Molecular basis set generation: Accurate slater basis sets for LiH− ground and excited state and Li2− ground state

A procedure for generating basis sets for diatomic molecule electronic structure calculations is described. In essence, this procedure maps the results of nearly exact numerical Hartree–Fock calculations into basis set form. Two applications of the procedure are proposed: (a) generation of very high accuracy basis sets, and (b) investigation of basis sets for unusual systems. The latter application is illustrated by some results for diatomic anions.     

Super-reltron theory and experiments

A highly efficient, high-power microwave tube called super-reltron is reported. The authors have achieved operation at >400 MW with ~50% efficiency at 1 GHz, and 250 MW with 40% efficiency at 3 GHz. The RF pulse durations are typically a few hundred nanoseconds. These compact lightweight tubes do not require an external magnetic field. The RF output coupling is straightforward and delivers the power directly via the fundamental TE₁₀ wave in a rectangular waveguide without a mode converter. The key features of the tube include (i) generation of a well-modulated electron beam by periodic virtual cathode formation, (ii) postacceleration of the modulated beam to reduce the relative electron energy spread, and (iii) a multicavity output section that efficiently extracts power without RF breakdown. Various theoretical aspects of the device are discussed and the experimental results are summarized     

Glued Langmuir-Blodgett bilayers from porous versus nonporous surfactants

Poly(4-styrenesulfonate) (PSS) has been used to ionically cross-link (glue together) single Langmuir-Blodgett bilayers derived from 1,2,4,5-tetrakis[N,N-dimethyl-N-(1-hexadecyl)-ammoniummethyl]benzene (2a) and tris(N,N-dimethyl-N-hexadecylammoniummethyl)mesitylene (3). The resulting films are of high quality as judged by He/N2 permeation selectivities of ca. 100. Such selectivity is well in excess of the Knudsen diffusion limit of 2.6 and approaches that which has been found for glued bilayers of 5,11,17,23,29,35-hexakis[(N,N,N-trimethylamonium)-N-methyl-37,38,39,40,41,42-hexakis-n-hexamedecyloxy-calix[6]arene hexachloride (1). The significance of these findings to LB technology, in general, is briefly discussed.     

A synthesis of 2-methyleneindane

After difficulties encountered in a conventional Wittig approach, a synthesis of 2-methyleneindane was achieved $\text{via}$ a β-silylsulphone intermediate.     

An analysis of limiting conditions on empirical nonbonded potential functions

Summary The use of empirical potential functions for describing the interaction between molecules has suffered from the difficulty of finding suitable potential constants. In particular, the barrier to rotation about a C-C bond is open to the question of how to partition the energy between nonbonded through space interactions and intrinsic resistance to bond rotation. Using the equation for the cohesive energy and its derivative for each of the three lattice parameters,a, b, and of the unit cell of polyethylene, we obtain four equations which are linear in the six potential constants required to write these quantities in terms of aMie potential. Instead of making additional assumptions, we have applied a series of inequalities and used linear programming to assess the range of permissible values. Many of the reported potential function parameters do not fall within this permissible range. The results show that the total contribution of nonbonded interactions to the barrier to rotation must be in the vicinity of 10–25%. Permissible ranges for the potential constants were very sensitive to the value of the chain setting angle, with no possible solutions lying outside the range 44°<<49°.

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Zusammenfassung Der Gebrauch von empirischen Potentialfunktionen für die Beschreibung der Wechselwirkung zwischen Molekülen leidet unter der Schwierigkeit, brauchbare Konstanten in den Funktionen zu finden. Insbesondere ist die Rotations-Barriere um eine C-C-Bindung in bezug auf die Frage offen, wie sich die Energie zwischen nicht gebundenen Atomen und der Hemmung der Rotation um die Bindung aufteilt.Unter Benutzung der Gleichung für die Kohäsionsenergie und ihrer Ableitungen für jede der 3 Gitterparametera, b und der Einheitszelle von Polyäthylen erhalten wir 4 Gleichungen, die in den 6 Potentialkonstanten, die für die Formulierung einesMie Potentials erforderlich sind, linear sind. Anstelle von zusätzlichen Annahmen haben wir eine Anzahl von Ungleichungen angewendet und eine lineare Programmierung verwendet, um die Bereiche der erlaubten Werte abzugrenzen.Viele der bisher genannten Parameter der Potentialfunktion fallen nicht innerhalb des erlaubten Bereiches. Die Ergebnisse zeigen, daß der Gesamtbeitrag an Wechselwirkung nicht gebundener Atome zu der Rotationshemmung um die C-C-Bindung bei etwa 10–25% liegt. Erlaubte Bereiche für die Potentialkonstanten erwiesen sich als sehr empfindlich für den Wert des Neigungswinkels der Ketten, wobei sich zeigt, daß Lösungen im Bereich 44°<<49° liegen müssen.

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Dedicated to Prof. Dr.G. Hosemann on the occasion of his 60th birthday.     

Poly(2,6-diphenyl-1,4-phenyl oxide): Characterization by gel-permeation chromatography,light scattering,and solution viscosity

Ten unfractionated poly(2,6-diphenyl-1,4-phenylene oxide) samples were examined by gel permeation chromatography (GPC) and intrinsic viscosity [η] at 50°C in benzene, by intrinsic viscosity at 25°C in chloroform, and by light scattering at 30°C in chloroform. The GPC column was calibrated with ten narrow-distribution polystyrenes and styrene monomer to yield a “universal” relation of log ([η]M) versus elution volume. GPC-average molecular weights, defined as M?gpc = \documentclass{article}\pagestyle{empty}\begin{document}$\Sigma w_i [\eta ]_i M_i /\Sigma w_i [\eta ]_i$\end{document}, w_i denoting the weight fraction of polymer of molecular weight M_i, were computed from the GPC and [η] data on the polyethers. The M?GPC were then compared with the weight-average M?_w from light scattering. The intrinsic viscosity (dl/g) versus molecular weight relations for the unfractionated poly(2,6-diphenyl-1,4-phenylene oxides) determined over the molecular weight range 14,000 ≤ M?_w ≤ 1,145,000 are log [η] = ?3.494 + 0.609 log M?_w (chloroform, 25°C) and log [η] = ?3.705 + 0.638 log M?_w (benzene, 50°C). The M?_w(GPC)/M?_n(GPC) ratios for the polymers in the molecular weight range 14,000 ≤ M?_w ≤ 123,000 approximate 1.5 according to computer integrations of the GPC curves with the use of the “universal” calibration and the measured log [η] versus log M?_w relation. The higher molecular weight polymers (326,000 ≤ M?_w ≤ 1,145,000) show slightly broadened distributions.     

Halonium ion-mediated reaction of unsaturated hydroperoxy acetals. Competition between the formation of cyclic peroxides and the migration of the methoxy (or hydroxy) group

Monoozonolyses of dienes 2 in methanol gave in each case the corresponding unsaturated alpha-methoxy hydroperoxides 3. Capture of 2-alkyl-substituted cyclohexanone oxides by methanol was highly diastereoselective, thereby providing exclusively the hydroperoxides derived from attack by methanol from the less hindered face of the carbonyl oxide intermediates. Halonium ion-mediated reactions of the hydroperoxides 3 gave the novel methoxy- or hydroxy-migrated products, together with the expected halogen-substituted 1, 2-dioxanes and/or 1,2-dioxepanes, the composition of the product mixture being a function of the halogenating agent utilized and the structure of 3.