bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of scaling for fluctuations in thermal explosion conditions
Authors: Fernandez Ariel
Published: March 2014

We demonstrate that fluctuations in the transient bimodality regime for gaseous thermal explosions scale with the inverse of an effective size parameter Ω. The ratio between this parameter and the volume V is obtained analytically for a nonturbulent heat conduction regime. We show that as the system departs from the laminar flow limit towards a turbulent regime, the fluctuations are enhanced since Ω decreases. We also prove that as V tends to zero, the ratio Ω/V tends to one, an intuitively expected result. The theory is inspired and confirmed by experiments on the decomposition of ethyl azide. Within the induction period, we use a corrected parabolic approximation for the potential determining the drift term in the Fokker‐Planck equation. The maximum occurs at the ignition temperature. The correction arises from size effects (Ω/V ≠ 1) due to an inhomogeneous distribution of temperature. The parabolic approximation is valid only within the induction period, until the fluctuations have macroscopic consequences. Our study reveals that the following anomalies bear a common origin that can be explained quantitatively if the correction is introduced: a) Discrepancy between the experimental and theoretical value for the Frank‐Kamenetsky constant. Early work by O.K. Rice on the gaseous thermal explosion of ethyl azide indicates that this discrepancy is enhanced when the size of the vessel increases. — b) Reduction of the induction period, or, equivalently, contraction of the time‐scale for the transient bimodality during which heat accumulates in the system. This anomaly is accompanied by an enhancement of the growth rate for the Gaussian width of the probability density distribution for the temperature due to fluctuations. This phenomenon will be interpreted by the observer as a premature ignition.
Kinetics of the isotrop‐nematic phase transition in liquid crystals. I. Nucleation theory of phase transition
Authors: Oranth Norbert , Strohbusch Frank
Published: March 2014

The kinetics of the isotropic‐nematic phase transition under adiabatic conditions is described by the nucleation theory with a rate law of droplet growth derived from the time dependent Landau‐Ginzburg equation. As an example the time evolution of the nematic phase in supercooled 8CB is calculated. The results reveal a strong dependence of the size distribution function of nematic droplets, on the temperature and also significant changes during the process. The completion times are much longer than under isothermal conditions.
Kinetische Untersuchungen zur Reversibilität der Makromoleküladsorption an der Grenzfläche Wasser/Luft
Authors: Nitsch Walter , Kremnitz Wilfried , Schweyer Georg
Published: March 2014

With measured changes of surface pressure of spreaded monolayers (Polyethylenglycol) on aqueous subphases in a Langmuir trough. the kinetics of desorption was studied for different states of compression. — Because of an observed strong influence of the forced convection and the verification of the second Pick's law for desorption into the quiescent bulkphase it is concluded, that the molecular diffusion controls the desorption. This result leads to the conclusion of an always established equilibrium between monolayer and subsurface corresponding to a reversible state. — With the diffusion law for the measured desorption it is possible to calculate the concentrations in the subsurface equilibrated with the monolayer. These subsurface concentrations are shown to be very strong dependent from the state of compression. With the equilibrium values it is possible to derive that the high stability of the layers are caused by the very low diffusion flux as a consequence of an very low equilibrium concentration in the subsurface.
Surface enhanced raman scattering at electrodes: A status report
Authors: Chang Richard K.
Published: March 2014

Progress during the first decade of surface enhanced Raman scattering (SERS) is briefly reviewed. Examples of SERS of adsorbed H2O. OH−, and H3O+ on Ag electrodes which have undergone an oxidation‐reduction cycle (ORC) are discussed in some detail in order to bring out the unique and general features of SERS in an electrochemical system. Experimental techniques to further enhance the SERS signal, as well as to decrease the SERS signal after an ORC, are reviewed as such results can provide clues to possible surface enhancement mechanisms. The two enhancement mechanisms (electromagnetic and charge transfer) are presented in a unified but simplistic picture which involves the nearly free s,p‐electron band and the more localized d‐electron band for the noble metals (Ag, Cu, and Au). The role of the intraband transitions in the electromagnetic and charge transfer enhancement processes is discussed in terms of the wave‐vector uncertainty associated with the Raman dipole located on or near the surface and with the localized metal clusters which are often referred to as SERS‐active sites. Several examples are cited in which experiments initially designed to prove the presence of one enhancement mechanism end up proving the existence of both enhancement mechanisms. Progress expected in the SERS field during the next decade is also suggested.
Infrared reflection‐absorption spectroscopy of adsorbed species on electrode surfaces using a laser source
Authors: Sass J.‐K. , Roe D. K. , Bethune D. S. , Luntz A. C.
Published: March 2014

A substantial increase in optical sensitivity of infrared reflection‐absorption Spectroscopy (IRRAS) was achieved by the combination of a pulsed, tunable infrared laser and a novel thin layer cell which was designed to provide uniformity and control of solution layer thickness. The importance of these cell parameters is illustrated by optical model calculations and experimentally verified by vibrational spectra of CO adsorbed on Pt electrodes. Peak values of relative reflectance changes exceeding 10% were obtained at near‐monolayer coverages without any modulation technique. In view of these results, the ramifications of the wide range of incidence angles and of the lack of precise control of solution layer thickness in previous IRRAS studies are examined with regard to spectral fidelity and response to potential transients.
Ellipsometric study of the growth of thin organic polymer films
Authors: Hamnett Andrew , Hillman A. Robert
Published: March 2014

