bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraslow Relaxation Phenomena in Gels
Authors: Dorfmüller Thomas , Stellbrink Jörg
Published: July 2012

The dynamics of a polyacrylamide gel was studied by means of photon correlation spectroscopy. The gels display, in addition to the relatively fast modes observed with the correlator, very slow intensity fluctuations which appear to be constitutive of the equilibrium dynamics of these systems. The relation between the gel mode as described in the Tanaka theory, the mode ascribed to the diffusion of latex particles introduced into the gel and the ultraslow modes is discussed.
Scaling Behaviour of Structural Relaxation near the Glass Transition: A Critical Analysis
Authors: Mezei F.
Published: July 2012

Inelastic neutron scattering has proved to be a powerful tool for exploring the characteristic dynamics in glassy systems on the time and length scale of atomic motions. Results obtained in a number of chemically very different sample systems of the fragile glass category reveal a catalogue of common features including a complex structural relaxation pattern. This relaxation pattern displays a two step nature, tentatively identified with the “α” and “β” relaxation processes, as predicted by recent mode coupling theories. The data also show a remarkable compatibility with the theoretically predicted scaling features, which partially corresponds to the so‐called time‐temperature superposition property. In this respect there is a contradiction between the neutron scattering results and macroscopic type relaxation experiments. A critical analysis of new, extended neutron data in an archetypical ionic glassy system reveals that in a broader temperature range deviations from the time‐temperature superposition scaling become evident and, in addition, considering worst case errors, there remains no hard evidence for the asymptotic validity of scaling near a critical temperature. Thus, even if the compatibility of neutron scattering and mode coupling results is impressively broad, in the light of an advocatus diaboli approach the remarkable two step character of the structural relaxation and the roughly wavenumber independent dynamics only remain as real and arguably decisive evidence in favour of mode coupling theories.
A Redetermination of the Rate Constant of the Reaction F + HNO3 → HF + NO3
Authors: Becker E. , Benter Th. , Kampf R. , Schindler R. N. , Wille U.
Published: July 2012

The rate constant k(1) of the reaction F + HNO3 → HF ± NO3 at 298 K has been redetermined using two fast flow systems employing different detectors. In the first, growth of NO3 was measured by mass‐spectrometric detection of the ion signal at m/e 62. In the other, the decay of F‐atoms was measured by following their ESR signal. Uncoated quartz flow tubes were used in both cases. The reactants were kept in the range 12 < [HNO3]/[F] < 140 in all experiments such that pseudo‐first‐order evaluation of the data was possible and secondary reactions were suppressed. A total of 52 experiments with [HNO3] in the range (2.5–8.2) · 1013 cm−3 yielded k(1) = (2.2 ± 0.2) · 10−11 cm3 molecule−1 s−1, where the error stated is the random error 2σ for 96% confidence limit. Model calculations have shown that the systematic error in k(1) due to secondary reactions is less than 2%. The total systematic error in k(1) is estimated to be 10%. The effect of poisoning the flow tube with halocarbon wax was studied in a few experiments and an interpretation for the observation is suggested.
Lower Critical Solution Point in Aqueous Mixtures: Enhanced Water Activity
Authors: Balevicius Vytautas
Published: July 2012

Some aspects of the lower critical solution point (LCSP) of binary aqueous mixtures have been studied by means of renormalization‐group (RG) and decorated lattice (DL) methods. The fitting of symmetrized experimental and calculated coexistence curves has revealed the advantage of the DL method. A new theoretical approach‐enhanced water activity, i.e. the activity of water being much higher than that of the second component, has been developed yielding satisfactory agreement with unsymmetrized experimental composition (in mole fractions)‐vs.‐temperature curves in the vicinity of LCSP. It has been shown that the lower critical concentration is determined by the coordination number of the primary lattice. Thus, the information about the structure of the solution is being lost by the symmetrization. It follows that the second component containing oxygen, i.e. atom with two lone‐pairs of electrons, stabilizes the ice‐like structure of the solution. In the case of components with nitrogen atoms (one lone‐pair) the structures with the higher coordination numbers are realized.
Order Parameters of Guest/Host Systems from UV Spectra – A Test of a New Method and its Application to Rigid Guest Molecules –
Authors: Kuball H.‐G. , Junge M. , Schultheis B. , Schönhofer A.
Published: July 2012

For a determination of the order parametersS*,D* of nematic guest/host phases from polarized UV and sometimes IR spectroscopy, the experimental information is often not sufficient because of overlapping absorption bands. For molecules with only one purely polarized band, the temperature dependence of the degree of anisotropy and a theoretical relationD* =f(S*) can be used to overcome this lack of information. A method introduced earlier [7] is examined with respect to its range of applicability. It can be shown that in the region of overlapping bands an amount of about 30% of the band with the proper polarization direction is sufficient to determineS* andD* with an error of at most 2 to 5% and 5 to 10%, respectively. The temperature dependence ofS*,D* for the rigid molecules azulene, phenanthrene, anthracene, 9,10‐dichloro‐, 9,10‐dibromo‐, 9,10‐dimethylanthracene, phenazine, and acridine in ZLI 1695 has been determined. Three different types of structural dependence can be derived from the experimental data.
Berechnung des zweiten Virialkoeffizienten B(T) für gasförmigen molekularen Wasserstoff im Temperaturintervall von 1 K bis 3000 K
Authors: Artym R. , Kliem M.
Published: July 2012

The second virial coefficient B(T) of hydrogen (H2) has been calculated at temperatures over the range 1 K to 3000 K using the Woolley potential function. The potential constants ε/k = 28,79 K, rm = 0,34473 nm, e1 = 0,01 have been determined from the B(T)‐data of Michels et al. (1959). The calculated second virial coefficients B(T) agree very well with the available experimental data over the whole temperature range from 13 K to 3000 K. A new method of calculating second virial coefficients has been suggested for low temperatures based on the representation of (y–y0)/(x–x0) vs x by a straight line (x = T1/2, y = T5/4 B).
Ultrathin Metal Films: From One to Three Dimensions Plenary Lecture
Authors: Bauer E.
Published: July 2012

The growth, structure, thermodynamic and electronic properties of ultrathin metal films is discussed, starting from the submonolayer range up to thicknesses at which bulk properties are reached. The following topics are selected from the wide field of phenomena: one‐dimensional crystals, shape and stability of twodimensional crystals, film‐substrate and lateral interactions, electronic structure and bonding, structural transitions and quantum size effects. The substrates used are mainly W(110), Mo(110) and Si(111) surfaces, the film materials several fcc metals.
Interface Properties of Thin YBa2Cu3O7–x Films
Authors: Ziegler Ch. , Frank G. , Göpel W.
Published: July 2012

Structures and stability ranges of the YBa2Cu3O7–x interface were studied with AES, SIMS, XPS, and TEM. For silicon substrates, the formation of Ba silicates can be detected which even at T = 550 K leads to reduced Tc values and non‐epitaxial growth of YBa2Cu3O7–x (YBCO). Yttria stabilized zirconia (YSZ) buffer layers between Si substrates and YBCO lead to epitaxial overlayer growth and improved superconducting properties whereas CaF2 is not suitable for this purpose.—Furthermore, SiO2, YSZ, and CaF2 were tested for their suitability as passivation layers against the influence of humidity. As‐passivated superconducting films are stable up to 500 K in 100% humid air. Above this temperature the superconductor is reduced chemically. Non‐passivated films, however, are stable only at temperatures below 450 K and are destroyed totally in humid air at higher temperatures.
CO2 Laser Chemical Vapor Deposition of Amorphous Silicon: Gas Phase Processes and Thin Film Properties
Authors: Golusda E. , Lühmann K.‐D. , Mollekopf G. , Stafast H. , Wacker M.
Published: July 2012

CW CO2 laser CVD of a‐Si:H was performed in a parallel configuration of the substrate and a horizontal CO2 laser beam. During deposition in situ gas analysis was performed by sampling through an orifice in the substrate surface (Ts = 400 °C) using a molecular beam and mass spectrometry. Time resolved measurements revealed a start‐up period of several minutes. Its influence onto the a‐Si:H film quality was investigated with respect to the dark and photo conductivities, optical band gap, fermi level, hydrogen bonding in SiH and SiH2 groups, density of defects in the mobility gap, and Urbach energy.
The Phase Behaviour of Amphiphilic Monolayers
Authors: Peterson I. R.
Published: July 2012

Amphiphilic monolayers display a wealth of condensed phases. It is only recently that these have been widely recognised as being distinct, but they are in fact quite analogous to the well‐known lamellar gel phases of bulk lyotropic and thermotropic mesogens. An understanding of these phases has proved to be important for controlling the defect structure of the monolayers used in the fabrication of Langmuir‐Blodgett films. This understanding is being achieved by developments in a number of techniques, including X‐ray diffraction and isotherm miscibility. The phase diagrams of the materials studied so far are all very closely related, lending new credibility to the principle of corresponding states, which although proposed on many occasions, has not until now received much in the way of quantitative confirmation.
On the Electrostatic Component of the Adhesional Interaction between Solid Substrates and Langmuir Monolayers
Authors: Riegler Hans , Eugel Maria
Published: July 2012

The work of adhesion between Langmuir monolayers and solid surfaces in a hydrophilic Langmuir‐Blodgett configuration has been measured as function of the surface charge densities σ of the contacting surfaces. It was derived from the equilibrium meniscus height which was measured with the transfer fluorescence microscope. The surface charge density of the contacting surfaces was varied by changing the subphase pH. With both surfaces negatively charged (dimyristoylphosphatidylethanolamine onto SiO2‐substrates) and low charge densities (σ < 1 e−/100 Å2)) we observe a decrease of the adhesion with increasing charge density. At high charge densities (dimyristoylphosphatidic acid onto SiO2‐substrates, σ < 1 e−/100 Å2) the work of adhesion is hardly affected by charge density variations, as theoretically predicted for electrostatic double layer forces. Systems with only one surface of varying negative charge density (dipalmitoylphosphatidylcholine onto SiO2) unfold the predicted decrease of the work of adhesion with increasing charge density. Control experiments with varying pH and uncharged surfaces (dipalmitoylphosphatidylcholine onto polymethylmethacrylate surfaces) show a pH‐independent work of adhesion and thus corroborate that the measured behaviour is caused by the electrostatic double layer interaction.
Scanning Tunneling Microscopy of the Initial Stages of Metal Condensation on Semiconductor Surfaces Progress Report
Authors: Brodde A. , Harazim E. , Kliese R. , Röttger B. , Neddermeyer H.
Published: July 2012

After a brief description of the theoretical and experimental basis of scanning tunneling microscopy (STM) typical results from the initial stage of metal condensation on semiconductor surfaces will be presented. As substrates Si(111) and Si(100) are used. Their reconstruction is explained by the current atomic models and compared with STM images of the clean surfaces. While the 7 × 7 reconstruction of Si(111) can be prepared with a defect concentration in the order of 0.03% of a monolayer, Si(100) shows a higher density of imperfections by at least one order of magnitude. STM images from nonreactive systems (Ag/Si(111) and Ag/Si(100)) are described and from a reactive system (Fe/Si(111)), which forms well defined silicides. In case of Ag/Si and room temperature condensation the initial stage is characterized by a two‐dimensional interface layer, which does not cover the substrates completely and the growth of rather regular three‐dimensional Ag islands, whose shape is consistent with metallic character. After Fe deposition on Si(111) the surface is covered by islands, which due to their irregular size and shape indicate compound formation or intermixing with Si. After annealing Fe/Si(111) shows the development of well ordered Fe silicide layers.
Time Evolution of :CF2 in the IR Multiphoton Dissociation of CF2Cl2: RRKM Considerations
Authors: Chowdhury Pradyot Kumar
Published: July 2012

