bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scanning electrochemical microscopy: A new scanning mode based on convective effects
Authors: Borgwarth K. , Ebling D. G. , Heinze J. 
Published: July 2012

AbstractA new measuring technique for the scanning electrochemical microscope (SECM) is presented, which we call picking mode. The influence of the tip‐surface distance on the current signal is separated from the current due to the electrochemical properties of the surface by this new method. Based on convective effects, the fast approach of the tip towards samples revealed a sharp increase of the tip current close to the samples' surface. During this strongly instationary stage, the current is dominated by convective flows and the influence of the electrochemical surface properties is negligible. Using this convective current, the tip‐surface distance can be adjusted within a few microns. In a second step after reaching the steady‐state transport conditions again, the electrochemical processes are characterised by the current at this position. The capability of the new mode is proven by scanning a bended platinum sheet and a PVC sample. The new method enables the separate acquisition of the height profile due to the surface's morphology and of the topology due to local variations of electrochemical properties.
A direct measurement of the reaction NH3 + NH→2NH2
Authors: Röhrig M. , Römming H.‐J. , Wagner H. Gg. 
Published: July 2012

AbstractThe reaction of NH in its electronic ground state with ammonia was investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ−). The initial concentrations of HN3 which was used as source of NH(X3Σ−) were very low in order to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reaction of NH(X3Σ−) + NH3 (1) directly. In a temperature range from 1300 to 1700 K a rate constant k1 = 10(14.5±0.3)exp (–(112±9)kJ mol−1/RT)cm3/mol s was obtained. The apparent energy of activation fits well into an Evans Polanyi plot for H abstraction reactions of NH(X3Σ−).
Die physikalische Chemie fester Stoffe
Authors: Schmalzried Hermann 
Published: July 2012

AbstractStructure and activity of solids and their physico‐chemical interpretation are the subject matter of this overview. After sketching briefly the history of the development of the physical chemistry of solids, solid state kinetics in particular is treated here. Examples are given which show how physico‐chemical concepts influence technologies that are responsible for many aspects of modern civilization. We discuss in particular (1) Point defect thermodynamics and point defect kinetics as the basis of amplifying devices. (2) Diffusional transport in crystals as the basis of solid state reactions and the formation of modern materials and tools. (3) The influence of the elastic potential on solid state kinetics and (4) Morphological stability and its influence on the course of solid state reactions.
Electrochemical reduction of CO2 at an activated silver electrode
Authors: Kostecki R. , Augustynski J. 
Published: July 2012

AbstractThe electrochemical reduction of CO2 to CO in aqueous NaClO4 solution saturated with CO2, at polycrystalline Ag cathodes was investigated as a function of the potential, temperature and electrolysis duration. A poisoning process has been found to occur in parallel with the CO formation. Building‐up of the surface species closely similar to the detected poison has been observed at a Ag electrode immersed (at open‐circuit) in a solution containing small amounts (10−4mol dm−3) of formaldehyde. A periodic anodic stripping of these inhibiting species was shown to produce stable current densities and faradaic efficiencies of CO over 4 – 5 h electrolysis runs. A tentative reaction pathway for CO2 reduction to CO, taking into account the experimentally determined onset potential, is proposed.
Transport coefficients and apparent charges of concentrated electrolyte solutions – Equations for practical use
Authors: Chhih Aziza , Turq Pierre , Bernard Olivier , Barthel Josef M. G. , Blum Lesser 
Published: July 2012

AbstractSimple expressions for the transport coefficient in the mean spherical approximation (MSA) have been derived. We study the self‐diffusion, conductance and apparent charge of simple electrolytes, where we find good agreement for the concentration dependence. Associated electrolytes are also well described by a natural extension of this theory. The MSA equations extend the concentration range of the chemical model (CM) calculations which, in turn, are a reliable source for the input parameters of the MSA calculations.
The T,x,p‐phase diagram of binary phospholipid mixtures
Authors: Landwehr A. , Winter R. 
Published: July 2012

