bluuebunny/crossref_metadata_2025 huggingface dataset:
Die Messung der Ultraschall‐Diffusion an einer Elektrode und ihre praktische Anwendung
Authors: Huck H.
Published: March 2014

Under the action of ultrasound (Iup to 2 W/cm2) quasi‐stationary current voltage curves were obtained, from which the densities of the exchange, the diffusion‐limited currents and the transfer coefficient were calculated. The acceleration of diffusion with ultrasound was attributed to surface cavitation involving pulsating bubbles surrounded by microstreaming. At higher sound intensities a limiting current due to cavitation saturation was observed. In order to explain this saturation effect a Langmuir kinetic for the enrichment and the depletion of cavitation bubbles beyond the threshold intensity was proposed. In the case of acoustic resonance (h=nλ/2) standing waves are generated in the solution. At the pressure loops the sound action has then a maximum. — Reproducible results were only obtained in the presence of cavitation nuclei, how they are given at rough surfaces or at smooth surfaces after adsorption of colloidal particles. The measurements were performed with Pt, glassy carbon and graphite electrodes in solutions of Fe3+/Fe2+and [Fe(CN)6]3‐/[Fe(CN)6]4‐. According to the obtainedi0values it is suspected that the complex bounded cyanid ions are favoring the exchange of electrons between the central atom and the electrode surface by an inner‐sphere mechanism.
Anomalous Behavior of Glassy GeO2 in the Reduction Process by Hydrogen
Authors: Yoshida N. , Nakanishi M. , Ikegami K. , Shimura S. , Kishimoto S.
Published: March 2014

The reaction of GeO2 glass with hydrogen was studied with special attention to the initial process under different conditions and the results were compared with those of crystalline GeO2. The reaction curves for the crystalline materials were a simple type which is commonly encountered in solid state reactions, whereas the curves for glassy materials at reaction temperatures above 400°C showed complicated behavior which is characterized by the presence of two steps in a reaction course. It seemed that this behavior could be understood in terms of the structural changes of the reactant involving glass transition and crystallization which are caused by the progress of the reaction. On the other hand, in the case of the reaction below 400°C, no special abnormalities were observed during the reaction.
Hydrogen Abstraction Reactions by NH2(X̄2B1)‐Radicals from Hydrocarbons in the Gas Phase
Authors: Ehbrecht J. , Hack W. , Rouveirolles P. , Gg. Wagner H.
Published: March 2014

Rate constants for the reactions of the NH2(X2B1) radical with ethane, propane and cyclohexane were measured in an isothermal flow system. Kinetic data were obtained at 4 mbar helium pressure in the high temperature range given below. [NH2](t)‐profiles were mapped at pseudo‐first order conditions [NH2]0→[RH]0 with the laser induced fluorescence technique. The temperature dependance of the rate constants is represented by the following Arrhenius‐expressions: A in [cm3/mol·s] and EA in [kJ/mol]: magnified image A correlation of the activation energy with the energy of the broken C–H bond of various hydrocarbons is discussed.
Statistics of Disordered Polymers: An Effective Hamiltonian and its Associated Gibbs Measure
Authors: Fernandez Ariel
Published: March 2014

An ensemble of random polymers made of two kinds of monomers is considered. The effect of quenched randomness on two and three body interactions is evaluated by comparing the Gibbs measure for an effective Hamiltonian with that for a homogeneous polymer with the same bare Flory interaction constants.
Dynamic Viscosity of Supercritical Ethene
Authors: Stanislawski Ulrich , Luft Gerhard
Published: March 2014

The viscosity of ethene was determined using a self‐constructed rolling ball viscometer up to pressures of 200 MPa at four temperatures ranging from 293 to 413 K. The recommended empirical equations of Reichenberg and Jossi, Stiel and Thodos predict the measured values only below 100 MPa with sufficient accuracy. The correlation of the residual viscosity with the density leads to a single curve for all temperatures and up to the greatest observed density σ = 2.7 σ. Since an exponential expression is given, the viscosity range can be extended to higher temperatures provided the density is known. The applicability of Dymond's correction of the Enskog dense fluid theory to the measured values is discussed.
Impurity Diffusion in a Chemical Potential Gradient (I): Theoretical Results
Authors: Martin M.
Published: March 2014

A theoretical analysis has been made of the simultaneous diffusion and drift of aliovalent cation impurities B moving in a transition metal oxide AO which has been exposed to an oxygen potential gradient. Starting from linear transport theory and using the known five‐frequency‐model of impurity diffusion, expressions for the impurity and defect fluxes are derived. The corresponding coupled diffusion equations are solved analytically for the limiting cases of weak and strong impurity‐vacancy binding, and are solved numerically in the general case.
Diffusion in Binary Mixtures of Ammonia with Noble Gases
Authors: Dunlop Peter J. , Bignell C. M.
Published: March 2014

Diffusion coefficients are reported for binary mixtures of ammonia with helium, argon, krypton and xenon. An approximate HFD‐C potential is given for the He – NH3 interaction.
Use of a Wien Filter for Mass and Velocity Analysis of Charged Soot Particles in a Nozzle Beam
Authors: Homann K. H. , Traube J.
Published: March 2014

