bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements and Analysis of Excess Enthalpies of Ester + n‐Alkane Using the UNIFAC Model
Authors: Ortega J. , Legido J. L. , Fernández J. , Pías L. , Paz Andrade M. I.
Published: July 2012

We present new experimental data of the excess molar enthalpies at 298.15 K for eighteen different binary mixtures of nine methyl alkanoates (ethanoate to decanoate) with n‐heptane and n‐undecane. The results show that all the systems are endothermic, hE values increase with the length of the n‐alkane and decrease with the length of the methyl ester. The data have been analysed with a version of the UNIFAC model, and the parameters corresponding to the CH2/COOC interaction have been recalculated using a larger base of experimental data. New values for the CH2/COO interaction parameters have been obtained.
Solvent Polarity Dependent Formation Dynamics of TICT States. I. Differential Solvatokinetics
Authors: Rettig Wolfgang
Published: July 2012

Comparison of the fluorescence kinetics of two dialkylaminobenzonitriles with different hindrance to planarity is used to extract information on the polar‐solvent induced shape changes of the excited‐state potential surface for TICT formation. The conical intersection between B* and A* states is shown to move to smaller twist angles as solvent polarity increases.
Rate Processes in Proteins
Authors: Frauenfelder Hans , Ulrich Nienhaus G. , Bruce Johnson J.
Published: July 2012

Flash photolysis experiments on carbonmonoxymyoglobin over wide ranges in time and temperature provide information about the rate processes involved in the rebinding reaction. The non‐exponential rebinding at low temperatures shows that the myoglobin molecules are frozen into a large number of conformational substates with different enthalpic barriers. Above 160 K we observe a relaxation process that shifts the peak of the barrier distribution from ∼ 10 kJ/mol to ∼ 21 kJ/mol. This process is non‐exponential in time and does not obey the Arrhenius law. Above 220 K equilibrium fluctuations between the conformational substates lead to an averaging of the binding rate distribution and to the opening of pathways for the ligands to escape from the protein molecules.
Stiffness Effects in Multidimensional Diffusive Barrier Crossing
Authors: Agmon Noam , Rabinovich Savely
Published: July 2012

The model of Agmon and Kosloff for two‐dimensional diffusive barrier crossing is extended. We demonstrate how an increase in stiffness of the potential perpendicular to the reaction coordinate leads to viscosity dependent rates which are closer to the one‐dimensional Kramers result. The range over which the dynamics are truly two dimensional is characterized by a fractional viscosity dependence of reaction rates and viscosity dependent activation energies. It is a transition region between Kramers behaviors observed in the two extreme limits. A simple kinetic approximation rationalizes these observations as arising from two competing pathways. It shows surprisingly good agreement with the full calculation.
Energy Dissipation in Chemical Reactions on Ultrafast Timescales
Authors: Russell Daniel J. , Paige Mark E. , Harris Charles B.
Published: July 2012

A series of picosecond experiments and computer simulations will be presented that test collisional and hydrodynamic models for vibrational relaxation in liquids. The relationships between isolated binary collision models (IBC) and stochastic dynamics will be presented. The appropriateness of IBC theory in describing vibrational relaxation in liquids will also be discussed.
Stochastic Resonance
Authors: Moss Frank
Published: July 2012

Stochastic Resonance (SR) is a term given to an effect which is manifest in multi stable nonlinear systems driven simultaneously by noise and a weak periodic function, whereby the information flow through the system, in the form of the frequency of the periodic function, is assisted by the noise. For every frequency of the modulation, the information flow is optimum for a specific noise intensity, that is for a specific Kramers transition rate, hence the term resonance. Two physical quantities which characterize the response of such a system have been the objects of a flurry of recent experimental and theoretical activity: the Fourier transform, or auto correlation function of the appropriate state variable, and the probability density of the residence or escape times. The former have been used to obtain the power spectra and hence the signal‐to‐noise ratios of the response, while the latter directly reflect the rates and symmetry properties of the system. Calculation of these quantities pose specific problems for theorists characteristic of non stationary Fokker‐Planck systems. In this paper, I will briefly review the recent activity and include some remarks on the historical foundations of SR.
Effect of Periodic Driving on the Escape in Periodic Potentials
Authors: Jung Peter , Hänggi Peter
Published: July 2012

We consider activation processes in multistable systems exposed to external fluctuations and periodic modulation. The concept of defining escape rates out of a basin of attraction as the ratio of total flux over the basin boundary and the population inside the basin of attraction is generalized for periodically driven systems. Thereby, the escape rate is connected with the Floquet‐spectrum of the time inhomogeneous Fokker‐Planck operator. Our formalism is demonstrated for the particular case of a multistable washboard potential. Numerical results are compared with theoretical results in the limits of small and large driving frequencies, respectively.
Dynamics of Multidimensional Barrier Crossing in the Overdamped Limit
Authors: Carmeli Benny , Mujica Vladimiro , Nitzan Abraham
Published: July 2012

Two methods for numerical solution of multidimensional diffusion problems are presented and applied to the two dimensional barrier crossing problem in the overdamped limit. One of these methods is based on evaluating the smallest non‐vanishing eigenvalue of the Smoluchowski equation, and the other is based on an adaption of Chandler's steady state correlation function approach. Both methods make use of the fast Fourier transform algorithm for solving a transformed version of the Smoluchowski equation. The numerical solutions are compared to results based on the Kramers theory and some observations concerning effects of the dynamics of barrier crossing problems are made.
Interrelations of Different Methods for the Determination of Rates: Flux Over Population, Generalized Reactive Flux, the Lowest Eigenvalue and Its Rayleigh Quotient
Authors: Talkner Peter
Published: July 2012

