Trennung von Derivaten der 3,5-Dichlor-o-anissÄure und 3,6-Dichlor-salicylsÄure und ihrer Acetylhomologen durch Gas-Chromatographie

Analytical and Bioanalytical Chemistry -     

Gas-chromatographische Analyse eines Wasserstoff/Sauerstoff-Gemisches mit einer modifizierten Probeneingabevorrichtung

Ohne Zusammenfassung     

Comparison of Benzyl Celluloses Synthesized in Aqueous NaOH and Dimethyl Sulfoxide/Tetrabutylammonium Fluoride

Cellulose was benzylated starting from the dissolved polymer in dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) and heterogeneously in aqueous NaOH as reaction media. Differences in the distribution of benzyl moieties within the anhydroglucose unit in dependence on the synthesis pathway couldn't be found. However, as revealed by means of ¹H-NMR spectroscopy, significant differences in the distribution of substituents along the cellulose chains occurred. Conventionally synthesized samples (in aqueous NaOH), even in the presence of a phase transfer catalyst, possess a block-wise distribution of substituents, while a dissolution of cellulose in DMSO/TBAF prior to the reaction gives products that are uniformly substituted along the cellulose chains.     

Investigation of Ti/CuO interface by X-ray photoelectron spectroscopy and atomic force microscopy

The Ti/CuO interface has been studied by the techniques of X-ray photoelectron spectroscopy and atomic force microscopy. Thin films of titanium were deposited on a CuO substrate at room temperature by the e-beam technique. The photoelectron spectra of titanium and copper were found to exhibit significant chemical interaction at the interface. The titanium overlayer was observed to get oxidized to TiO₂, while the CuO was observed to get reduced to elemental copper. This chemical interaction was observed to occur until a thickness of 7 nm of the titanium overlayer. For thicknesses greater than this value, the presence of unreacted titanium in the sample was detected. Barrier characteristics at the Ti/CuO interface were also carried out for substrate temperatures of 300°C, 400°C, 500°C, and 600°C as a function of the titanium overlayer thickness. A linear trend in the barrier thickness of the overlayer was observed between 400°C and 600°C substrate temperatures. The atomic force microscopy micrographs of the unannealed samples depicted layer-by-layer growth of elemental titanium on copper. At the Ti/CuO interface in such samples, the micrographs exhibited island formation of TiO₂ corresponding to the Volmer-Weber growth model. This formation has been interpreted as the relaxation in the strain energy. The percentage coverage of the underlying substrate by the TiO₂ islands showed a linear trend for the thicknesses of the titanium overlayer investigated. The average size of these islands also showed a linear trend as a function of the thickness of the overlayer.     

Probing electron correlations in molecules by two-dimensional coherent optical spectroscopy

The nonlinear optical signal generated in phenol by three femtosecond pulses with wavevectors k1, k2, and k3 in the phase-matching direction k1 + k2 - k3 is simulated. This two-dimensional coherent spectroscopy (2DCS) signal has a rich pattern containing information on double-excitation states. The signal vanishes for uncorrelated electrons due to interference among quantum pathways and, thus, provides direct signatures of correlated many-electron wavefunctions. This is illustrated by the very different 2DCS signals predicted by two levels of electronic structure calculations: state-averaged complete active space self-consistent field (SA-CASSCF) and multistate multiconfigurational second-order perturbation theory (MS-CASPT2).