On concentration self-quenching of chromium phosphorescence in K3[Cr x Co1−x (CN)6] mixed crystals

The self-quenching of chromium phosphorescence in K₃[Cr_xCo₁-x(CN)₆] mixed crystals has been studied in the range of very high chromium concentration and a minimum in emission quantum yield has been found at about 80% Cr. Comparison of the Cr emission intensities from K₃[Cr(CN)₆] doped with 1% of various impurities suggests that the impurity quenching observed in the range 90 to 100% Cr may be a result of the site asymmetry introduced by the impurity. It is suggested that at least two mechanisms of self-quenching are operative in this concentration range and the nature of these is discussed in relationship to present theories of radiationless transitions.

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Zusammenfassung Die Eigenlöschung der Cr(III)-Phosphoreszenz wurde in K₃[Cr_xCo₁-x(CN)₆]-Mischkristallen im Bereich hoher Cr-Konzentrationen untersucht. Die Quantenausbeuten der Emission zeigten ein Minimum bei etwa 80% Cr. Ein Vergleich der Lumineszenzintensitäten von K₃[Cr(CN)₆] mit 1% verschiedener Zusätze läßt vermuten, daß die im Bereich von 90–100 % Cr beobachtete Löschung von einer durch die Verunreinigung verursachten Gitterstörung herrührt. — Es wird angenommen, daß in dem untersuchten Konzentrationsbereich mindestens zwei Mechanismen der Eigenlöschung wirksam sind, die anhand der gegenwärtigen Theorien der strahlungslosen Übergänge diskutiert werden.

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Résumé L'auto étouffement du chrome phosphorescent à partir de K₃[Cr_xCo₁-x(CN)₆], cristaux mélanges avait été étudié dans la région de très haute concentration de chrome et un minimum d'émission quantique, il en résultait environ 80% Cr. Comparé à l'intensité d'émission de chrome à partir de K₃[Cr(CN)₆] contaminé par 1% de diverses impuretés indique que l'étouffement d'impureté qui était observé dans la région de 90 à 100% Cr, peut être le résultat de l'emplacement assimétrique introduit par l'impureté. — II a été suggéré qu'au moins deux mécanismes d'auto étouffement sont à l'oeuvre dans cette région de concentration et leur nature décrite en relation avec les présentes théories de transitions sans radiation.

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Dedicated to the memory of Professor Hans-Ludwig Schläfer.     

Water-Soluble imide-amide copolymers. II. Preparation and characterization of poly (acrylamide-co-p-maleimidobenzoic acid)

The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol.     

Control of oxo-molybdenum reduction and ionization potentials by dithiolate donors

The compounds (L-N3)MoO(qdt) and (L-N3)MoO(tdt) [(L-N3) = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; tdt = toluene-3,4-dithiolate; qdt = quinoxaline-2,3-dithiolate] have been studied by cyclic voltammetry and photoelectron, magnetic circular dichroism, and electronic absorption spectroscopies, and the experimental data have been interpreted in the context of ab initio molecular orbital calculations on a variety of dithiolate dianion ligands. The PES data reveal very substantial differences between (L-N3)MoO(qdt) and (L-N3)MoO(tdt) in that the first ionization (originating from the Mo dxy orbital) for (L-N3)MoO(qdt) is about 0.8 eV to deeper binding energy than that of (L-N3)MoO(tdt). This stabilizing effect is also reflected in the solution reduction potentials, where (L-N3)MoO(qdt) is approximately 220 mV easier to reduce than (L-N3)MoO(tdt). A direct correlation between the relative donating ability of a given dithiolate ligand and the reduction potential of the (L-N3)MoO(dithiolate) complex has been observed, and a linear relationship exists between the calculated Mulliken charge on the S atoms of the dithiolate dianion and the Mo reduction potential. The study confirms previously communicated work (Helton, M. E.; Kirk, M. L. Inorg. Chem. 1999, 38, 4384-4385) that suggests that anisotropic covalency contributions involving only the out-of-plane S orbitals of the coordinated dithiolate control the Mo reduction potential by modulating the effective nuclear charge of the metal, and this has direct relevance to understanding the mechanism of ferricyanide inhibition in sulfite oxidase. Furthermore, these results indicate that partially oxidized pyranopterins may play a role in facilitating electron and/or atom transfer in certain pyranopterin tungsten enzymes which catalyze formal oxygen atom transfer reactions at considerably lower potentials.     

Terpenoic acid glycerides from the dorid nudibranch Archidoris montereyensis

Extracts of the dorid nudibranch $\text{Archidoris montereyensis}$ contain a diterpenoic acid glyceride 1 whose structure has been determined by x-ray diffraction analysis. The structure of a minor metabolite, the sesquiterpenoic acid glyceride 2, was determined by chemical correlation.     

Study of the centrally produced ωρ0 and ωω systems inpp interactions at 300 GeV/c

We have performed a search for vector-vector final states centrally produced in proton proton interactions at 300 GeV/c using the CERN Ω spectrometer. Evidence is found for ωρ⁰ production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s and for ωω production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s . However no evidence is found for ωø production in the reactionpp→p _f (K ⁺ K ^?π⁺π^?π⁰)p _s .     

Dense electron-positron plasmas and ultraintense γ rays from laser-irradiated solids

In simulations of a 10 PW laser striking a solid, we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10(26) m(-3) can be achieved, 7 orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of γ rays of intensity 10(22) W cm(-2), potentially the most intense γ-ray source available in the laboratory. This absorption results in a strong feedback between both pair and γ-ray production and classical plasma physics in the new "QED-plasma" regime.