A simple Wien filter in combination with an energy‐discriminating detector was used to determine mass and velocity distributions of positively and negatively charged particles in a nozzle beam. The particles were sampled from different heights in a 26.7 hPa flat, premixed C2H2/O2 flame. The method allows the measurement of mass distributions of particles with different velocities in the beam, of velocity distributions of particles with different masses, and of over‐all mass and velocity distributions, examples of which are given. There is a velocity slip of the large species during expansion of the flow. Particles with larger mass reach a lower final velocity in the beam. The velocity distributions are non‐gaussian displaying a long tail to lower velocities. The growth of positively charged soot particles from an average mass of about 1·103 u to 1·104 u takes place over a distance of 4 mm in the flame.
Precision Conductivity Measurements and DSC on Single Crystals of the Organic Conductor (FA)2PF6
Authors: Schimmel Th. , Rieß W. , Denninger G. , Schwoerer M.
Published: March 2014

The temperature dependence of the dc conductivity of (FA)2PF6 single crystals has been investigated using low cooling and heating rates, up to six temperature cycles between 45 K and 300 K and a very high density of data (about 80000 data points per temperature sweep). Phase transitions detected at 180 K and 200 K have been confirmed by DSC measurements. Because of the accuracy and reproducibility of the measurements, a new and detailed picture of the conductivity could be derived: at the “metal‐to‐semiconductor” phase transition at 180 K, no sudden change to a semiconductor with constant band gap occurs. Instead, an intermediate range exists between 180 K and 120 K, in which the band gap opens gradually. Thermally activated conductivity (ΔE = 60 meV – 70 meV) is observed only below 120 K. Above 215 K, the high temperature phase of fresh crystals can be fitted to a model of charge density wave (CDW) fluctuations in a one‐dimensional metal. Aged crystals above 215 K exhibit the behaviour of a onedimensional variable range hopping resistance. Conductivity hystereses can be explained as a dynamic effect of the real crystal.
Knight Shift in the Organic Conductor (Fluoranthenyl)2AsF6
Authors: Hentsch F. , Helmle M. , Köngeter D. , Mehring M.
Published: March 2014

Proton and 13C NMR Knight shift investigations performed in the organic conductor Fa2AsF6 provide locally resolved information on the electronic states of the conducting band. From single crystal measurements the principal axis values of the proton hyperfine tensor for two positions are determined.
Preparation, Crystal Structure and Dielectric Properties of the New Unsymmetrically Substituted Diacetylenes NP/R2
Authors: Strohriegl P. , Schultes H. , Heindl D. , Gruner‐Bauer P. , Enkelmann V. , Dormann E.
Published: March 2014

We report on the preparation, the crystal structure and the dielectric properties of several new unsymmetrically substituted diacetylenes R1,‐CC‐CC‐R2 of the general constitution NP/R2. They carry a polar nitrophenoxy‐group on one side and different urethanes on the other.
Organic Electrochemistry in the Solid State‐Overoxidation of Polypyrrole
Authors: Beck Fritz , Braun Petra , Oberst Manfred
Published: March 2014

Anodic overoxidation of polypyrrole in the presence of nucleophiles such as H2O, OH−, CH3OH, CH3O−, Br− and CN− has been studied in detail. At potentials up to 2.1 V (vs. SCE), irreversible anodic peaks are observed with 200 nm layers on Pt. In most of the cases, a total of z = 4 – 6 F/mol monomer unit initially oxidized in the reversible potential region to the radical cation has been evaluated. Only every third ring is involved by this way. Characteristic products in aqueous systems are pyrrolinones (with a keto group in 3‐position), z = 4, and the product of further hydroxylation in 4‐position (z = 6). In the presence of the other nucleophiles, corresponding substitution products seem to be generated. The central reactive intermediate seems to be the dication. Pronounced deviations from this scheme, which is confirmed by IRRAS results, seem to proceed in the presence of strong nucleophiles as OH−, which add initially to the radical cation, and upon strong polarization, which may lead to an attack of the other rings and/or polymer destruction. Practical implications are due to polymer modification and battery material optimization.
Two‐dimensional MAS NMR: New prospects for the investigation of partially oriented polymers
Authors: Blüimich B. , Böffel C. , Harbison G. S. , Yang Y. , Spiess H. W.
Published: March 2014

Of many interesting materials single crystals are difficult if not impossible to obtain. Examples are synthetic liquid crystalline and biological polymers. Often such materials can, however, be partially oriented. If a set of rotor‐synchronized 13C MAS NMR spectra is taken of a macroscopically anisotropic sample for different initial rotor phases, a two‐dimensional sideband spectrum can be generated by a subsequent second Fourier transformation over the rotor phase. From the sideband intensities in the new dimension the orientational distribution function can be derived for the individual carbon positions. This yields the order of the macromolecules as well as their conformation. — The new method does not require isotope labelling, the acquisition times are short compared with other two‐dimensional NMR techniques, and from a single experiment the orientational distribution function can be determined for each molecular segment with a distinguishable chemical shift. The method is reviewed and demonstrated on samples of liquid crystalline polymers and drawn polyethylene terephthalate.
Fortschritte in der 2D‐NMR‐Spektroskopie mit Rauschanregung
Authors: Armitage H. , Blümer U. , Genge I. , Khuen A. , Wille E. E. , Ziessow D.
Published: March 2014

