On strongly stable normal operators in Krein spaces

For bounded normal operators in Krein spaces we give a necessary and sufficient condition for strong stability. The same result for unitary operators was obtained by M.G.Krein [1] (see also [2]). For selfadjoint operators we refer to the papers of P.Jonas, H.Langer [3] and H.Langer [4].     

ENDOR-investigations of iron doped GaAs and GaP

From ENDOR-measurements of GaAs:Fe³⁺ the symmetries and hyperfine parameters of three groups of neighbour nuclei have been obtained. The values of ||², r ^–3 and of the electric field gradients at the sites of the neighbour nuclei have been determined for GaAs:Fe³⁺ and GaP:Fe³⁺. The comparison of our results with those of NMR-investigations indicates the Fe³⁺-ion to be an interstitial impurity surrounded by four groupV atoms in a tetrahedral arrangement.     

Control of molecular architecture by the degree of deprotonation: self-assembled di- and tetranuclear copper(II) complexes of N,N'-bis(2-pyridylmethyl)pyrazine-2,3-dicarboxamide

In the absence of added base, a deep navy-blue dimeric copper complex [CuII(H2L)(MeCN)]2(BF4)4 (1) of the non-deprotonated bis-terdentate diamide ligand H2L self-assembles whereas in the presence of base a grass-green [2 x 2] grid complex [CuII(HL)]4(BF4)4 (2) of the monodeprotonated ligand HL-, a rare example of a discrete grid of pyrazine-bridged metal ions, is formed.     

Schottky Mass Measurements of Cooled Exotic Nuclei

Projectile fragments of a ²⁰⁹Bi beam were separated in flight with the fragment separator FRS and injected into the experimental storage ring ESR. In the ESR a beam containing up to about 100 different isotopes was cooled to a relative velocity spread of δv/v=10⁻⁶ by means of the electron cooler. The image currents of the ions induced in a Schottky pick-up probe at each turn were recorded. A subsequent Fast Fourier Transformation of these signals yields the revolution frequencies of the different isotopes stored in the ESR. Unknown masses of more than 150 neutron-deficient nuclides in the element range of 52≤Z≤85 have been measured directly by Schottky Mass Spectrometry and in addition more than 60 new masses have been obtained from α-decay chains. These new mass data allow the location of the one-proton dripline and the prediction of the two-proton dripline for heavy nuclides. The experimental masses are compared with different theoretical predictions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distorted fused porphyrin-phthalocyanine conjugates: synthesis and photophysics of supramolecular assembled systems with a pyridylfullerene

In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin-phthalocyanine (P-Pc) conjugates and a pyridylfullerene. The ZnP-ZnPc conjugate was synthesized in three steps starting with a Diels-Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2(1),2(2)-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H(2)P-ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin-phthalocyanine-fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H(2)P to ZnPc followed by an intramolecular charge transfer to yield ZnP-(ZnPc)˙(+)-(C(60))˙(-) and H(2)P-(ZnPc)˙(+)-(C(60))˙(-), respectively.     

Elektronenspinresonanz vonU 2-Folgezentren in Alkalihalogenid-Kristallen

UV-irradiation at low temperatures may bring hydrogen atoms into interstitial sites (produceU ₂ centers) in alkali halides. At about 100 °K the hydrogen atoms begin to leave their sites and may react with any diamagnetic centerX to a paramagnetic center HX. In this paper CN^? and NCO^? ions are used for X. The paramagnetic centers are investigated by the method of ESR. The spectra and thermal properties of¹H¹²C¹⁴N^?,²H¹²C¹⁴N^?,¹H¹³C¹⁴N^?,¹HNCO^? and²HNCO^? are described. As well signals are found, which may be attributed to the²H¹³C¹⁴N^? center. A simple cryostat is described for use at temperatures continously variable between 25 °K and 500 °K.     

Neue Kupferzentren in Zinkoxid

Electron spin resonance investigations of electron irradiated zinc oxide single crystals doped with copper have been performed. Beside the known Jahn-Teller spectrum of the Cu _ioct ⁰ centre the resonances of four new copper defects have been observed. The ESR parameters are explained assuming one unpaired electron in the otherwise filled 3d shell. The electron configurations are discussed under the conditions of the covalent ZnO bond.     

Forbidden ESR transitionsΔS = ±2 of Fe3+ and Mn2+ in zinc oxide

Forbidden ESR transitions were investigated at 9 GHz in zinc oxide doped with Fe³⁺ and Mn²⁺. The crystal field parameters were determined by means of a computer program. Furtheron, the splittings of the lines for general orientations of the crystal axes relative to the magnetic field were calculated.