Electronic spectroscopy of UO2 isolated in a solid Ar matrix

Dispersed fluorescence spectra have been recorded for UO(2) isolated in a solid Ar matrix. Near UV excitation produced groups of emission bands in the 370-420 and 465-645 nm spectral regions. These bands originated from two energetically close upper levels and terminated on a range of low-lying electronic states. Comparisons with electronic structure calculations indicate that the ground and low-lying electronic states of UO(2) are derived from the U(5f7s) configuration. The level of agreement between the observed and predicted electronic energies provides an impressive validation of the calculations. In previous studies of matrix isolated UO(2), it had been suggested that the ground state in solid Ar is U(5f(2)) (3)H. The present results do not appear to be consistent with this hypothesis.     

An exceptionally facile homolytic displacement in the reaction of nitrogen trichloride with trialkylboranes

Nitrogen trichloride undergoes an exceptionally facile reaction with trialkylboranes, apparently by a free radical chain process involving a homolytic substitution at the boron center, providing a new route from organoboranes to the corresponding alkyl chlorides.     

Crown Ether Phase Transfer Catalysts for An Ionic Polymerization of Bisphenol A / 4,4′‐Dichlorodiphenyl Sulfone

Various crown ethers were prepared and applied as phase transfer catalysts for the an ionic copolymerization of bisphenol A and 4,4′‐dichlorodiphenyl sulfone monomers with alkali salts, e.g., NaNH₂, NaOH and KOH, as initiators. The catalytic abilities of various crown ethers for the an ionic polymerization of bisphenol A / 4,4′‐dichlorodiphenyl sulfone were found to be in the order: 15‐crown‐5 ? monobenzo‐15‐crown‐5 > 18‐crown‐6 > Dicyclohexano‐18‐crown‐6 > Dibenzo‐18‐crown‐6 > 12‐crown‐4 with sodium amide (NaNH₂) as initiator. Sodium amide was shown to be a better initiator than NaOH or KOH with monobenzo‐ 15‐crown‐5 as a catalyst. Effects of solvents and temperature on the crown ether catalytic polymerization were also investigated. Dimethyl sulfoxide (DMSO) exhibited much better for the polymerization than other organic solvents, e.g., toluene, p‐xylene, dimethyl formamide and dioxane. Higher polymerization was found at higher temperatures and about 100% yield of poly(bisphenol A / sulfone) was obtained at 125 °C in 3 hr. The molecular weight of poly(bisphenol A / sulfone) as a function of reaction time was determined with gel permeation chromatography. Concentration effects of crown ether on % yield and molecular weight of poly(bisphenol A / sulfone) were also investigated and discussed.     

A Convenient Method for the Preparation of Dialkyl Telluride

Treatment of various alkyl nalides with sodium telluride which is generated by reduction or elemental tellurium with hydrazine hydrate in basic medium using DMF as aprotic solvent affords the corresponding symmetric dialkyl tellurides in moderate to good yields.     

Technique d'optimisation de l'energie SCF en fonction des exposants de slater

We describe a method to optimize simultaneously Slater orbital exponents. The procedure is based on Newton's method and requires the derivatives of the energy as a function of the exponents. The calculation of these derivatives is described explicitly. The method has been applied to the hydrogen molecule.     

手性胶束中的有机反应9;手性胶束中a一二酮的不对称还原

本文报道在手性表面活性剂N,N一二甲基一N一十二烷基麻黄素澳化按(Ia), N,N一二甲基一N一十六烷基麻黄素澳化钱(Ib>及N,I}r一二甲基一N一十六烷基嗅化薄荷钱(I,)形成的手性胶束水溶液中，a一二酮被TiCI:还原为光学活性的a_轻基酮，对映体过量最高·可达30男.     

Diffusivity enhancement of water vapor in poly(vinyl alcohol)–fumed silica nano-composite membranes: Correlation with polymer crystallinity and free-volume properties

The diffusion coefficients of water vapor in poly(vinyl alcohol)–fumed silica (PVA–FS) nano-composite membranes were determined using the gravimetric method. Water vapor was observed to diffuse more rapidly in membranes with increased FS content. The vapor diffusion coefficient was determined as 1.2 × 10⁻¹³ m²/s in pure PVA and was observed to increase to 3.0 × 10⁻¹³ m²/s in PVA composites containing 30% FS nano-particles. The free-volumes of PVA–FS membranes were characterized using positron annihilation lifetime (PAL) spectroscopy. PAL results showed that both the ortho-positronium (o-Ps) lifetime and intensity increased with the addition of FS. The intensity (I₃) was found to be higher than the estimated value determined from the linear combination of the data from pristine PVA and FS, and correlated excellently with the polymer amorphous content. The PAL results indicate that a higher FS content in PVA increases the free-volume hole size (a volume increase from 40 to 55 Å³) and free-volume hole density (an I₃ increase from 23 to 28%), resulting in a higher fractional free-volume in the nano-composites. The increase in the relative polymer free-volume with higher FS content was associated with a decrease in the PVA crystallinity, as determined from differential scanning calorimetry measurements. It is postulated that the incorporated FS nano-particles interrupt polymeric chain packing and retard crystallization during membrane formation. More crystalline segments were transformed into amorphous regimes in the nano-composites containing more FS. A correlation between water diffusivity and the fractional free-volume was obtained, and the water diffusivity was successfully expressed by the free-volume theory.     

Preparation of CLA ascorbyl ester with improved volumetric productivity by an ionic liquid-based reaction system

A new approach to the enzymatic production of conjugated linoleic acid (CLA) ascorbyl ester with a remarkably high volumetric productivity (120-200 g L(-1)) has been developed, in which strong solvation by tOMA.TFA (methyltrioctylammonium trifluoroacetate) enables a high concentration of ascorbic acid to be applied, and in which t-butanol enhances conversion by changing the equilibrium constant of the activity coefficients. This work has experimentally demonstrated the practicability of achieving efficient reactions of polar compounds at high concentrations in ionic liquids without significant loss of enzyme activity.