The ratio of Kramers' current carrying stationary probability density and the equilibrium probability density is utilized as smoothed characteristic function in the generalized reactive flux method recently proposed by Borkovec and Talkner [J. Chem. Phys. 92, 5307 (1990)]. Under a certain condition on the potential, as generalized transition state rate Kramers' phase space diffusion limited rate is obtained. It then represents an upper bound for the true rate. An approximate expression for the plateau value of the generalized reactive flux yields a Rayleigh quotient for the lowest eigenvalue of the considered Fokker Planck process.
Periodic Orbit Approach to the Quantum‐Kramers‐Rate
Authors: Hänggi Peter , Hontscha Waldemar
Published: July 2012

The quantum analog of Kramers reaction rate for a dissipative environment is derived on the basis of a periodic orbit approach for multidimensional tunneling. The resulting reaction rate expression holds at all temperatures, thus covering [in contrast to the imaginary free energy method (“bounce‐” method)] the classical and the quantum regime on the same basis.
Traversal Time in Tunneling
Authors: Landauer Rolf
Published: July 2012

Traversal time in tunneling has become a somewhat controversial subject, and this note presents a personal perspective on some of these discussions. There is a widely invoked linear relationship yielding dwell time as a weighted average of traversal time and reflection time. I assert that it is totally without basis. Many authors follow wave packets through barriers. The results of such calculations are hard to correlate with experiment. Stevens has provided a wave packet approach which avoids some of the problems typically faced by such analyses; nevertheless its analytical details are questioned. The significance of complex traversal times, favored by some investigators, is questioned. The relative merit of various possible “clocks” in the analysis of traversal time is discussed, but without definitive conclusions.
Electronic Structure and Bonding in Cyclic B‐S and B‐Se Compounds Studied by Solid State 11B NMR
Authors: Conrady‐Pigorsch R. , Müller‐Warmuth W. , Schwetlik G. , Wienkenhöver M. , Krebs B.
Published: July 2012

Solid state 11B (and in one case 10B) NMR spectra of four cyclic boron‐chalcogen compounds have been measured at various frequencies and analysed in terms of nuclear quadrupole and chemical shift interactions. Application of the Townes‐Dailey theory to the quadrupole results, corrected for ionic contributions to the electric field gradient and to the bonding, yields detailed information about the importance of μ‐bonding in the respective materials. The occupation number of the 2pz orbitals of the sp2‐hybridized boron atoms appear to be particularly large for systems containing chalcogen‐chalcogen bridges. From both the chemical point of view and the spectroscopic result, among the six‐ and five‐membered rings, diiodotriselenadiborolane is distinguished by an exceptional position.
On the Stability of Microclusters with Three‐Body Forces
Authors: Yurtsever Ersin , Elmaci Nuran
Published: July 2012

A structural analysis of microclusters is carried out on 36 high‐symmetry structures using classical and quantum mechanical minimization methods. For the classical calculations, the total energy is optimized utilizing two‐body potential functions first and then the effects of three‐body forces to these structures are analyzed. The same set of high‐symmetry clusters made of Carbon atoms are studied by a semi‐empirical quantum mechanical method (AM1) and correlations between two approaches are studied. – At large three‐body intensity parameter Z*, both AM1 and static results show that linear conformations are preferred to two‐dimensional structures. Three‐dimensional structures seem to be the least stable ones. But at small Z*, these results are reversed. Overall there is a good agreement between both set of results for Z* = 0.8, suggesting that a qualitative analysis of Carbon clusters can be done with simple potential functions provided that properly weighted three‐body interactions are also employed.
The Dielectric Properties of tert.‐Butanol/Water Mixtures as a Function of Composition
Authors: Kaatze U. , Schumacher A. , Pottel R.
Published: July 2012

At 25°C the complex (dielectric) permittivity of the system tert.‐butanol/water has been measured as a function of frequency v(3 MHz ≦ v ≦ 70 GHz) and mole fraction x (0 ≦ × ≦ 1). Different relaxation functions are fitted to the measured spectra. It is found that within the complete composition range an empirical function is appropriate, which is based on an unsymmetric continuous distribution of relaxation times. Other than expected on grounds of previous light scattering and ultrasonic absorption studies there are neither indications for the formation of microphases nor for special hydrophobic hydration effects. The parameters of the relaxation spectral function are discussed to yield information on the liquid structure and molecular motions of the mixtures. Comparison is made with further aqueous systems which had been measured over a wide composition range, in particular other alcohol/water mixtures but also aqueous solutions of nearly non‐dipolar quinoxaline and of dimethyl sulfoxide.
Precise Measurements of Second Virial Coefficients of Simple Gases and Gas Mixtures in the Temperature Range Below 300 K
Authors: Schramm B. , Elias E. , Kern L. , Natour Gh. , Schmitt A. , Weber Ch.
Published: July 2012

A new apparatus for measurements of second virial coefficients of gases or gas mixtures at room temperature is described. It was used to determine virial coefficients of He, H2, N2, CO2, NH3, and the interaction virial coefficient of Ar/NH3. Furthermore, low temperature interaction virial coefficients of Ar/NH3and H2/CO are reported and finally a critical revision of second virial coefficients of He, H2, Ar, N2, and CO at 77.3 K is presented. The virial coefficients are discussed in their relation to new intermolecular potentials.
The Inverse Photopyroelectric Technique for the Measurement of Concentration and Transport Properties in Binary Systems: The Thermal Effusivity of Ethanol‐Water Mixtures
Authors: Chirtoc Mihai , Toşa Valer , Bićanić Dane , Torfs Paul
Published: July 2012