Ellipsometry has been used to study the contrasting electrochemical growth mechanisms and properties of two organic redox polymer films on Pt. The first part of the work is a study of the anodic polymerisation of thionine from aqueous solution. Initially, a monolayer of PtO is formed on the electrode. Thereafter uniform growth of polythionine proceeds under diffusional control, as evidenced by the square root dependence of film thickness on time. Quantitation of this relationship shows that the film contains ∼50% (by volume) organic polymer, ∼25% counterions and ∼25% H2O. Reduction requires additional counterion ingress, but the absence of significant expansion implies some solvent loss. Optical properties of the film are rather similar to those of the monomeric redox system and show a Nernstian potential dependence, in agreement with coulometric data. The second part of the work is an analogous study on the polymerisation of thiophene from CH3CN solutions. This process is kinetically controlled. At short times there is evidence for nucleation. At longer times, nuclei overlap and uniform growth is indicated by a linear increase of film thickness with time. The evolution of polymer optical properties during this process was monitored. Optical properties of both redox states were determined at several wavelengths and contrast markedly with parameters for the monomer. Switching between redox states is rapid and involves swelling via solvent ingress on reduction. Ellipsometric data acquired during voltammetric scans reveal, however, that the sequence of events in this process is complex.
Photoetching of polycrystalline n‐CdS film electrodes in a photoelectrochemical cell: An electrolyte electroreflectance study
Authors: Ferrer I. J. , Salvador P.
Published: March 2014

Photoelectrochemical etching (photoetching) of polycrystalline CdS electrodes has been investigated, by the first time, by electrolyte electroreflectance (EER) technique. EER is shown to be a very powerful tool for the “in situ” study of the potential distribution changes occurring at the semiconductor‐electrolyte interface, even in the case of polycrystalline electrodes with scarce specular reflection. The EER study of the effect of photoetching on the photoelectrochemical behaviour of polycrystalline CdS electrodes allows a further insight into the origin and mechanisms involved in this interesting etching technique.
Intensity modulated photocurrent spectroscopy of n‐GaAs
Authors: Peat R. , Peter L. M.
Published: March 2014

Surface recombination at n‐GaAs photoelectrodes in alkaline selenide solutions has been investigated by intensity modulated photocurrent spectroscopy (IMPS). The technique involves sinusoidal modulation of the incident photon flux and frequency response analysis of the photocurrent. Recombination processes give rise to characteristic changes in the phase and amplitude of the periodic photocurrent, and the time constants for the relaxation of carriers in surface states can be obtained conveniently from analysis in the complex plane. The method can detect shifts in the band edge energies that result from changes in the surface dipole at the semiconductor solution interface, and the results indicate that the band edge energies of GaAs vary with electrode potential and illumination intensity. The effect of ruthenium treatment on surface recombination has also been explored by the technique.
Remarkably high photovoltages generated at n‐type silicon semiconductor electrodes coated with extremely small platinum islands
Authors: Nakato Yoshihiro , Tsubomura Hiroshi
Published: March 2014

A photoelectrochemical solar cell, equipped with an n‐type silicon semiconductor electrode coated with sparsely scattered, extremely small platinum islands, generates a remarkably high open‐circuit photovoltage of 0.68 V compared with that of a normal p‐n junction silicon solid solar cell (0.59 V). This result is explained by our theory recently proposed on the mechanism of the generation of photovoltages at semiconductor electrodes covered with discontinuous metal layers. The present result is encouraging as a novel approach to highly efficient solar cells.
Growth and morphology of electrodeposited semiconducting films
Authors: Decker F. , Moro J. R. , Ferreira J. L. S. , Vanzi M.
Published: March 2014

Semiconducting CdSe films have been electrodeposited on a variety of substrates by means of two techniques. The processes of nucleation, coalescence and growth have been accompanied ex‐situ by scanning electron microscopy, and in‐situ by optical reflectance. We analyze the growth mode for different film thicknesses and we discuss the applications in solar cells and other devices.
Simulation of electrochemical interface properties: UHV‐investigation on CuInSe2 and CuInS2
Authors: Sander M. , Lewerenz H.‐J. , Jaegermann W. , Schmeißer D.
Published: March 2014

The interaction of water and chlorine with cleaved CuInSe2 and CuInS2 surfaces is studied by XPS and UPS. Whereas water appears to adsorb undissociatively, chlorine interacts chemically with the surfaces. Photoinduced changes of valence band spectra are investigated and their relevance with respect to surface states and band bending is discussed.
Photocurrent spectroscopy of anodic films on metal electrodes
Authors: Peter L. M.
Published: March 2014

The mechanisms of photocurrent generation in thin anodic films on metals are reviewed. It is shown that photocurrent spectra can be analysed to give absorption spectra or film thickness data, and several experimental examples of the quantitative application of photo‐current Spectroscopy are discussed in order to illustrate the main features of the analysis.
Amorphous semiconductor‐electrolyte junctions. Photoelectrochemical behaviour of thin Nb2O5 anodic films
Authors: Quarto Francesco Di , Piazza Salvatore , Sunseri Carmelo
Published: March 2014