The CO2 laser induced multiphoton dissociation of CF2Cl2 takes place in atomic and molecular chlorine elimination channels, with about 8% of the reaction by the latter channel. Time resolved experiments show a fast formation of :CF2 from the primary reaction, followed by a secondary slow growth from the decomposition of CF2Cl. The experimental rates are consistent with the RRKM rate constants with an excitation energy of nearly 343 kJ/mol in CF2Cl2. At high laser fluences, addition of argon has improved the dissociation yield, due to rotational hole filling mechanism. The internal energy of CF2Cl2 decreases from 356 to 343 kj/mol on addition of argon as buffer gas. The nascent vibrational temperature of the CF2 is 950 K, whereas an overall temperature of the thermalized ensemble in milliseconds time is computed to be 480 K.
Cationic Self‐Diffusion in the Metastable Ionic‐Plastic Phase of CH3NH3Br Studied by 1H NMR
Authors: Tansho Masataka , Nakamura Daiyu , Ikeda Ryuichi
Published: July 2012

The plastic nature of the highest‐temperature metastable phase of CH3NH3Br obtainable above 483 K was studied by X‐ray diffraction, differential scanning calorimetry, and 1H NMR spin‐lattice and spin‐spin relaxation time measurements. The CsCl‐type cubic structure determined for this phase implies the presence of highly disordered cationic orientations in accordance with the reported results in the other ionic‐plastic crystals. 1H NMR relaxation times observed in this phase were well explained by the motional model of the slow translational self‐diffusion and rapid overall rotation of the CH3NH3+ cations. The obtained activation energy (51 kJ mol−1) and correlation times (1.1 · 10−8 s at the melting point) were shown to be reasonable values as compared with those in stable plastic crystals. The melting condition derived from the dynamic parameters obtained in molecular and ionic plastic crystals was generally discussed.
Interactions in Dodecylammonium Chloride/Dodecyl Sulfate Systems
Authors: Filipović‐Vinceković N. , Škrtić D. , TomaŠić V.
Published: July 2012

Phase boundaries for mixtures of dodecylammonium chloride (DDACl) and sodium dodecyl sulfate (NaDS) are determined over a wide range of concentrations. The phase behavior strongly depends on the molar ratio and concentration of surfactant present. In the range of concentrations where monomer‐micelle equilibrium prevailed the mixed micelles of different composition are formed. The addition of oppositely charged surfactant enhance the apparent degree of counterion dissociation (α). Results reveal the existence of asymmetry on NaDS‐rich systems; more pronounced shift of CMCNaDS with DDACl addition, higher increase of αNa values and the two regions of mixed micelles formation. The deviation of precipitate‐solubility boundary from linearity is explained by phase transitions from precipitate and coacervate to mixed micelles. The concentrations at which coacervate is formed are lower than it would be found in the absence of DDADS.
A Characterization of the Aliphatic/Hydroxyl Interactions using a Group Contribution Model (Disquac)
Authors: Gonzalez J. A. , Garc Fuente I. ÍA De La , Cobos J. C. , Casanova C.
Published: July 2012

The data available in the literature for the molar excess Gibbs energiesGE, azeotropes, molar excess enthalpiesHE, activity coefficients γi∞, and partial molar excess enthalpiesHiE,∞, at infinite dilution, and molar excess heat capacitiesCpE, of n‐alkan‐1‐ol (1) + n‐alkane (2) mixtures are examined on the basis of the DISQUAC group contribution model. Being available the interaction parameters for systems containing methanol or ethanol, we report the interchange coefficients from propanol to hexadecanol:Cah.1DISandCah,1QUAC(1 = 1,2 or 3). For the dispersive coefficients:Cah,1DISincrease with the size of the n‐alkan‐1‐ol;Cah,3DISdecrease as far as propanol, and then increase regularly, an opposite behaviour is encountered forCah,3DISthe quasichemical coefficients:Cah,1.DISandCah,3.DISare constant, andCah,3CUACvaries in a similar way to the maximum of theHEof the mixtures under study; from decanol, they are constant. The model describes consistently the molar excess functions for the systems investigated, even theCpEand, qualitatively, the temperature dependence of this magnitude. Partial molar excess quantities at infinite dilution are reasonably well represented. Larger differences are obtained forH1E,∞.
Comment on the Low Lying Singlet States of Acenaphthene
Authors: Swiderek Petra , Hohlneicher Georg
Published: July 2012

In the absorption spectrum of acenaphthen the onset of the second singlet transition is obscured by a strong overlap of the S1and the S2band. Comparison of absorption spectra taken in solution and in the gas phase allows an identification of the 0–0 transition of S2through the different solvent shift of S1(120 cm−1) and S2(1200 cm−1). The gas phase spectrum is shown up to 48000 cm−1.
Analysis of the Phase Diagrams of Mixtures of a Nematic Liquid with n‐Alkanes
Authors: Orendi H. , Ballauff M.
Published: July 2012

The complete phase diagrams in liquid range of mixtures of the nematic liquid crystal 4,4′‐azoxyanisole (PAA) with n‐dodecane, n‐octadecane, and n‐tetracosane have been determined. The experimental results are analyzed quantitatively in terms of a theory based on the Flory lattice model of nematic fluids. It is shown that all features present in the experimental phase diagrams are in accord with the theoretical predictions. Nearly quantitative agreement of theory and experiment can be reached if a concentration‐dependent interaction parameter is used to describe the isotropic interaction between the nematic liquid crystal and the dissolved n‐alkane.
Electrochemical Analysis of Anomalous Conductivity Effects in the AgClAgI Two Phase System
Authors: Lauer Ute , Maier Joachim
Published: July 2012

