bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Changes in the Retinal Chromophore of Bacteriorhodopsin Studied by Resonance Raman Spectroscopy
Authors: Alshuth Th. , Stockburger M. 
Published: July 2012

AbstractResonance Raman (RR) spectra were obtained from aqueous suspensions of the purple membrane of Halobacteria. The RR spectra reflect the photolabile retinal chromophore of bacteriorhodopsin which induces proton translocation across the membrane. RR spectra of the all‐trans chromophore BR570 and its 13‐cis component BR548 were recorded both in H2O and D2O suspension. The vibrational analysis revealed characteristic hydrogen bending modes of the Schiff base linkage by which retinal is bound to the protein. These bands are very sensitive to structural changes of the Schiff base and allow conclusions on geometrical and electronic changes of this group which play an important role in the proton translocation process.
Raman Spectra of Aqueous NaClO4 and NaBF4 Solutions
Authors: Schiöberg D. 
Published: July 2012

AbstractThe OD stretching vibration band in Raman spectra of liquid HOD containing ClO4− or BF4− ions is splitted into two components. The higher frequency band vw is assigned to ODw groups which are weakly H‐bonded to neighbouring anions (A): ODw = (OD... A). In Raman spectra of fully deuterated aqueous NaClO4 or NaBF4 solutions the vw band is splitted once again. The higher frequency band v3, wb is attached to the partially antisymmetric stretching vibration of unsymmetrically H‐bonded D2O molecules with a weak H‐bond at one OD group and a strong H‐bond at the other OD group (= bDODw). The lower frequency band must be assigned to the symmetric stretching vibration of D2O weakly H‐bonded to anions with both OD groups (= wDODw). The bands were separated into Gaussian‐Lorentzian product functions. The OD and D2O concentration were calculated from the band areas.
Kinetics and Mechanism of Hydrocarbon Formation in the System C2H2/H
Authors: Homann K. H. , Schweinfurth H. 
Published: July 2012

AbstractThe formation of C3H4(Propyne and Allene), C4H2(Butadiyne) and also of formaldehyde in the system C2H2/O with and without added H atoms was studied at 298 K and in a pressure range between 1.4 and 8.0 mbar. H atoms have a strongly positive influence on the rates of formation of these species. The results obtained for largely varying initial conditions were described quantitatively by a reaction mechanism of 25 reactions. Experiments with D atoms and with different O2concentrations gave additional evidence of the radical reactions involved.
On the Orientation of Liquid Crystals by Monolayers of Amphiphilic Molecules
Authors: Hiltrop K. , Stegemeyer H. 
Published: July 2012

AbstractThe orientation of nematic liquid crystals (LC) by monolayers of suitable amphiphilic compounds on solid substrates has been studied by systematic experiments using polarizing microscopy, magnetic Freedericksz‐transition, and contact angle measurements. Orientation is influenced mainly by the following parameters: 1. temperature; 2. physical properties of the substrate surface; 3. chemical properties of the substrate surface. Molecular models describing the orientating action of amphiphilic monolayers are developed and discussed in terms of the obtained quantitative results. Changes in LC orientation with film packing density and temperature can be understood as phase transitions of the system “amphiphilic monolayer + embedded LC”.
Interfacial Phenomena of TiO2‐Photoanodes
Authors: Lam R. U. E.'t , Schoonman J. , Blasse G. 
Published: July 2012

AbstractThe small‐signal a.c. response of photoelectrochemical cells with Nb‐doped TiO2 anodes has been studied for frequencies in the range 10−2‐104 Hz. A non‐linear least‐squares analysis of the complex admittance/impedance data leads to a detailed equivalent circuit for the cell. The analysis and results are compared with a recently reported Relaxation Spectrum Analysis [4]. The equivalent circuit contains passive elements, and a constant‐phase‐angle (CPA) element Q = kα(iω)−α. It is shown that a “distribution of relaxation times” model, and a “universal dielectric response” model describe frequency‐dependent elements, which are of the CPA‐form. The space‐charge capacitance in the present equivalent circuit obeys the Mott‐Schottky relation, while the CPA‐element is attributed to current inhomogeneities. Solid state aspects of H2 reduction provide a rationale for the current inhomogeneity model.
Thermodynamics of (1‐Chloronaphthalene + n‐Alkane): Excess Enthalpies, Excess Volumes and Excess Heat Capacities
Authors: Grolier J.‐P. E. , Inglese A. , Roux A. H. , Wilhelm Emmerich 
Published: July 2012