Stochastic excitation of nuclear spin systems and subsequent nonlinear analysis of acquired excitation/response (e/r) data pairs (multidimensional stochastic method, MUDISM) yields 2D NMR spectra which provide information similar to the conventional E‐COSY and NOESY pulse schemes. For the study of complex molecules such as peptides and proteins, hardware and software has been developped which allows the continuous recording of 106 e/r data pairs where one pair occupies one 16 bit word. Many such sets are commonly measured and stored on a large‐volume hard disk, the total number of pairs being 107–108 depending on the size of the spin system. The r.f. carrier is modulated with suitable pseudo random sequences which are generated in a home‐made computer‐controlled digital pulse generator. The design and properties of these sequences are described and quaternary noise is shown to provide an excellent compromise between ease of generation and similarity to Gaussian white noise. The spin response to this noise has been simulated for coherent and incoherent interactions in order to examine the overall procedure, most notably the dependence of the residual systematic noise upon the number of measured data for given resolution. Experimental results are reported for phenylacetylene (strong coupling case), glucose in water (strong solvent line), and the cyclic decapeptide cyclosporin (complex molecule). For the latter, 80 Megapairs raw data have been acquired for a total spectral range of 3246 Hz (7.5 h magnet time) from which 2D subspectra with 512·512 points at 0.4 Hz step size are calculated. They provide evidence that the structure of complex molecule may indeed be determinded with stochastic NMR.
Microcomputer controlled 4π‐zeeman split NQR spectroscopy of 35Cl in single crystal p‐chloroanilinium trichloroacetate. Crystal structure and activation energy for the bleaching out process
Authors: Markworth Axel , Weiden Norbert , Weiss Alarich
Published: March 2014

A computer controlled 4π‐Zeeman split pulse fourier transform NQR spectrometer has been constructed. The NQR spectra for more than 200 different magnitutes and orientations of the magnetic field in the sphere can be obtained and stored under software control. This allows an almost fully automatic determination of the zero splitting cones by refining grids of field orientations in the space. — The crystal structure of p‐chloroanilinium trichloroacetate (4‐ClC6H4NH⊕3) (Cl3CCOO⊖), has been determined (C52h ‐ P21/c, z = 4, a = 942.3 pm, b = 722.8 pm, c = 1748.6 pm, β = 100.54°). — The direction cosines of the principal axes and the asymmetry parameters η of the electric field gradient tensors have been obtained together with the nuclear quadrupole coupling constants e2Qφzzh−1 of the chlorine atoms of the CCl3 group (η(1) = 0.0255, e2Qφzzh−1 (35Cl(1)) = 76.790 MHz, η(2) = 0.0355, e2Qφzzh−1 (35Cl(2)) = 76.410 MHz, η(3) = 0.0132, e2Qφzzh−1 (35Cl(3)) = 75.910 MHz and of the chlorine atom bound to the ring (η(4) = 0.0996, e2Qφzzh−1 (35Cl(3)) = 69.244 MHz) at T = 295 K. — The frequencies v(35Cl), linewidths Δv(35Cl) and the spin lattice relaxation times T1(35Cl) have been investigated as function of temperature for v1…v4 and the activation energy for the bleaching out process has been calculated from the Δv = f(T) data (Ea = 65 kJmol−1) and T1 = f(T) data (Ea = 72 kJmol−1). The results are discussed in context with the crystal structure.
Structures and phase transitions in piperazinium hexachlorometallates, (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn. A X‐ray diffraction and 35Cl NQR study
Authors: Borchers Dirk , Weiss Alarich
Published: March 2014

Crystal structures and the nature of the chemical bond in piperazinium hexachlorometallates (C4H12N2)[MCl6], M = Te, Pb, Pt, and (C4H12N2)[MCl6] · 3H2O, M = Sn, were studied by X‐ray diffraction and 35Cl NQR spectroscopy. Piperazinium hexachlorostannate trihydrate shows a solid‐solid phase transition at Tc = 256 K. A disorder of the piperazinium ring and of one of the three water molecules appears in the high temperature phase (space group D122h‐Pnnm, a = 1147.5 pm, b = 959.9 pm, c = 719.4 pm, Z = 2). The disorder affects the 35Cl NQR spectrum. The low temperature phase of (C4H12N2)[SnCl6] · 3H2O reveals two 35Cl NQR lines, whereas in the high temperature phase only one resonance line was observed besides the existence of two crystallographically different chlorine atoms in the unit cell. — Piperazinium hexachlorotellurate crystallizes with space group D162h‐Pnma (a = 1398.5 pm, b = 1203.1 pm, c = 822.2 pm, Z = 4). The TeCl6 octahedra is strongly distorted, with the Te‐Cl bond lenghts differing by about 15%. This distortion is reflected in the 35Cl NQR spectra; the resonance lines are spread over a wide frequency range. — The crystal structure of piperazinium hexachloroplatinate (space group C32h‐C2/m, a = 1016.0 pm, b = 1184.7 pm, c = 695.2 pm, β = 130.227°, Z = 2) shows only small distortions in the PtCl6 octahedra. The two line 35Cl NQR spectrum at lower temperature is in agreement with the crystal structure. — Piperazinium hexachloroplumbate reveals a three 35Cl NQR lines at lower temperature. At Tc = 310 K a phase transition occurs and a one line 35Cl NQR spectrum appears. A hysteresis, about 5 K wide, is connected with the transition.
Time‐resolved fluorescence of bichromophoric rotors — confermational dynamics of 1,3‐di(N‐carbazolyl)propane
Authors: Buchberger Eva M. , Mollay Bernhard , Weixelbaumer Wolf‐Dieter , Kauffmann Harald F. , Klöpffer Walter
Published: March 2014