The overall conductivity of the system AgCl/AgI is studied and distinct anomalies are found in the miscibility gap (Ag+‐conductivity enhancement up to 1.5 orders of magnitude). An impedance spectroscopic investigation accompanied by studies of phase diagram and microstructure proposes two main conclusions: i) the conducting interfacial pathways are composed of homo‐ (AgX/AgX) and hetero‐(AgX/AgX′) contacts, both exhibiting enhanced conductivities (compared to AgCl and β‐AgI bulk). ii) Both pathways are characterized by vacancy conduction in the relevant space charge layers.
The Phase Diagram of the Quasiternary System (ZnkCd1–k)(SelTl1–t)
Authors: Leute Volkmar , Wulff Birgit
Published: July 2012

The Phase Diagram of the Quasiternary System (ZnkCd1–k)(SelTe1–l) in the temperature region 800 K ≤ T ≤ 1300 K is investigated by X‐ray measurements and by electron microprobe analysis. Experimental results concerning the miscibility gap between phases with zincblende and wurtzite structure and concerning the spinodal miscibility gap within the zincblende region are compared with calculations of the equilibrium tie line fields based on a four particle cluster model. – Moreover, calculated distributions of cluster probabilities are used to explain special features of the phase diagram.
Solubility of Hydrogen in Palladium‐Yttrium‐Silver Alloys
Authors: Sakamoto Y. , Ishimaru N. , Inoue Y.
Published: July 2012

Thermodynamic quantities for absorption of hydrogen by Pd95–xYxAg5 solid solution alloys with up to x = 6.3 at.% Y have been determined from measurements of pressure‐composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 1000 Torr. The hydrogen absorption characteristics have been compared with those of the previously reported Pd–Ag and Pd–Y binary alloys. The relative partial molar enthalpy, ΔHH0, at infinite dilution of hydrogen in Pd95–xYxAg5 alloys increases in exothermicity with increasing Y content from that of Pd–5.0 at.% Ag, almost parallel to that in Pd–Y binary alloys. The relative partial molar entropy, ΔSH0, at infinite dilution in the ternary alloys decreases with Y content from that of Pd–5.0 at.% Ag alloy. The hydrogen solubility behavior at low hydrogen concentration in the Pd–Y–Ag alloys under a “constant volume” condition can be described as due to mainly the strong H–Y attractive pair interaction in the Pd host lattice. The stability of β‐hydride and hydrogen concentration at αmax phase boundary increase following alloying with Y from that of Pd–5.0 at.% Ag alloy, respectively, and the changes in the properties with Y content are similar to that in Pd–Y binary alloys.
e Effect of Alkyl Groups on Carbanion Stability Part I. Interaction of Small Rings with Adjacent Carbanion Centers
Authors: Balcioǧlu Nurettin , Sevin Fatma , Evin Özden , Peynircioǧlu N. Bekir
Published: July 2012

Relative kinetic acidity measurements have shown that the cyclobutyl group has the ability to stabilize an adjacent carbanion center similar to vinyl and cyclopropyl groups, although to a lesser extent. The results of semiempirical calculations (MNDO) covering all the mentioned substituents, including the isopropyl group correlate well with the experimentally determined relative kinetic acidities.
Multinuclear Spin‐Lattice Relaxation Studies of Undercooled Aqueous Potassium Fluoride Solutions Under High Pressure
Authors: Radkowitsch H. , Lang W.
Published: July 2012

In this investigation we report2H,1H and19F spin‐lattice relaxation (SLR) rate experiments performed in undercooled aqueous KF‐solutions of concentrationc≤ 12 molal under an external pressure ofp≤ 225 MPa. The relaxation rate curves of the various nuclei are consistently interpreted with a two mode – two site approximation of the dynamic structure of the H‐bond network in these ionic solutions. The local arrangement of water molecules coordinated to an F−‐anion can be obtained from Fluor‐19 relaxation rate curves and is found to correspond to an almost linear ion‐water configuration. This finding is in accord with predictions from theory and computer simulations and corrects earlier findings from other NMR experiments.
Gas Phase Reactions of Transition Metal Clusters
Authors: Riley S. J.
Published: July 2012

The chemical reactions of isolated clusters of transition metal atoms with small molecules will be reviewed. Reactions of iron, cobalt, and nickel clusters with hydrogen, ammonia, water, and nitrogen will be considered. Experiments which determine the uptake of adsorbate molecules vs. reagent gas pressure provide information on kinetic and equilibrium processes, as well as a measure of the number of adsorbate binding sites on a cluster's surface. More detailed, quantitative determinations of reaction rate constants often show dramatic variation of reactivity with cluster size. Equilibrium studies provide measurements of cluster‐adsorbate binding energies. A knowledge of the number of adsorbate binding sites often provides information about cluster geometrical structure.
Reactions of Alkali‐Halide Clusters
Authors: Whetten Robert L. , Homer Margie L. , Li Xiuling , Livingston Frank E. , St. John Pamela M. , Beck Rainer D.
Published: July 2012

This article reviews recent experimental work on reactive processes involving alkali‐halide clusters (AHC). The processes discussed include: adsorption of molecules on AHCs [1]; reactive collisions of alkali‐fluoride clusters with silicon surfaces [2]; and the primary photochemistry of alkali‐bromide and ‐iodide clusters [3,4]. Earlier work on evaporation and cleavage processes, and experiments on clusters with excess electrons, are not reviewed.
Chemical Reactions in Clusters Induced by Low Energy Electrons
Authors: Hashemi Reza , Jaffke Thomas , Illenberger Eugen
Published: July 2012

