Isomeric states and rotational structure in the doubly-odd nucleus176Ta

The doubly-odd nucleus¹⁷⁶Ta is investigated by means of in-beamγ-ray spectroscopy techniques using the reactions (α, 3n), (d, 2n) and (p, n). Life-time measurements in thens-region yield low-lying isomeric states withT _1/2=13±1 ns and 30.5±1 ns, while measurements in the ms-region show the existence of a 1.1±0.1 ms isomeric state. A rotational sequence, withK=5 or 6 for the band-head, is also observed.     

Conformations and enthalpies of formation of methylenecyclohexane, 1,4‐dimethylenecyclohexane,cyclohexanone, 4‐methylenecyclohexanone, 1,4‐cyclohexanedione,and their mono‐ and dioxa derivatives by G3(MP2)//B3LYP calculations

A computational study of the stable conformations and gas‐phase enthalpies of formation at 25 °C of the title compounds has been carried out by G3(MP2)//B3LYP calculations. The work stems from our early observations on the thermodynamic and NMR spectroscopic properties of 2‐methylenetetrahydropyran and related compounds suggesting a dominating chair conformation, with poor p–π overlap in the ? O? C?C moiety, for these compounds. Besides computational verification of the chair conformation of 2‐methylenetetrahydropyran, the work was extended to find out the stable conformations of a number of other related compounds and to evaluate the relative stabilities of the various conformers. Another important goal of the work was the estimation of the gas‐phase enthalpies of formation of the present compounds, for which such literature data are scarce. A significant error in the literature value of the enthalpy of formation of methylenecyclohexane was found. Finally, the relative enthalpy levels of the isomeric compounds of this work are discussed. The high thermodynamic stability of the compounds containing an ester functional group, ? O? C?O, relative to the stability of isomeric compounds with an ? O? C?C moiety in place of the ester function, is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.     

Chain conformations on the surface of polyethylene single crystals

New conformations for the shortest folds of polyethylene single crystals were determined from the principles: (1) the conformations of polymethylene chains are basically determined by the rotational isomeric approximation, (2) the crystal part is deformed where it is connected with the fold part, and (3) the conformation of the fold must be determined as the minimum of surface energy, not of conformation energy. It was shown that the surface energy, assuming the crystal state as the reference state, was composed of four terms: (i) the deformation energy of the crystal part, (ii) the sublimation energy of the fold part, (iii) the conformation energy of the fold part, and (iv) the interaction energy between folds. The conformations of the shortest fold were basically (GTGGTGGG) for (110)-folds and (G'G'TTGG) for (200)-folds. The setting angles of all the chains in the crystal part are rotated from their normal angle (41°) to 41 + a° at the boundary between the two parts. The fold part is deformed so as to fit in with the deformed boundary of the crystal part. The conformations with minimum surface energy were obtained at a = 30° for both (110)-and (200)-folds. Their surface energies were about 16 kcal/mole of fold (300 erg/cm2). The surface energies, assuming the liquid state as the reference state, were about 7 kcal/mole of fold (130 erg/cm²).     

Effect of properties of superheavy nuclei on their production and decay

Properties and stability of superheavy nuclei resulting from hot fusion are discussed. It is shown that the microscopic–macroscopic approach allows obtaining the closed proton shell at Z ≥ 120. Isotopic trends of K-isomeric states in superheavy nuclei are predicted. Evaporation residue cross sections in hot fusion reactions are calculated using the predicted properties of superheavy nuclei. Interruption of α decay chains by spontaneous fission is analyzed. Alpha decay chains through isomeric states are considered. Internal level densities in superheavy nuclei are microscopically calculated.     

Structure of polymer solutions at interfaces: a Monte Carlo simulation study

The canonical ensemble Monte Carlo method is applied to study the structure of polymer solutions confined between surfaces. The polymer molecules are modeled as fused-sphere freely rotating chains with fixed bond length and bond angles and the solvent as hard spheres. The simulation results for the configurational and conformational properties of the chains are presented with varying interfacial distances, chain concentrations, and chain lengths. The chains are depleted at the wall at lower density, which, however, becomes less at higher density. With an increase in the interfacial distance, the enhancement/depletion of the chains at the wall becomes more marked. At all interfacial distances and chain lengths, increasing the concentration of the solvent makes the oscillation in the density profile of the chains more pronounced. Conformational properties provide important indications regarding the behaviour of chains as they approach surfaces.     