AbstractHigh pressure differential thermal analysis (DTA) has been applied to the study of the temperature‐composition‐pressure phase diagram of the binary saturated phospholipid mixtures dimyristoyl/palmitoyl phosphatidylcholine (DMPC/DPPC) and dimyristoyl/stearoyl phosphatidylcholine (DMPC/DPPC) in excess water. A temperature range from 10 to 100°C and a pressure range from ambient up to 1500 bar has been covered. The experimentally obtained phase equilibria of these binary systems are compared with thermodynamic calculations for ideal and non‐ideal mixing behaviour, and with recent results from Monte Carlo computer simulation studies, which not only permit determination of the phase diagram but also reveal a pictorial view of the local structure of the mixtures in the different parts of the phase diagrams.
Au‐induced decomposition of N2O
Authors: Dietrich G. , Lützenkirchen K. , Becker St. , Hasse H.‐U. , Kluge H.‐J. , Lindinger M. , Schweikhard L. , Ziegler J. , Kuznetsov S. 
Published: July 2012

AbstractReactions between small gold cluster ions, Au, and N2O were studied in a Penning trap mass spectrometer. Gold clusters were produced by laser vaporization and injected into a Penning trap. After reaction times of 50–7000ms the products were detected by time‐of‐flight mass spectrometry. For the major reaction channel, Au + N2O→Au1,2N + NO+, rates of (0.9±0.1)×10−12 cm3 s−1 and (2.4±0.4)×10−12 cm3 s−1 were determined which are about a factor 500 below the collision rate. The corresponding activation energies for N2O decomposition were estimated to lie below 0.6 eV and 0.3 eV. Additional products with small branching ratios were detected, viz. the ions Au1O+, Au1N2O+, Au2N+, Au2NO+, Au2N2O+, Au3O+, Au3N2O+, and Au4N2O+. This indicates a preference for nitrogen‐oxygen bond rupture in the case of Au and Au, and for nitrogen‐nitrogen bond rupture in the case of Au.
Dipole‐bound electron states in HCN gas
Authors: Klahn Th. , Krebs P. 
Published: July 2012

AbstractWe have measured for the first time the drift mobility μ of electrons in HCN gas in the number density range 2.96×1017 ≤ n ≤ 3.60×1018 cm−3 at T = 294 K. The strong density dependence of the density‐normalized mobility (μn) of electrons at these low densities which has never been observed in less polar gases cannot be explained by multiple scattering effects. Assuming a dynamical electron attachment/detachment equilibrium involving the dipole‐bound electron state we can describe this anomalous density dependence. The striking density dependence of the mobility of anions observed for n≥ 1.98×1018 cm−3 is briefly discussed.
Instability of Moving Interfaces between Ionic Crystals KCl/AgCl
Authors: Schimschal‐Thölke S. , Schmalzried H. , Martin M. 
Published: July 2012

AbstractThe morphological evolution of initially planar phase boundaries between ionic crystals due to ion fluxes which are driven by an externally applied electric field is investigated. In this particular study, the boundaries under investigation are interfaces between KC1 and AgCl. It is shown that the moving boundary is morphologically unstable if the flux of silver ions is directed towards the KCl‐crystal, whereas it is stable if the flux of potassium ions is driven towards AgCl. This behaviour can be explained by the rules which derive from a formal stability analysis. The geometrical evolution of the moving phase boundary in its later stages is mainly governed by the elastic properties of the contiguous phases.
Electronic Energy Distribution in SrF by Investigation of the Molecular Chemiluminescence SrF(A2II1/2,3,2B2Σ+ → X2Σ+) and the Atomic Resonance Fluorescence Sr(53P1‐51S0) in the Time‐Domain following the Pulsed Dye Laser Generation of Sr(53PJ) in the presence of CH3F
Authors: Antrobus Stephen , Carl Shaun A. , Husain David , Lei Jie , Castaño Fernando , Sanchez Rayo Maria N. 
Published: July 2012