Time‐Resolved Fluorescence Spectroscopy has been used to reinvestigate the conformational pathways for 1,3‐di(N‐carbazolyl)propane, 1,3‐DCP, in toluene as solvent. Excited‐state dynamics of 1,3‐DCP triggered by rotational diffusion has been probed by analyzing the transient profile of monomer and excimer fluorescence as a function of temperature. In the intermediate temperature regime, numerical reconvolution of excimer raw data yields a significant triple‐exponential fluorescence response (biexponential rise + single‐exponential decay) which degenerates to a biexponential result at higher temperatures. On the basis of a transient scheme (two monomeric conformations X1, X2 and one excimer X3, the experimental patterns have been analyzed with the help of the exact δ‐pulse solutions to the scheme, for two different boundaries. Simulation of plausible parameter sets proves useful for recovering a) the time constants and b) the signs of the amplitudes in the experimental data profile. The kinetic procedure gives insight into the time scales of serial, conformational transitions in a three‐state model, it allows a discussion of ground state distribution for X1 and X2, and, finally, it leads to a preliminary understanding of the pseudo‐Birks behavior at higher temperatures.
Photochromism of spirooxazines II. CARS‐investigation of solvent effects on the isomeric distribution
Authors: Schneider S. , Baumann F. , Klüter U. , Melzig M.
Published: March 2014

The isomeric distribution of metastable “photomerocyanines” produced by UV‐photolysis of spiroindolinonaphthoxazine derivatives is examined by resonance‐enhanced CARS spectroscopy. — In unpolar and polar aprotic solvents CARS spectra prove the existence of two pairwise similar isomeric species. They differ, however, in Franck‐Condon factors for excitation S0 → S1. In the protic solvent methanol an additional isomer is found for certain derivatives.
X‐ray absorption spectroscopy
Authors: Lytle Farrel W.
Published: March 2014

The X‐ray absorption near‐edge structure (XANES) of transition metal oxides is analyzed in terms of scattering resonances from neighboring atoms. Spectra from reference compounds of simple, known structure were used to facilitate identification of XANES peaks with scattering from specific coordination spheres. The resulting correlation between bond distance and energy of the absorption feature allows determination of bond distances in unknown materials. This is illustrated with the Cu K‐edges of YBa2Cu3O7 and Lau1.8Sr0.2CuO4. — The intensity of the L‐edge absorption resonances of the 5d elements is shown to be proportional to the number of 5d holes as determined by band structure calculations. In principle even the spin codiguration of the 5d orbitals can be determined. This is illustrated with data for a Re on A1203 catalyst.
Rotational tunnelling of methyl groups in bis(trimethyltin) sulfate dihydrate
Authors: Zhang Da , Walz Leonhard , Prager Michael , Weiss Alarich
Published: March 2014

Rotational tunnelling and librations of methyl groups in bis(trimethyltin) sulfate dideuterate, [(CH3)3Sn)]2SO4·2D2O, have been studied by inelastic neutron scattering (INS) technique. Tunnel splittings of 11. 36 μeV and 1.10 μeV and librational peaks at 9.98 meV and 14.8 meV were observed. The corresponding activation energies are calculated to be 4. 4 kJmol−1 and 2.6 kJmol−1, respectively. The INS measurements showed the existence of two types of inequivalent methyl groups of the occurrence ratio 1:2. The crystal structure of bis(trimethyltin) sulfate dihydrate was determined by single crystal X‐ray diffraction. [(CH3)3Sn)]2SO4·2H2O crystallizes orthorhombic, space group D142h‐Pbcn with 4 molecules in the unit cell. The lattice constants are a = 1124.4(2) pm, b = 1269.3(2) pm and c = 1080.9(2) pm. The sulfur atom lies on a twofold axis and therefore the two “(CH3)3Sn(H2O)” units in the molecule are crystallographically equivalent. The crystal structure analysis shows the three methyl groups bond to one tin atom to be inequivalent. This is not in agreement with the INS results. The discrepancy is discussed.
EXAFS studies of ammonia catalysts at synthesis conditions
Authors: Niemann W. , Clausen B. S. , Topsøe H.
Published: March 2014

The reduction of the precursors of different NH3 catalysts and the structure of the catalysts at reaction conditions are investigated by in situ X‐ray absorption spectroscopy at the K‐edge of Fe. From the XANES and EXAFS data a different reduction behaviour is found for K‐promoted and Cs‐promoted catalysts, respectively.
On the flash photolysis of bromide ions in aqueous solutions
Authors: Wagner I. , Strehlow H.
Published: March 2014

The flash photolysis of bromide ions has been studied using conductometric detection. Together with earlier results from (lash photolysis [1, 2, 5] and pulse radiolysis investigations [3, 4] a mechanism is proposed consistent with the experimental observations.
The role of geminate reaction in the self‐sensitized photooxygenation of helianthrene and hetianthrene‐derivatives encounter‐ and reencounter probabilities
Authors: Brauer H.‐D. , Acs A. , Schmidt R.
Published: March 2014

The probabilities pexpRQ of the geminate reaction between singlet oxygen (1Δ) and helianthrene (H), mesodiphenylhelianthrene (MDH) and mesodiphenylbenzhelianthrene (MDBH) were determined in several solvents of different viscosity. pexpRQ strongly depends on the viscosity of the solvent. For H pexpRQ increases from 0.17 (n‐pentane) over 0.44 (benzyl alcohol) to 0.97 (m‐cresol). For the first time experimental results clearly demonstrate that the reaction already takes place in the initial encounter, which is formed in the energy transfer from the T1‐states of the hydrocarbons to molecular oxygen. The solvent dependence of pexpRQ is only caused by the solvent dependence of the total reencounter probability, po. The results permit calculation of the probabilities per encounter (αR) and rate, k01, for an equilibrium distribution of 1Δ and the hydrocarbons.
Viscosity of Potassium Nitrate + Silver Nitrate Melt Mixtures
Authors: Schardey A. , Richter J. , Øye H. A.
Published: March 2014

