Observation of hydroxyl groups by 17O solid-state multiple quantum MAS NMR in sol-gel-produced silica

17O NMR parameters (CQ, eta, delta(iso) and T1) are reported for both Si-O-Si and Si-OH fragments within a silica gel. The Si-OH units have a wide spread of parameters but are typically characterised by a very short T1 (approximately 0.1 ms) and CQ < 200 kHz. These observations have extremely important implications for the quantification of such units in these gels and related glassy materials by 17O NMR. In light of these observations, the 17O NMR experiments have been optimised and a distinct resonance from the OH group is observed in 1D static and magic angle spinning (MAS) NMR measurements as well in the multiple quantum (MQ) experiment.     

Correlation effects in the surface energy of metals

It is argued that the correlation energy plays a minor role in the surface energy of metals, compared to kinetic, electrostatic and exchange energies. Recent work in which the surface energy is attributed primarily to changes in plasmon zero point energy during the creation of the surface is criticized.     

Optical spectra of CsI,CsBr, ZuGeP2, and SbSI

We report here the study of the normal reflectivity spectra R and the corresponding derivative spectra (1/R) dR/dE of SbSI between 2 and 6 eV. The spectra show very strong anisotropy. We have also tried to use the change of the wavelength modulation spectrum to monitor the change in the band structure of SbSI due to the phase transition at 292 °C (D_2h¹⁶→C_2v⁹). Careful examination of the spectra at various temperatures around T_c shows no observable change. We report also the wavelength-modulated reflectivity spectra of the chalcopyrite crystal ZnGeP₂ at 5 K between 2 and 6 eV, for E∥ C and E⊥ C. The experimental results are compared with the theoretical band structure calculation by de Alvarez and Cohen. We also present measurements on CsBr, CsI in the vacuum uv (between 5 and 8 eV) at 1.8K, showing noticeable difference with previous reflectivity measurements at 77 K.     

Fermionic atoms in a three dimensional optical lattice: observing Fermi surfaces, dynamics, and interactions

We have studied interacting and noninteracting quantum degenerate Fermi gases in a three-dimensional optical lattice. We directly image the Fermi surface of the atoms in the lattice by turning off the optical lattice adiabatically. Because of the confining potential, gradual filling of the lattice transforms the system from a normal state into a band insulator. The dynamics of the transition from a band insulator to a normal state is studied, and the time scale is measured to be an order of magnitude larger than the tunneling time in the lattice. Using a Feshbach resonance, we increase the interaction between atoms in two different spin states and dynamically induce a coupling between the lowest energy bands. We observe a shift of this coupling with respect to the Feshbach resonance in free space which is anticipated for strongly confined atoms.     

33S solid state NMR of sulphur speciation in silicate glasses

³³S solid-state NMR is reported from some model crystalline sulphides, sulphates, sulphites and thiosulphates. This is the first report of ³³S NMR signals of the latter two species from a solid. Good quality spectra, which have distinct, well separated shift ranges can be identified for all these groupings, except for sulphites and hydrogen sulphites whose resonances are very broad. Nonetheless the presence of sulphites and hydrogen sulphites can be confirmed from their characteristic sharp, intense time domain echoes. ³³S MAS NMR is also applied to a range of dry and hydrous silicate glasses with 1wt% 99 at% ³³S-enriched sulphur. It is clear that in all these glasses sulphate is present, and in mixed cation systems there is some evidence of preferential association of sulphate with a specific cation. In a dry potassium silicate glass sample two resolved ³³S resonances are observed, a sulphate, and the second from thiosulphate. Hence solid state ³³S NMR is shown to be a feasible probe that can be applied to this problem that can readily distinguish different sulphur species.     

Resonator-enhanced optical dipole trap for fermionic lithium atoms

We demonstrate a novel optical dipole trap that is based on enhancement of the optical power density of a Nd:YAG laser beam in a resonator. The trap is particularly suited for experiments with ultracold gases, as it combines a potential depth of the order of 1 mK with storage times of several tens of seconds. We study the interactions in a gas of fermionic lithium atoms in our trap and observe the influence of spin-changing collisions and off-resonant photon scattering. A key element in reaching long storage times is the use of an ultralow-noise laser. The dependence of storage time on laser noise is investigated.     

Determination of the magnetic symmetry of hexagonal manganites by second harmonic generation

Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination of complex magnetic structures. Experimental efforts are simplified and new degrees of freedom are opened. Thereby, some principal or technical restrictions of neutron or magnetic x-ray diffraction experiments are overcome. High spatial resolution leads to additional information about magnetically ordered matter. As an example, the noncollinear magnetic structure of the hexagonal manganites RMnO3 ( R = Sc, Y, Ho, Er, Tm, Yb, Lu) is analyzed. The results show that some earlier conclusions on their magnetic symmetry and properties should be revised.     

Iodometric determination of ferricyan in the presence of copper,silver, cadmium and zinc

Ferricyan can be determined in the presence of copper, silver and cadmium by addition of potassium ferrocyanide, filtration of the ferrocyanides of copper, silver and cadmium formed in this reaction, and titration of the potassium ferricyanide contained in the filtrate. In the case of silver, the ferricyan can also be determined without filtration by addition of potassium iodide and titration of the ferricyanide. In the case of zinc, potassium, ferrocyanide is added and without filtration the ferricyanide titrated.     

Extremely Low Vapor-Pressure Data as Access to PC-SAFT Parameter Estimation for Ionic Liquids and Modeling of Precursor Solubility in Ionic Liquids

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10⁻⁵ Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C₂mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF₄]⁻, hexafluorophosphate [PF₆]⁻, bis(trifluoromethylsulfonyl)imide [NTf₂]⁻) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term.