AbstractA kinetic study is presented of the electronic energy distribution in SrF following the reaction of the electronically excited strontium atom, Sr(5s5p(3Pj)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH3F. This optically metastable atom was generated by pulsed dye‐laser excitation of ground state strontium vapour to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1←51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The decay of Sr(53PJ) was then monitored by time‐resolved atomic fluorescence from Sr(53P1) at the resonance wavelength following rapid Boltzmann equilibration within the 3PJ spin‐orbit manifold. Electronically excited SrF resulting from reaction of the excited atom with CH3F was also recorded in the time‐domain via the systems SrF(A2→1/2ΣX2Σ+) (νv = 0, λ = 662 nm), SrF(A2×3/2ΔX2Σ+) (ν = 0, λ = 652 nm) and SrF(B2Σ+X2Σ+) (νv = 0, λ = 579 nm). The A2 (181.9 kJ mol−1) and B2Σ+ (206.6 kJ mol−1) states of SrF are both energetically accessible on collision between Sr(3P) and CH3F. Both the atomic and molecular (A,B‐X) chemiluminescence emissions are shown to be exponential in form and characterised by first‐order decay coefficients which are found to be equal under identical conditions within experimental error. SrF(A2) and SrF(B2Σ+) are thus both shown to arise from direct reaction with CH3F. Further, the combination of integrated atomic and molecular intensity measurements, coupled with optical sensitivity calibration, enables estimates of the branching ratios into the A1/2,3/2, B and X states arising from Sr(53PJ) + CH3F to be made yielding the following results: A1/2, 6.4 × 10−3; A3/2, 1.5×10−3; B, 1.1x10−4; X, 0.992. The results obtained here are compared with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements and with previous kinetic measurements on SrCl, Br(A2, B2 + ‐X2Σ+) that we have reported. The results are also compared with those from a series of investigations we have presented from time‐domain investigations of molecular emissions from CaF, Cl, Br, I (A,B‐X) arising from the collisions of Ca(43PJ) with appropriate halides.
Electroosmotic and Hydrodynamic Oscillations in the Teorell Membrane System
Authors: Drouin Herbert R. L. 
Published: July 2012

AbstractA system of two time‐dependent, first order differential equations of electrical membrane resistance and of hydrostatic pressure is derived. The equations are based on a set of flux equations for a 1,–1 valent electrolyte, combined with the equation of continuity, and the condition for conservation of mass. New insight into the functioning of the membrane oscillator is gained by the strict derivation of the relaxation equation of the averaged salt concentration with convection from the general partial differential equation. This relaxation equation is successfully transformed into the useful time‐dependent first order differential equation of the function of the electrical membrane resistance. Thereby the postulated relation for the concomitant changes of the electrical membrane resistance and the averaged salt concentration in the membrane phase is employed. The equations describe both the stationary and the non‐stationary states of Teorell's membrane oscillator. Particularly, the stationary pressure‐dependent, non‐monotonous current‐voltage curves and the current‐dependent, non‐monotonous pressure‐volume flux relations are calculated. These characteristics form the basis for mechano‐electrical transduction. Furthermore, the relaxation oscillations of membrane voltage, volume flux and hydrostatic pressure and the corresponding electroosmotic and hydrodynamic phase planes, representing stable limit cycles, are described. The stability criteria of the time‐dependent states are discussed.
Photoisomerization of Asymmetric Indobenzimidazolo Cyanine Dyes
Authors: Tatikolov Aleksandr S. , Derevyanko Nadezhda A. , Ishchenko Aleksandr A. , Baraldi Ivan , Caselli Monica , Momicchioli Fabio , Ponterini Glauco 
Published: July 2012

AbstractThe isomerization kinetics of three indobenzimidazolo polymethine cyanines have been investigated and compared with the corresponding properties of the parent symmetric dyes. A significant alternation of the π bond orders in the polymethine chain was found in the ground states (S0) of the asymmetric dyes. A similarly alternant behaviour was exhibited by the calculated S0 potential energy barriers for twisting around the polymethine chain bonds of the asymmetric carbocyanine, whereas uniform barriers were found for the symmetric parent compounds. The experimentally observed sequence of back‐isomerization activation energies was interpreted on the basis of these theoretical results. It was suggested by some spectral and kinetic fluorescence properties, and it was confirmed by the calculated polymethine‐chain π bond orders of the lowest singlet excited states (S1) that the electronic asymmetry induced by the different terminal heterocycles was strongly reduced upon excitation of these dyes to their S1 states. In spite of this, the trans‐cis photoisomerization of asymmetric cyanines occurred invariably around those bonds having the highest π bond orders in the ground state. A tentative theoretical explanation of this systematic behaviour is reported.
Recombination and Decomposition of Methylene Radicals at high Temperatures
Authors: Bauerle S. , Klatt M. , Wagner H. G. G. 
Published: July 2012