AbstractA flow microcalorimeter of the Picker design has been used to measure molar excess enthalpies at 298.15 K of the seven binary liquid mixtures 1‐chloronaphthalene + n‐hexane, + n‐heptane, + n‐octane, + n‐decane, + n‐dodecane. + n‐pentadecane, and + n‐hexadecane. Experiments were performed in the discontinuous mode, covering essentially the whole composition range. The overall imprecision of the measurements is characterized by standard deviations from Redlich‐Kister type smoothing equations of generally less than ± 1 per cent of the maximum value HEmax of the excess enthalpy (with respect to mole fraction). The most striking feature is that for 6 ± n ± 16 (n denotes the number of C‐atoms of the n‐alkane) HEmax decreases with increasing n, the correlation being approximately linear. – For the mixtures 1‐chloronaphthalene + n‐hexane, + n‐heptane, + n‐octane, + n‐dodecane, + n‐pentadecane, and + n‐hexadecane molar excess volumes VE at 298.15 K were obtained, as a function of mole fraction, from measurements of the density with a vibrating‐tube densimeter. The excess volumes are negative in all cases and become less negative with increasing chain length of the n‐alkane. At equimolar composition, for (1‐C10H7Cl + n‐C6H14) we find VE = ‐1.555±10−6 m3 mol−1, and for (1‐C10H7Cl + n‐C16H34), VE = ‐0.397±10−6 m3 mol−1. A Picker flow calorimeter was used to determine molar excess heat capacities at constant pressure CEp at 298.15 K for all mixtures except for 1‐C10H7Cl + n‐C10H22, and + n‐C16H34. The excess heat capacity is essentially zero for the mixture with n‐hexane, and increases with increasing chain length up to (1‐C10H7Cl + n‐C12H26); for (1‐C10H7Cl + n‐C15H32), CpE is somewhat smaller, thus indicating a trend inversion.
Effect of Deuterium Substitution on the Vapour Pressure of Acetonitrile
Authors: Jákli Gy. , Koritsánszky T. , Jancsó G. 
Published: July 2012

AbstractThe vapour pressure difference between CH3CN and CD3CN was measured by differential capacitance manometry between – 40 and + 80°C and the results can be expressed by the equation: In (pH/pD) = 871.8K2/T2 – 13.58K/T + 0.00687. The vapour pressure of acetonitrile between the melting point and 30°C has also been determined. The experimental data were interpreted within the framework of the statistical theory of isotope effects in condensed systems. The largest contribution to the vapour pressure isotope effect arises from the shifts in the CH stretching vibrations on condensation and these were found to undergo a blue shift with increasing temperature. The results also indicate that the rotation of the molecules about the 3‐fold symmetry axis can be considered quasi‐free whereas the rotations about the axes perpendicular to the top axis are restricted.
Messung der spezifischen Wärme und des Joule‐Thomson‐Koeffizienten von Kohlendioxid bei Temperaturen von – 40°C bis 200°C und Drücken bis 15 bar
Authors: Bender R. , Bier K. , Manrer G. 
Published: July 2012

AbstractIn order to improve the experimental data for the thermal properties of carbon‐dioxide, the isobaric heat capacity and the adiabatic Joule‐Thomson‐coefficient of carbon‐dioxide have been measured with a flow calorimeter in the temperature range from −40°C to 200°C at pressures up to 15 bar. In the investigated range, the accuracy is better than 0.15 per cent for the heat capacity and 0.5 per cent for the Joule‐Thomson‐coefficient. The isothermal throttling coefficients at zero pressure, obtained by extrapolation of the experimental values, are consistent with the temperature dependence of the second virial coefficient as measured by A. and C. Michels.
A Structural Investigation of Liquid Chloroform
Authors: Bertagnolli H. 
Published: July 2012

AbstractStarting from neutron scattering experiments on the species CDCl3, CD35Cl3, CD37Cl3 and CHCl3 the expansion coefficients of the generalized pair correlation function g00000(R), g00101(R), g00202(R), and g00110(R) are determined and analyzed quantitatively, thus providing preferred positions and orientations of the molecules in liquid chloroform. From the same set of experimental data the chlorine‐chlorine pair correlation function and the weighted sum of the chlorine‐hydrogen and chlorine‐carbon pair correlation functions are evaluated. The most probable configuration between two chloroform molecules in the liquid phase is derived from the position of the first peak of the corresponding pair correlation function. Both ways of description yield a consistent structural picture; namely the dipole axes are inclined and the hydrogen atoms point into the hollow between two chlorine atoms.
Tracer Experiments on the Exchange Equilibrium of Tritium between Hydrogen Gas and the Hydrogen‐Storage Material TiMn1.5‐Hydride
Authors: Sicking G. , Magomedbekov E. , Hempelmann R. 
Published: July 2012