Electron attachment reactions in pure CF4 clusters and heterogeneous clusters composed of CF2Cl2 and O2 are studied. In the system CF4, effective energy randomization leads to the formation of CF monomers which occurs through dissipation of several electronvolts of excess energy among the target aggregate. From the mixed clusters, ions of the form ClO and ClO− are generated. ClO− is the result of a complex scattering reaction in the ionized aggregate associated with the cleavage of two chemical bonds and the formation of a new molecule.
Fragmentation Analysis of Size Selected Sodium Clusters
Authors: Bewig L. , Buck U. , Mehlmann Ch. , Winter M.
Published: July 2012

We investigate the fragmentation behaviour of size selected sodium clusters Nan, n ≤ 4, for different ionization methods. The experimental technique, size selection by means of scattering the cluster beam from a helium target beam and subsequent time resolved measurement of the scattered particles, enables us to find a unique correlation between the detected cluster ions and their neutral precursors. In the case of photoionization we use the light from a Xe‐arc lamp in a broad spectral range down to a wavelength of about 220 nm, whereas for the pulsed, frequency doubled dye laser the wavelength is tuned to 290 nm. Electron impact ionization has been examined with an electron energy of 25 eV, which is far above the ionization threshold of all sodium clusters. The ionization by electron impact with the large excess energy results in a total fragmentation of the sodium trimer. In the case of photoionization the fragmentation probabilities do not follow always the energetically favoured pathways, which will be demonstrated for the sodium tetramer.
Clusters of Divalent Elements: Electronic Properties of Cdx‐Aggregates
Authors: Rademann K. , Ruppel M. , Kaiser B.
Published: July 2012

We have recently succeeded in generating and detecting neutral cadmium clusters Cdx (x < 80) in a seeded supersonic molecular beam. The mass spectrometric abundances of photoionized clusters exhibit remarkable intensity variations. There are large intensity ratios for Cd10/Cd11 as well as Cd20/Cd21 indicating the closing of electronic shells with 20 and 40 electrons. The photoelectron spectra of neutral cadmium clusters show the formation and filling of shells, indeed. Discrete electronic states (2s2) have been observed directly in the photoelectron spectra of mass specified Cd10 clusters. Pronounced electronic shell closings are also clearly observed for clusters with 70 electrons (Cd35), 92 electrons (Cd46, and 138 electrons (Cd69). Furthermore, we have obtained quantitative information on the size dependence of ionization potentials and photoionization cross sections. The ionization potentials (7.7 ± 0.1 eV for the dimer Cd2 and 5.0 ± 0.1 eV for Cd46) decrease rapidly but rather smoothly with increasing cluster size.
The ZEKE Spectrum of the Phenol‐Water Cluster
Authors: Dopfer Otto , Reiser Georg , Lindner Reiner , Müller‐Dethlefs Klaus
Published: July 2012

The vibrational spectrum of the hydrogen bonded phenol‐H2O cation cluster is obtained by two‐colour resonant pump‐probe ZEKE spectroscopy (“Zero Kinetic Energy” Photoelectron Spectroscopy). The results are a well resolved vibrational spectrum assigned to intermolecular modes and an accurate value of the adiabatic ionisation energy.
Theoretical Interpretation of Optical Response Properties of Simple Metal Clusters
Authors: Bonačić‐Koutecký V. , Fuchs C. , Pittner J. , Koutecký J.
Published: July 2012

The ab‐initio configuration interaction study of excited states of small alkali metal clusters accounts fully for the spectroscopic patterns recorded by depletion or/and femtosecond spectroscopy and permits geometrical assignment. Specific structural and electronic properties responsible for excitations in small Ia/IIa clusters allow for the interpretation of theoretical and experimental findings in the framework of a molecular many‐electron description. Similarities and differences between optical response properties of Lin and Nan clusters are discussed. The influence of the position of a divalent heteroatom in the geometrical structures of NaxMg clusters on spectroscopical patterns will be presented. The reliability of simplified methods such as random phase approximation (RPA) and multiconfigurational linear response method (MCLR) for optically allowed transitions in metal clusters has been examined.
Time‐resolved TPI‐Spectroscopy of the B‐ and D‐State of Na3‐Clusters
Authors: Schreiber E. , Kühling H. , Kobe K. , Rutz S. , Wöste L.
Published: July 2012

The dynamical behaviour of excited states of cold Na3‐clusters in the gas phase was investigated in a transient two‐photon‐ionization (TPI)‐experiment, employing picosecond pump technique followed by mass‐selective detection. The results exhibit for the first time the pseudo‐rotational motion of the B‐state as a temporal sequence. The precise measurement of the beat frequencies affirms a pseudo‐Jahn‐Teller‐model for the interpretation of the spectroscopic data. For the D‐state, known to predissociate very rapidly the temporal evolution of fragmentation directly could be observed. Decay‐times of the TPI‐signal were estimated to be in the order of 5 picoseconds.
Elementary Reactions in the Methanol Oxidation System. Part II: Measurement and Modeling of Autoignition in a Methanol‐Fuelled Otto Engine
Authors: Driver H. S. T. , Hutcheon R. J. , Lockett R. D. , Robertson G. N. , Grotheer Horst‐Henning , Kelm Siegfried
Published: July 2012

