Introduction to Hardy Spaces

Basic material from the theory of Hardy spaces is presented. The principle of positive energy representations is used as motivation to introduce these spaces.     

Photoreaktionen kleiner organischer Moleküle. 4. Mitt. Absorptions-spektren,Photoionen- und Resonanzphotoelektronenspektren von Vinylbromid.

Ohne Zusammenfassung     

Formation and dissociation of the chloroethylene anions

Electron attachment spectroscopy is employed to study the formation of negative ions from the chloroethylenes. It is found that the resonances recently observed in the total electron scattering cross section are predominantly associated with the formation of Cl^?. Only in tetrachloroethylene is a long-lived parent negative ion observed.     

Electrochemical formation and clevage of bis-imidazolyls

Bis-(2,4,5-triphenylimidazolyls) result from the dimerization of 2,4,5-triphenylimidazolyls and from the nucleophilic attack of 2,4,5-triphenylimidazole anions upon 2,4,5-triphenylimidazolylium cations. The isomeric bis-imidazolyls consist of imidazole and isoimidazole systems. Imidazoles undergo only anodic oxidation, isoimidazoles only cathodic reduction. Therefore the bis-imidazolyls may be analyzed from their electrochemical behaviour. Bis-(2,4,5-triphenylimidazolyl)-1,2′ and bis-(2,4,5-triphenylimidazolyl)-1,4′ undergo reductive bond cleavage in an ē.c?.ē. mechanism from which 2,4,5-triphenyl-imidazole anions result. The electrochemical properties of one of the bis-imidazolyls agree with that of 1,4,5-triphenyl-2-(2,4,5-triphenylisoimidazolyl-4)-imidazole and not with that of bis-(2,4,5-triphenylimidazolyl)-2,4′ as reported in literature.     

On the role of dissociative ionization in the formation of argon dimer ions

The formation of Ar ₂ ⁺ ions has been investigated by means of the threshold photoelectron photoion coincidence (TPEPICO) technique. Two pathways for the formation of Ar ₂ ⁺ ions are important. One is a direct path via excitation of Rydberg states of Ar₂ with consecutive autoionization. The other path is dissociative ionization of larger argon clusters, in this case argon trimers. These two pathways lead to Ar ₂ ⁺ ions with different internal energy. The pathways are easily distinguished in the TPEPICO-TOF spectra by the kinetic energy released (KER) in the dissociative ionization. The KER for the reaction Ar ₃ ⁺ → Ar ₂ ⁺ + Ar was measured as a function of the photon energy and compared to the KER expected from statistical theory. The agreement is satisfying and confirms that Ar ₃ ⁺ ions do indeed dissociate at the thermochemical threshold. At higher photon energy the excited²Π(3/2)g state of Ar ₃ ⁺ is also detected from a second component in the KER. By applying a kinetic energy discrimination it is possible to measure cluster ion spectra in the presence of larger clusters but essentially without interference from the latter.     

Fragmentation of doubly charged argon clusters

Fragmentation of doubly charged argon clusters is reported. Neutral argon clusters are excited with monochromatized synchrotron radiation in the energy regime of the argonL ₃/L ₂ absorption edges (240–260 eV) leading predominantly to cluster dication formation. All charged particles are detected in a photoelectron-photoion-photoion-concidence (PEPIPICO) experiment. Symmetric and asymmetric charge separation reactions (Coulomb explosion) are identified for clusters below the critical size of stable dication formation. The peak shapes of the coincidence signals are investigated as a function of neutral cluster size. Characteristic changes in peak shape are observed which are used to derive fragmentation mechanisms involving sequential evaporation of neutrals before and after charge separation. The spectra indicate in accordance with low kinetic energy releases occurring in charge separation of large dissociative cluster dications (Ar _n ²⁺ , withn>50) that due to large charge separation distances the momenta of both singly charged fragments are not any more directed into opposite direction, as it is typical for Coulomb explosion. The results are compared to collision induced fragmentation of mass selected argon cluster dications as well as photon stimulated desorption spectra of condensed argon.     

The Susceptibility of Non-UV Fluorescent Membrane Dyes to Dynamical Properties of Lipid Membranes

Fluorescence spectroscopy and microscopy are powerful techniques to detect dynamic properties in artificial and natural lipid membrane systems. Unfortunately, most fluorescent dyes that sense dynamically relevant membrane parameters are UV sensitive. Their major disadvantage is a high susceptibility to fluorescence bleaching. Additionally, the risk for hazardous damages in biological components generally increases with decreasing excitation wavelength. Therefore the use of non-UV–sensitive membrane dyes would provide significant advantage, particularly for applications in fluorescence microscopy, which usually implies high local excitation intensities. We applied steady-state fluorescence spectroscopy techniques to several UV and non-UV membrane dyes to detect and compare dynamically relevant excitation and emission characteristics. Small unilamellar liposomes (composed of egg yolk phosphatidylcholine) served as a model system for biological membranes. The dynamic properties of the membranes were varied by two independent parameters: the intrinsic cholesterol content (0–50 mol%) and temperature (10–50°C). We tested four non-UV–sensitive membrane dyes: 9-diethylamino-5H-benzophenoxazine-5-one (Nile Red), 4-(dicyanovinyl)julolidine (DCVJ), N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM 4-64), and 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate (DiIC₁₈). We also tested three derivatives of DiIC₁₈: DiIC₁₆ and DiIC₁₂ differ in acyl chain length and Fast-DiIC₁₈ provides double bonds between hydrocarbon atoms. The spectral results were compared to established fluorescence characteristics of four UV membrane dyes: the anisotropy of 1-6-phenyl-1,3,5,-hexatrien (DPH), two derivatives of DPH (TMA-DPH and COO^–-DHP), and the generalized polarization of 6-dodecanoyl-2-dimethyl-aminonaphthalene (Laurdan). Our results indicate that the tested non-UV dyes do not reveal dynamically relevant membrane parameters in a direct manner. However, spectral characteristics make DiIC₁₈, Nile Red, and DCVJ promising probes for the microscopic detection of lateral lipid organization, an indirect indicator of membrane dynamics. In particular, DiIC₁₈ showed very selective shifts in the emission spectra at defined temperatures and cholesterol contents that have not been reported elsewhere.