An approach to the study of the photocharacteristics of amorphous semiconductor/electrolyte junctions is proposed which takes into account the main differences in the electronic structure and the transport properties of the amorphous semiconductors (a‐SC) with respect to the crystalline counterparts. The influence of the wavelength of the incident light on the photocurrent vs electrode potential curves is explained on the basis of the geminate recombination theory in a‐SC. The implications of the model are shortly discussed.
Mechanisms of charge transfer at the semiconductor‐electrolyte interface: Oxygen electroreduction at naked and platinized n‐TiO2 electrodes
Authors: Tafalla D. , Salvador P.
Published: March 2014

The electroreduction of oxygen at a n‐TiO2 single crystal was studied by the rotating ring‐disc electrode technique. The overpotential of the reaction was found to be higher at acidic than at basic pH, this pH effect being more important at low bandbending than at high bandbending. At potentials positive of flat band the cathodic current was not found to be proportional to the O2 concentration of the electrolyte, both at acidic and basic pH. The amount of H2O2 generated as final product of the reaction was found to be higher in the low current region (high bandbending) than in the high current region (small bandbending). — All these experimental features was explained on the basis of a two‐step kinetic model involving bandgap surface states probably associated with chemisorbed OH− groups. The first, limiting step of the reaction was considered to be the formation of the superoxide ion. The generation of H2O2 as final product was determined by the facility of these species to be chemisorbed on the TiO2 surface. — The main effect of Pt deposition is to reduce the overpotential for O2 electroreduction, the same mechanism as for the naked electrode being apparently valid.
Physical and electrochemical aspects of charge transfer reaction inverse photoemission spectroscopy (CTRIPS): Photon energy enhancement for high injection currents
Authors: McLntyre R. , Roe D. K. , Sass J. K. , Gerischer H.
Published: March 2014

Transient measurements of the faradaic current due to hole injection into Au(111) electrodes and of the light emission caused by radiative decay of the excited holes are reported. By compensating for the ohmic solution resistance the time constant for charging the double layer was greatly reduced, such that much higher injection currents were achieved at the desired potential. With this provision, the spectral distribution of the emitted radiation was characterized by photon energies well above the difference between the Gibbs free energies for electrons at the Fermi‐level of the metal and in the injecting thianthrene cationic species. Regularly spaced structural features were also observed in the CTRIPS spectra. As an explanation of the photon energy enhancement a 2‐quantum process, involving the interaction of a primary hole and a secondary electron, is proposed.
Monte Carlo Simulation of Model Three‐Component Liquid Systems
Authors: Yurtsever Ersin , Karaaslan Hasan
Published: March 2014

A two‐dimensional model for studying the miscibility of binary liquid mixtures is proposed. The parameters are optimized so that the phase separation can be observed. The degree of mixing is investigated by the distribution functions and the structural drawings of the system at equilibrium. It is shown that immiscible liquid mixtures can be “remixed” by the addition of small chains with polar ends.
Vapour‐Liquid Equilibrium of n‐Tetradecane and of n‐Hexadecane with Hexafluorobenzene and with Hexafluorobenzene + Benzene at 323.15 K
Authors: Aracil J. , Rubio R. G. , Renuncio J. A. R. , Peña M. Diaz
Published: March 2014

The vapour pressures of the binary systems formed by n‐hexadecane and by n‐tetradecane with hexafluorobenzene and of the corresponding ternary systems with benzene have been measured at 323.15 K using a static technique. Thermodynamic consistency of the data has been checked using a Padé approximant for the binary systems, and several empirical equations for describing the GEm of the ternary systems. The predictions of several GEm and group contribution models have been compared with the experimentals results.
Deuterium Isotope Effects in Binary Critical Mixtures Study of the Systems Methanol/Isooctane and Acetonitril/Water
Authors: Hürth M. , Woermann D.
Published: March 2014

The shift of the critical temperature of binary mixtures with an upper critical point caused by a replacement of hydrogen atoms by deuterium in different parts of the molecules is studied. The systems are methanol (methanol, methanol‐d1, methanol‐d4)/isooctane and acetonitrile (acetonitrile, acetonitrile‐d3)/water (H2O, D2O). It is found that replacement of hydrogen atoms involved in hydrogen bonding (OH‐group of methanol, OH‐group of water) by deuterium leads to an increase of the miscibility gap.
Photospannung in monomolekularen Schichtsystemen mit Farbstoffaggregaten
Authors: Schreiber H. , Försterling H. D. , Kuhn H.
Published: March 2014

A glass slide evaporated with a metal film is covered by Cd‐arachidate and dye monolayers of various architecture. The assembly is inserted in water. In case of aggregate‐forming dyes we observe a photovoltage (up to 60 mV) between metal and water. The results are interpreted by assuming the formation of electron‐hole pairs in the aggregate after excitation of the dye; the electrons are tunneling through the monolayer of the fatty acid to acceptors in the water; the holes are filled by electrons from the metal.
Structures in Mixtures of p‐tert‐Octylphenol Polyoxyethylene and Water. 1. Triton X‐114
Authors: Heusch Rudolf , Kopp Friedrich
Published: March 2014

On the basis of the phase diagram of water and the nonionic detergent Triton X‐114R (p‐tert‐octylphenol polyoxyethylene with 7 to 8 moles oxyethylene units), results of polarization microscopy and rheological studies are compared with results obtained by freeze‐fracture electron microscopy. The ultrastructure of the mesomorphic phase, the optically isotropic solution, and the phases separated in the miscibility gap are shown in detail.
Enthalpy of Demixing of a Binary Liquid Mixture of Critical Composition: Study of the System Isobutyric Acid/Water
Authors: Harnisch F. P. , Woermann D.
Published: March 2014

A fast pressure jump technique is used to measure calorimetrically the temperature dependence of the enthalpy of demixing of an isobutyric acid/water mixture of critical composition in the vicinity of its upper critical point at temperatures below the critical temperature.
The Nature of the Reduced Defect and the Diffusion of GeO2 in Germaniadoped Vitreous Silica
Authors: Rau Hans , Hermann Wilhelm
Published: March 2014

Diffusion constants of GeO2 in vitreous silica and absorbances at 242 nm were determined as a function of temperature, time and oxygen content of the gas surrounding the samples during annealing. The samples were prepared by the PCVD method (Plasma‐activated Chemical Vapour Deposition). Computer modelling showed that the reduced germanium centre absorbing at 242 nm is an antistructure defect (germanium on an oxygen site) and not GeO, as suggested by other publications. The diffusion constant of O2 molecules, relevant in the computer model, is given by magnified image The GeO2 diffusion constant decreases at a given temperature with increasing oxygen content of the sample and increases with the GeO2 content. An average value is given by magnified image.
Conducting Polymers from 3,4‐Disubstituted Polypyrroles
Authors: Rühe J. , Kröhnke C. , Ezquerra T. A. , Kremer F. , Wegner G.
Published: March 2014

Pyrrole derivatives, which were substituted in the 3,4‐position by a fused alkyl ring have been synthesized and their electrochemical and electrical properties have been investigated. — Compounds with a five, six, seven and twelve membered ring fused to the pyrrole moity were obtained by means of a 3 + 2 cycloaddition of tosylmethylisocyanide to an α,β‐unsaturated ketone. Electrooxidation in acetonitrile/ tetrabutylammonium perchlorate led to the deposition of brittle, black, conducting polymer films on the anode, which could be reversibly reduced and reoxidized in the range of +1 to −1 [V] vs. Ag/Ag+. The electrodeposited films swell in polar aprotic media. — The conductivity decreased with increasing ring size of the substituent from 0.4 S cm−1 (five membered ring) to 2 ± 10−4 S cm−1 (twelve membered ring), while the temperature dependence increased. — The polypyrrole derivative containing the twelve membered ring showed a strong frequency dependence of the conductivity at 100 K. By changing the frequency from 0.01 to 1000 KHz the conductivity increased by two orders of magnitude.
Variable Temperature15N CPMAS NMR Studies of Dye Tautomerism in Crystalline and Amorphous Environments
Authors: Wehrie Bernd , Limbach Hans‐Heinrich , Zimmermann Herbert
Published: March 2014

This paper deals with the question of how symmetric double minimum potentials of isolated bistable molecules are affected in the ordered or disordered solid state, in a timescale of slow molecular motion. It is shown that high resolution solid state NMR under conditions of magic angle spinning (MAS) and cross‐polarization (CP) can contribute to answering this question. In particular, variable temperature high resolution solid state15N CPMAS NMR spectra (CP = cross polarization, MAS = magic angle spinning) of15N enriched tetraaza[14]annulene dyes in the crystalline state and imbedded in disordered glassy polystyrene are presented. These dyes interconvert fast between different tautomeric states whose gasphase degeneracy is lifted in the solid. By contrast to the crystalline state where all dye molecules experience the same solid state perturbation i.e. the same equilibrium constants of tautomerism, molecules dissolved in the glass exist in a multitude of different inequivalent sites with different solid state perturbations. This effect leads to a broad distribution of equilibrium constants of dye tautomerism. This interpretation is confirmed by NMR lineshape simulations and two‐dimensional15N CPMAS NMR experiments by which the temperature dependent distribution can be characterized. High temperature experiments in the region of the glass transition give insights into the process leading to motionally averaged symmetric double minimum potential of tautomerism within the NMR timescale. Thus, solid solution NMR studies provide information about elementary steps of molecular rearrangements in a timescale of slow solvent reorientation. In addition, dyes such as tetraaza[14]annulenes can be used as novel NMR probes for microscopic order and motion in glasses.
Structure and Phase Transitions of Aromatic Radical Cation Salts — a New Class of Organic Metals
Authors: Enkelmann V. , Göckelmann K.
Published: March 2014

Stable radical cation salts of a variety of simple arenes can be prepared by anodic oxidation. These highly conducting crystals of the composition (Ar2‐y)+X− (0 < y < 1, X = BF−4, ClO−4, PF−6, AsF−6, SbF−6) are deposited on the anode during the electrocrystallization. They can be considered as new family of organic conductors built up from simple, easily obtainable building blocks. — The packing found between the aromatic rings can be regarded as a model for the interchain interactions in conducting polymers, e.g. doped poly‐p‐phenylene. — The crystal structures of most radical cation salts can be characterized as columnar structures. The molecular overlap plays an important role in the electrical and magnetic properties. The geometry of this overlap is changed in metal‐insulator transitions which occur near 200 K. The phase transition in FA2PF6 has been investigated in detail and recent results are discussed. — In contrast to most radical cation salts which owing to their columnar structures are one‐dimensional conductors the salt of 2,6‐dimethylnaphthalene can be characterized as two‐ or three‐dimensional organic metal. The crystal structure of DMN3(SbF6)2(CH2Cl2) has been solved and is discussed in this paper.
Optical Absorption and Symmetries in Conducting Polymers
Authors: Sum U. , Fesser K. , Büttner H.
Published: March 2014