The viscosity of KNO3 +AgNO3 melt mixtures has been determined in the range 0.25 ≤ χ ≤ 1.460 K. to 610 K. The viscosity of pure KNO3 was measured over the temperature span 620 K to 720 K. An oscillating‐cylinder viscosimeter was used. This method is absolute and requires no calibration against reference liquids. The viscosities in units of mPa s conform to the expanded Arrhenius type equation

with 0.04 to 0.31% standard deviations in the fit.
Das Dampf‐Flüssigkeitsgleichgewicht des ternären Systems Ammoniak‐Kohlendioxid‐Wasser bei hohen Wassergehalten im Bereich zwischen 373 und 473 Kelvin
Authors: Müller G. , Bender E. , Maurer G.
Published: March 2014

Experimental results for the vapor‐liquid equilibrium in the ternary system ammonia‐carbon dioxide‐water are reported for six temperatures between 373 and 473 Kelvin at total liquid concentrations from 4 to 30 mole percent of ammonia and up to 14 mole percent of carbon dioxide as well as for the binary gaseous electrolyte‐water mixtures at the same temperatures and liquid phase concentrations of up to one mole percent (CO2) and 30 mole percent (NH3) respectively. The newly measured data agree well with the very limited literature data for the binary as well as for the ternary systems. Caused by the low solubility of carbon dioxide in water, the experimental results for that binary are described applying Henry's law. For correlating the results for the ammonia‐water system. Henry's law has to be corrected by introducing activity coefficients. The model of Edwards et al. with recently published new parameters is used to compare the experimental results for the ternary with existing correlations. Deviations between predicted and measured total and partial pressures amount up to 60 percent, thus indicating that the model needs further improvement.
Uni molecular Reaction Dynamics on Ab Initio Potential Energy Surfaces
Authors: Troe J.
Published: March 2014

One‐parameter fit versions of unimolecular rate theory for complex elimination and simple bond fission reactions are compared with detailed experiments. The agreement generally is so good that no further extension of this operational version of the theory is required. However, the relation between the fit parameter and properties of the potential surface not always is transparent. The article discusses the implementation of ab initio calculations of the potential by constructing adiabatic channel potential curves. Explicit results for charge‐dipole interactions are presented. SACM‐modified PST applies for selected conditions. Strategies for handling more complex potentials are outlined. The treatment closes the gap between operational fit parameters and potential properties.
The Optical Spectrum of NO2: Is it or Isn't it Chaotic?
Authors: Lehmann Kevin K. , Coy Stephen L.
Published: March 2014

We have used the technique of microwave detected, microwave‐optical double resonance to study the optical absorption spectrum of NO2 in the region near 17000 cm−1 above the ground state [1 – 3]. Spectra were recorded from ten lower states, ranging in rotational excitation from the 20.2 through the 101.9 states. Each lower state was scanned between 150 and 300 cm−1, and between 54 and 510 lines were observed in each spectrum. The method of double resonance uniquely identified the lower state of the observed transitions. Because the optical spectrum is dominated by a parallel transition and all of the observed lower states are K = 0 or 1, most of the observed transitions belong to either a qR or qP branch. For two pairs of lower states, states differing in J by two were studied, which allowed at least a partial assignment of transitions between P and R branches. Also, by studying spectra that have the same value for J and overall symmetry, but different values for N (the rotational angular momentum of the molecular frame), the extent of the breakdown of N selection rules could be quantified.
IVR Viewed Through State‐Selected Dispersed Fluorescence Spectroscopy of Jet‐Cooled Polyatomics
Authors: Knight Alan E. W.
Published: March 2014

State selected dispersed fluorescence spectroscopy provides a means of unscrambling the identity of emitting states in polyatomic manifolds that are extensively mixed relative to the basis set pertinent to lower parts of the manifold. A view is presented of the methodology that may be used to unravel complex electronic spectra when information from dispersed fluorescence is available. The dispersed fluorescence spectrum serves as a means of projecting the excited state electronic wave function onto the ground state potential surface, thereby allowing the vibrational composition of the (mixed) excited state eigenvector to be evaluated in terms of a ground state vibrational basis. Examples are drawn from experimental data relating to the spectroscopy of benzene and azulene. In the case of benzene‐d6, Fermi resonances between the levels comprising the progressions 61 1n and 61 1021n‐1 lead to an interesting pedagogical example of how dispersed fluorescence spectroscopy may be used to chart IVR as it progresses from isolated mixing of a few states to more widespread scrambling of vibrational identity among many states. Azulene serves as an example of the more extreme case of widespread state mixing that in large polyatomics has its onset in relatively low regions of the excited state vibrational manifold. It is demonstrated that vibrational state mixing in azulene is still amenable to a detailed analysis that yields the composition of mixed eigenvectors.
The Dynamics of Polar Solvation
Authors: Castner E. W. , Bagchi B. , Maroncelli M. , Webb S. P. , Ruggiero A. J. , Fleming G. R.
Published: March 2014

Fluorescence upconversion experiments with subpicosecond resolution are described. The time dependent fluorescence spectra of several probe molecules in polar solvents are measured and used to construct the Stokes shift correlation function C(t). The correlation functions decay nonexponentially in contrast to the predictions of simple Debye/Onsager continuum theory. At high values of the static dielectric constants the solvation times are much slower than predicted from standard continuum theory. Generalizations of continuum theory to include non‐spherical shapes, non‐Debye dielectric response and saturation effects are discussed. The experimental data are qualitatively in accord with predictions based on a frequency and position dependent dielectric response.
Time Dependent Absorption of Fragments During Dissociation
Authors: Bersohn R. , Zewail A. H.
Published: March 2014

