Applications of micro-analysis to individual environmental particles

An overview is given of the recent applications of micro-analytical techniques to single particle environmental research performed at the University of Antwerp since 1990. Automated electron probe X-ray micro-analysis, laser microprobe mass spectrometry and micro-particle induced X-ray emission are the techniques most used for aerosol, aqueous suspension and sediment characterisation. Other techniques like scanning transmission electron microscopy, electron energy loss spectroscopy, Fourier transform infra red microscopy and secondary ion mass spectrometry have only recently been implemented into environmental research.     

The computed force constants and vibrational spectra of cubane

The geometry, complete harmonic force field, and dipole moment derivatives of cubane, C₈H₈, have been calculated at the Hartree-Fock level using a 4–21 Gaussian basis set. The infrared and Raman spectra of cubane and four deuterated derivatives were calculated and compared with previously observed spectra. A set of five scale factors for the calculated force constants was then derived by least-squares fitting of the fundamental vibrational frequencies calculated from the scaled force field to the frequencies obtained by direct experimental measurement. The resulting scaled quantum-mechanical (SQM) force field, containing 73 unique elements, is believed to give an accurate representation of the harmonic vibrational potential of cubane. In most cases, the spectral assignments previously made from purely empirical considerations were confirmed, but a few corrections are proposed. The only major alteration is for an A_2u mode revised to appear at 1030 cm^?1 in the undeuterated molecule. Coriolis constants and approximate infrared intensities are also calculated.     

Surface- and microanalysis as a tool for studying the corrosion of aluminium

Corrosion phenomena of Al-1 % Si bond wires, observed after life testing of certain transistors, are studied. The following information is derived from laboratory simulation tests: the kinetics of the corrosion process, information about the corrosion mechanism and critical parameters, especially the influence of the environmental gas and Si content and finally the identification of the corrosion products and their comparison with those found for the transistor. It is demonstrated, using a combination of several surface analytical techniques, that the A1 pitting corrosion is induced and enhanced by the presence of water as a transport medium and surface electrolyte in an oxygen-rich atmosphere, with chloride ions as a stimulating and activating species. The effect of 1 % Si in the wire consists in acceleration of the corrosion rate, and is probably due to grain boundary effects. All critical corrosion parameters could be traced in the transistor system by electron microscopy, laser microprobe mass analysis and residual gas (and moisture) analysis by mass spectrometry.     

Multiple collisions in molecular beam scattering experiments

Due to the forward peaked differential cross section for elastic atom—atom scattering the effect of multiple collisions has to be considered in the analysis of crossed beam measurements of the total cross section and especially of the small angle differential cross section at large values of the beam attenuation. At angles θ ≈ θ₀, with θ₀ the quantum mechanical scaling angle of the elastic differential cross section, the correction for the latter case amounts to 20% at beam attenuations I/I₀ = exp(?1). Firstly, a careful analysis of the probabilities for single and multiple scattering is given, resulting in an expression for the measured beam signals which is correct for all values of the beam attenuation. The probability for multiple scattering is then calculated for an inverse power potential V(r) = ?C_sr^?s, with s = 4 through s = 7, which include both the case of ion—atom scattering (s = 4) and atom—atom scattering (s = 6). The results are given as effective differential cross sections σ_n(θ) for n-fold scattering. They are described by a single, simple analytical function with four free parameters that have been determined for n = 2, 3 and 4 by a least squares method. The σ_n(θ) are normalised to the total cross section Q.     

485—Spectroelectrochemical evidence for imine-alcohol intermediate formed upon electrochemical oxidation of uric acid

Electrochemical oxidation of uric acid in phosphate-containing supporting electrolytes between pH 3–9 at a reticulated vitreous carbon electrode in a thin-layer spectroelectrochemical cell leads to formation of U.V.-absorbing intermediate species. Electrochemical reduction of the intermediate-containing solution leads to the partial regeneration of uric acid. This behavior provides compelling evidence that an imine-alcohol is one of the U.V.-absorbing intermediate species since only this compound may be expected to be reduced to a species which can regenerate uric acid.     

Rates and mechanisms of indole and 3-Methylindole polymerization in cation exchange resin beads

Batch extraction and polymerization of indole and 3-methylindole (skatole) with acidic cation exchange resins functioned as pseudo first-order reactions. Activation energies of 3.4 and 5.7 keal/mole indicated greater steric hindrance to skatole polymerization, as would be expected from 2,2′ bonding of skatole compared to 3,2′ bonding for indole. Linear polymerization occurred, although a heterocyclic ring opened at the trimer stage of poly(indole). 2-Methylindole did not polymerize. General acid-base catalysis caused unreproducible partial depolytnerization when the polymers were extracted from resin beads. Thus, compounds chromatographically separated probably were of lower degree of polymerization than were the polymers formed in the resin matrix.     

1-Methylallyl(cyclooctatetraene)titanium

The complex 1-methylally(cyclooctatetraene)titanium has been prepared by the reaction of cyclooctatetraenetitanium chloride and 1-methylallylmagnesium bromide. The IR spectrum shows the vibrations of the h⁸-C₈H₈ ligand and of a π-bonded methylallyl group. The mass spectrum is also discussed.