A new method and apparatus are described for the determination of concentration in liquid mixtures through the measurement of their thermal effusivity. The inverse photopyroelectric method (IPPE) implies the front illumination of a thin pyroelectric sensor the rear side of which is brought into the intimate thermal contact with the sample. The feasibility of this novel technique is demonstrated with ethanol‐water mixtures. Good agreement between the experiment and theory has been obtained.
UV‐Resonance‐Raman Studies of Protonated Nucleic Acid Bases
Authors: Gfrörer A. , Schnetter M. E. , Wolfrum J. , Greulich K. O.
Published: July 2012

UV‐resonance‐Raman‐spectra of protonated adenine, guanine, cytosine and 5‐methyl‐cytosine (mono‐phosphates) were taken with a UV‐spectrometer based on an excimer laser system. Four different wavelengths (220, 230, 260 and 270 nm) were used for resonant excitation of the Raman spectra and most of the spectra were taken both in H2O and in D2O. The very different excitation patterns obtained for different wavelengths, clearly demonstrate that an appropriate choice of the excitation wavelength for resonance enhancement increases the potential of Raman spectroscopy for the detection of protonated bases in complex nucleic acid structures significantly. For adenine the protonation is most clearly seen with an excitation wavelength of 220 nm, whereas for cytosine the most prominent changes occur at 260 nm. Apart from a couple of skeletal modes that undergo both frequency and intensity changes, the spectral region of the exocyclic modes (1550–1700 cm−1) yields additional information with resonant excitation. The enlarged spectral data basis obtained with the variation of the excitation wavelength is used to assign bands of the protonated species to molecular bond structures.
Photochemistry of Colloidal Silver Particles: The Effects of N2O and Adsorbed CN−
Authors: Linnert Thomas , Mulvaney Paul , Henglein Arnim
Published: July 2012

Colloidal silver particles (∼ 3 nm diameter) are photo‐oxidized in aqueous solution in the presence of nitrous oxide, the quantum yield increasing with decreasing wavelength. Nitrogen is formed simultaneously. The effect is explained by photo‐electron emission from the particles, followed by the capture of the emitted electrons by N2O. In the presence of propanol‐2, the silver particles are not destroyed but catalyse the photo‐decomposition of N2O.—Silver particles carrying adsorbed CN− ions are also photo‐oxidized even in the absence of N2O. At the same time, hydrogen is formed by reduction of the aqueous solvent. The silver particles even dissolve when illuminated at 420 nm, i.e. into the long‐wavelength tail of the plasmon absorption band. The effect is attributed to enhanced photo‐electron emission due to 1) the increased negative potential of the Fermi level in the CN− ‐modified silver particles, 2) the negative overall‐charge of these particles, and 3) rapid hole capture by pre‐complexed surface atoms.—For a long time, metals have been thought to possess practically no photochemistry. The observations made here show that metals, when present as a fine dispersion, are demonstrably photoactive.
The Static Dielectric Constant of the Water‐Benzene Mixture System to 400°C and 2800 bar
Authors: Deul R. , Franck E. U.
Published: July 2012

The water‐benzene mixture system at high temperature and high density is considered as a model system to study the dielectric properties of polar‐nonpolar binary mixtures. The static dielectric constant or permittivity ε and the density have been measured at 300, 350 and 400°C between 100 and 2800 bar for 7 different water‐benzene mixtures covering the whole range between pure water and pure benzene. Apparatus and procedure are described. An autoclave contains a cell closed with a flexible bellows. Inside the cell is a cylindrical condenser, filled with a sample mixture, separated from the pressurizing fluid. Thus dielectric and density measurements can be performed simultaneously with one sample.—Extensive tables with data are given. The uncertainty is believed to be below ±1% for most data. At 400°C and 2000 bar ε(χw = 1.0) is 19.40 and decreases to 9.67 (χw = 0.9) and to 3.68 (χw = 0.5). For pure benzene the value is 2.1. Several continuum theories are examined and discussed to represent the data. The best result was obtained with the Landau‐Lifshitz‐Looyenga relation. It needs dielectric constants of the pure partners and the mixture densities but requires no adjustable parameters. On the basis of the present investigation this relation is recommended also to estimate dielectric constants for dense, supercritical binary systems of water with nonpolar gases.
Pressure Effect on the Radiationless Deactivation of Singlet Oxygen by 1,4‐Diazobicyclo [2.2.2] octane in Six Different Solvents
Authors: Seikel K. , Brauer H.‐D.
Published: July 2012

The rate constantkqof quenching of singlet oxygen (1O2) by 1,4‐diazobicyclo [2.2.2] octane (DABCO) has been determined in six solvents in dependence of pressure using time resolved phosphorescence techniques. Experimental activation volumes vary between −19.0 ml·mol−1(chloroform) ≤ ΔVobs# ≤ −10.0 ml·mol−1(benzonitrile). The data are analyzed by means of a kinetic scheme assuming a preequilibrium of1O2and DABCO to form a singlet contact complex1C. The data are consistent with the assumption that the deactivation of1O2occurs via a charge transfer process between the collision partners of C converting1C to3C, which subsequently splits into the deactivation products. The statistical model developed by Yoshimura and Nakahara is used to calculate the reaction volume ΔVcof the preequilibrium. ΔVcand the activation volume ΔVCT# of the actual deactivation of1O2by DABCO contribute practically in equal parts to ΔVobs.# ΔVCT.# values strongly depend on the solvent polarity. On the basis of Kirkwood's electrostriction model the actual activation volume (ΔCT#)° without electrostriction effect and the dipole moment of the transition state μCT* have been estimated to: (ΔVCT#)° = −4.3 ml·mol−1and μCT# = 7.8 Debye, respectively.
Apparently “Universal” Dielectric Behaviour of Electrolytic Solutions
Authors: Adams J. , Aust A. , Brockmann U. , Klockgeter K. , Schütz G. , Steffen A. , Stockhausen M.
Published: July 2012

The real part of conductivity was measured for a number of salt solutions in different polar (nonaqueous) solvents over a broad frequency range up to 72 GHz at 20°C. The slope of the double log representation of conductivity versus frequency decreases with increasing salt concentration and solution viscosity. An extrapolation to infinite viscosity yields slope values similar to those found with vitreous systems which are claimed to exhibit “universal” behaviour.
Nuclear Spin Relaxation. Nuclear Spin Relaxation and Electrical Conductivity in Lithium Germanate Glasses
Authors: Kanert O. , Kloke M. , Küchler R. , Rückstein S. , Jain H.
Published: July 2012

7Li nuclear spin relaxation (NSR) in the laboratory frame (T1) as well as in the rotating frame (T1ϱ) and electrical conductivity measurements were performed in (1 – x) GeO2 · xLi2O glass series, where x = 0.001 to 0.36, between 3 K and the glass transition temperature (≃ 700 K). Below about 250 K the NSR data can be interpreted consistently in the framework of thermally activated low‐frequency excitations of disordered modes intrinsic to the glassy state of matter. The modes are described by asymmetric double well potential (ADWP) configurations with suitable densities of states. Above about 250 K the NSR rates increase exponentially with rising temperature due to diffusive jumps of the Li ions. Deduction of corresponding transport properties, however, from such data by means of standard NSR theories turns out to be difficult. Models are discussed to overcome these difficulties by relating NSR with electrical conductivity. The results are found to correspond best with Funke's model of a coupled motion of the ions caused by Coulomb interaction.
Reorientational Correlation Functions of Simple Supercooled Liquids as Revealed by NMR Studies
Authors: Rössler E. , Börner K. , Tauchert J. , Taupitz M. , Pöschl M.
Published: July 2012

31P,1H and2H NMR investigations on supercooled simple organic liquids are presented. Combining measurements of spin‐lattice relaxation, spin‐spin relaxation and stimulated echo decays the reorientational correlation functionF2(t) of the second Legendre polynomial is probed over a wide temperature interval. Correlation times in the range of 10−11– 1s are covered, and the scaling property of the correlation functionF2(t) corresponding to the α‐relaxation, i.e., the main relaxation in the supercooled liquid, is checked. The functionF2(t) can be described equally well by a Cole‐Davidson distribution of correlation times or by a Kohlrausch‐Williams‐Watts function (10−8< τ < 1s). NearTgin the highly viscous regime the correlation times become independent from the molecular size. At similar temperatures the bifurcation of a secondary process (β‐process) is observed. Combining results from neutron scattering and NMR the completeF2(t) has to be described by a three‐step function near the glass transition temperatureTgand by a two‐step function at temperatures well aboveTg. The transition atTgis accompanied by the onset of non‐exponential spin‐lattice relaxation and by a discontinuous change of the temperature coefficient of the relaxation.
Flash CIDNP Study of Photosensitized Electron Transfer Reactions of Methoxybenzenes
Authors: Goez Martin , Eckert Gerd
Published: July 2012

The photoreactions between 9,10‐anthraquinone and the donors C6H6–n (OMe)n, where n = 1 …3, in acetonitrile‐d3 have been investigated by time resolved measurements of chemically induced dynamic nuclear polarization (“flash CIDNP”). The activation parameters for the degenerate electron transfer between five of the donors and their radical cations have been determined. For these, the same isokinetic relationship as in the previously studied case of para‐substituted N,N‐dimethylanilines was found to hold. Theoretical rate constants for the self exchange processes were calculated from AM 1 data by a model based on the Marcus theory. Their agreement with the experimental values was satisfactory over the whole range of investigated temperatures (237 K … 298 K).
Slowing Down of Electrolytic Conductance in the Critical Region of Partially Miscible Ternary Liquid Mixtures
Authors: Flindt S. , Steiger A. , Becker F.
Published: July 2012

The electrolytic conductance and the capacitance of 6 ternary liquid systems of the type carboxylic acid + tertiary amine + hydrocarbon are investigated in the neighbourhood of critical solution points (C.P.) A stirred conductance cell is used which yields information not only from the one‐phase region but also from a small section along the rectilinear diameter in the two‐phase region. The plots of conductance resp. capacitance vs. temperature exhibit a fall‐off by 5 to 20 per cent in the critical region which is virtually symmetric with respect to the C.P. Evaluation of the data in the fall‐off region, the width of which – depending on the chemical nature of the system – ranges from ±0.035 to ±0.45 K, yields critical exponents ∂ between 0.53 and 0.67. This suggests that the fall‐off of conductance resp. capacitance results mainly from the critical slowing down of the transport phenomena by the divergence of the correlation length ζ.
A Large Bathochromic Shift from the Solution to the Solid State in 1,4‐Diketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole
Authors: Mizuguchi Jin , Wooden Gary
Published: July 2012

A large bathochromic shift (about 1400 cm−1) from the solution to the solid state in the title compound has been investigated from the standpoint of the change in electron density on the nitrogen atom caused by deprotonation or by intermolecular hydrogen bonding. The electronic state of the diketopyrrolopyrrole chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group. Mono and di‐deprotonation in solution brings about large bathochromic displacements of 2650 and 3400 cm−1, respectively. The deprotonation leads to increased electron density on the nitrogen atom and, as a consequence, more overall electron density in the chromophore which contributes to the bathochromic shift. Similar increase in electron density is also operative in the solid state through the intermolecular hydrogen bonding between the NH of one molecule and the oxygen of another. The contribution of the hydrogen bond to the large shift is estimated to be about 1000 cm−1 in the solid state.
Quantum Sized Semiconductor Particles in Solution and in Modified Layers
Authors: Weller Horst
Published: July 2012

The preparation of highly monodisperse, quantum‐sized CdS particles is described. In these samples a band splitting into discrete exciton‐like states is observed.—Quantum‐sized CdS and PbS particles prepared in situ on highly porous, polycrystalline TiO2 electrodes work as highly efficient sensitizers. Photocurrent yields of more than 70% are reported. In the case of PbS it is shown that an efficient electron transfer is only possible with particles in the size quantization regime.
Use of a Scanning‐Kelvinprobe in the Investigation of Electrochemical Reactions at the Metal/Polymer Interface
Authors: Stratmann M. , Wolpers M. , Streckel H. , Feser R.
Published: July 2012

It is possible to measure the work‐function of polymer coated materials with a Kelvin‐probe. In a humid atmosphere this work‐function is mainly given by the corrosion‐potential of the metal substrate. The use of a scanning Kelvinprobe then allows to map the corrosion potential of polymer coated material with a local resolution of approx. 20 μm and to follow the delamination of polymer coatings as well in the vicinity of defects as on metal substrates, which are contaminated at the metal/polymer interface. Simultaneously, the diffusion of oxygen can be followed with a high local resolution after a jump of the oxygen activity within the gas phase.—The same techniques are used to analyse intrinsic defects within monomolecular LB‐films. In a dry gas phase the Volta potential map corresponds to the distribution of dipole‐potentials and therefore allows to distinguish between covered and uncovered parts of the substrate, as the ordered LB‐film shows rather large dipole‐potentials. In a humid atmosphere the Volta potential map again is dominated by the corrosion potential of the substrate and therefore the delamination of the LB‐film in the vicinity of defects can be studied as well as the stability of the film on the metal substrate far away from any defect.
Buildup of Ultrathin Multilayer Films by a Self‐Assembly Process: II. Consecutive Adsorption of Anionic and Cationic Bipolar Amphiphiles and Polyelectrolytes on Charged Surfaces
Authors: Decher G. , Hong J. D.
Published: July 2012

We have recently reported on the consecutive physisorption of anionic and cationic bipolar amphiphiles onto charged surfaces, adsorbed out of aqueous solutions [1]. Here, we extend our previous concept to multipolar compounds such as polyelectrolytes. In contrast to the bipolar amphiphile system, it is not necessary to separate single charges by a rigid unit, when the polyelectrolyte is adsorbed from sufficiently concentrated solutions. In this case the physisorbed layer does not bind with all ionic groups to the surface and exposes free ionic groups at the new film/solution interface. Therefore a polyelectrolyte layer can replace a layer of bipolar amphiphiles in the consecutive buildup of a multilayered assembly. The buildup of multilayers can then be described as follows: A solid substrate with a positively charged planar surface is immersed in the solution containing the negatively charged bipolar amphiphile, a monolayer of the amphiphile is adsorbed and due to its bipolar structure the surface charge is reversed. After rinsing in pure water the substrate is immersed in the solution containing the positively charged polyelectrolyte. Again a monolayer is adsorbed but now the original surface charge is restored. By repeating both steps in a cyclic fashion alternating multilayer assemblies of both compounds are obtained. In the same way multilayer assemblies can be prepared by using negatively charged polyelectrolytes and positively charged bipolar amphiphiles. It is demonstrated that multilayer films composed of at least 39 consecutively alternating layers, which corresponds to a total film thickness of 151 nm, can be assembled.
Semiconducting and Metallic States in Conducting Organic Low‐dimensional Materials
Authors: Schmeißer D. , Bätz P. , Göpel W. , Jaegermann W. , Pettenkofer Ch. , Wachtel H. , Jimenez‐Gonzales A. , Von Schütz J. U. , Wolf H. C. , Taborski J. , Wüstenhagen V. , Umbach E. , Erk P. , Meixner H. , Hünig S.
Published: July 2012

Films of conducting organic materials can be prepared in either a metallic or a semiconducting state as will be demonstrated for polymeric and crystalline films of polypyrrole and of DCNQI salts, respectively. The specific features of each state are described by the electronic structure of the materials near the Fermi level which is deduced from electron spectroscopies. Further, the transitions between these different conduction states are shown to be based on different mechanisms.
Mobility of Ionic Space Charges in Thin Insulating Films
Authors: Kluger K. , Lohrengel M. M.
Published: July 2012

The anodic oxide formation on high‐purity aluminium electrodes in an acetate buffer of pH 5.9 has been studied by potentiostatic pulse measurements. When the field strength E is low, the concentration of mobile charge carriers is close to zero. When the field strength is increased, ions are transferred through the phase boundaries forming vacancies or ions at interstitial sites to guarantee a sufficient ionic conductivity of the oxide. Using multiple pulse measurements the presence and the dwell time of the mobile charge carriers can be monitored. The modifications of the conventional high field model are described. At low field strength the injected mobile charge carrier concentration decreases exponentially with waiting time.
Measurement of Chemical Resonance by Multiplexing a Chemical Steady State
Authors: Münster A. F. , Schneider F. W.
Published: July 2012

A new method for the measurement of chemical resonance is presented. In the proposed “multiplex”‐procedure a chemical focus in a CSTR (Continuous – Flow – Stirred – Tank – Reactor) is perturbed by superimposing flow rate noise on the steady state. The resonance frequency of the focus is determined from its normalized power spectrum. The multiplex method does not provide precise information about the absolute value of the damping constant since the response is a finite time series of transients and not a free induction decay as measured in NMR, for example. The “scanning” method, which measures stationary response amplitudes at various frequencies should be used for the precise determination of the damping constant.
Quantum‐Classical Mixed Mode Analysis of Nonlinearly Coupled Oscillators: A Time‐Dependent Self‐Consistent‐Field Approach
Authors: Yurtsever E. , Brickmann J.
Published: July 2012

A two‐dimensional vibrational system with a strong nonlinear coupling is studied using a quantum‐classical mixed mode self‐consistent‐field approach. The classical equations of motion as well as the time‐dependent Schrödinger equation are solved for respective modes under the influence of the average fields generated by the other modes. This vibrational system was previously shown to be chaotic under classical mechanical treatment but quantum mechanical observations pointed out to highly regular behaviour. The results of the mixed mode calculations give periodic trajectories, regular Poincare maps and Lyapunov numbers, k = 0. These observations support the previous findings that during the transition from classical to quantum mechanics, regularity dominates the dynamical behaviour.
Kinetics of the Reaction of OH Radicals with CH2CO
Authors: Oehlers C. , Temps F. , Wagner H. Gg. , Wolf M.
Published: July 2012

The kinetics of the homogeneous gas phase reaction OH + CH2CO → products (1) has been investigated at room temperature and pressures between 1.4 mbar ≤ p ≤ 2.5 mbar using the discharge flow method. Reactors with Teflon wall coatings and with different surface‐to‐volume ratios were employed to exclude effects of heterogeneous reactions. OH radicals were generated via the reaction F + H2O. Their concentration‐versus‐time decay profiles were followed under pseudo‐first‐order conditions, [CH2CO] → [OH]0 with a Far Infrared Laser Magnetic Resonance (FIR‐LMR) spectrometer. The rate constant of the title reaction was found to be k1, (296 K) = (7.2 ± 2.0)·1012 cm3/mol·s.
X‐Ray Diffraction Measurements for Expanded Fluid Selenium up to the Supercritical Region
Authors: Tamura Kozaburo , Hosokawa Shinya
Published: July 2012

The X‐ray diffraction measurements for fluid Se have been carried out in the temperature and pressure range up to 1500°C and 815 bar. We have developed a new type of high‐pressure vessel and a new sample cell made of single‐crystal sapphire for the X‐ray diffraction measurements using the energy‐dispersive method. We have obtained the structure factor and the pair distribution function as functions of temperature and pressure. From the detailed analysis of the pair distribution function we conclude that the twofold coordinated structure is largely preserved in the region where the optical gap disappears and the progressive increase of conductivity becomes evident. On the basis of the findings we speculate on the existence of the small chain molecule with the planer zig‐zag conformation which may cause the transition to the metallic state in fluid Se.
Photochromic Response of Vacuum‐Evaporated Nb2O5 Thin Films in Ethanol Vapor
Authors: Yao J. N. , Loo B. H. , Hashimoto K. , Fujishima A.
Published: July 2012

Amorphous Nb2O5 thin films are obtained by vacuum evaporation of high‐purity Nb2O5 powders onto NESA glass substrates. These films were found to exhibit both photochromism and electrochromism. Reasonably good photochromic responses were observed in ethanol and in the N2 atmosphere, but no photochromism was observed in the air or in a pure O2 atmosphere.
Comparison between the Photo Induced Chemical Reaction in the NO2 – C2H4 van der Waals Complex and the O + C2H4 Gas Phase Reaction
Authors: Loison J. C. , Dedonder‐Lardeux C. , Jouvet C. , Solgadi D.
Published: July 2012

The photodissociation of NO2 within NO2–C2H4 complexes or small clusters excited at 355 and 266 nm leads to the formation of vibrationally and rotationally cold vinoxy radicals (CH2CHO). On the other hand, the vinoxy radicals produced in gas phase thermal collisions are vibrationally and rotationally hot. Comparison between these experiments seems to show that two different competitive reaction paths are responsible for the different internal energy content in the vinoxy radical.
Strong Bipolar Electrokinetic Charging of Thin Liquid Jets Emerging from 10 μm PtIr Nozzles
Authors: Faubel M. , Steiner B.
Published: July 2012

In a very thin liquid jet of pure water which flows with high speed into a vacuum chamber we observe unexpectedly large streaming currents and electrokinetic charging. This potential shift at the liquid surface is interfering with planned photoelectron spectroscopy. It is quantitatively studied as a function of the jet flow rate, the electric dissociation and the pH value of the fluid. The standard electrokinetic model and a nonequilibrium electrochemical diffusion current model are discussed for a semiquantitative explanation.
Shell Structure in Photoionization Spectra of Trivalent Metal Clusters
Authors: Pellarin M. , Lermé J. , Baguenard B. , Broyer M. , Vialle J. L. , Perez A.
Published: July 2012

Photoionization mass spectra of large AlN and InN clusters, produced by laser vaporization technique, have been recorded via standard TOF spectroscopic methods. Ionization potentials are measured in the size range N = 37–112 for aluminum and N = 31–132 for indium. Comparison between these two trivalent simple metals is presented, as well as with the electronic shell structure predictions of the spherical jellium model. In the large size range N = 200–1400, regular oscillations are observed in the AlN mass spectra. This oscillating behaviour, which is a manifestation of the electronic shell structure of the Ne = 3N valence electrons, is analyzed within the semiclassical theory of single‐particle quantum level density. The oscillation period as a function of Ne3, two times shorter than the period obtained in alkali cluster experiments, is well explained by the classical two‐turn star orbit contribution, whereas for alkali metals the electronic structure near the Fermi energy is governed by the single‐turn triangular and square orbit contributions.
Influence of Microsolvation on the Molecular Dynamics: Structure‐Dependent Intramolecular Vibrational Redistribution Process in the Benzene‐Arn Heteroclusters
Authors: Schmidt Martin , Mons Michel , Calvé Jacques Le
Published: July 2012

Recent two‐color R2PI spectroscopic results combined with Monte Carlo simulations have shown that the first benzene‐Arn clusters exhibit a large variety of isomeric forms: one‐sided and two‐sided conformers as well as two different one‐sided isomers for the Bz–Ar3 complex. Taking advantage from the existence of these different arrangements of argon “solvent” atoms around the Bz molecule, the influence of the microsolvation characteristics on the dynamical properties of the clusters has been investigated: in particular the occurrence of intramolecular vibrational energy redistribution (IVR) in the S1 state. The results presented on the first Bz–Arn clusters (n ≤ 3) show that the IVR process is not only n‐dependent, but also, within a well‐defined complex, strongly isomer‐dependent.
High Temperature Reactions of Phenylacetylene
Authors: Herzler J. , Frank P.
Published: July 2012

Hydrogen atom abstraction from phenylacetylene (C6H5‐C2H) like its reaction with hydrogen atoms have been studied at elevated temperatures behind reflected shocks. ‐ The unimolecular decomposition of very low initial concentrations (3 ‐ 22 ppm) of phenylacetylene was investigated in the temperature range 1600 to 1900 K by monitoring the temporal H‐atom production. ‐ For C6H5‐C2H + H, the thermal decomposition of very low concentrations (1 ‐ 3 ppm) of C2H5I served as H‐atom source. Atomic resonance absorption spectrometry (ARAS) was used to record simultaneously H‐atom and I‐atom profiles. The experiments covered the temperature range 1190 to 1530 K. ‐ For both series of experiments, the total pressure was about 2.3 (+/‐0.3) bar.

For the unimolecular reaction R1: C6H5‐C2H → C6H4‐C2H + H a rate constant expression of: magnified image was found.

For the bimolecular reaction R2: C6H5‐C2H + H → products a rate constant of: magnified image was deduced.

From the available thermochemical data two product channels have to be discussed: magnified image Detailed evaluation of existing thermodynamic data enables the calculation of an equilibrium constant for reaction R 2a. From this and under the assumption that reaction R 2a is the dominant product pathway at elevated temperatures, a rate constant expression of magnified image is deduced for the reaction of phenyl readicals with acetylene, which is an important process in sooting flames: magnified image This rate constant agrees within a factor of 2 with the data from recent studies executed by Fahr et al. [1a, 1b].
Elementary Reactions in the Methanol Oxidation System. Part I: Establishment of the Mechanism and Modelling of Laminar Burning Velocities
Authors: Grotheer Horst‐Henning , Kelm Siegfried , Driver H. S. T. , Hutcheon R. J. , Lockett R. D. , Robertson G. N.
Published: July 2012

A set of combustion relevant rate coefficients recommended by a group of European kineticists has been tested by calculating laminar burning velocities. Virtually without any adjustments, a good match with experimental data has been achieved for H2/CO/air flames, H2/CO/air flames, and CH4/air flames. In order to extend this set by inclusion of the reactions forming the CH3OH oxidation subsystem, the current knowledge of these reactions if first reviewed. The extended set yields calculated burning velocities for CH3OH/air flames in good agreement with measurements recently obtained under stretch free conditions. By using a sensitivity analysis, the remaining deficiencies of the model are highlighted and it is made clear where further experimental work is particularly needed.
Stabilization of Premixed, Conical Methane Flames at High Pressure
Authors: Eberius H. , Kick Th.
Published: July 2012

A new high pressure burner has been designed and built in order to investigate stationary, premixed flames at high pressure. The burner exhibits several unique features such as modular design, small dimensions, excellent optical access for spectroscopic measurements, provisions for the use of probes, a system for accurate flow and pressure control, and various safety devices. The operating pressure regime could be raised in successive stages up to the present 100 bar. Methane/air flames have been stabilized in this pressure regime as flat flames on porous disc burners and as conical flames above nozzle burners. The very small conical high pressure flames showed regular shape and good stability in the fuel rich regime. Thus, it was possible to derive from the cone angle burning velocities, which agree favourably with model calculations.
Dielectric Relaxation of Aqueous Electrolyte Solutions II. Ion‐Pair Relaxation of 1:2, 2:1, and 2:2 Electrolytes
Authors: Barthel J. , Hetzenauer H. , Buchner R.
Published: July 2012