The temperature inside the cylinder of a methanol‐fuelled single‐cylinder research engine running under knocking conditions is measured by means of Coherent Anti‐Stokes Raman Scattering (CARS) spectroscopy, and the pressure is measured with a piezoelectric transducer. In order to obviate any errors arising from possible deficiencies in the spectral scaling laws which are commonly used to represent nitrogen Q‐branch CARS spectra at high pressure, a purely experimental technique is employed to derive temperatures from CARS spectra by cross‐correlation with a reference library of spectra recorded in an accurately calibrated high‐pressure high‐temperature optical cell. — The temperature and pressure profiles measured in the running engine are then used as input data for chemical kinetic modeling of the endgas autoignition. Exactly the same exhaustive chemical mechanism and exactly the same rate coefficient expressions are used for the autoignition modeling as are employed in Part I [1] for the modeling of methanol flame velocities. A good qualitative understanding of the mechanism underlying endgas autoignition in the engine can be obtained, although the calculated autoignition point occurs slightly earlier than the observed point. — The importance in the autoignition mechanism of hydroperoxyl radical reactions and of the thermal decomposition of hydrogen peroxide is demonstrated by means of a sensitivity analysis. – For purposes of comparison, the autoignition modeling is also undertaken using earlier reaction schemes and rate coefficient data, notably those of Grotheer and Kelm (1989), Norton and Dryer (1989), Esser and Warnatz (1987), and Dove and Warnatz (1983). The discrepancies between results of the various models can be understood in terms of a very small number of sensitive reactions for which there are conflicting kinetic data.
Predicting the Gas‐Liquid Critical Properties of Binary Mixtures: An Alternative to Conventional Mixing Rules
Authors: Sadus Richard J.
Published: July 2012

The critical properties of binary mixtures are predicted using a theoretical alternative to the conventional mixing rules for the contribution of the attractive equation of state parameter for the mixture. The method does not require adjustable combining rule parameters and the only experimental input data are the critical properties of the component pure substances. The comparison of calculated critical properties with experimental data yields very good agreement. The discrepancy between theory and experiment is often similar to that obtained by using optimized adjustable combining rule parameters. Consequently, genuinely accurate a priori predictions of critical equilibria are possible for many binary mixtures containing either non‐polar or weakly polar components.
Spectroscopy and Thermodynamics of Electrons in Yttria‐Stabilized Zirconia
Authors: Wiemhöfer H.‐D. , Vohrer U.
Published: July 2012

Electronic energy gap, position of Fermi level in the gap and the density of states in the valence band range have been measured for Y2O3‐stabilized cubic ZrO2 as function of oxygen partial pressure and temperature using UV‐Photoelectron‐Spectroscopy (UPS) and Electron‐Energy‐Loss‐Spectroscopy (EELS). A thermodynamic evaluation for the position of the Fermi energy gives the scale of electrode potentials for oxygen electrodes on stabilized zirconia with regard to the band scheme. The data are compared with further literature results from electrochemical and spectroscopic techniques and a model for the electronic band scheme of yttria‐stabilized cubic zirconia is proposed. The differences of thermal and optical values for the band gap are discussed as well as the comparability of thermal and spectroscopic values for electronic energies.
On the Persistence of Molecular Symmetry in the Solid State and the Role of Molecular Group Dipole Moments. Centrosymmetry in Bis‐(Chloromethyl)benzenes
Authors: Basaran Rcha , Dou Sli‐Qi , Weiss Alarich
Published: July 2012

The crystal structures and the 35Cl NQR spectra of 1,4‐bis(chloromethyl)‐2,3,5,6‐tetrachlorobenzene, 1,4‐(CH2Cl)2C6Cl4; 1,4‐bis(chloromethyl)‐2,3,5,6‐tetramethyl‐benzene, 1,4‐(CH2Cl)2C6(CH3)4; 1,4‐bis(chloromethyl)benzene, 1,4‐(CH2Cl)2C6H4; 1,2‐bis(chloromethyl)benzene, 1,2‐(CH2Cl)2C6H4 are reported. – The compounds 1,4‐(CH2Cl)2C6Cl4 and 1,4‐(CH2Cl)2(CH3)4 are isostructural, space group C–P1, Z = 1. 1,4‐(CH2Cl)2C6Cl4: a = 893.1(4) pm, b = 655.1(3) pm, c = 494.5(2) pm, α = 98.32(2)°, β = 96.87(2)°, γ = 103.60(2) 92°; 1,4‐(CH2Cl)2C6(CH3)4: α = 902.3(4) pm, b = 809.4(4) pm, c = 442.5(2) pm, α = 87.38(2)°, β = 83.02(2)°, γ = 65.00(2)°. 1,4‐(CH2)2C6H4 crystallizes monoclinic, C–P21/c, Z = 2, a = 848.8(4) pm, b = 465.0(2) pm, c = 1042.2(5) pm, β = 99.21(2)°. 1,2‐(CH2Cl)2C6H4 is noncentrosymmetric, orthorhombic, C–Fdd2, Z = 8, a = 1562.0(4) pm, b = 1358.0(3) pm, c = 790.4(2) pm. – The 35Cl NQR spectra of 1,4‐(CH2Cl)2C6(CH3)4, 1,4‐(CH2Cl)2C6H4, and 1,2‐(CH2Cl)2C6H4 are singlets, with negative temperature coefficients dν(35Cl)/dT over the temperature range 77 K–Tmelt and the frequencies are in the range 34.4 ≥ ν(35Cl)/MHz ≥ 31.8. 1,4‐(CH2Cl)2C6Cl4 shows a 35Cl NQR triplet, with negative temperature coefficients for 77 ≤ T/K ≤ 420, 37.5 ≥ ν(35Cl)/MHz ≥ 33.8, too. In this compound a phase transition occurs, with a wide hysteresis, Tc, up = 366 K, Tc, down = 328 K. The inductive effect on the 35Cl NQR in the CH2Cl group is strong. – In molecular crystals the complete symmetry of the free molecule seldom persists in the solid state. The molecular symmetry in the condensation process is fully or partially lost due to the van der Waals interaction of neighboring molecules. The compensation of the partial dipole moments of the two chloromethyl group in para position retains the molecular symmetry Ī in the solid phases. It will be discussed that in benzene derivatives either Ī, m or 2 are the “hard” symmetry elements, preserved in the solid state.
Aggregation of Silver Particles in Silver Alginate Films
Authors: Yonezawa Y. , Kijima M. , Sato T.
Published: July 2012

