Die Funktionalgleichung der DirichletschenL-Funktionen

Ohne Zusammenfassung     

Observation of laser-induced off-resonance intermolecular electronic energy transfer

We report the observation of off-resonance electronic energy transfer from an excited rhodamine 6G molecule to an azulene molecule in solution. The process requires the coupling of the radiation field in the transfer process. We demonstrate that the relation Y _A I ^1/2 between the acceptor's induced fluorescence intensity and the laser intensity, predicted by Jortner et al. is observed.     

Intramolecular electronic energy transfer via exchange interaction in bichromophoric molecules

A theory is presented for intramolecular electronic energy transfer in bichromophoric molecules. Expressions are given for the donor moiety fluorescence (phosphorescence) decay and for its fluorescence (phosphorescence) quantum yield in terms of the average distance between the donor and acceptor moieties and the donor—acceptor bridge flexibility. Comparison with available experimental data supports the predictions of the analysis.     

Reduction of nitric oxide,nitrous acid and nitrogen dioxide at platinum electrodes in acidic solutions: Review and new voltammetric results

The literature concerning the chemical and electrochemical reactions of nitric oxide, nitrous acid and nitrogen dioxide in aqueous solutions is reviewed briefly, with emphasis on electrochemical reductions at platinum electrodes in acidic solutions. The voltammetric behavior of NO and NO₂ at a Pt electrode in perchloric acid is virtually identical to that for HNO₂ and this is explained on the basis of a common electroactive precursor concluded to be NO⁺. Three cathodic waves are obtained for acidic solutions of NO, HNO₂ and NO₂. The first two waves correspond to reduction of NO⁺ to NO and N₂O₃ to NO, respectively. The presence of N₂O₃ results from decomposition of the parent compounds. The presence of Br^- or Cl^- in acidic solutions of the title compounds promotes the voltammetric reductions at lower H⁺ concentrations. This probably results from formation of electroactive nitrosyl halides.     

Classification of gasoline data obtained by gas chromatography using a piecewise alignment algorithm combined with feature selection and principal component analysis

A fast and objective chemometric classification method is developed and applied to the analysis of gas chromatography (GC) data from five commercial gasoline samples. The gasoline samples serve as model mixtures, whereas the focus is on the development and demonstration of the classification method. The method is based on objective retention time alignment (referred to as piecewise alignment) coupled with analysis of variance (ANOVA) feature selection prior to classification by principal component analysis (PCA) using optimal parameters. The degree-of-class-separation is used as a metric to objectively optimize the alignment and feature selection parameters using a suitable training set thereby reducing user subjectivity, as well as to indicate the success of the PCA clustering and classification. The degree-of-class-separation is calculated using Euclidean distances between the PCA scores of a subset of the replicate runs from two of the five fuel types, i.e., the training set. The unaligned training set that was directly submitted to PCA had a low degree-of-class-separation (0.4), and the PCA scores plot for the raw training set combined with the raw test set failed to correctly cluster the five sample types. After submitting the training set to piecewise alignment, the degree-of-class-separation increased (1.2), but when the same alignment parameters were applied to the training set combined with the test set, the scores plot clustering still did not yield five distinct groups. Applying feature selection to the unaligned training set increased the degree-of-class-separation (4.8), but chemical variations were still obscured by retention time variation and when the same feature selection conditions were used for the training set combined with the test set, only one of the five fuels was clustered correctly. However, piecewise alignment coupled with feature selection yielded a reasonably optimal degree-of-class-separation for the training set (9.2), and when the same alignment and ANOVA parameters were applied to the training set combined with the test set, the PCA scores plot correctly classified the gasoline fingerprints into five distinct clusters.     

Supersonic jet spectroscopy of naphthalene–fluorene bichromophoric cluster

We have investigated the supersonic jet spectroscopy and photophysics of 1-methylnaphthalene–fluorene (1MN–FL) cluster, and looked for indications of intramolecular electronic energy transfer (Intra-EET) from the FL (donor, D) to 1MN (acceptor, A). The clusters were identified by their time of flight (TOF) mass spectra. We observed clusters bands in the LIF spectrum near the region of 1MN origin. We have also observed cluster TOF–resonance enhanced multi-photon ionization (REMPI) spectrum near the electronic origin of the fluorene moiety. However, this spectrum was almost independent of the excitation wavelength, and was not observed in the LIF spectrum. This is probably due to fast Intra-EET resulting in lifetime broadening of the donor chromophore cluster spectrum, similar to that observed previously for the naphthalene–anthracene bichromophoric system.     

Potential of electrophilic epoxide reactions for the monitoring of acid gases in the environment

Mineral and short-chain carboxylic acid vapours and NO(x) gases were reacted with cyclohexene oxide (1,2-epoxycyclohexane) to quantitatively produce specific, thermally stable cyclohexyl derivatives. Subsequent analysis of these derivatives by gas chromatography with mass spectroscopy and flame ionisation detection afforded a multi analyte method for the assay of these gaseous acidic atmospheric species. Derivatisation was found to be quantitative for the derivatives tested and the method highly sensitive (to 0.3 mg/m3 for a 30 l sample), accurate, precise and free from apparent interferences. The technique has been applied to "acid stack gases" and a number of other acid rich atmospheres and the results obtained show good agreement with the single analyte wet chemical determinations indicating that the approach has considerable potential as a routine analytical method for measuring such atmospheric pollutants. The high specificity of the reaction mechanism and its potential for the analysis of analyte mixtures is illustrated in the assay of nitric acid and its acid anhydride, dinitrogen pentoxide.