Ground state and lattice dynamical study of ionic conductors CaF2, SrF2 and BaF2 using density functional theory

The present paper reports a comprehensive and complementary study on structural, electronic and phonon properties of face centered cubic fluorites, namely CaF₂, BaF₂ and SrF₂, using first principles density functional calculations within the generalized gradient approximation. The calculated lattice constants and bulk modulus are in good agreement with available experimental data. The analysis of band structure and density of states confirms the ionic character for all the three fluorides. The phonon dispersion curves and corresponding phonon density of states obtained in the present work are consistent with the available experimental and other theoretical data. The LO-TO splitting is maximum for CaF₂, which confirms that the ionicity is maximum in the case of CaF₂. The phonon properties for SrF₂ have been calculated for the first time.     

Understanding the Role of Parallel Pathways via In‐Situ Switching of Quantum Interference in Molecular Tunneling Junctions

This study describes the modulation of tunneling probabilities in molecular junctions by switching one of two parallel intramolecular pathways. A linearly conjugated molecular wire provides a rigid framework that allows a second, cross‐conjugated pathway to be effectively switched on and off by protonation, affecting the total conductance of the junction. This approach works because a traversing electron interacts with the entire quantum‐mechanical circuit simultaneously; Kirchhoff's rules do not apply. We confirm this concept by comparing the conductances of a series of compounds with single or parallel pathways in large‐area junctions using EGaIn contacts and single‐molecule break junctions using gold contacts. We affect switching selectively in one of two parallel pathways by converting a cross‐conjugated carbonyl carbon into a trivalent carbocation, which replaces destructive quantum interference with a symmetrical resonance, causing an increase in transmission in the bias window.     

2-Phosphaindolizines

Abstract

An overview of 2-phosphaindolizines, i.e. 1,3-azaphospholo[1,5-a]pyridines along with their 1-aza-, 3-aza- and 1,3-diaza analogues has been presented. It includes their methods of syntheses, characterization and reactions. Under reactions, electrophilic substitutions, N-alkylation, Diels-Alder (DA) reactions with the >C=P- functionality in the absence of the catalyst and also in the presence of the catalyst, other 1,2-additions across the >C=P- functionality, cheletropic cycloaddition of tetrachloro-o-benzoquinone (TCQ) with the phosphorus atom and co-ordination with the metal pentacarbonyls and other derivatives have been described.     

Amberlyst-15–Catalyzed Efficient Cyclization of γ- and δ-Unsaturated Alcohols: Green Synthesis of Oxygen Heterocycles

Amberlyst-15 (H⁺) resin catalyzes efficient cationic endo-cyclization of γ- and δ-unsaturated alcohols to yield tetrahydro-(2 H)-pyrans and oxepanes. The merits of the present protocol are good yield of the products under mild conditions, simple workup, and reusability of the resin.     

Working group report: Low energy and flavour physics

This is a report of the low energy and flavour physics working group at WHEPP-8, held at the Indian Institute of Technology, Mumbai, India, during 5–16 January 2004.     

Soliton with valence quarks in the chiral invariant σ-model

The chiral invariant σ-model is used to obtain bound states (solitons) of valence quarks. A hedgehog shape is assumed for the pion field. A soluble model is presented and compared to a self-consistent calculation. The results are discussed in the light of the possible effective baryon number carried by the chiral fields.     

Properties of tetra-N-glycidyl-4,4′-diamino diphenyl methane (TGDDM) cured thick films

Thick films of tetra-N-glycidyl epoxy resin of p,p′-diaminodiphenyl methane (TGDDM) were prepared using p,p′-diaminodiphenyl methane (DDM), p,p′-diaminodiphenyl sulfone (DDS) and diethylene triamine (DETA) as curing agent with or without the epoxy fortifiers PGEHA and VCDRC (at 20 phr level). These thick films were used to evaluate various physical, mechanical, chemical resistant and dielectric properties.     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.