The variation of the absorption spectra of silver alginate (SA) films upon irradiation with 253.7 nm light has been studied. When the SA film was photolyzed at room temperature (T = 300 K) in vacuum, the intense colloidal absorption band around λ = 407 nm due to large silver particles (metallic silver particles) appeared. Irradiation at liquid nitrogen temperature (T = 77 K) caused the growth of a small peak around 337 nm, together with a broad background absorption extending from 600 nm to less than 200 nm. Major products at low temperature seem to be small silver particles (relatively large silver clusters and quasi‐metallic silver particles). After photolysis at 77 K and heating until 300 K was achieved, the variation of the absorption spectrum of the SA film during dark storage in vacuum was monitored. The 337 nm peak was slightly decreased in the initial stage and then, the colloidal absorption band (415 nm) increased monotonously for 20 h. Rapid diffusion of silver atoms and clusters under irradiation in air at room temperature has been suggested.
Optically Detected Small‐Polaron Hopping in Manganosite, Mn1‐δO
Authors: Becker K. D. , He T.
Published: July 2012

The absorption spectrum of single crystalline MnO has been measured at 1000°C as a function of oxygen partial pressure, p. The observed p‐dependence of the spectra is discussed in the framework of the point defect structure of the compound. From the line‐shape of the defect‐induced contribution to the absorbance and from its p‐dependence it is concluded that this contribution is due to small‐polaron hopping of electron holes.
Dynamic Light Scattering Experiments with Aqueous Solutions of a Cascade Molecule: Benzene[9]3‐arborol
Authors: Engelhardt Th.‐P. , Belkoura L. , Woermann D. , Grimme W.
Published: July 2012

Results of dynamic light scattering experiments with aqueous solutions of benzene[9]3‐arborol (molar mass, M = 1.486 · 103 g mol−1; spherical dimension (radius) estimated on the basis of molecular models, a ≈︁ 1 nm) at 25° are reported. They indicate that benzene[9]3‐arborol molecules in aqueous solution form aggregates which have dynamic properties similar to that of single polymer chains in good solvents in the cross over region (q rh) ≈︁ 1 (q, absolute value of the scattering vector, (rh, hydrodynamic radius of the scattering particles). A double logarithmic plot of maximum value of the distribution of relaxation rates of the autocorrelation function of the scattered light intensity Γmax versus the q (0.68 ≤ (q/q+) ≤ 2.40; q+ = 105 cm−1) gives a straight line with a slope D* = (2.46 ± 0.05) independent of concentration (Γmax ∼ (q/q+)D*). The size of the scattering particles appear not to change with concentration in the concentration range studied (3.5 · 10−3c+ ≤ c ≤ 13.37 · 10−3c+; c+ = 1 mol dm−3). Values of D* (2 ≤ D* ≤ 3) indicate that the experiments are carried out in the non‐universal crossover regime (q rh) ≈︁ 1. From the ratio (Γmax/q2) refering to the limit q 0 a hydrodynamic radius of rh of the order rh = O(100 nm) is calculated. This is in agreement with the conclusion drawn from the q‐dependence of Γmax (i.e. (q rh) ≈︁ 1). – The partial molar volume of benzene[9]3‐arborol in aqueous solution increases with concentration only in very dilute solutions. It is practically constant in the concentration range in which the dynamic light scattering experiments are carried out. The surface tension of these solutions at the air/solution interface decreases only slightly with concentration reflecting the hydrophilic character of the surface of the aggregates.
Microscopic Origins of Photorheological Effects Induced by the Photoisomerization of Stilbene Carboxylic Acids in Aqueous Cetyltrimethylammonium Bromide Solutions
Authors: Kerperin Karl Josef , Wolff Thomas
Published: July 2012

Aqueous micellar solutions containing cetyltrimethylammonium bromide (CTAB) and solubilized 3‐stilbene carboxylic acid (3‐SC) or 4‐stilbene carboxylic acid (4‐SC) known to exhibit photorheological effects were investigated via (i) oscillatory shear viscometry, (ii) static and dynamic light scattering and (iii) electrically induced birefringence. The presence of 3‐SC and 4‐SC induces the formation of swollen micelles as revealed from light scattering data. The viscosity increase observed upon in situ photoisomerization of 3‐SC and 4‐SC is accompanied by a further increase in micelle size as shown by light scattering data. Only solutions containing 3‐SC at concentration ratios cCTAB/c3‐sc ≤ 6.5 show non‐Newtonian flow such as shear thinning, thixotropy and viscoelasticity, which are indicative of the presence of anisometric micelles. Photoisomerization induces non‐Newtonian features in systems containing 4‐SC and increases these features in 3‐SC solutions. Two shear stress relaxation mechanisms are resolved from relaxation spectra.
Estimation of Nitta‐Chao Interaction Parameters for Low Molecular Mass Analogues of Polymers. 1‐Chloroalkane + n‐alkane mixtures
Authors: Fernández J. , Pías L. , Paz Andrade M. I. , Legido J. L. , Lorenzana T. , Diez J.
Published: July 2012