Entropic and conformational study of isolated double-tethered chains by three-dimensional lattice simulations

Double-tethered polymers are a kind of linear polymer with a peculiar topological constraint; that is, both of its end-points are attached to a plane which the polymer segments cannot penetrate. The effects of the constraint on the polymer's configurational and entropic properties were investigated by means of a three-dimensional lattice simulation that combined a previously proposed idea with a very efficient chain generation algorithm. In particular, the value of a topology-dependent critical exponent was estimated for the double-tethered configurations. This data is the first report on isolated and double-tethered chains. Also, two optional types of tethered-polymer were investigated as asymptotes of the double- and single-tethered configurations.     

Neutronh 11/2 alignments in the triaxial nucleus133La

High spin states have been studied in¹³³La via the¹²²Sn (¹⁵N, 4ny) fusion evaporation reaction. Bands build on low lying h_11/2,g_7/2 and d_5/2 proton states have been identified. At higher spin a h_11/2 neutron alignment is observed. The softness with respect to the triaxial deformation makes the nuclear shape sensitive to the quasiparticle configurations and coexistence between states withy ≈ + 30°,y ≈ ? 30° andy ≦ ? 60° was found. The results have been interpreted using total routhian surface (TRS) model calculations.     

不同形态MEH-PPV的构象及其光学特性

通过对在固溶体、稀溶液、薄膜和纳米孔中MEH—PPV的PL和PLE谱的测量分析,研究不同形态下MEH-PPV分子链的构象及其对电子能带和光学性质的影响。在THF稀溶液中,MEH—PPV分子链基本上皆为分立态;在MEH—PPV薄膜中,分子链基本上皆为聚集态;在MEH-PPV／PS固溶体中,MEH—PPV分子链为聚集态和分立态两构象并存,聚集态的比例随MEH-PPV浓度的增加而升高;在多孔氧化铝模板纳米孔中,MEH—PPV分子链形成链束。分立态、聚集态和链束这三种不同构象的分子链具有不同的电子能带结构和光学性质。     

Interaction studies of cysteine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cation complexes

The coordination geometries, electronic features, metal ion affinities, entropies, and the energetics of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible conformations of cysteine complexes were studied. The complexes were optimized using density functional theory (B3LYP) and second order Moller–Plesset Perturbation (MP2) theory methods using 6‐311 + +G** basis set. The interactions of the metal cations at different nucleophilic sites of cysteine conformations were considered after a careful selection among several binding sites. All the metal cations coordinate with cysteine in a tridentate manner and also the most preferred position for the interaction. It is found that, the overall structural parameters of cysteine are not altered by metal ion substitution, but, the metal ion‐binding site has undergone a noticeable change. All the complexes were characterized by an electrostatic interaction between ligand and metal ions that appears slightly more pronounced for lithium and beryllium metal complexes. The metal ion affinity (MIA) and basis set superposition error (BSSE) corrected interaction energy were also computed for all the complexes. The effect of metal cations on the infrared (IR) stretching vibrational modes of amino N? H bond, side chain thiol group S? H bond, hydroxyl O? H bond, and Carbonyl C?O bond in cysteine molecules have also been studied. The nature of the metal ion‐ligand bond and the coordination properties were examined using natural bond order (NBO) at bond critical point (electron density and their Laplacian of electron density) through Atoms in Molecules (AIM) analyses. Copyright © 2010 John Wiley & Sons, Ltd.     

Isomerieverschiebung und Quadrupolaufspaltung beim Mößbauer-Effekt von Fe57 in Eisenverbindungen

Data from previous measurements are discussed from the point of view of isomeric shift and quadrupole splitting. For a comparison of isomeric shifts the magnitude of temperature shifts have to be regarded. Information about electric field gradients arises from the magnitude and the temperature dependence of quadrupole splittings. After putting the data into a suitable form, characteristic regions of the value of line shift, quadrupole splitting and temperature dependence of the splitting for different bond types are obtained. Besides this, influences of the crystal field are to be considered. Different types of contributions to the electric field gradient are discussed. The main features of field gradients in iron ions and molecules with and without closed electron shells are derived and compared with the experimental results. The result that the isomeric shifts for covalent bond iron in the oxydation states 0, +2, +3 and metallic bond iron are distributed over the same region whilst the ions Fe²⁺, Fe³⁺ and [Fe^VIO₄]^2? each have characteristic values is discussed.π-bonds in addition to σ-bonds and partially ionic bonds have to be considered. Based on the foregoing discussion the connection between the strength ofπ-bonds and the value of isomeric shifts and quadrupole-splittings and the sign of field gradients is regarded for iron ions and molecules, where ligands have been exchanged. Finally examples for the interdependence of the structure of multicenter-molecules and -ions and the data are given.     

Rotational spectrum of sulfuryl bromide fluoride

The rotational spectra of SO₂⁷⁹BrF and SO₂⁸¹BrF have been obtained between 18 and 40 GHz. Both molecules are near-prolate symmetric rotors with a and b-type dipole components. A least-squares fit of the observed moments of inertia obtained by correcting for the bromine quadrupole interaction yields $\text{r}\text{(SBr) = 2.155 ± 0.006}\text{A}\text{?}$ and ? FSBr=100.6°±1.5° structural parameters when $\text{r}\text{(SO) = 1.407}\text{A}\text{?}$, $\text{r}\text{(SF) = 1.56}\text{A}\text{?}$, and ? OSO=123.7° are assumed.     

Enhancement in electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes by 100 MeV Si9+ swift heavy ion irradiation

Swift heavy ion (SHI) irradiation has been used as a tool to enhance the electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes dispersed with dedoped polyaniline (PAni) nanorods; 100 MeV Si⁹⁺ ions with four different fluences of 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions cm^?2 have been used as SHI. XRD results depict that with increasing ion fluence, crystallinity decreases due to chain scission up to fluence of 5?×?10¹¹ ions cm^?2, and at higher fluence, crystallinity increases due to cross-linking of polymer chains. Ionic conductivity, electrochemical stability, and dielectric properties are enhanced with increasing ion fluence attaining maximum value at the fluence of 5?×?10¹¹ ions cm^?2 and subsequently decrease. Optimum ionic conductivity of 1.5?×?10^?2 S cm^?1 and electrochemical stability up to 6.3 V have been obtained at the fluence of 5?×?10¹¹ ions cm^?2. Ac conductivity studies show that ion conduction takes place through hopping of ions from one coordination site to the other. On SHI irradiation, amorphicity of the polymer matrix increases resulting in increased segmental motion which facilitates ion hopping leading to an increase in ionic conductivity. Thermogravimetric analysis (TGA) measurements show that SHI-irradiated nanocomposite polymer electrolytes are thermally stable up to 240–260 °C.     

Semiphenomenological Model of the Nucleus and its Application to Description of the Rotational Spectra. I

The general structure of the semiphenomenological model as a unified nuclear model describing the rotational, charge oscillation and configurational states is considered. The basic HAMILTONIAN of the model including the average field and short -range “residual” interactions is given.     

Understanding liquid-liquid immiscibility and LCST behaviour in polymer solutions with a Wertheim TPT1 description

The aim of the work presented in this paper is to help in the understanding of the lower critical solution temperature (LCST) fluid phase behaviour exhibited by polymer solutions. It is well recognized that the LCST in polymer solutions is a consequence of density (compressibility) effects; the solvent is much more compressible than the polymer and the increasing difference in compressibility when the temperature is increased leads to a negative volume of mixing. The separate roles that the repulsive and attractive intermolecular interactions play in this regard are less well understood. In this study we use the Wertheim first-order thermodynamic perturbation theory (TPT1) [Wertheim, M. S., 1987, J. chem. Phys., 87, 7323; Chapman, W. G., Jackson, G., and Gubbins, K. E., 1988, Molec. Phys., 65, 1057] to describe the phase equilibria of model polymer solutions of hard spheres and hard-sphere chains where the diameter of the solvent and the polymeric segments are the same (symmetrical system). The thermodynamic functions (volume, enthalpy, entropy and Gibbs function) of mixing are determined to assess the possibility of a demixing instability in such a system. No fluid-fluid phase separation is found for the purely repulsive (athermal) system, regardless of the chain length of the polymer. The role of the attractive interactions is then investigated by incorporating attractive interactions at the mean-field level; the simplest system with equivalent (symmetric) solvent-solvent, solvent-polymer segment, and polymer segment-polymer segment interaction energies is examined. The attractive interactions are found to be essential in describing the liquid-liquid phase separation; LCST behaviour is found for mixtures with ‘polymer’ chains of seven segments or more. In this case we show that the phase behaviour is driven by an unfavourable (negative) entropy of mixing due to an increase in the density of the solvent on addition of small amounts of polymer. We also determine the thermodynamic properties of mixing for a system of spherical molecules of the same size with directional interactions that give rise to LCST and closed-loop behaviour. As expected the mechanism for phase separation in such systems is very different to that in polymer solutions.     

