Paracyclophanes as model compounds for strongly interacting π-systems. Part 2: mono-hydroxy[2.2]paracyclophane

The structure of the electronic ground- and first excited state of mono-hydroxy [2.2]paracyclophane (MHPC) and the S(1)← S(0) electronic transition have been investigated by resonance-enhanced multiphoton ionisation (REMPI) and by quantum chemical spin-component-scaled-approximate coupled cluster second order (SCS-CC2) computations. The origin of the S(1)← S(0) transition was located at 30,772 cm(-1) (3.815 eV) in the REMPI spectrum. The value has to be compared with a computed excitation energy of 3.79 eV. The vibrational structure of the spectrum confirms a significant geometry change upon excitation along the coordinates corresponding to twist- and shift-motions in the molecule. It gives rise to an experimentally observed progression with a fundamental of +30 cm(-1) and an inverse anharmonicity. From the experimental data a shallow potential along the twist coordinate was derived for the S(1) state. For the shift vibration a wavenumber of +91 cm(-1) was observed, while +85 cm(-1) was computed. The ionisation energy of MHPC was determined to be 7.63 ± 0.05 eV using synchrotron radiation. When compared to earlier results on the parent compound [2.2]paracyclophane and pseudo-ortho-dihydroxy[2.2]paracyclophane it can be seen that already small variations in the substitution pattern have a significant impact on the shapes of the involved potential energy surfaces leading to strong variations in ground and excited state geometries and opto-electronic properties governing the exciton transfer processes.     

Noethersche Gruppen II

Ohne Zusammenfassung Ernst Hölder zum 65. Geburtstag gewidmet     

Kriterien für die Zugehörigkeit von Elementen zu Oω G

Ohne ZusammenfassungFriedrich Karl Schmidt zum 22. September 1976 in alter Freundschaft gewidmet     

Zum relativen Donor-Akzeptor-Verhalten einzähniger Liganden. Eine EHT-Studie

On the Relative Donor-Acceptor-Properties of Monodentate Ligands. An EHT-Study The relative donor-acceptor properties of some important monodentate ligands are investigated by means of the extended Hückel method and a suitable graduation is determined. Charge gradations are discussed and results compared with known facts. Acceptor properties of ligands with phosphorous and sulfur atoms are described in the best manner using charge iterations at the atoms mentioned.     

On the imaginary simple roots of the Borcherds algebra II9,1

In a recent paper [O. Bärwald, R.W. Gebert, M. Günaydin and H. Nicolai, preprint KCL-MTH-97-22, IASSNS-HEP-97/20, PSU-TH-178, AEI-029, hep-th/9703084, to appear in Commun. Math. Phys.] it was conjectured that the imaginary simple roots of the Borcherds algebra _II9,1 at level 1 are its only ones. We here propose an independent test of this conjecture, establishing its validity for all roots of norm − 8. However, the conjecture fails for roots of norm −10 and beyond, as we show by computing the simple multiplicities down to norm −24, which turn out to be remarkably small in comparison with the corresponding E₁₀ multiplicities. Our derivation is based on a modified denominator formula combining the denominator formulas for E₁₀ and _II9,1, and provides an efficient method for determining the imaginary simple roots. In addition, we compute the E₁₀ multiplicities of all roots up to height 231, including levels up to l = 6 and norms −42.     

Verbesserte Darstellung und Raman-Spektrum von Oktafluortrisilan Kurze Mitteilung

Si₃F₈ can be synthesized in good yield by treating Si₃(OCH₃)₈ with BF₃ in a sealed tube. The Raman spectrum of Si₃F₈ is reported and assigned.