AbstractThe equilibrium distribution of3H between hydrogen gas and the intermetallic hydrogen storage material Ti0.4Mn0.6Hn, being in equilibrium with the light hydrogen, was determined by tracer experiments in the α‐phase region and in the temperature range from 23°C. to –60°C. The equilibrium separation factors follow the relationshipThe values of the separation factors show up an enrichment of tritium in the solid solution, whereas in the PdHn‐system the opposite observations are made. It is shown that the isotope distribution at higher hydrogen contents is not only determined by energy differences of vibrational states. but may also be influenced by non‐idealities within the solid solution. From the non‐idealities calculated in case of P‐PdH” together with the equilibrium separation factor measured in the P‐phase, a local mode energy of the interstitial hydrogen ofis derived ‐ For Ti0.4Mn0.6Hnin the α‐phase region a value about twice as highturns out, which we confirmed by neutron scattering experiments. From these results H is concluded to occupy interstitial tetrahedral holes in Tio,Mno”H, . ‐ From hydrogen sorption isotherms at low equilibrium pressures, measured in addition to the exchange experiments with a‐Tio,Mno,6H” contributions from “surface hydrogen” are deduced. These contributions are not reflected by the values of the separation factor because of the vibrational frequencies of “surface hydrogen” are similar to those of H in tetrahedral holes. With systems, however, dissolving hydrogen in octahedral positions (as e.g. PdH,), an inversion of the isotope effect is observed going from “bulk”‐ to “surface hydrogen”.
Oxygen Reduction on Transition‐Metal Porphyrins in Acid Electrolyte I. Activity
Authors: van Veen J. A.R , van Baar J. F. , Kroese C. J. , Coolegem J. G. F. , De Wit N. , Colijn H. A. 
Published: July 2012

AbstractThe oxygen reduction characteristics of metalloporphyrins adsorbed at monolayer levels on a high surface area carbon, Norit BRX, have been studied in 8 N H2SO4 and also in 6N KOH. In an acid, oxygen reduction activity is found to be correlated with the MeII/MeIII redox potential. Most Co complexes have too high a redox potential, while too low a redox potential is observed for Fe, Ru, Os, Mn, and Cr. Ir porphyrins have the highest activity. In KOH, Ru porphyrins show the best performance. A heat treatment improves activity and stability strongly in an acid, but only mildly in an alkaline solution. A mechanism is proposed for oxygen reduction on transition metal chelates, both in acid and in alkaline solutions.
Oxygen Reduction on Transition‐Metal Porphyrins in Acid Electrolyte II. Stability
Authors: van Veen J. A. R. , Colijn H. A. 
Published: July 2012

AbstractThe stability of untreated and heat‐treated Co and FeT(p‐OCH3)PP/Norit BRX (T(p‐OCH3)PP = meso‐tetra(p‐methoxy)phenylporphyrin) has been studied under a variety of conditions: in pure electrolyte (6N H2SO4), in the presence of H2O2, and under a current load (O2 reduction); all at various temperatures. It appears that the heat‐treated Co catalyst has adequate stability for most low‐temperature applications (6NH2SO4, T ≤ 60°C, i ≤ 30 mA/cm2).
Einfluß von Tensiden auf Strömung und Stoffübergang in einer flüssig/flüssig‐Kanalströmung
Authors: Ollenik R. , Nitsch W. 
Published: July 2012

AbstractMeasurement of flow and mass transfer were performed in a two‐phase liquid/liquid‐channel arrangement in absence and presence of soluble surface active substances (Sodium‐dodecylsulfate).—Laser‐Doppler‐velocimetry was used to measure interfacial velocities and velocity profiles perpendicular to the interface in the water and in the solvent phase. Mass transfer measurements are related to the transfer of aceton across the plane interface between water and carbontetrachloride. It is shown that below the critical micell concentration (cmc) an almost rigid interface is formed with a highly suppressed mass transfer, near the cmc an increase of mass transfer and interfacial velocities was observed, and above the cmc mass transfer behaviour and interfacial flow is corresponding to an absolutely clean interface.—The compression of the surfactant layer was calculated applying the equation for Newtonian shear stress on the measured flow profiles. The resulting gradients of interfacial pressure are in good agreement with the interfacial pressures, calculated on the basis of the so‐called “cmc‐effect”.
Validity of Macroscopic Concepts for Fluids on a Microscopic Scale
Authors: Alder B. J. , Alley W. E. , Pollock E. L. 
Published: July 2012

