The Chiral Trimer and a Metastable Chiral Dimer of Achiral Hexafluoroisopropanol: A Multi‐Messenger Study

1,1,1,3,3,3‐hexafluoro‐propan‐2‐ol aggregates preferentially into an achiral dimer of achiral monomers, but the trimer is found to prefer three metastable chiral monomer units arranged into a strained OH???O hydrogen‐bonded ring, which is reinforced by secondary CH???FC interactions. This is shown by a combination of infrared, microwave, and Raman spectroscopy in supersonic jet expansions and supported by high‐level quantum chemical calculations. It involves an activation of the monomers by >15 kJ mol^?1, clearly driven by the much stronger hydrogen‐bond interaction available to the gauche and even more to the cis monomer units.     

Quantifying Conformational Isomerism in Chain Molecules by Linear Raman Spectroscopy: The Case of Methyl Esters

The conformational preferences of the ester group have the potential to facilitate the large amplitude folding of long alkyl chains in the gas phase. They are monitored by Raman spectroscopy in supersonic jet expansions for the model system methyl butanoate, after establishing a quantitative relationship with quantum–chemical predictions for methyl methanoate. This requires a careful analysis of experimental details, and a simulation of the rovibrational contours for near-symmetric top molecules. The technique is shown to be complementary to microwave spectroscopy in quantifying coexisting conformations. It confirms that a C−O−C(=O)–C–C chain segment can be collapsed into a single all-trans conformation by collisional cooling, whereas alkyl chain isomerism beyond this five-membered chain largely survives the jet expansion. This sets the stage for the investigation of linear alkyl alkanoates in terms of dispersion-induced stretched-chain to hairpin transitions by Raman spectroscopy.     

Methode zur technischen Herstellung kolloider Eisenhydroxydlösungen

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Untersuchung und Beurteilung von Tabakwaren

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Herstellung kolloider Eisenhydroxydlösungen durch Oxydation des Eisenoxydulbikarbonats

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Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.     

Computing convex hulls and counting integer points with <Emphasis FontCategory="NonProportional">polymake</Emphasis>

The main purpose of this paper is to report on the state of the art of computing integer hulls and their facets as well as counting lattice points in convex polytopes. Using the polymake system we explore various algorithms and implementations. Our experience in this area is summarized in ten “rules of thumb”.