The development of methods of generation of very short pulses of light with widths about or below 100 fs has enabled the measurement of the rate of direct photodissociation of a bond. The experiment measures absorption as a function of both time and the degree to which the probing light is off resonance with one of the fragments. A classical model with an exponential repulsion is used to relate experimental observables to the dissociation time and properties of the potential surface. The delicateness of the probe will improve as the photon energy approaches the threshold energy for dissociation.
Dynamics of Vibrational Predissociation of (C2H4)2 and of IR‐Multiphoton Excitation of SF6
Authors: Liedenbaum C. , Heijmen B. , Dam N. , Stolte S. , Reuss J.
Published: March 2014

High resolution measurements are discussed which indicate two decay channels for IR‐excited (C2H4)2; for cold dimers, from observed linewidths a 45 ns lifetime is derived after which the products are in their vibrational ground state. For hot dimers a many orders of magnitude shorter lifetime is indicated after which one of the product monomers is found in an excited v10 level. For highly excited SF6 (〈n〉 = 4 ÷ 5) narrow spectral features are observed attributed to rapid adiabatic passage processes. The IVR lifetime of the excited state is found to be longer than about 1 ms.
Understanding Unimolecular Dissociations with Loose Transition States: Photofragmentation Dynamics of Ketene at the Singlet Threshold
Authors: Green William H. , Chen I‐Chia , Moore C. Bradley
Published: March 2014

Photofragment excitation (PHOFEX) spectra of ketene (CH2CO) were taken by probing rovibronic transitions of the singlet methylene fragment while scanning the photolysis laser frequency. CH2(ã1A1) was detected by laser‐induced fluorescence in a supersonic free jet. The dissociation threshold of the reaction, CH2CO → 1CH2 + CO was determined to be 30116.2 ± 0.4 cm1. The nuclear spin is conserved during the dissociation. Sharp rises in the 1CH2 PHOFEX spectra are observed whenever a new CO rotational state becomes energetically accessible. Phase Space Theory (PST) is in excellent agreement with the experimental data. The Statistical Adiabatic Channel Model (SACM) and the related SACM‐PST theory fail to fit the experimental PHOFEX curves except in the limit where they become indistinguishable from PST (i.e. α/β > 0.7). The data show that there are no barriers to dissociation and that essentially every accessible product quantum state is equally likely to be formed. The implications of these findings for the theory of unimolecular dissociation are discussed.
Vibrational Relaxation of HBr (υ = 1) in Hydrogen Gaseous Mixtures at Low Temperature
Authors: Losert O. , Schwarz H.‐V. , Schramm B.
Published: March 2014

Measurements of vibrational relaxation rates of HBr (v = 1) in collisions with n‐H2, para‐enriched H2, HD and D2 are presented for temperatures ranging from room temperature down to 140 K. In all cases strong deviations of the V‐R, T rate from Landau‐Teller behaviour are observed. Neither the temperature dependence nor the mass dependence of the data can be explained by Landau‐Teller or Schwartz‐Slawsky‐Herzfeld theory.
An Investigation of Electrochemical Oxidation/Reduction Processes on Gold with the Kelvin Probe and Cyclic Voltammetry
Authors: Piller Gerd W. , Schumacher Rolf
Published: March 2014

The oxidation and reduction of gold electrodes contacted to acid and alkaline media were investigated with the Kelvin probe and cyclic voltammetry. The used set‐up allows a simultaneous operation of both methods. Surface processes to passivate and to repassivate gold electrodes were followed with these methods as function of the externally applied potential and time. The measurements provided kinetic data, which allows the identification of potential regions, in which either solid oxidic overlayers or adsorbed adlayers were formed at gold electrodes. The presented data are consistent with a recent XPS study, an investigation with the microbalance and data, obtained with classical electrochemical techniques.
Water Motion in Harmotome – Studied by Incoherent Inelastic and Quasielastic Neutron Scattering
Authors: Stuckenschmidt E. , Fuess H. , Stockmeyer R.
Published: March 2014

The mobility of the water molecules in the natural zeolite harmotome Ba2[(AlO2)4(SiO2)12] · 12H2O has been studied by incoherent neutron scattering on powder samples in several dehydration states and at different temperatures. – The external vibrational modes of the water molecules were determined from the inelastic part of the spectra (energy transfers 5 < ΔE < 100 meV) and were assigned to translational and rotational vibrations. The diffusive motion of water was evaluated from the quasielastic scattering and values of the residence time τ0 = 2.9 – 5.5 · 10−12 s, diffusion constant D = 5.0–25·10−5 cm2/s and mean jump length 〈I〉 = 0.41–0.66 nm were derived. – The results from the neutron scattering experiments were interpreted based on a redetermination of the crystal structure.
Systematic Investigations of the Dipolar Interaction in Aromatic Liquids. A Neutron Diffraction Experiment I. Structure Factors and Intramolecular Structure
Authors: Bertagnolli H. , Hummel I. , Chieux P.
Published: March 2014

The present work represents the experimental basis for the determination of short range order in some aromatic liquids as a function of the magnitude of the permanent dipole moment and the temperature. Neutron diffraction experiments were performed on liquid toluene, bromobenzene and nitrobenzene at various temperatures near the corresponding freezing points. These systems were chosen, as the sizes of the substituents are very similar, but the dipole moments are significantly different. After data reduction and evaluation the calculated intramolecular contributions of the investigated molecules were fitted to the corresponding total corrected differential cross section and the intramolecular geometries in the liquid phase were determined. As the temperature variation produced no significant change in the intramolecular structure, the determination of the molecular parameters for the various temperatures was based on an averaged molecular structure.
Elastic and Rheological Properties of Hydrocarbon Gels
Authors: Ebert G. , Platz G. , Rehage H.
Published: March 2014

