Post-adiabatic approach to atomic and molecular processes: The van der Waals interactions of some open shell systems

Summary Various properties of post-adiabatic representations of multichannel Schrödinger equations are described in the general context of adiabatic and classical path approximations as used in atomic and molecular physics. The van der Waals interactions of fluorine, chlorine, and oxygen atoms with rare gases, hydrogen, methane, and hydrogen halides are considered: it is found that in some of these systems, the first-order post-adiabatic scheme exhibits a smaller coupling than the adiabatic representation, thus providing an appropriate choice of the basis functions for a decoupling approximation.     

Electrochemical Organic Synthesis of Electron-Rich Biaryl Scaffolds: An Update

Biaryl scaffolds are widely spread in biologically important natural products, in numerous therapeutic agents, but they are also considered a privileged class of ligands and (organo)catalysts; therefore, the development of efficient alternative methodologies to prepare such compounds is always attracting much attention. The present review discusses the organic electrosynthesis of biaryls starting from phenols, anilines, naphthols, and naphthylamines. The most significant examples of the works reported in the last decade are presented and classified according to the single class of molecules: after the introduction, the first three sections relate to the reactions of phenols, naphthols, and anilines, respectively; the other two sections refer to cross-coupling and miscellaneous reactions.     

Thermal characterization of polycarbonate/polycaprolactone blends

In this work, we prepared blends of bisphenol A polycarbonate (PC) and poly(ϵ‐caprolactone) (PCL) in a wide composition range by melt mixing and solution mixing. Two different molecular weights of PCL were used (nominally, 10.000 g/mol, PCL10, and 80.000 g/mol, PCL80). The thermal behavior of both systems was studied via differential scanning calorimetry under dynamic and isothermal conditions. The blends were miscible in the entire composition range in the liquid and amorphous states, as indicated by the single glass‐transition temperature (T_g) exhibited by both the PC/PCL10 and PC/PCL80 blends. The compositional variation of the T_g was accurately described by the Fox equation for the PC/PCL80 blends, whereas slight deviations from this equation were exhibited by the PC/PCL10 blends. For blend compositions containing 40% or more PCL, either one or both blend components crystallized. Crystallization occurred during cooling from the melt or during subsequent heating in the form of cold crystallization. Although PCL crystallization was reduced and its crystallization rate decreased with the addition of PC, PCL was a very effective macromolecular plasticizer for PC, to the extent that crystallization during the scan was detected for some blend compositions. Isothermal crystallization experiments allowed the determination of equilibrium melting points (T) by the Hoffman–Weeks extrapolation method. A T depression was found for both PCL and PC components as the content of the other blend component was increased. The Avrami equation was closely obeyed by both blend components during the isothermal overall crystallization kinetics up to crystalline conversion degrees of 60–70% and with values of Avrami indices ranging from 3 to 4, depending on the crystallization temperature employed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 771–785, 2001     

Transition energies and oscillator strengths for electronic spectra of non planar conjugated molecules. I. Polyphenyls

Ultraviolet spectra of terphenyls and quaterphenyls are theoretically investigated by Molecules in Molecules (MIM) method and compared with experiment. Oscillator strengths are evaluated using the gradient operator and the mixed dipole-gradient operator. The results are compared with those obtained by the dipole-length operator. The calculation of oscillator strengths via the gradient operator is shown to be in general the most successful. All the components of the primitive integral, necessary for non planar -electron systems, are reported.

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Zusammenfassung Die Ultraviolettspektren von Terphenylen und Quaterphenylen wurden mit Hilfe der Molekül im Molekül (MIM) Methode theoretisch untersucht und mit den experimentellen Resultaten verglichen. Mit einem Gradient-Operator und einem gemischten Dipol-Gradient-Operator wurden die Oszillatorenstärken berechnet und mit Rechnungen mit Dipollängen-Operatoren verglichen. Es wird gezeigt, daß die Berechnung von Oszillatorenstärken mit dem Gradient-Operator im allgemeinen am erfolgreichsten ist. Es werden alle Komponenten des primitiven Integrals, die für nicht planare -Elektronensysteme nötig, angegeben.

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Résumé Les spectres dans l'ultraviolet des triphényles et des quadriphényles sont étudiés théoriquement par la méthode «Molécules dans les molécules» (MIM) et comparés à l'expérience. Les forces oscillatrices sont évaluées en utilisant l'opérateur gradient et l'opérateur mixte gradient dipolaire. Les résultats sont comparés avec ceux obtenus avec l'opérateur longueur dipolaire. Le calculades, forces oscillatrices à l'aide de l'opérateur gradient s'avère plus convenable. On reproduit toutes les composantes de «l'intégrale primitive», nécessaires pour les systemes d'électrons non plans.

     

Geometry of acetylene chemisorption on Ni(100) investigated by leed intensity analysis: The c(2 × 2) structure

Results from LEED dynamical calculations performed on the Ni(100) c(2 × 2)C₂H₂ structure, produced by adsorption of C₂H₂ at about 273 K and 1.5 L exposure, are reported. Among the several model geometries tried, the most favoured one appears to be a distorted acetylene molecule with the midpoint of the CC bond (1.20 Å long) placed above the fourfold hollow site at a vertical distance 2.02 Å from the topmost Ni layer and with the CC axis itself tilted by 50° with respect to the surface normal in the [011] direction. In this geometry the NiC distance is 2.2 Å.     

An ab initio study of the reaction of ammonium ion with hydride ion and lithium hydride

Both the abstraction and substitution mechanisms for the reaction of NH⁺₄ with H^? and the abstraction mechanisms for the reaction with LiH in the gas phase have been investigated by theoretical methods. LiH results to be a better reagent and reactions with and without scrambling are competitive in accordance with experimental findings.