Various extensions of the original Su‐Schrieffer‐Heeger model for conducting polymers are discussed. The main emphasis lies on mechanisms which break fundamental symmetries of the one‐dimensional electron‐phonon system, esp. charge conjugation symmetry and supersymmetry are considered. It is shown that the optical spectra are characteristically changed by breaking these symmetries.
On the Removal of Metallic Mirrors by Free Radicals
Authors: Rice Francis Owen , Tweedell Joan
Published: March 2014

Large Radicals can be formed by passing chlorinated organic compounds at pressures of a few ram., through a furnace containing a pellet of sodium and heated to 350–400°C. It seems to us that the only radicals that will remove metallic mirrors (of tellurium or antimony, etc., previously deposited beyond the furnace) are those that can decompose into methyl or ethyl radicals plus an unsaturated molecule, without undergoing any transmigration of atoms.
Nonequilibrium Phase Transitions in Solid Catalysts for Oxidation
Authors: Greger M. , Riekert L.
Published: March 2014

Nonequilibrium phase transitions in oxidation catalysts follow either one of two distinct patterns. The system CuO/Cu2O—C3H6+O2exemplifies the pattern of hysteresis. The influence of catalyst preparation on this pattern at 645 K is investigated as well as the influence of the presence of small amounts of Pd. The system Ni/NiO—H2+O2exemplifies the pattern of coexistence of two phases of the active component, which in this case coexist by alternating in time.
Plancks Strahlungsgesetz und die Quantisierung der Entropie
Authors: Zimmermanc Herbert W.
Published: March 2014

In order to derive Planck's law of black‐body radiation we consider a gas of photons which is in equilibrium with its surroundings at temperature T. Instead of the usual energy quanta of the photons ε = hv we introduce entropy quanta σ = ε/T. Now, ε and T are used from the beginning of the calculations and it is easy to derive Planck's distribution law of the photon gas, avoiding Lagrange's method of undetermined multipliers. Using ε instead of ε we get the entropy‐distribution of the black‐body radiation which may be transformed by ε = hv into the usual energy‐distribution formula. Conventionally, entropy is a property of an ensemble of particles. But the entropy quantum ε is a property of the particle itself which is in thermodynamic equilibrium with its surroundings.
Study of the System Nitrobenzene/Isooctane in the Vicinity of its Critical Point: Static and Dynamic Light Scattering and Reevaluation of Ultrasonic Absorption Data
Authors: Belkoura L. , Harnisch F. P. , Kölchens Silvia , Müller‐Kirschbaum Th. , Woermann D.
Published: March 2014

Static and dynamic light scattering measurements with nitrobenzene/isooctane mixtures of critical composition in combination with measurements of temperature dependence of specific heat and density are used to obtain values of parameters appearing in the Ferrell‐Bhattacharjee theory of ultrasound absorption of binary critical mixtures (σ0: characteristic temperature independent relaxation rate, ω0 = (43.8 ± 0.7) GHz; g: coupling constant, g = – (0.56 ± 0.01). Recent ultrasound absorption data of that system are reanalysed on the basis of Ferrell‐Bhattacharjee theory. The analysis of data measured at seven frequencies of ultrasound in the range 9 MHz to 45 MHz gives values of the parameters ω0 and g which are in satisfactory agreement with those obtained from light scattering and thermodynamic measurements (ω0 = (37 σ 3) GHz; lgl = 0.5).
Properties of Polar Gases and Their Dimer Structures
Authors: Ksiąz̊czak Andrzej , Anderko Andrzej
Published: March 2014

A method for predicting dimerization constants in the gas phase using vapour pressure data is presented. The probable dimer structures of polar compounds such as aldehydes, ketones, esters, nitrocompounds, nitriles and heterocyclic compounds are discussed. The dimerization constants are employed to predict virial coefficients, heat capacity and thermal conductivity. The predicted values are in good agreement with experimental data.
Nuclear quadrupole resonance of substituted anilinium halides. 127I and 79Br NQR studies of toluidinium and para‐phenylenediammonium halides
Authors: Hartmann Jutta , Weiss Alarich
Published: March 2014

The 79,81Br and the 127I NQR frequencies of several bromides and iodides of ring substituted anilines were studied in the range 77 ≦ T/K < decomposition temperature. Phase transitions have been observed for 2‐(CH3)C6H4NH⊕3 Br⊖ at T = 83 K, for 3‐(CH3)C6H4NH⊕3I⊖ at 145 K and for [1,4‐(H3N)2C6H4]2⊕ [I]2⊖2 at 139 K. Transitions do not occur in [1,4‐(H3N)2C6H4]2⊕ [I]2⊖2, 2‐(H3N)2C6H4I2⊕ [I]2⊖2, 3‐(H3N)2C6H4I2⊕ [I]2⊖2, 2,4‐(H3N)2C6H4I2⊕ [I]2⊖2, 2,4‐(H3N)2C6H4I2⊕ [I]2⊖2 and 3‐(H3N)2C6H4I2⊕ [I]2⊖2. The results are discussed in the light of known crystal structure data and they are compared with studies on other anilinium halides.
Fluorescence studies of excited state intramolecular proton transfer (ESIPT) in molecules isolated in solid argon: 3‐hydroxyflavone and 2,5‐bis(2‐benzoxazolyl)hydroquinone
Authors: Dick Bernhard
Published: March 2014