We have investigated high elastic gels which can be formed from biphasic systems of hydrocarbon, water and surfactant. These new phases contain up to 99% hydrocarbon, but there exists a well defined upper limit for the incorporation of excess oil. – The hydrocarbon gels exhibit strong elastic properties which can be described by a frequency independent static shear modulus. The influence of the surfactant concentration, the surfactant chainlength and the volume fraction of hydrocarbon on the modulus was systematically investigated. The experimental data are in fairly good agreement with theoretical models which have been derived for such hydrocarbon rich gels.
Structural Investigations of Electrode Surfaces
Authors: Kolb D. M.
Published: March 2014

A survey is given of the various ways in which information on the structure of electrode surfaces and their influence on the electrochemical behavior, especially on adsorption reactions, can be obtained. The techniques now at hand include a wide variety of spectroscopic methods, which are applicable in‐situ, such as reflectance spectroscopy over a broad range of photon energy, second harmonic generation, various X‐ray diffraction techniques and, most recently, scanning tunneling microscopy, which highlights the possibility of acquiring atomic‐scale resolution. In addition, the emersion of electrodes and their subsequent transfer into a vacuum chamber for detailed surface‐structural studies, e.g., by electron diffraction methods, is now widely used in electrochemistry, since it has been shown that electrodes can, in fact, be emersed with their electric double layer apparently intact. The combined venture incorporating all these techniques should lead to a truly microscopic description of electrochemical processes. The way in which structural information, even on an atomic scale, can be derived, is illustrated here by a few selected examples.
Measurement of Mass and Surface Stress at One Electrode of a Quartz Oscillator
Authors: Heusler K. E. , Grzegorzewski A. , Jäckel L. , Pietrucha J.
Published: March 2014

The theory for the calculation of changes of mass and surface stress from frequency measurements at a quartz oscillator subject to different onesided pressures is outlined. The various contributions to apparent changes of the mass are discussed. Experiments refer to the determination of effective molar masses of potassium ions and fluoride ions during electrostatic adsorption and of chemisorbed lead both on polycrystalline gold by a comparison of masses to charges. Effective molar masses of adsorbed species can also be determined by comparison of mass changes to surface concentrations e.g. determined by the radiotracer method as in the example of the adsorption of chloride at the passivating oxide film on iron. The density of very thin films like the passivating oxide film can be obtained by comparing mass changes to thicknesses from optical measurements. In agreement with theoretical expectation, compressive surface stresses were qualitatively found for the underpotential deposition of lead on gold. In the growing oxide film on passive iron very large compressive lateral pressures were observed.
Die Elektrode als Reagens in der organischen Synthese; CC‐Verknüpfungen
Authors: Schäfer Hans J. , Burgbacher Gerd , Schlegel Cornelia , Claus Harald
Published: March 2014

The mechanism of the anodic dimerization of olefins is investigated with the rotating ring‐disc‐electrode. The anodic coupling is applied to the preparation of a morphine derivative. By cathodic addition of organo halides to aldehydes trichloromethylcarbinols, β‐hydroxyesters and cyclopentanoid hydrocarbons become accessible.
The Investigation of the Corrosion of Metal Surfaces, Covered with Thin Electrolyte Layers – A New Experimental Technique
Authors: Stratmann M. , Streckel H.
Published: March 2014

If a metal surface is in contact with an aggressive atmosphere, then thin electrolyte layers are formed on top of the metal surface which may be as thin as a few monolayers of water. – Two techniques are described which allow to analyze the electrochemical processes involved in the corrosion of such a surface: the first technique measures corrosion rates and corrosion potentials as function of the electrolyte thickness without touching the surface under investigation, the second allows to measure polarization curves on metals covered with thin electrolyte layers using a Kelvin probe as reference electrode. Results are discussed which have been obtained with platinum and iron as working electrodes.
Electrochemical Investigations on the Diffusion of Perchlorate Ions in Thin Polypyrrole Layers
Authors: Herberg B. , Pohl J. P.
Published: March 2014

The polypyrrole electrode works as an insertion electrode for anions, e. g. for Perchlorate ions. The kinetics of the electrochemical insertion/dissolution reaction is determined mainly by diffusion processes within the polymer. Using H2O/NaClO4 and CH3CN/LiClO4 electrolytes the chemical diffusion coefficient ΔClO4 of “ClO4” in polypyrrole has been determined by means of potentiostatic and galvanostatic measurements. The values of ΔClO4, are in the range between 10−11 and 10−10cm2s−1; the partial conductivity of ClO4 ions in polypyrrole, calculated from the diffusion coefficient, is by about ten orders of magnitude smaller than the electronic partial conductivity due to electron defects within the polymer.
Influence of Interface Modification on Photoelectrochemical Behaviour of Amorphous Hydrogenated Silicon in Aqueous Electrolytes
Authors: Lewerenz H. J. , Stumper J.
Published: March 2014

The photoelectrochemical behavior of amorphous hydrogenated Si in aqueous electrolytes is investigated. Emphasis is put on competitive processes involving oxidation and depassivation and general possibilities of interface conditioning for modification of electronic properties. Photocurrent transients comparing the behavior of amorphous and crystalline samples are recorded to investigate the dynamics of interfacial processes. At potentials cathodic from flatband, a photoconductive gain effect is observed on a‐Si:H with quantum yields > 10 under appropriate bias and illumination.
Calculation of Osmotic Coefficients of Nonaqueous Electrolyte Solutions with the Help of Chemical Models
Authors: Barthel J. , Kunz W. , Lauermann G. , Neueder R.
Published: March 2014

