Wavelength independence of Eu quantum yields

A quantitative comparison between the excitation and absorption spectra of Eu³⁺ in aqueous solution is given which leads to the conclusion that fluorescence quantum yields are independent of the excitation wavelength. Use is made therefore of the series of homologous lines ⁵D₃, ⁵D₂, ⁵D₁, ⁵D₀ → ⁷F₁.     

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Escape from the unstable equilibrium in a random process with infinitely many interacting particles

We consider a one-dimensional version of the model introduced in Ref. l. At each site of Z there is a particle with spin ± 1. Particles move according to the Stirring Process and spins change according to the Glauber dynamics. In the hydrodynamical limit, with the stirring process suitably speeded up, the local magnetic densitym _t(r) is proven in Ref. 1 to satisfy the reaction-diffusion equation (*) $$\partial _t m_t (r) = \tfrac{1}{2}\partial _r^2 m_t (r) - V'(m_t )$$ \(V(m) = - \tfrac{1}{2}\alpha m^2 + \tfrac{1}{4}\beta m^4 \) ,α andβ being determined by the parameters of the Glauber dynamics. In the present paper we consider an initial state with zero magnetization,m ₀(r)=0. We then prove that at long times, before taking the hydrodynamical limit, the evolution departs from that predicted by (*) and that the microscopic state becomes a nontrivial mixture of states with different magnetizations.     

Homogeneous hydrogenation of ketones to alcohols with ruthenium complex catalysts

A number of ruthenium triphenylphosphine complexes catalyse the reduction of ketones to their corresponding alcohols in the presence of water. The most convenient catalyst precursors are carbonyl containing complexes which do not promote decarbonylation of the substrate. The hydrogenation of acetone with hydridochlorocarbonyltris(triphenylphosphine)ruthenium is first order with respect to the substrate concentration, the catalyst concentration, the hydrogen pressure and the water concentration. Turnover numbers up to 15,000 have been achieved with this catalyst. Other ketones are also reduced by RuHCl(CO)(PPh₃)₃ and the rate of the reaction is dependent on the nature of the substrate.     

k0-measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis

Recommended k₀-factors and related nuclear data for use in (n, γ) activation analysis are given for 72 isotopes. In addition the basic nuclear constants and experimental parameters needed in the k₀ standardization method are reviewed. For convenient data reduction, computer programs were developed.     

INTRAMOLECULAR EXCIPLEX FORMATION IN Nα-ACETYL-1-PYRENYLALANYL-1-METHYLTRYPTOPHAN METHYLESTER

Abstract— The synthesis, absorption and emission properties of erythro (e) and threo (t) Na-acetyl-1-pyrenylalanyl-1-methyltryptophan methylester (APTE) are reported. From the dependency of the exciplex emission maximum on the solvent polarity, the exciplex dipole moment of erythro and threo APTE were calculated. The evolution of the ratio of the quantum yield of exciplex emission and the quantum yield of emission from the locally excited state is correlated with solvent polarity and with the tendency of the solvent to interact with the peptide chain through hydrogen bonding. It is shown that solvents, inert towards the peptide function, shift the equilibrium between the two ground state conformations towards C₇, in which an exciplex geometry can be reached. Hydrogen accepting solvents shift the conformational equilibrium towards C₅, which cannot form an exciplex directly within the lifetime of excited pyrene.     

Interaction of aryldiazonium salts with some schiff-base complexes of cobalt and ruthenium

The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes.