bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton transfer between carbon acids and methoxide: Studies in methanol, the gas phase and by ab initio MO calculations
Authors: Koch Heinz F. , Mishima Masaaki , Zuilhof Han 
Published: July 2012

AbstractA detailed mechanism that features hydrogen‐bonded carbanions as well as free carbanions is presented for hydrogen transfer between carbon acids and methoxide ion in methanol. This is refined for several compounds by measuring their gas phase acidities, ΔG kcal/mol: C6H5CH(CF3)2 [335.3]; p‐C6H4CHClCF3 [337.4]; 9‐phenylfluorene [335.6]; C6F5H [349.2]. Ab initio molecular orbital calculations are reported to evaluate the stability of possible intermediates along the reaction pathway from 2‐hydro‐2‐phenyl‐perfluoropropane and methoxide ion to the carbanion and methanol. The intermediate, {C6H5C(CF3)2}−. HOCH3, is 6.8 kcal/mol more stable than the separated species, {C6H5C(CF3)2}− and CH3OH, and 43.2 kcal/mol more stable than C6H5CH(CF3)2 and −OCH3.
Ionic plastic phase in piperidinium hexafluorophosphate studied by solid NMR, X‐Ray diffraction, and thermal measurements
Authors: Ono Hiroshi , Ishimaru Shin'Ichi , Ikeda Ryuichi , Ishida Hiroyuki 
Published: July 2012

AbstractMeasurements of 1H, 19F, and 31P NMR, differential scanning calorimetry (DSC) and X‐ray powder diffraction were carried out in piperidinium hexafluorophosphate ([C5H10NH2]PF6). Three solid phases were observed by DSC in the range from 150 K to the melting point of 517 K. The highest‐temperature phase was determined to form a CsCl‐type cubic lattice with a=6.21(3) Å, Z=1, V=240(4) Å3, and Dx= 1.60(3) Mg m−3. From the NMR measurements in this phase, both cation and anion were revealed to perform self‐diffusion as well as isotropic rotation. These molecular motions and thermal properties indicate that this phase is an ionic plastic phase.
UV‐Vis spectroscopic study of molecular clustering in supercritical CO2‐acetone mixtures
Authors: Lu Jie , Han Buxing , Yan Haike 
Published: July 2012

AbstractSolvatochromic behavior of acetone in supercritical CO2 was investigated over a wide range of pressures from 75 to 240 bar and at 318.15 K using UV‐Vis spectroscopy. Local density of CO2 about the solute was estimated from the solvatochromic shift of acetone based on the McRae‐Bayliss dielectric continuum model. The most remarkable aggregation of CO2 about the solute occurs at the reduced density of 0.5 ∼ 0.6. A simple clustering model was presented to estimate the excess solvent number about each solute molecule to the bulk region. In the near‐critical region, the excess number of CO2 is larger than the cluster size at infinite dilution defined by Debenedetti, which may be attributed to the formation of solute‐solute clusters.
LIF spectra of n‐propoxy and i‐propoxy radicals and kinetics of their reactions with O2 and NO2
Authors: Mund Ch. , Fockenberg Ch. , Zellner R. 
Published: July 2012

AbstractFluorescence excitation spectra of CH3CH2CH2O (n‐propoxy) and (CH3)2CHO (i‐propoxy) radicals were obtained using a combined laser photolysis/laser‐induced fluorescence (LIF) technique and the kinetics of reactions of these radicals with (1) O2 as a function of temperature and with (2) NO2 as a function of pressure have been determined.Propoxy radicals were produced by excimer laser photolysis of the appropriate propyl nitrites at λ = 351 nm. The spectra of the (Ã←X̃) transitions show progressions of the CO‐stretching vibration in the electronically excited states with spacings of the bands of (560±10) cm−1 for i‐propoxy and (580±10) cm−1 for n‐propoxy. Fluorescence spectra taken after excitation in the (4,0) band at λ = 340.1 nm (i‐propoxy) and in the (1,0) band at λ = 342.4nm (n‐propoxy) show progressions of the CO‐stretching vibration in the electronic ground state of (900±60) cm−1 for i‐propoxy and (1000±50) cm−1 for n‐propoxy.The Arrhenius expressions for the ractions of n‐propoxy and i‐propoxy with O2 have been determined to be k1 (n) = (1.4±0.6)×10−14 exp (0.9±0.5) kJ mol−1/RT) cm3 s−1 and k1 (i) = (1.0±0.3)×10−14 exp (‐(1.8±0.4) kJ mol−1/RT) cm3 s−1 in me range 218–313 K. The rate coefficients for the reactions of NO2 with n‐propoxy and i‐propoxy at T = 296 K were found to be independent of total pressure with k2(n) = (3.6±0.4)×10−11 cm3 s−1 (6.7–53 mbar) and k2(i)=(3.3±0.3)×10−11 cm3 s−1 (6.7–106 mbar).
Architecture of J‐aggregates studied by pressure‐dependent absorption and fluorescence measurements
Authors: Spitz Christian , Daehne Siegfried 
Published: July 2012

AbstractThe spectral shift of absorption and fluorescence bands as well as the fluorescence decay of four J‐aggregate forming 5,5′,6,6′‐tetrachlorobenzimidacarbocyanine dyes have been investigated in solution under high pressure up to 50 kbar0 The investigated dyes differ only in their 1,1′ and 3,3′ nitrogen substituents which do not influence the chromophore itself. Whereas the spectral behaviour of the monomeric dyes is comparable to that of aromatic and polyenic compounds, the J‐aggregates show some unusual spectral features.Two types of J‐aggregates can be distinguished. One type exhibits a linear dependence of the absorption and fluorescence maximum on pressure wim vanishing Stokes shift over the whole pressure range. The second type is characterised by a limited shift of the absorption band to longer wavelengths whereas the Stokes shift increases even at pressures where the absorption energy remains constant.The spectral behaviour of the first type is consistent with the well‐known chain‐shaped or brickstone‐like structure of J‐aggregates. As one dye of the second type is known to form optically active, Davydov‐split J‐aggregates the pressure‐dependent spectral behaviour of such dyes corroborates the assumption mat their J‐aggregates consist of helical cylindrical micelles.
Pressure‐jump investigations on the kinetics of the isotropic‐nematic phase transition of a liquid crystal: Time behavior of the scattered and transmitted light intensities for PCH 5
Authors: Sinanis S. , Schneider G.M. 
Published: July 2012

AbstractA new optical high pressure cell was developed, which allows to induce pressure jumps within τ ≈︁ 0.5 ms and τ ≈︁ 50 ms and with an amplitude up to |ΔP| ≈︁ 6 MPa. With this cell the transmitted and scattered light intensities at fixed angles (θ = 20°, 50°, 80°, 110°, 140°) can be measured simultaneously as a function of time, e.g. at the phase transition isotropic‐nematic of a selected liquid crystal (here trans‐4‐n‐pentyl(4‐cyanophenyl)‐cyclohexane, PCH 5). The temperature changes during the pressure jumps are also registrated. The T(p) phase diagram of the liquid crystal is known from DSC measurements. Simultaneous time‐dependent measurements of transmitted and scattered light intensities allow a discussion of the processes that occur at the transition. The treatment of these processes has been approached according to existing theoretical models.
The structure of a methyl‐branched phospholipid monolayer in contact with hexadecane
Authors: Brezesinski Gerald , Bringezu Frank , Möhwald Helmuth 
Published: July 2012

AbstractMonolayers of the methyl‐branched phospholipid l‐(2‐methylstearoyl)‐2‐hexadecylphosphatidylethanolamine (1) at the air/water interface and in contact with hexadecane are studied by pressure‐area isotherm measurements and grazing incidence x‐ray diffraction (GKD). The monolayers exhibit at both interfaces two diffraction peaks indicating a rectangular unit cell with next‐nearest neighbor (NNN) tilt at 20°C and at all lateral pressures investigated. Compared to the double‐chain DPPE, the introduction of the medryl side group changes the tilt direction from nearest neighbour (NN) to NNN, increases me tilt angle drastically and prevents the transition to the untilted hexagonal phase. The hexadecane contact decreases the tilt angle of (1) which shows that hexadecane is incorporated into the monolayer. However, the tilt angle can be reduced only to 13°. Comparison of the isotherm with the molecular areas determined by GIXD indicates that the monolayer consists of ordered and non‐ordered parts, the latter of which do not contribute to the diffraction pattern.
Investigation of charge transport across the Ag|AgI‐interface: (II) Dilatometric study of the anodic dissolution of silver
Authors: Majoni S. , Janek J. 
Published: July 2012

AbstractThe anodic dissolution of silver at the solid‐solid interface Ag|α‐AgI has been studied by means of a high precision (capacitive) dilatometer. The dilatometer signal corresponds to the change of the anode thickness during the dissolution experiment. Under galvanostatic conditions and in a definite pressure range the dilatometer signal oscillates periodically, i.e., me length change of the anode with time is not a simple and linear function of the current density. The mean length change is, as expected, proportional to the electric current. The oscillation modes of the dilatometer signal are correlated with simultaneous electrochemical oscillations at the anode and give evidence for the influence of morphological effects on the interface kinetics. From the combination of both electrochemical and dilatometric (mechanical) experiments, we draw conclusions on a possible mechanism of the observed oscillatory kinetics.
A new unifying structural model of heteropolymolybdate salts: Microstructure and thermal stability of a series of molecular oxides
Authors: Berndt S. , Herein D. , Zemlin F. , Beckmann E. , Weinberg G. , Schütze J. , Mestl G. , Schlögl R. 
Published: July 2012

AbstractPowder X‐ray diffraction and cryo electron diffraction techniques supported by computer simulations were used to determine the secondary structures of the series of heteropoly acid (HPA) compounds CsxH4‐x PVMo11O40·nH2O (0≤x≤4). The structures of the caesium salts (2≤x≤4) are simple cubic with space group Pn3m. The free acid exhibits a triclinic lattice (P−1) for the majority of all crystals. A small fraction of thin crystals was detected with simple cubic structure (Pn3m). Computer simulations of the X‐ray diffraction patterns suggested that the structure of Cs2H2PVMo11O40·5H2O contains defects in the cation lattice. The caesium ion occupancy is 2/3. [H5O2]+‐groups occupy 1/3 of the cation positions. The diffraction pattern of Cs4PVMo11O40·5H2O could be simulated when only 3/4 of the anion positions are occupied. Cs3HPVMo11O40·7H2O crystallises in a simple cubic lattice without any defects.The secondary structures of the investigated heteropoly salts can, therefore, be described by a single structure with variable site occupations, with the exception of Cs3HPVMo11O40·7H2O (caesium ion occupancy of 1 and poly anion occupancy of 1). All salts belong to one phase with large stoichiometric variations. A mixture of acid and caesium salt, with the acid epitactly grown on the salts, an intergrowth‐structure witii varying caesium ion content, mixed crystals as well as the coexistence of a nanocrystalline X‐ray‐invisible form of free acid besides caesium salt could be excluded for the partly neutralised materials. Selected physico‐chemical properties of the HPA compounds, which depend on the caesium ion content, will be rationalised widi the knowledge of the secondary structures.
Measurements of Henry's law constant for hydrogen in water utilizing a palladium differential resistance sensor
Authors: Yang Lietai , Sun Xiaodong , Steward F.R. , Morris D.R. 
Published: July 2012

AbstractA differential‐resistance hydrogen sensor utilizing palladium, has been used for determining Henry's Law coefficient for hydrogen in water. This method does not necessitate equilibration of the gas and liquid phases. In the temperature range 187°C < T < 306°C, Henry's Law coefficient so determined is about 16 to 22% lower than the value determined from equilibration experiments.
Flame deposition of diamond films: An experimental study of the effects of stoichiometry, temperature, time and the influence of acetone
Authors: Bergmann Ulf , Lummer Karsten , Atakan Burak , Kohse‐Höinghaus Katharina 
Published: July 2012

AbstractThe deposition of diamond films in acetylene‐oxygen flames with different amounts of acetone in the source gas was investigated. Diamond films were deposited on molybdenum at temperatures between 1070 and 1420 K using a welding torch. The temperature as well as the stoichiometry dependence of the growth rate and quality of the diamond films were examined. The concept of supersaturation was adapted in order to have an transferable measure of the equivalence ratio. A sharp change of the diamond morphology from (111) to (100) planes between 1320 and 1370 K and between 6 and 7% supersaturation was found. The growth rate as a function of time was measured for deposition times between 2.5 and 180 min. Acetone influences the optimal conditions of the diamond deposition, the growth rate and the quality of the films. This influence was investigated in two different experiments. First, the acetone/acetylene ratio was varied with fixed supersaturation, whereas, in the second series, the supersaturation was increased by adding acetone, with keeping the acetylene flow fixed. It was found that small amounts of acetone have a positive effect on the film quality and increase the growth rate. This result may be qualitatively understood by an increase of hydrogen atom and methyl radical concentrations upon acetone addition.
Enhanced electrical conductivity of CuBr‐TiO2 composites: Dependence on temperature, volume fractions and grain sizes
Authors: Knauth P. , Albinet Gilbert , Debierre Jean‐Marc 
Published: July 2012

AbstractComposites of a solid ionic conductor (copper(I) bromide) and an insulator (titanium dioxide) with carefully characterized purity and grain size are studied by impedance spectroscopy. The experimental dependence of electrical conductivity on temperature, volume fractions and grain sizes of the components is reported and interpreted in the framework of the space charge layer concept. An enhancement of conductivity by several decades compared with pure copper(I) bromide is observed and described by a percolation‐type model, which takes the effects of grain sizes and interfacial interactions into account.
Thermodynamics of alkanol + amine mixtures. Experimental results and ERAS model calculations of the heat of mixing
Authors: Heintz A. , Naicker P.K. , Verevkin S.P. , Pfestorf R. 
Published: July 2012

AbstractExperimental data of the molar excess enthalpy of 17 binary alkanol+amine mixtures are presented obtained at 298.15 K by using an isoperibolic titration calorimeter (LKB 8700). The data are used for testing the ERAS model which accounts for self association and cross association of mixtures containing hydrogen bonds in the liquid state as well as for free volume effects based on an equation of state which incorporates the chainlike association of the molecules. Self association and cross association enthalpies of the hydrogen bonds are obtained as well as association constants providing an insight into the intermolecular structure of this kind of liquid mixtures.
Slow relaxation of conducting polymers: Differences between ring‐ and N‐substituted polyanilines
Authors: Malinauskas Albertas 
Published: July 2012

AbstractA slow relaxation (“memory effect”) was found to proceed in a poly(o‐toluidine) layer, placed at platinum electrode, whereas no slow relaxation was observed in poly(N‐methylaniline). The difference between these two ring‐ and N‐methylsubstituted polyaniline derivatives is discussed in terms of redox and doping processes, taking place during their redox interconversion.
Rate constant for the reaction CH3+CH2(X̃3B1) at 298 K
Authors: Deters R. , Otting M. , Wagner H. Gg. , Temps F. , Dóbé S. 
Published: July 2012

AbstractThe rate constant for the reaction between CH3 and CH2 (X̃3B1 = 3CH2) radicals,

was determined at T=298 K and p=1.33 mbar in an isothermal discharge flow reactor. Far Infrared Laser Magnetic Resonance (FIR‐LMR) was employed for monitoring 3CH2 and CH3 radical concentration‐versus‐time profiles. CH3 was determined in the form of NO via the conversion reaction CH3+NO2 → CH3O+NO. The CH3 and 3CH2 radicals were generated by the reactions F+CH4 → CH3+HF and F+CH3 → 3CH2+HF. The rate constant for the recombination reaction

was determined together with the rate constant for reaction (1). The measurements gave a rate constant value for reaction (1) of k1 = (6.5±1.2)·1013 cm3/mol s.
An in situ UV‐Vis spectroelectrochemical investigation of the dichromate reduction at a polyaniline‐modified electrode
Authors: Malinauskas Albertas , Holze Rudolf 
Published: July 2012

AbstractThe electroreduction of dichromate at polyaniline (PANI) modified ITO glass electrodes in acidic solution was investigated with in situ UV‐Vis spectroelectrochemistry. It has been shown that under open circuit conditions dichromate does irreversibly oxidise the PANI layer. Under controlled potential conditions cathodic reduction of dichromate was shown to proceed at PANI‐modified electrodes. The overall rate of dichromate reduction was shown to be independent on the electrode potential of the PANI‐modified electrode in the range of ERHE=+0.2 to +0.8 V. From the data obtained it was concluded that a redox reaction between dichromate and PANI is the rate‐determining step of the overall electrocatalytic process.
Computer simulation of chiral liquid crystal phases — VII. The Chiral Gay‐Berne Discogen
Authors: Memmer R. 
Published: July 2012

AbstractThe phase structures of chiral discotic liquid crystals were studied by computer simulations. Bulk systems composed of uniaxial chiral discotic molecules with interactions described by the Gay‐Berne potential and an additive term for the energy of the chiral interaction were investigated using Monte Carlo (MC) simulations in the NVT ensemble. A discotic cholesteric phase (ND* and a discotic blue phase (BPDII) were observed along an isotherm in dependence on the chirality parameter describing the strength of the chiral interaction. All phases were characterised by order parameters, scalar and pseudoscalar orientational correlation functions, and visual representations of selected configurations.
Electrooxidation mechanism of glyoxylic acid on Au polycrystalline electrodes in acidic medium
Authors: Ocón P. , Velasco J. González 
Published: July 2012

AbstractThe electrooxidation mechanism of glyoxylic acid has been investigated on an Au polycrystalline electrode in acidic medium. The kinetic parameters deduced: Tafel slope, reaction order with respect to glyoxylic acid concentration, reaction order with respect to the pH, apparent activation enthalpy, entropy and Gibbs energy, and the final products detected after oxidation are in agreement with an electrooxidation mechanism beginning with an adsorption and a rate determining step in which the adsorbate becomes oxidized in a monoelectronic transfer reaction.
Angular axis distribution of asymmetric top molecules by the absorption of plane and circularly polarized light
Authors: Cong Shu‐Lin , Han Ke‐Li , Lou Nan‐Quan 
Published: July 2012

AbstractExpressions used for describing optical preparation of aligned and oriented reagents are derived. The plane polarized light can only be used to control the alignment of reagents, and the circularly polarized light can be used to control the alignment and orientation of reagents. For asymmetric top molecules, the degree of alignment can often be chosen to be high, and the degree of orientation is often low. Specially, if reagents are symmetric top molecules, both degrees of alignment and orientation can often be chosen to be high for the K‐selected state.
Estimation of the thermodynamic stability of amorphous alloys Fe‐Si‐B and Co‐Si‐B
Authors: Kutsenok I. B. , Kunze S. , Mikhailovsky B. V. , Geiderikh V. A. 
Published: July 2012

AbstractThe estimation of thermodynamic functions of crystallization of amorphous alloys was carried out using a two‐stage procedure. The main approximation for this consists in the consideration of amorphous alloys as a supercooled metastable liquid solution. The first stage describes the thermodynamic properties of the melts Co‐Si‐B and Fe‐Si‐B by means of the ideal association model. A method of mathematical optimization was used to get the most reliable model parameters. All experimental thermodynamic data (integral and partial enthalpies, entropies and chemical potentials received by different experimental methods) available in the literature for both the ternary system and all composed binary systems were taken into account for this purpose. The second stage of estimation consists in the extrapolation of the calculated temperature and concentration dependences of the thermodynamic functions of the melts to low temperatures, using known models for the heat capacities of undercooled melts, and their comparison with appropriate thermodynamic functions of crystalline phases. The estimated values for the enthalpy of crystallization of the Fe‐B, Co‐Si‐B and Fe‐Si‐B amorphous alloys are in good agreement with experimental data.
Computer simulation of liquid ionic alloys and metal‐molten salt solutions
Authors: Koslowski T. H. 
Published: July 2012

AbstractWe present a numerical study of simple models of liquid ionic alloys and metal‐molten salt solutions. The microscopic structure is modeled using the primitive model of charged hard spheres, the electronic structure is described by a right‐binding Hamiltonian including the crucial component of Madelung potential fluctuations. We discuss the nature of the nonmetal‐metal crossover as a function of composition in these systems and present a computation of thermodynamic properties within the screened mean spherical approximation.
Interfacial properties of liquid alloys: An experimental study on Ga‐Bi and Ga‐Ge
Authors: Nattland D. , Chadli H. , Zell C.A. , Müller S.C. , Blanckenhagen B. V. , Freyland W. 
Published: July 2012

AbstractInterfacial phase transitions like wetting and prewetting transitions are of considerable interest in physics and chemistry of condensed matter since they represent phase transitions in reduced dimensionality. Besides this interfacial properties are of profound practical and technological interest. Most systems studied experimentally in this respect are characterized by Van der Waals intermolecular interactions. However, in the last few years it was shown that Coulomb liquids like liquid alloys or metal molten salt solutions exhibit interfacial phase transitions similar to those known in Van der Waals systems.In order to get more insight into these phenomena the fluid‐vapor interface of two different alloy systems have been studied using ellipsometry. Gallium‐bismuth is a binary alloy with large positive deviations from Raoult's law, exhibiting a distinct miscibility gap. Approaching liquid‐liquid coexistence a Bi‐rich film completely wets the fluid‐vapor interface. As can be estimated from the ellipsometric results the film thickness jumps at the monotectic temperature to a value of about 50 Å. In contrast, gallium‐germanium shows continuous miscibility and deviates much less from ideal mixing. As the Ge concentration in liquid Ga increases along the solid‐liquid coexistence curve the optical properties at the surface also vary continuously, which can be modelled within a simple effective medium approach.