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Coordination chemistry of the bis(trifluoromethylsulfonyl)imide anion: molecular interactions in room temperature ionic liquids

Room temperature ionic liquids composed of bis(trifluoromethylsulfonyl)imide anions and 1,3-ethylmethylimidazolium (EMI) cations are shown to stabilize monomeric ligand deficient transition metal complexes via four distinct binding modes: monodentate nitrogen or oxygen coordination and/or bidentate oxygen-oxygen' or nitrogen-oxygen coordination (eta1-N, eta1-O, eta2-O,O' and eta2-N,O).     

William B. Guenther,Chemical Equilibrium. A Practical Introduction for the Physical and Life Sciences,Plenum Press,New York-London (1975), 248 pp., price U.S. $ 23.40

The adsorption and related interfacial behavior of uracil at a mercury electrode/electrolyte solution interface has been studied by differential capacitance and maximum bubble pressure methods in 0.5 M NaF plus 0.01 M Na₂HPO₄ buffer pH 8.0. At concentrations below 24 mM uracil is adsorbed in a flat orientation on the electrode surface and occupies an area of 63 Ų. At higher concentrations and at potentials close to ?0.5 V the adsorbed uracil undergoes a reorientation and adopts a perpendicular stance on the electrode surface where it occupies an area of 39 Ų. In this perpendicular stance uracil undergoes a strong intermolecular stacking interaction with its neighbors similar to that observed between adjacent pyrimidines in nucleic acids.     

Modelling of solid state voltammetry of immobilized microcrystals assuming an initiation of the electrochemical reaction at a three-phase junction

The electrochemical reduction of a solid compound characterized by mixed ionic/electronic conductivity, immobilized on an electrode surface and in contact with an electrolyte solution, has been studied theoretically. The uptake or expulsion of electrons and electrolyte cation is coupled to maintain electroneutrality and is assumed to obey Fick's law of diffusion. Starting with the fully oxidized species, the simultaneous uptake of cations and electrons will be possible at the three-phase junction only, where electrode, solid and electrolyte solution meet. From this point, electrons and cations diffuse perpendicularly into the crystal lattice. The reaction zone grows owing to the formation of the electronically and ionically conducting reduced product. Two- and three-dimensional models have been utilized to simulate the diffusion and the current flow in response to an applied potential step. The resulting chronoamperometric curves have been analyzed with the help of fitting procedures. Under certain conditions, a transition of the three-phase reaction to a pure two-phase reaction occurs. This transition to a two-phase condition is the reason that a number of equations for the exhaustive conversion are similar to those known for planar diffusion, for example. To illustrate this, and for a better understanding of the phenomena, concentration profiles are presented for different degrees of the reaction and for varied simulation conditions. It is demonstrated how geometrical properties like crystal shape (cuboid with x ≠ y ≠ z) and crystal size as well as physical properties, e.g. the diffusion coefficients, govern the electrochemical behavior of mixed ionic/electronic conductors and form the basis of the current-time functions. The numerical simulation of a two-dimensional semi-infinite model of the reaction at the three-phase junction gives results comparable to an algebraical approach. The finite-difference method turned out to be suitable to solve the problems arising from the three-dimensional and finite diffusion conditions and from different crystal shapes. Received: 24 November 1999 / Accepted: 22 February 2000     

A rapid technique to determine the internal area function of finite-length ducts using maximum length sequence analysis

This paper describes a rapid technique for reconstruction of the internal area function of a duct using blockage-induced eigenvalue shifts determined from eigenfrequencies measured under two sets of duct termination boundary conditions. A single broad band maximum length sequence (MLS) measurement of short duration is utilized to obtain the transfer function of the duct, which in turn can be utilized to determine its eigenvalue shifts and subsequently its internal area function using an inverse perturbation technique. The reconstruction results display the same order of accuracy as those obtained previously using swept sine measurements of extended duration. An expression for the determination of the area function is presented utilizing resonant frequency information alone, thus rendering duct length determination unnecessary. A computational routine further simplifies the process such that the accuracy of the technique could be ascertained for a range of configurations including longer ducts and ducts that initially have nonuniform internal cross section over their length. Development of a relationship between obstacle length and wavelength of the lowest eigenfrequency required for successful reconstruction is also described. This is an important result for longer ducts where measurement of lower eigenfrequencies may present problems using standard measurement equipment.     

A new technique for the activation analysis of bromine

In the 14 MeV activation analysis of the halogens it has been customary practice to utilise the gamma-spectra of the various radioactive isotopes produced for the determination involving gamma-spectral analysis of a conventional kind. In this work the Cerenkov radiation produced in perpex is measured in the tritium channel of a liquid scintillation counter. The method shows an increased sensitivity particularly in the case of bromine determinations.     

Characterizing holes in duct walls using resonance frequencies

The current paper demonstrates that the technique recently used by de Salis and Oldham for the sizing and location of blockages in ducts using resonance and antiresonance value shifts [J. Sound Vib. 221(1), 180-186 (1999)] may be successfully applied to the detection, location, and sizing of small holes in duct walls. It is shown that when the blockage area function reconstruction process is applied using resonance and antiresonance frequencies determined from a single measurement of sound pressure within a duct, the position of a hole in the duct wall is revealed as the beginning of an apparent gradual expansion. This expansion is termed the effective expansion function and emanates from an initial positive dc shift. Once the hole has been located, a simple impedance model of the duct incorporating the hole location and the measured wave number at the first-order duct resonance may be derived which allows the determination of the radius of the side hole from a simple quadratic equation. This hole-sizing technique is also successfully applied to thin slits in duct walls using an equivalent radius approach, and is shown to be highly accurate for slit-shaped holes with cross-sectional length to width aspect ratios of up to 28:1.