The superimposition of Coulombian long range ion‐ion and non‐Coulombian short range interactions yields mean force potentials which are used to calculate the osmotic coefficients of various organic solvent systems via pair correlation functions. – The agreement with osmotic coefficients from vapor pressure experiments on 22 methanol, ethanol, 2‐propanol, and acetonitrile solutions of alkali metal and tetraalkylammonium salts shows the reliability of the chemical model of electrolyte solutions from infinite dilution to high concentrations.
Potentiostatic Current Oscillations of Cobalt Electrodes in Hydrochloric Acid/Chromic Acid Electrolytes
Authors: Hudson J. L. , Bell J. C. , Jaeger N. I.
Published: March 2014

Autonomous potential oscillations of Co wires immersed in a hydrochloric acid/chromic acid electrolyte were thoroughly studied by Franck and Meunier [1]. The experimental system has now been reinvestigated under potentiostatic conditions using a rotating Co disk for easy and reproducible control of transport parameters. After reaching a plateau the cathodic current enters a region of negative resistance where the oscillations start with a hard bifurcation. The width of the oscillating regime depends on the experimental conditions and can be up to 100 mV. Within this range a transition between limit cycle oscillations and aperiodic oscillations can be observed. The onsetpotential for the oscillations depends on the logarithm of the HCl‐concentration. A mechanism for the oscillations will be proposed based upon pitting corrosion of a cathodic film formed during the cathodic reduction of chromic acid [2].
Forces and Torques Acting on Two Parallel Dielectric Cylinders in a Periodic Transverse Field. C. Limiting Case of Contacting Cylinders
Authors: Schlögl Reinhard W.
Published: March 2014

The interactions between two dielectric bodies in an outer field show rather strong deviations from the “long distance laws” if the surfaces of the two bodies approach contact. Image forces occur that require another type of mathematical procedure. Instead of a partial differential equation an integral equation has to be solved. In the special case of cylindrical bodies these solutions lead to Fourier transforms that can be integrated explicitly (in contrast to the case of two spheres where the integral equation is not yet solved).
Delayed Fluorescence of the Kautsky‐Müller Type from Liquid Solutions of Aromatic Compounds and Oxygen
Authors: Nickel Bernhard , Flor M. , Prieto Rodríguez
Published: March 2014

Triplet‐singlet annihilation (TSA) T, + 1Δg → S1 + 3Σg− of the metastable triplet state (T1) of an aromatic compound and the metastable singlet state (1Δg) of molecular oxygen may lead to an observable delayed fluorescence (DF) S1 → S0 (DF of the Kautsky‐Müller type). A DF of this type has been observed with liquid solutions of phenanthrene and quinoxaline in perfluorohexane and of fluoranthene in 1,1,2‐trichloro‐1,2,2‐trifluoroethane in the presence of oxygen. The DF due to TSA can be kinetically distinguished from the DF due to triplet‐triplet annihilation (TTA). The results indicate a very long lifetime of 1Δg in perhalogenated alkanes. The DF from phenanthrene due to TTA can be assigned to the fluorescence from an excited dimer.
Investigation of Current Doubling Reactions at SiC/Aqueous Electrolyte Junction in Relation to the Band Energetics
Authors: Manivannan A. , Fujishima A. , Rao G. V. Subba
Published: March 2014

The current doubling behaviour of organic reagents especially alcohols by oxidation and persulfate by reduction was studied at n‐ and p‐SiC single crystals, respectively. In the case of n‐SiC no photocurrent increase was observed even under the acidic conditions with the addition of iso‐propyl alcohol whose alcohol radical potential lies most negative among the alcohols used. This implies that the conduction band position of n‐SiC is very negative. The radical intermediates formed during irradiation of n‐SiC suspension in various alcohols were analyzed by ESR spin trapping technique. On the other hand, current doubling behaviour was observed at p‐SiC during the reduction of persulfate ion by a hole injection into the valence band. This hole injection process was also confirmed by the EL (electroluminescence) studies. These results are discussed in terms of the interface energetics of SiC/aqueous electrolyte junction.
Influence of Hydrogen/Deuterium Isotope Substitution on the Critical Parameters of the System Polystyrene/Cyclohexane
Authors: Engels Th. , Belkoura L. , Woermann D.
Published: March 2014

The critical composition, the upper critical temperature and the critical amplitude ξ0 of local concentration fluctuations of the systems PSH/C6H12 and PSH/C6D12 are determined (PSH: poly(protostyrene); Mw = 3 · 105 g · mol−1; C6H12: cyclohexane; C6D12: cyclohexane‐d12). Both systems have the same critical composition (mole fraction of monomer unit of PSH: xc = 0.0573; volume fraction of PSH: ϕc(PSH/C6H12) = 0.0512; ϕc(PSH/C6D12) = 0.0500) and the same value of ξ0 within the accuracy of the measurements (PSH/C6H12: ξ0 = (6.83 ± 0.09) · 10−8 cm; PSH/C6D12: ξ0 = (6.86 ± 0.05) · 10−8 cm). Only the critical temperature of the system PSH/C6H12 (Tc(PSH/C6H12) = 26.338°C) is different from that of the system PSH/C6D12 (Tc(PSH/C6D12) = 30.582°C; Tc(PSH/C6D12) – Tc(PSH/C6H12) = 4.2 K). These findings suggest that the influence of a H/D substitution on the critical parameters follows the same pattern as that of binary critical mixtures of small molecules.