AbstractRecombination and decomposition of methylene radicals have been investigated over a wide range of experimental conditions. It has been found that H atom forming channels play only a minor role in the reactions investigated. The rate constants for the recombination channels CH2+CH2°C2H2+H2 (1a) and C2H2+2H (1b) have been determined to bek1a = 1015.2·.0.2Σ2·exp(‐(50±5) kJ mol−1/RT) cm3 mol−1 s−1k1b = 1014.3±0.2·exp(‐(46±5) kJ mol−1/RT) cm3 mol−1 s−lin the temperature range from 1100–2700 K.The H atom channel in the decomposition of methylene in argon leading to CH+H (2 b) has been found to bek2b = 1015.75±0.15·exp((‐375±15) kJ mol−1/RT) cm3 mol−1 s−lat temperatures between 1900–2700K. A comparison with literature data available for channel (2a) leading to C+H2 shows that the contribution of the H atom channel (2b) in the decomposition reaction of CH2 is around 10–15%. The energy of activation is in good agreement with the theoretically calculated value.
Aggregation of Pseudoisocyanine Chloride in Aqueous Solutions at High Pressures
Authors: Neumann B. , Pollmann P. 
Published: July 2012

AbstractThe aggregation behavior of pseudoisocyanine chloride (= PIC) (1,1′‐diethyl‐2,2′‐cyanine chloride) in dilute aqueous solutions was observed up to 375 MPa by absorption spectroscopy. From the pressure dependence of the dimerization constant the change in volume associated with the dimerization, Δ VD = −12.6 cm3·mole−1, could be obtained. By means of this value of ΔVD the interplanar spacing of the quinoline rings in the dimer was estimated to 3.0·10−8 cm. At higher concentrations the pressure dependence of the pressure‐induced absorption‐band (Scheibeband) yields the volume contraction (Δ VS) caused by the aggregation. Evaluation of Δ VS/ Δ VD allows a rough determination of the mean aggregation number n of monomer units per Scheibe‐aggregate. n increases with increasing concentration of PIC. The values of n lie between 5 to 29.
Monolayers of Multichain Molecules: A Monte Carlo Study
Authors: Stettin H. , Schweigert T. , Wahab M. , Mögel H. J. 
Published: July 2012

AbstractThe aim of this work is to understand how the chain orientational order in monolayers depends on intramolecular connectivity. Therefore monolayers of one‐, two‐, three‐, and four‐chain flexible molecules have been simulated using the Monte Carlo technique. The chains are linked up in the head group region. Three‐ and four‐chain molecules can have both: linear rigid as well as flexible head groups. The simulations were carried out within a lattice model on the simple cubic lattice. Only the excluded volume effect was taken into account. For the calculation of the orientational order we used end‐end vectors of each chain in the molecule and vectors pointing from the centre of mass of the whole molecule to the centre of mass of the head group. If the chains in the molecules have equal lengths the degree of order calculated from end‐end vectors is neither influenced by connectivity in the head group region nor by the flexibility of the head group. The degree of order based on the centre of mass vectors clearly indicates an effect of the intramolecular connectivity and for short chains also an influence of the flexibility of the head groups.
A Novel Concept for Modeling the Time‐Temperature Dependence of Polar Order Relaxation in Nonlinear Optical Active Polymers
Authors: Winkelhahn H.‐J. , Servay Th. K. , Neher D. 
Published: July 2012

AbstractThe widely accepted concept of introducing a fictive temperature (Tf) to describe the structural relaxation below the glass transition temperature is transposed to explain the orientational dynamics of nonlinear optical (NLO) active chromophores in poled polymer systems. The influence of different thermal histories on the results of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) gives evidence for a direct connection between the structural relaxation as measured by DSC and the relaxation of polar order as measured by TSDC. With the fictive temperature being determined from the DSC experiments it is possible to relate the equilibrium dynamics of the NLO chromophores above the glass transition temperature as determined by dielectric spectroscopy to the nonequilibrium relaxation times of polar order relaxation below Tg over 12 decades in time. The obtained time‐temperature dependence for the relaxation times, based on Scherer's extension of the Adam‐Gibbs theory (AGV), shows a Vogel‐Fulcher behavior above Tg and an Arrhenius‐like behavior far below Tg. Below Tg the temperature dependence of the relaxation times of polar order is in excellent agreement with an empirically found modified Vogel‐Fulcher equation, which modeled the relaxation of polar order of different poled polymer systems in an universal manner. The AGV theory further offers a direct approach to introduce the influence of the thermal history on the time‐temperature characteristics of polar order relaxation.
Tris‐2,2′‐Bipyridylruthenium(II) Peroxydisulphate as a Photosensitizer in the Oxidative Degradation of 4‐Chlorophenol
Authors: Silva M. I. , Burrows H. D. , Miguel M. Graça , Formosinho S. J. 
Published: July 2012