AbstractBy Fourier decomposition of the appropriate fluctuation it is possible within the regime of linear response to extend the concept of both thermo‐dynamic quantities and transport coefficients to their dependence on both wavelength and frequency. Experimentally these generalized macroscopic properties are accessible through neutron diffraction and, as examples, the dependence of the sound speed on wavelength and the diffusion coefficient on time are discussed. Through the molecular dynamics computer method the dependence of the viscosity on wavelength is calculated and applied with spectacular success to predict the dependence of the friction coefficient on the size of a Brownian particle all the way to atomic dimensions. On the other hand, the dielectric constant continuum concept, as applied to a charge or dipole in a cavity, generally fails to predict even the correct field at large distance from the charge. Avoiding the introduction of a cavity cures that problem, but the generalized dielectric constant fails badly in predicting the field at shorter distances from the charge.
Transport Properties of Liquids. II. Self‐Diffusion of Almost Spherical Molecules in Athermal Liquid Mixtures
Authors: Vogel Herbert , Weiss Alarich 
Published: July 2012

AbstractBy 1H‐NMR spin‐echo spectroscopy the self‐diffusion coefficients Dte of almost spherical test molecules—Sn(CH3)4, Si(OCH3)4, Ti(OtBu)4, and SnOct4—in the solvents—CCl4, Si(OCD3)4, and Si(O1Pr)4‐d28—were studied as a function of temperature and concentration.—The excess volumes of the mixtures investigated are approximately zero. The measurements show:
If the diameter dte of the test molecule is larger than, or equal to, that of the solvent molecule (dso), Dte∞ (infinite dilution) approaches Dso0.
If dte < dso, then Dte∞ > Dso0.
The activation energy of the self‐diffusion process of the test molecules at infinite dilution approaches the activation energy for the diffusion process of the solvent molecules.
Application of the free‐volume model to the experimental results is quite satisfactory except the situation of large test molecules diffusing in solvents composed of small molecules (dte > dso).
Formation of Clusters in 1‐Propanol/Water‐Mixtures
Authors: Großmann Georg H. , Ebert Klaus H. 
Published: July 2012

AbstractVery sensitive and accurate elastic light scattering (LS) measurements have been carried out on mixtures of water with methanol, ethanol, 1‐propanol and 2‐propanol. Methanol showed no particular effect, while ethanol, 2‐propanol and 1‐propanol showed signs of increasing cluster formation at a composition of 1 alcohol molecule to 5 water molecules. For the mixture of 1‐propanol with water, additional measurements of the quasielastic light scattering have been made and the hydrodynamic radii of the clusters have been calculated. This led to the suggestion of a cluster consisting of 8 1‐propanol molecules and a solvation envelope of about 40 water molecules. The concentration of this cluster was determined by elastic LS to be 83% of the total solution weight at 25°C and a composition of 40% by weight 1‐propanol in water. The clusters appear to be rather stable, as the hydrodynamic radius showed no significant variation with temperature in the 5° to 50°C range. The concentration was however temperature dependent, as could be shown with elastic LS.
The Mercury Sensitized Photolysis of Tetramethylsilane in the Temperature Range 650 K – 800 K. The Heat of Formation of 2‐Methyl‐2‐Silapropene
Authors: Potzinger P. , Reimann B. , Roy R. S. 
Published: July 2012

Abstract(CH3)3SiCH2 radicals, formed in the primary process (1)magnified imagedecompose according to (4)magnified imagein the temperature range 650 K ‐ 800 K. The activation energy for process (4) has been measured to be 170 ± 8 kJ/mol. This value allows one to calculate an upper limit for the heat of formation of 2‐methyl‐2‐silapropene ΔHf0 ≤ ‐2 kJ/mol which is in very good agreement with other values calculated from literature data and supports earlier findings that the back reaction (‐4) has a negligible activation energy. The combined average from our results and the literature is ΔHf0 ((CH3)2Si = CH2) = 2−13+9 kJ/mol.—Furthermore it is shown that 2‐methyl‐2‐silapropene is more stable than the corresponding silylene and carbene isomers. The ζ bond energy has been estimated to be 189 kJ/mol, in excellent agreement with calculations by Ahlrichs and Heinzmann [20].
Über das magnetische Verhalten von Cs2ASmF6 (A = Na, K, Rb)
Authors: Urland W. 
Published: July 2012