Branching in anionic polyacrylonitriles

The morphological and hydrodynamic properties of three series of anionic polyacrylonitrile fractions (10⁵<M _w< 5 × 10⁶) have been studied in dilute dimethylformamide (DMF) solution. All the observed values of the molecular parameters (M _w, S ² _w A₂, [η], S) are consistent with a trifunctional randomly branched structure characterized by a decrease of branching density with molecular weight. The sample obtained in a strongly dipolar solvent (DMF, ?70°C, diphenylmethylsodium) shows a unimodal molecular weight distribution and higher branching densities (2.5 × 10^?2 to 10^?1); on the other hand, the sample obtained in a nonpolar solvent (toluene, ?70°C, n-butyllithium) shows a binodal molecular weight distribution and smaller branching densities (10^?4 to 1.4 × 10^?3). These characteristic branched structures may be explained by transfer to polymer as the main branching process, taking into account the polarity of the medium and its thermodynamic quality for the polymer.     

Arrhenius Lifetimes of RNA Structures from Free Energy Landscapes

We develop a novel method to define an effective free energy barrier between various conformations available to an RNA sequence. Our approach utilizes the energy landscape computed using the ViennaRNA package. Replacing the energies with configurational free energies yields improved agreement with the Arrhenius law provided we account for the entropies of both the basin states and the barrier states. This improved agreement comes without altering the computational complexity class of the algorithm. We discuss the combinatorial explosion of high-energy states available to RNA, and the properties of Kawasaki and Metropolis transition models that affect the applicability our method.     

Zur Deutung der Protonenspinrelaxation in Glycerin

In contrast with the usual assumption that proton spin relaxation in glycerol originates from rotational molecular diffusion, quantitative evaluation of the temperature and Larmor frequency dependence in the ranges ?30 °C to+70 °C and 10 kHz to 120 MHz, respectively, gives extensive agreement with Fick's translational random walk model. This observation is supported by direct measurements of the self-diffusion constant by means of the pulse gradient method, which reveals the same activation barrier as relaxation spectroscopy.     

Twenty-parameter eigenfunctions and energy values of the 23 S States of He and He-like Ions

Twenty-parameter calculations of the energies and wave functions of the first excited states 2³ S of He, Li⁺, Be⁺⁺, B⁺⁺⁺, O⁶⁺, Ne⁸⁺, Mg¹⁰⁺, have been carried out using Hylleraas' method. The energy values have been corrected for mass polarization. The coefficients of the best wave functions are listed. Similar calculations for the 2³ S state of the H^? ion yield an energy value which cannot be distinguished from the energy of a free H atom. For He and Li⁺, in addition, forty-parameter calculations have been carried out. The results compare well with the recent calculations of Pekeris using a somewhat different method. Even after the inclusion of the relativistic correction, the theoretical energy values deviate slightly from the observed. The differences, ?0·10±0·05 cm^?1 for He and ?1·07±0·10 cm^?1 for Li⁺, represent observed values of the Lamb shifts in the 2³ S states. These values agree within their uncertainties with the values predicted from quantum electrodynamics.     

Dependence of the GaAs (110) surface electronic state dispersion curves on the surface relaxation angle

The surface state dispersion curves E($\text{k}$) of the dangling bond states near the fundamental band gap, C₃ and A₅, are computed for both the established θ?27° model and the recently proposed θ?7° model of the (110) surface relaxation of GaAs, where θ is the surface bond rotation angle. The two models produce surface state dispersion curves that are similar to one another and to the data.     

分子动力学模拟研究熔态硅的局部结构

采用Tersoff势,修正试用不同的粒子间相互作用距离R,S的取值,进行了液态硅的分子动力学模拟.模拟的结果表明,修正Tersoff势下得到的径向分布函数能与X射线衍射、中子散射实验相一致.模拟得到在液态硅中,Si的配位数为6.9,键长为0.254nm.分子动力学模拟表明,液态硅中Si原子间联接成一种网络状结构,但大多数Si原子与其近邻Si原子仍保持近似于正四面体的局部构型.键角概率分布出现两个峰值~57°和~102°.通过键序参量分析,得到在液态硅近邻结构中,正四面体构型约占82%,键取向波动方差为5. 关键词：