The fluorescence properties of 3‐hydroxyflavone and 2,5‐bis(2‐benzoxazolyl)hydroquinone have been investigated in solid argon matrices at 15 K. In both cases dominant emission from the tautomeric form of the molecules is observed. The excitation spectra of this fluorescence and a weak fluorescence at shorter wavelength show that the latter is due to molecules with a different ground state, presumably dimers or conformers lacking an internal hydrogen bond. For both molecules no fluorescence from the normal form is found indicating the absence of a barrier to excited state intramolecular proton transfer (ESIPT).
Photochromism of spirooxazines I. Investigation of the primary processes in the ring‐opening reaction by picosecond time‐resolved absorption and emission spectroscopy
Authors: Schneider S. , Mindl A. , Elfmger G. , Melzig M.
Published: March 2014

The heterolytic bond cleavage between the spiro‐carbon and the neighbouring oxygen is commonly accepted as the primary photochemical step after exciting indolino‐spirooxazines with UV‐photons. The nonplanar intermediate “X” generated in this way is said to relax very fast to a distribution of open forms, which are in structure similar to merocyanines. In this paper, the existence of an intermediate “X” is proven for various derivatives of indolino‐spironaphthoxazines. The build‐up time of these “X”‐forms is generally shorter than 2 ps, and the following reaction to the planar forms takes 2 to 12 ps depending on the nature of the solvent as well as the kind of substituent added to the parent molecule. In contrast to nitro‐substituted compounds the triplet route is found to be negligible in the investigated derivatives.
NBr (b1Σ+, a1Δ) in solid argon: Effect of the rare gas matrix on radiative and radiationless processes
Authors: Becker A. C. , Schurath Ulrich
Published: March 2014

Heterogeneous structure in the laser‐induced b1Σ+ ↔ X3Σ− and a1Δ ↔ X3Σ− fluorescence bands of NBr in solid argon has been assigned to multiple trapping sites. A stacking‐fault model accounts for the spectral observations. Symmetry properties of the trapping sites can be correlated with photophysical properties of the emitter.
Crystal dynamics and phase transitions of malononitrile
Authors: Bougeard D. , Le Calvé N. , Pasquier B.
Published: March 2014

The crystal dynamics of the three phases, α, β and γ of malonitrile are calculated by using atom‐atom potentials from the literature and considering the dipole and quadrupole moments. The experimental frequencies used for comparison are extended by new FIR measurements and low temperature single crystal Raman spectra. The overall agreement obtained is satisfactory. The splitting of some internal modes iu the triclinic β phase is mostly caused by the atom‐atom potential. The form of the calculated soft mode agrees nicely with the values expected from crystallographic data. Finally, the influence of the multipole in the crystal energy is only of the order of 10%.
Nonlinear optical properties of polymeric materials
Authors: Willand C. S. , Williams D. J.
Published: March 2014

In this paper we discuss the molecular and macroscopic requirements for large second order nonlinear optical effects in polymeric systems. A new enhancement mechanism attributable to cooperative interactions between dipoles in polar polymer chains is proposed and tested by the synthesis and characterization of asymmetric condensation copolymers derived from p‐oxy‐α‐cyanocinnimate derivatives. An enhancement of a factor of 20 in electric field induced second harmonic generation relative to an equivalent concentration of chemically identical nonpolymerized chromophores in solution is obtained. Conformational and perhaps alignment restrictions in the rubbery state result in a reduction in alignment relative to what would be expected for an equivalent concentration of the polymerized chromophores in a moderately viscous medium. A model is proposed to account for the enhancement factors.
Phase transition and anionic motion in solid [(CH3)2NH2]2SnCl6 as studied by the temperature dependence of 35Cl NQR frequencies and chlorine nuclear relaxation times determined with a pulsed NQR spectrometer
Authors: Horiuchi Keizo , Ikeda Ryuichi , Nakamura Daiyu
Published: March 2014

The temperature dependence of 35Cl NQR frequencies of [(CH3)2NH2]2SnCl6 was precisely determined between 78 and ca. 250 K. by means of an FT NQR spectrometer. The high‐frequency line of the two 35Cl NQR signals having the intensity ratio of 2:1 already reported was observed to be split below 102 K. into sharp and broad lines with approximately equal integrated intensify. This clearly indicates the occurrence of a structural phase transition of a second‐order nature at this temperature. The presence of phase transition around this temperature has been anticipated from the IR and NQR studies previously done. The temperature dependence of chlorine nuclear spin‐lattice relaxation time, T1Q shows a dip with a clear depression at 102 K. The mechanism of the phase transition is discussed from the T1Q results and the fact that the frequency separation of the doublet increases with decreasing temperature. Above 180 K, T1Q of both lines decreased rapidly and the log T1Q vs. T−1 curves were almost linear. This decrease of T1Q was explained through the onset of the C4 reorientation of the anions with the activation energy of ca. 35 kJ mol−1. The fade‐out phenomenon of the two NQR lines occurring far below room temperature can be well explained by the onset of the above motion with the very low activation energy.
Photochemistry of colloidal semiconductors 24. Interparticle electron transfer in Cd3P2—TiO2 and Cd3P2—ZnO sandwich structures
Authors: Spanhel Lubomir , Henglein Arnim , Weller Horst
Published: March 2014

