Luminescence of Ni doped CaF2

Luminescence measurements of CaF₂ : Ni are reported. Before X-irradiation an emission band at 680 nm is observed with the corresponding excitation band at 255 nm. After RT X-irradiation the emission spectrum consists of three peaks at 290, 375 and 680 nm, all of them with an excitation band at 255 nm. The same emission spectrum together with the electron-hole recombination band is obtained by X-ray excitation.A comparison with previous EPR and optical absorption measurements indicates that the emission bands are due to different kinds of Ni²⁺ centers. The emission processes are similar to those found in CaF₂ : Co and CaF₂ : Mn.     

Ruthenium‐Catalyzed CC Bond Cleavage in Lignin Model Substrates

Ruthenium–triphos complexes exhibited unprecedented catalytic activity and selectivity in the redox‐neutral C? C bond cleavage of the β‐O‐4 lignin linkage of 1,3‐dilignol model compounds. A mechanistic pathway involving a dehydrogenation‐initiated retro‐aldol reaction for the C? C bond cleavage was proposed in line with experimental data and DFT calculations.     

Ueber das Atomgewicht des Bors

Ohne Zusammenfassung     

Nickel‐Catalyzed Cyclopropanation with NMe4OTf and nBuLi

Nickel was identified as a catalyst for the cyclopropanation of unactivated olefins by using in situ generated lithiomethyl trimethylammonium triflate as a methylene donor. A mechanistic hypothesis is proposed in which the generation of a reactive nickel carbene explains several interesting observations. Additionally, our findings shed light on a report by Franzen and Wittig published in 1960 that had been retracted later owing to irreproducibility, and provide a rational basis for the systematic development of the reaction for preparative purposes as an alternative to diazomethane or Simmons–Smith conditions.     

Characterization of Na precipitates in electron irradiated NaCl crystals by wide angle X-ray scattering (WAXS)

Samples of synthetic NaCl crystals have been exposed to different doses of electron irradiation up to 1500 MGy (150 Grad) at elevated temperatures, and studied subsequently by X-ray diffraction. Our experimental results clearly show that there is a close correspondence between the geometrical properties (such as lattice distances and the crystal orientation) of the host crystal and the radiation-induced Na precipitates, which is referred to as the Kurdjumov-Sachs orientation relationship (K-S OR). The size of the precipitates has been estimated.     

Electron spin resonance and nuclear magnetic resonance of sodium macrostructures in strongly irradiated NaCl-K crystals: Manifestation of quasi-one-dimensional behavior of electrons

Data from an investigation of electron spin resonance and nuclear magnetic resonance of NaCl-K (∼1 mole%) crystals strongly irradiated with electrons imply the observation of a metal-insulator transition with decreasing temperature and the manifestation of quasi-one-dimensional electron motion in sodium macrostructures. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 178–183 (10 February 1998)     

Molecular Dynamics simulations of borate glasses

Abstract

The results of Molecular Dynamics simulations of borate glass (B₂O₃) using three-particle interactions are presented. These calculations yield a glass consisting of randomly connected BO₃ triangles. Infrared and Raman spectra have been calculated and compared with experimental spectra. The calculated infrared spectra show two main bands, one at 650 cm^?1 and one at 1250 cm^?1, in agreement with experiment. The Raman spectra reproduce the experimental peak at 805 cm^?1 but the peak width is a factor of ten too large. Apparently, the simulated glasses have less short range order than the laboratory glasses.     

Control of density fluctuations and electron transport in the reversed-field pinch

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.     

A straightforward synthesis of 1,3-dichloro-5,8-dihydroisoquinoline by consecutive Stille cross-coupling and metathesis reactions

An efficient three-step synthetic route from 2,6-dichloro-4-iodopyridine to 1,3-dichloro-5,8-dihydroisoquinoline is described. A ring-closing-metathesis reaction constitutes the key step in this synthetic sequence. The reactivity of both chloro atoms is demonstrated in a Suzuki arylation reaction.