AbstractThe magnetic behaviour of Cs2NaSmF6, Cs2KSmF6 and Cs2RbSmF6 has been studied in the temperature range between 3.0 and 251.3 K. The magnetic data are interpreted by means of a previously developed model in which the influence of the crystal field is theoretically described by the angular overlap model. The angular overlap parameter eπ (R) is determined for given ratio eπ (R)/eπ (R). As basis the 66 state functions of the ground term 6H as well as the 108 state functions of the sextet terms 6H and 6F are used. The dependence of the angular overlap parameters eπ (R) and eπ (R) on the basis is investigated. The energy. The energy values of the crystal‐field levels of the two lowest states 6H5/2 and 6H7/2 are calculated.
Self Diffusion in Carbon Dioxide Near the Critical Point
Authors: Krynicki K. , Meragi A.‐L. , Powles J. G. 
Published: July 2012

AbstractMeasurements of the self diffusion coefficient, D, by the nuclear‐magnetic‐resonance field‐gradient method for carbon dioxide (13CO2) are reported for the coexisting liquid from the triple point to the critical point and for the fluid at the critical density from the critical temperature upwards. No anomaly in D is observed near the critical point and the behaviour is similar to that of other liquids. It seems likely that the previously reported anomalous behaviour (Duffield and Harris, 1976), in 14CO2, measured by the capillary method, is erroneous.
Zum thermischen unimolekularen Zerfall von Methanol
Authors: Spindler K. , Gg. Wagner H. 
Published: July 2012

AbstractThe thermal unimolecular decomposition of methanol was investigated behind reflected shock waves in the temperature range 1600 to 2100 K, using argon as a diluent and monitoring CH3‐ and OH‐absorption signals. —Methanol decomposes in the main channel according tomagnified imageThe reaction takes place in the fall off region when total densities are varied from 1.1 · 10‐6 to 5.6·10−6 5.6·10‐5 mol/cm3. Using the theory of unimolecular reactions the rate constantsmagnified imagein the high pressure limit andmagnified imagein the low pressure limit could be obtained. A computer simulation of the decomposition of methanol and the consecutive reactions was carried out.
Transformations in Ag2+δS and Ag2+δSe: A Calorimetric Study
Authors: Shukla A. K. , Sen P. , Sarma D. D. 
Published: July 2012

AbstractCalorimetric studies of transformations have been carried out in single crystals of Ag2+δS and Ag2+δSe of coulometrically controlled compositions. The entropy changes accompanying the α‐β transitions of these solids with different degrees of non‐stoichiometry are discussed in the light of crystal structures and statistical arguments.
Surface Enhanced Raman Scattering of Cyanide Chemisorption Layers on Silver/Electrolyte Interfaces. Part II
Authors: Plieth W. , Roy B. , Bruckner H. 
Published: July 2012

AbstractThe dependence of the surface enhanced Raman signal of CN− ions on silver/electrolyte interfaces at 2114 cm−1 was investigated by varying the laser intensity, the laser frequency, the angle of incidence, and the angle of observation. The Raman signal was also observed on electrolytic deposits of silver on gold substrates.
Capacity and Photocurrent Measurements at Passive Titanium Electrodes
Authors: Schultze J. W. , Stimming U. , Weise J. 
Published: July 2012

AbstractThe capacity and photocurrent behaviour of passive titanium electrodes has been investigated in dependence on the film thickness and the electrode potential, the photocurrents additionally on the wavelength. From capacity measurements a high donor concentration of 1020 cm−3 and a dielectric constant of D = 9 can be concluded. Compared to bulk TiO2 electrodes, the onset of the photocurrent is shifted to higher photon energies. The band gap is estimated to be Eg = 3.4 eV. At constant electrode potential ε the photocurrent decreases with increasing film thickness though the absorption of the film should be higher. This indicates the strong influence of the field strength in the film on the photocurrent which increases with thickness at constant field.
Flash Photolysis in Aqueous Periodate‐Solutions
Authors: Wagner I. , Strehlow H. 
Published: July 2012

AbstractIn the flash photolysis of periodate in the pH‐range 2.44 to 4.90 using conductometric detection three reactions are observed with time constants of the order 10−4 s, 10−2 s and 1 s (at 298 K and pH = 3). The fastest reaction is attributed to the general acid catalyzed hydration reaction of IO−4 to H4IO−6. The two slower reactions are due to the hydrolysis of I2O8 and I2O6. The relative amounts of these latter reactions depend on the concentration of oxygen in the solution. Oxygen atoms formed rapidly by the photolysis of periodate are scavenged by oxygen with the production of ozone. Ozone oxidizes IO3 to IO4 which dimerizes to I2O8.