Colloidal solutions of Q‐Cd3P2 of different particle size were illuminated with visible light. The solutions also contained colloidal TiO2 or ZnO. The fluorescence of Cd3P2 was quenched by the oxide colloids. The rate of the photo‐anodic corrosion in aerated solution was drastically increased by TiO2, the quantum yield being 0.7. These effects are explained in terms of improved charge separation by rapid electron transfer from illuminated Cd3P2 into the conduction band of TiO2 or ZnO particles that are bonded to the Cd3P2 particles. — Electron injection into ZnO was more efficient for Q‐Cd3P2 particles of smaller size. This is attributed to the shift of the conduction band to more negative potentials in these particles. The injected electrons caused a blue‐shift of the absorption threshold of the ZnO part of the Cd3P2—ZnO sandwich structure.
Ionisation and dissociation of diarylmethyl chlorides in BCl3/CH2Cl2 solution: Spectroscopic evidence for carbenium ion pairs
Authors: Schneider Reinhard , Mayr Herbert , Plesch Peter Hl
Published: March 2014

The ionisation equilibria of diarylmethyl chlorides Ar2CHCl (Ar = p‐CH3O‐C6H4, p‐PhO‐C6H4, p‐CH3‐C6H4 reacting with BCl3 in CH2Cl2 to give ion‐pairs Ar2CH BCl−4 (KI), and the dissociation of these (KD) were studied by conductimetry and spectro‐photometry. The molar conductivities are almost independent of the nature of the aryl group (3.5 · 10−3 Sm2/mol at — 70°C). The ionisation constants KI increase strongly with increasing electron releasing ability of the p‐substituents. The standard ionisation enthalpies and entropies for (p‐CH3‐C6H4)2CHCl and (p‐PhO‐C6H4)(Ph)CHCl, calculated from the KI at different temperatures are negative. The dissociation constants KD [(1.9—2.9) · 10−4 mol/L at — 70°C] do not show a systematic dependence on the electron donating abilities of the substituents in the aryl groups. Small differences between the UV‐vis absorption spectra of unpaired and paired ions were used to confirm the conductimetrically determined values of KD.
A New Statistical Model for the Kinetics of the Desorption of Mixtures from Heterogeneous Adsorbing Surfaces
Authors: Liedy W. , Schlünder E.‐U.
Published: March 2014

A new model for the desorption kinetics of single substances and of mixtures is developed. The heterogeneity of the adsorbing surface is included in the model. A comparison with experimental data shows, that the new equation can predict the mixture behavior even for a system with strong deviations from ideality.
Electro‐optic and Rheological Behaviour of Aqueous Dispersions of Polytetrafluorethylene (PTFE) Fibrilles
Authors: Angel M. , Hoffmann H. , Huber G. , Rehage H.
Published: March 2014

Electro‐optic and rheological measurements were carried out on PTFE‐fibrilles. The crystalline fibrilles had an axial ratio of about 100 and a thickness of 200 Å. The dispersions were stabilized by ionic Perfluorosurfactants and could be kept for months without precipitation. — The rotational diffusion constant of the fibrilles was determined as a function of the volume fraction. Both electric birefringence and rheological measurements gave identical results for the orientation times. In the dilute and semidilute concentration range the rotational diffusion constant was the same and did not change at the overlap concentration. The shear modulus was found to increase in the semidilute concentration with the square of the volume fraction of the PTFE fibrilles. — Electric birefringence measurements with AC‐pulses showed a remarkable result. The stationary birefringence changed sign as a function of the frequency. It is concluded that this phenomenon is related to the adsorption/desorption equilibrium of the surfactant ions on the PTFE fibrilles. The equilibrium is shifted by the electric field. These conclusions could be confirmed by light scattering measurements in AC‐fields.
Pressure Effect on Dimerization Equilibria of a Series of Substituted Nitrosobenzenes in Solution
Authors: Yoshimura Y. , Nakahara M.
Published: March 2014

The effect of pressure was studied on the dimerization reactions of six di‐ and tri‐substituted nitrosobenzenes in carbon tetrachloride at 25°C. The obtained configurational volume changes for the prototype one bond formation reactions are in the range of —17 to —21 cm3 mol−1 at 6.13 MPa. The volume changes were interpreted in terms of the perturbation theory of liquid; they were dominated by the volume change in the reference system composed of hard spheres. Small differences between the observed and theoretical reference volume changes were ascribed to the perturbation due to electrostatic interactions between the solute and solvent; the perturbation volume changes were estimated by the Kirkwood theory of dipolar solvation.
Description of Three Phase Systems and Liquid‐Liquid Equilibria at High Pressures on the Basis of a Mean‐Field Lattice‐Gas Model
Authors: Kajtor J. , Peter S.
Published: March 2014

The calculation of phase equilibria in systems with dense supercritical components by means of a method developed by Kleintjens and Koningsveld was investigated. The three phase equilibria (gas, liquid, solid) in the systems H2O/NaCl (18.0—92.0 MPa, 673 — 873 K) and H2O/KBO2 (16.0—70.0 MPa, 670—771 K) can be successfully represented by using substance specific parameters derived from VLE equilibria. — Also the representation of the liquid‐liquid equilibria in the binary systems of 2‐methoxyethanol with different alkanes, which have upper critical solution temperatures and lower critical solution pressures in the temperature range 250 — 430 K and at pressures from 0.1 —400 MPa can be achieved.
UV/VIS‐Spectroscopic Studies of Cold Condensed Metal/Metal Halide Films With and Without Matrix‐Isolation
Authors: Gottwald Helmut , Weil Konrad G.
Published: March 2014

