Electronic states near the band gap for the GaAs(110) surface

The recent theoretical controversy regarding empty surface states at the GaAs cleavage plane is examined by the exact solution of several tight binding models applied to a semi-infinite crystal. We correlate the existence of an empty surface gap state with the anion p/cation p character of this state. This work isolates the specific properties of a Hamiltonian for GaAs which yield band gap states on a relaxed surface and clarifies the essential differences among current theoretical treatments.     

Sensitive new test for formaldehyde and pyruyaldehyde with 2-hydroxycarbazole

Summary A new, extremely simple spot test for formaldehyde, formaldehydeyielding compounds, pyruvaldehyde, and pyruvaldehyde-yielding compounds is described. The limits of detection of formaldehyde and pyruvaldehyde are 0.004g. Interferences and methods of increasing the selectivity are discussed.

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Zusammenfassung Eine neue, sehr einfache Tüpfelprobe auf Formaldehyd, formaldehydbildende Verbindungen, Brenztraubenaldehyd und brenztraubenaldehydbildende Verbindungen wird beschrieben. Die Erfassungsgrenzen sind 0,004g für Formaldehyd und für Brenztraubenaldehyd. Störungen und eine Möglichkeit zur Erhöhung der Selektivität werden besprochen.

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Résumé On décrit une nouvelle réaction à la touche extrêmement simple du formaldéhyde, des composés qui donnent du formaldéhyde, de l'aldéhyde pyruvique et des composés qui en donnent. Les limites de dilution du formaldéhyde et de l'aldéhyde pyruvique sont de 0,004g. On discute les interférences et les procédés pour augmenter la sélectivité.

     

High-pressure phases in polymers. I. Spherulitic growth kinetics in cis-polyisoprene

This is the first paper in a series dealing with the crystallization of high polymers at elevated pressures. Through an extension of the thin-film technique using osmium tetroxide staining, the measurement of lamellar growth kinetics at high pressures as well as the observation of micromorphological changes has proved possible. Three different morphological species of cis-polyisoprene have been detected in the pressure–temperature plane. A review is given of the conditions governing their formation and the growth kinetics of lamellar crystals are discussed in detail. Secondary nucleation theory is obeyed, the major effect of pressure being to alter the kinetics through the thermodynamic transitions. Variations in lamellar thickness with pressure may be explained simply in terms of the elevation by pressure of the equilibrium melting point.     

The preparation,polymerization and copolymerization of (η5-vinylcyclopentadienyl)dicarbonylnitrosylchromium, (η5-C5H4CHCH2)Cr(CO)2NO

The first report on the preparation, polymerization, and copolymerization of a nitrosyl-containing vinylcyclopentadienylmetal monomer, (η⁵-C₅H₄CHCH₂)-Cr(CO)₂NO, is described. (η⁵-Vinylcyclopentadienyl)-dicarbonylnitrosylchromium (A) was prepared in good yield by the acylation of η⁵-cyclopentadienyl-carbonylnitrosylchromium followed by sodium borohydride reduction of the keto function and acid-catalyzed dehydration. Monomer A homopolymerizes and copolymerizes with styrene, N-vinylpyrrolidone, and vinyl cymantrene in the presence of azo initiators. Reactivity ratios in the copolymerization of A with styrene were r₁ = 0.30 and r₂ = 0.82 from which the value of e for A was found to be ?1.98. Thus, A is an exceptionally electron-rich monomer.     

μ-Fluoro complexes peroxydes du molybdene VI

On a mis en évidence un pont Mo-F-Mo dans des oxoperoxomolybdates VI complexes de coordinence sept de formule M^I{Mo₂O₂(O-O)₂(dipic)₂F}; M^I = {(C₂H₅)₄N}⁺, {(CH₃)₄N}⁺, Cs⁺, Rb⁺, K⁺, Na⁺ -(dipic) = {C₇H₃NO₄}^2-. L'ion est mononucléaire pour M^I = NH⁺₄ et si le ligand halogéno eset Cl.     

A novel synthesis of 1,4-diarylpiperazines

1,4-Diarylpiperazines are readily prepared, generally in good yields, by the reaction of substituted aromatic amines with two thirds of an equivalent of tris(2-chloroethyl)phosphate.     

Permutational symmetry of reduced density matrices

The problems of permutational symmetry of the density matrices in reduction are studied. Some necessary and sufficient conditions for N, [λ₁], [λ₂]-derivability problem are given.