AbstractThe photolysis of aerated aqueous solutions of 4‐chlorophenol in the presence of Ru(bpy)2+3 and peroxydisulphate has been followed by UV/visible absorption spectroscopy, and reveals a relatively rapid oxidative decomposition of the phenol. Confirmation of the formation of benzoquinone and dihydroxybenzene as the principal products comes from product separation and spectroscopic characterization, HPLC, and TLC. 4‐Chlorocatechol is also produced, while the main inorganic products are shown to be chloride and sulphate ions. Ru(bpy)2+3 is regenerated in the reaction scheme, making this an overall catalytic process. Prolonged irradiation leads to further degradation into CO2 and HCL. From the study of the kinetics of the reactions and considerations of literature data, a mechanistic scheme is presented.
I. Experimental Facts: Water‐Nonionic Surfactant Systems, and the Effect of Additives
Authors: Strey R. 
Published: July 2012

AbstractIn this introductory article we approach microemulsions from the binary water‐surfactant side. Model systems of the water ‐ nonionic surfactant (CiEj) type are examined. Many features of microemulsions are observable in these binary systems. As such we discuss the dependence of the cloud points on i and j, the temperature dependence of the viscosity within the micellar phase, and the formation of dilute bilayer phases. The effect of additives is examined, as it permits to gain insight into the structures and interactions. Towards the end of the paper the most important additive for microemulsion formation, the oil, is considered. A special feature of long‐chain surfactants is highlighted, namely, non‐monotonic critical lines leading to very peculiar two‐phase lobes as precursors to the formation of the three‐phase bodies.
Wetting, Unbinding, and Ultralow Tensions in Amphiphilic Systems
Authors: Schick M. 
Published: July 2012

AbstractWetting phenomena in ternary amphiphilic systems is reviewed with a particular emphasis on the effect of fluctuations on the location of the wetting transition, both in balanced and unbalanced systems. A rich prewetting behavior, yet to be observed, is also described. Unbinding transitions of lamellar phases in these systems are related to their wetting counterparts, and the possibility of observing a pre‐unbinding transition is discussed. It is shown that were a complete unbinding of a lamellar phase to occur, the interfacial tension between oil and water phases coexisting with it would be identically zero. It is argued that the origin of the ultralow interfacial tensions in strong amphiphilic systems is the proximity to such an unbinding transition, one which is prevented by van der Waals forces. A consequence of this assumption is that the interfacial tension between oil and water phases coexisting with a structured phase of given wavelength should vary as the inverse square of that wavelength, a result confirmed by experiments on microemulsions.
Theory of Vesicles and Droplet Type Microemulsions: Configurational Entropy, Size Distribution, and Measurable Properties
Authors: Kegel Willem K. , Reiss Howard 
Published: July 2012

AbstractA model of vesicles and droplet type microemulsions is presented. It is shown that the size distribution of the droplets (either vesicles or microemulsions) coexisting with excess fluid is determined in general by only two terms: the free energy of the interface between the drops and the continuous phase, and a size dependent entropic factor commonly referred to as ‘the entropy of mixing’. The last mentioned term arises from translational configurations of the droplets. In this work we use an estimate of the translational contribution as derived in earlier work. A conjecture of the finite size effects coupled to the entropy of the interfacial layer is made based on experimental data.We treat the summation over the size distribution as an ‘effective partition function’ from which all relevant measurable properties are calculated. The necessity of invoking a curvature dependence of the interfacial tension is proved. For vesicles, their average size is shown to scale as the volume fraction raised to a universal power, whereas their polydispersity is fully determined by a universal coefficient.Because of the existence of a finite preferred curvature, no such universal behavior is found for microemulsions. Approximate analytical expressions for their size, interfacial tension of the planar oil‐water interface, and polydispersity are obtained. A limit (though not a physical one) is found at which universal behavior is recovered.The model is compared to experimental data found in the literature. Quantitative comparison reveals full agreement at a consistency level. Good agreement is found even when using only a single free parameter in the theory.However, this comparison points to an additional size independent term in the size distribution.