Films of about 200 nm thickness were prepared by vacuum deposition of the halides onto fused silica windows, which were kept at 12 K by a closed cycle helium refrigerator. AgCl, CuCl, and TlCl films showed an structureless absorption edge which extended from about 350 nm to 200 nm. Annealing of the films below 170 K (150 K in the case of CuCl) for more than two hours gave no changes in the absorption spectra. Films which were annealed above this temperature showed at 12 K the exciton bands which are characteristic for the crystalline state of the materials. — Cocondensation of 1 to 30 mol% of metal Me to the halide MeCl gave rise to a broad absorption band around 300 nm which can be assigned to a surface plasmon excitation of small particles. When the films are annealed, these bands disappear simultaneously with the crystallization of the matrix, and a broad band between 400 and 500 nm is formed. We assume that this band is due to Mie scattering of metallic colloid particles. — The non‐crystalline state apparently is a metastable ionic glass phase. ‐Silver chloride, matrix isolated in Ar or Kr matrices on LiF windows shows an UV/VIS spectrum which is different from the gas spectrum. No new bands appear when it is cocondensed with silver atoms.
Spectroscopic Investigation (INS, FIR) of Structural Phase Transformations of Ferroelectric CH3NH3HgCl3
Authors: Körfer M. , Fuess H. , Prager M. , Zehnder E.‐J.
Published: March 2014

The mechanism of the structural phase transformation from the ferroelectric room temperature to the paraelectric high temperature phase at T = 333(2) K in methylammonium trichloromercurate (CH3NH3HgCl3 and CD3NH3HgCl3) was investigated by inelastic neutron scattering and FIR‐measurements. Energies for an internal torsional mode of CH3 (ΔE(CH3) = 13.7 meV) and an external librational mode of NH3 (ΔE(NH3) = 37.2 meV) are derived from the inelastic part of neutron time of flight spectra. The evaluation of the quasielastic intensity revealed a jump rotation at T ≈ 100 K and a rotational diffusion at T ≈ 295 K for the CH3NH⊕3‐group around the C —N axis. For CH3− this rotational diffusion still exists in the paraelectric phase. It is, however, strongly reduced for NH⊕3 at the phase transition where an end over end libration for the whole CH3NH⊕3‐group is activated. The FIR and neutron fixed window studies give some indications of two further phase transitions at T ≈ 20 K and T ≈ 120 K.
Über die Quantisierung der Entropie und die Verteilungsfunktionen von Boltzmann, Bose‐Einstein und Fermi‐Dirac
Authors: Zimmermann Herbert W.
Published: March 2014

In a foregoing communication the concept of quantization of entropy has been introduced to derive Planck's law of black‐body radiation. In the following it is extended from photons to non‐relativistic particles. — We consider an ensemble of N particles with the total energy U which is the sum of the particle energies ε. The particles are in equilibrium with their surroundings at temperature T. In order to derive the distributions of Boltzmann, Bose‐Einstein, and Fermi‐Dirac we introduce the entropy quantum σ = ε/T which is a property of the particle itself. Again, ε and T are used from the beginning of the calculations and the distribution functions can be derived avoiding Lagrange's method for constrained maximum. Conventionally, the maximum of the entropy S for N = const, and U = const, describes the thermal equilibrium of the particle system. Instead we use the condition that the entropy quanta σ = ε/T of all particles have the same temperature T. Employing conventional particle statistics the concept of quantization of entropy leads to the same distribution functions as ordinary statistical thermodynamics, but in an easier manner.
The Shear Viscosity of Liquid Hg Based Alloys Containing In
Authors: Nozaki M. , Morikawa Y. , Itami T. , Shimoji M.
Published: March 2014

The shear viscosity η was measured as a detailed function of composition for liquid Hg based alloys containing 0–16 at% In in the temperature range from 320 K. to 520 K. A capillary viscometer of the Ostwald type was used for measurements. — The η increases linearly with the addition of In. This concentration dependence could be well explained by a simple hard sphere theory for η of liquid mixtures, in which the correction of back scattering took an important role. — The isothermal curves of ∂η/∂Tshow a slight depression at a few at% In, particularly at lower temperatures. This phenomenon appears to be related to higher order correlation (HOC) effects, which have been proposed recently for some liquid Hg based alloys by the present authors.
Electronic Transport in Molten Salt Rich Na — NaX Solutions (X = Br, I)
Authors: Haarberg G. M. , Osen K. S. , Egan J. J. , Heyer H. , Freyland W.
Published: March 2014

The electronic conductivity of liquid Na—Nal and Na—NaBr has been measured over a wide concentration range from dilute to concentrated nonmetallic solutions at different temperatures between 700 and 900°C. Two methods have been applied, the Wagner polarization technique at low metal activities and an ac‐technique at high activities where the concentration has been varied by coulometric titration. A thermodynamic defect model previously used for solids is developed and extended to liquid solutions. It quantitatively describes the concentration and temperature dependence of the thermodynamic properties as well as the charge carrier concentration in these nonmetallic systems. The electronic mobility has been determined and the transport mechanism approaching the nonmetal‐metal transition is discussed.