The low‐frequency relaxation process contributing to the complex permittivity spectra of aqueous solutions of MgSO4, CdSO4, Na2SO4, CdCl2, and CuCl2 is investigated. The dispersion amplitudes are analysed with the help of model calculations, based on a modified Cavell equation for ellipsoidal bodies. It is shown that ion pairs are responsible for the low‐frequency relaxation process with solvent separated ion pairs dominating for the sulfates, whereas contact ion pairs are formed by the chlorides. The observed relaxation time is analysed as the superposition of chemical and reorientational relaxation. For the ion pairs the effective volumes of rotation and the rate constants of formation are determined. The results are compared with information from the literature.
Dielectric Studies of Butyl Chloride Solutions
Authors: Jadżyn J. , Kȩdziora P. , Bonnet P.
Published: July 2012

The results of dielectric polarization and non‐linear dielectric effect studies for three isomers of butyl chlorides in solutions are presented. It is shown that in the systems of weak molecular interactions the shape of molecules is the main factor which determines the dielectric properties of solutions.
The Specific Heat of Butoxyethanol/Water Critical Mixtures
Authors: Würz U. , Grubič M. , Woermann D.
Published: July 2012

Results of measurements of the specific heat capacity of n‐butoxyethanol/water and iso‐butoxyethanol/water of critical composition as function of temperature are reported. Both systems have in common that in the vicinity of the critical temperature aggregates of butoxyethanol molecules and concentration fluctuations with unusual long range correlations (critical amplitude ξ0+ ≈︁ 0.4 nm) coexist. The analysis of the data shows that both systems belong to the same universality class as “simple” binary mixtures. The value of the critical amplitude ratio of specific heat capacity (A/A+) and the value of the critical exponent α are consistent with the predictions of the Landau‐Ginzburg‐Wilson model (d = 3, n = 1). The same is true for the value of the amplitude ratio RA,ξ+ calculated from the specific values of the critical amplitudes ξ0+ and A+.
X‐ray Investigation of Supercooled Water
Authors: Corban R. , Zeidler M. D.
Published: July 2012

X‐ray diffraction curves were measured for water at – 20°C, – 10°C, –5°C in the supercooled region and in addition for comparison at +4°C and + 30°C. The data were corrected for polarization and absorption, Compton scattering was completely included. Evaluation was based on molecular form factors and the molecular center correlation function was obtained. A continuous change of the pair correlation function from the normal to the supercooled region is found, all peak amplitudes increase with decreasing temperature and the first peak shifts in position. Comparisons with available literature data on deuterated water and with computer simulation results on ST2‐water are presented.
Solution of Hydrogen in Cold‐Worked Pd‐Ag Alloys
Authors: Kishimoto Shozo , Yoshida Noritetsu , Yao Takeshi , Itani Tsukasa , Flanagan Ted B.
Published: July 2012

The effect of annealing temperature on hydrogen solubilities in the dilute region (α phase) has been investigated for cold‐worked Pd‐Ag alloys containing from 5 to 40 atomic % Ag by measuring pressure‐composition isotherms between 273 and 348 K. These data have been correlated with changes in physical properties arising from the recoveries of lattice defects during annealing between 373 and 1073 K. It is found that the magnitude of the solubility enhancements for the alloys having the same degree of cold‐working decreases with increasing Ag content reaching zero at 40 atomic % Ag; this result suggests that the dislocation densities in Pd‐Ag alloys do not lead to concomitant solubility enhancements.
Fast Processes in UV‐Two‐Photon Excitation of Pare Liquids
Authors: Sander Martin , Brummund Uwe , Luther Klaus , Troe Jürgen
Published: July 2012

Decomposition and ionization reactions of neat liquid alkanes, alcohols, water, and halomethanes after UV‐two‐photon absorption were investigated by pump‐and‐probe measurements with subpicosecond time resolution. Previous suggestions are revised and new mechanisms proposed which consistently explain the transient absorption signals obtained. In particular, it is shown that the importance of free or “quasi‐free” electrons as intermediates in the photodecomposition of liquids has commonly been largely overestimated.
Thermodynamics of Ammonium Halopallidates II. Heat Capacity and Thermodynamic Properties of (ND4)2PdCl6 at Temperatures from 5 K to 325 K
Authors: Callanan Jane E. , Weir Ron D. , Westrum Edgar F.
Published: July 2012

The heat capacity of deuterated ammonium hexachloropallidate (ND4)2pDCl6 was measured from 5 K to 325 K by adiabatic calorimetry. One λ‐shaped phase transition, absent in the protonated salt, was found in the curve for heat capacity against temperature. This transition reaches its maximum Cp.m ≃ 150 · R at (30.2 ± 0.1) K with ΔtrsSm0 = (2.005 ± 0.009) · R (R = 8.31451 J · K−1 · mol−1) and marks the change from the high temperature cubic structure to the low temperature tetragonal structure. The Debye temperature at 0 K equals (96.5 ± 2.4) K and below 10 K, only lattice vibrations make significant contributions to the heat capacity. Smoothed values of the standard thermodynamic quantities for pure (ND4)2PdCl6 are tabulated up to 320 K and the Sm0(273.15 K) = (49.80 ± 0.05) · R.