Excess molar volumes at 298.15 K, vE, were measured for binary mixtures of a 1‐chloroalkane (from 1‐chloropentane to 1‐chloroheptane) with a n‐alkane (from n‐heptane to n‐decane). These vE values together with literature data on vapor‐liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing, excess capacities and excess volumes of 1‐chloroalkane + n‐alkane were examined on the basis of the Nitta‐Chao group‐contribution model. The properties of many other systems can be predicted using the CH2/Cl parameters determined in this paper. A comparison with the predictions of DISQUAC and UNIFAC (version of Larsen et al.) models is presented. The new data and the calculated parameters could be used for the predictions of thermodynamical properties of mixtures involving polymers.
On the Influence of Steps on the Rotational Anisotropy of the Second Harmonic Generation from Ag Electrodes
Authors: Friedrich K. A. , Richmond G. L.
Published: July 2012

The second harmonic generation (SHG) from stepped Ag(111) based surfaces in an electrolyte solution have been measured and analyzed. The rotational anisotropies from these surfaces show a pronounced effect due to the lowering of the surface symmetry relative to a (111) surface. The results from the stepped surfaces are interpreted in terms of a pseudo mirror plane. The SH response has also been measured during the underpotential deposition (UPD) of lead onto the stepped crystals and the results are compared to the well known Ag(111)/Pb2+ system. The SH response during adsorption on defect and terrace sites on Ag(111) are monitored separately and the contribution from the steps to the SH anisotropy is discussed.
Wavelength Dependent Second Harmonic Generation: A New Spectroscopic Tool for the Study of Interfaces
Authors: Buck M. , Eisert F. , Grunze M. , Träger F.
Published: July 2012

The adsorption of n‐hexadecane thiol on gold in ethanol has been examined by wavelength dependent second harmonic generation (SHG). In addition to the amplitude, the phase of the second harmonic signal has been measured. At fundamental wavelengths of 1064 nm and 532 nm the temporal dependence of the SH signal reveals that the second order susceptibility is linearly related to the thiol coverage. Between 610 nm and 660 nm a dramatic variation of the time dependent second harmonic signal both in magnitude and in phase is observed due to a coverage dependent resonance. The results demonstrate the potential of second harmonic generation as a spectroscopy for monitoring the effect of adsorbates on the electronic properties of surfaces.
In situ UV‐VIS‐Spektroelektrochemie an LIGA‐Strukturen
Authors: Neudeck A. , Dunsch L.
Published: July 2012

A new electrochemical cell for in situ UV/VIS‐spectroscopy using micro‐structurised metal foils (LIGA‐structures) as working electrodes is presented. With this new type of a spectroelectrochemical cell high‐sensitive spectroscopic studies of redox components can be carried out in the transmission procedure during dynamic electrochemical experiments. The capability of this new cell is shown for the electron‐transfer reaction of methylviologen and Wursters blue. The thin layer behavior of this cell is demonstrated.
Evaluation of the IR Attenuated‐Total‐Reflection (IR‐ATR) Technique for Detecting Adsorbates on Electrodes
Authors: Johnson Brian W. , Pettinger Bruno , Doblhofer K.
Published: July 2012

Theoretical spectroscopic responses of various different IR‐ATR crystal/metal combinations (Ge, BaF2/Pt, Au) in contact with a third medium consisting of an adsorbate and/or water have been calculated via the well known Fresnel formulae. The theoretical results are compared to experimental IR spectra. — The sensitivity for detecting the third phase in the IR‐ATR spectrum varies widely for the different systems. However, with all systems the highest sensitivity was found at an angle of incidence of the IR radiation close to the critical angle (defined by the crystal/solution combination). Adsorbates on the metal films were found to yield remarkably high IR‐ATR signals which should allow their convenient experimental detection.
Transient Spectroscopy of Donor‐Acceptor Complexes
Authors: Anders J. , Byrne H. J. , Reichenbach J. , Kaiser M. , Schmelzer M. , Wagner Th. , Roth S.
Published: July 2012

This paper gives an introductory review into molecular electronics, discussing shift registers and cellular automata as examples of long‐term goals. Langmuir‐Blodgett films of functionalised polyenes are presented as steps towards such final goals. The switching behaviour of some prototype molecules (in particular of substituted bianthrone) is investigated by transient spectroscopy in the picosecond regime.
An EXAFS Study of Binuclear Group VIA Complexes in Solution: Distinction Between Metal‐Phosphorous Single and Double Bonds
Authors: Ertel Teja , Hückmann Sabine , Bertagnolli Helmut
Published: July 2012

An EXAFS spectroscopical distinction between tungsten‐phosphorous single and double bonds in three binuclear group VIA complexes of the type R1R2P = MLn with R1=Mes, R2 = CpW(CO)2PH2Mes and MLn = CpW(CO)2 (compound 1) or R1 = Mes, R2 = CpW(CO)3 and MLn = CpW(CO)2 (compound 2) or R1 = Mes, R2 = CpW(CO)3 and MLn = CpMo(CO)2 (compound 3) in benzene solution is presented. The obtained distances are compared with results of X‐ray diffraction and 31P‐NMR studies.
Preparation of Thin Cation‐Exchanger Films from Benzenesulfonyl Fluoride by Glow Discharge Plasma Processes
Authors: Uchimoto Yoshiharu , Yasuda Kazuaki , Ogumi Zempachi , Takehara Zen‐Ichiro , Tasaka Akimasa , Imahigashi Takashi
Published: July 2012

Novel ultra‐thin films of a sulfonate cation exchanger were prepared by plasma polymerization followed by hydrolysis. The use of gas mixtures of 1,3‐butadiene and benzenesulfonyl fluoride or benzenesulfonyl chloride as starting monomers was investigated. Benzenesulfonyl fluoride was found to be adequate to introduce sulfonyl halide into plasma polymers, whereas benzenesulfonyl chloride tended to be decomposed during exposure to glow discharge plasma. The influence of the level of input RF power on the properties of the resulting cation‐exchange films was also investigated. The films produced using benzenesulfonyl fluoride has a cation‐exchange capacity of 1.45 meq g−1, which is comparable to those of commercially available cation exchange membranes.