to the $Ar-Cl_{2}$ Van der Waals complex. Microwave spectra of $ArCl_{2}$ have been calculated for two ground state PES, one purely ab initio, and one empirically corrected in terms of effective ArCI potentials, and compared with experiment. The purely {ab initio} PES has a well for the linear conformer slightly deeper than that for the T-shaped conformer, which topology can be at least qualitatively predicted by a simple atom-atom model. Inclusion of the zero-point energies revises the relative binding in the two configurations, due to the degeneracy of the bending vibrations for the linear configuration. The linear conformer supplies additional lines to the microwave spectrum of the system, as yet unobserved experimentally. A simple correction involving empirical information for the ArCI potentials alone transforms the well for the T-shaped conformer into the global minimum, with the dissociation energy reproducing the experimental value to within 0.5%, and provides microwave transition energies deviating from experimental values by 1% only. A further 2-parameter scaling allows reproduction both of the experimental $D_{e}$ (within the uncertainties of the measurements) and of the positions of all observed microwave lines (within 0.02%) for both the purely {ab initio} PES and the empirically corrected PES. The relative energies of the rotational levels for the {ab initio} $Ar-Cl_{2}$ potential indicate a much weaker population of the well associated with the linear conformer relative to that for the T-shaped conformer, thus strongly affecting the observability of the corresponding transitions. A series of new microwave lines are predicted, associated with the rotational levels of the linear $Ar-Cl_{2}$ conformer, which may be populated under appropriate experimental conditions. Reasons for their inaccessibility for previous observations are discussed

PREDICTED MICROWAVE SPECTRUM AS A SIMULTANEOUS PRODUCT OF BOTH LINEAR AND T-SHAPED CONFORMERS OF THE GROUND STATE He−Cl2He-Cl_{2} SYSTEM

Author Institution: Department of Chemistry, University of WaterlooLowest energy rovibrational states are calculated for a high quality ab initio potential energy surface (PES) of the $HeCl_{2}$ Van Der Waals complex. The PES has wells of comparable depths for both linear (L) and T-shaped (T) conformers and thus produces two sets of rovibrational levels, the set associated with the L-well having higher energies due to difference between the two $D_{0}$ values. Although the ground rovibrational levels of each conformer lie above the potential barrier separating the two wells, the associated wavefunctions reflect the presence of the other well only weakly, as indicated by the low local maxima in the probability densities at the other well positions. The presence of the L-well is found to affect the order of the rotational levels associated with the T-well. The microwave spectra originating from each of the two conformers are simulated, and suggest a possibility for direct confirmation of the existence of the L-well. The positions of spectral lines associated with the T-shaped conformer are found to be quite sensitive to the binding energy for the linear conformer

Analyse des diagraphies de forage, sequences sedimentaires et paleogeographie des series argilo-greseuses deposees au passage Silurien-Devonien dans la syneclise est-saharienne (bassin d'Illizi et partie algerienne du bassin de Ghadames)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc