bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectrical Relaxation Measurements in Binary Liquid Mixtures with an Upper Critical Point
Authors: Kaatze U. , Woermann D. 
Published: July 2012

AbstractThe complex (dielectric) permittivity of the systems isobutyric acid/water and butyric acid/water is measured as function of frequency (0.001 GHz ≤ v ≤ 38 GHz), concentration (1 mol · dm−3 ≤ c ≤ 5 mol · dm−3) and temperature (25°C ≤ T ≤ 35°C). Both systems have an upper critical point (isobutyric acid/water: ccrit = 4.36 mol · dm−3, Tc = 26.30°C; butyric acid/water: ccrit = 4.33 mol · dm−3, Tc = ‐ 3.0°C).—The temperature dependence of permittivity of isobutyric acid/water mixtures of critical composition shows no critical contribution near the critical temperature (0.01 K ≤ (T–Tc) ≤ 9 K) within the accuracy of the measurements (±1%).—Different relaxation functions based on different models of the solution are fitted to the measured dielectric spectra. The results of this analysis can be interpreted by assuming that butyric acid and isobutyric acid molecules form associates in solution even well below the critical concentration. On the basis of this assumption it is possible to understand:(a) the concentration dependence of the main relaxation time of water in the Cole‐Cole‐distribution function;(b) the concentration dependence of the number of water molecules per molecule of solute having relaxation times different from that of pure water;(c) the concentration dependence of the relaxation time of hydration water.
Defects and Cation Diffusion in Magnetite (IV): Nonstoichiometry and Point Defect Structure of Magnetite (Fe3‐δO4)
Authors: Dieckmann R. 
Published: July 2012

AbstractNonstoichiometry and point defect structure of magnetite have been studied experimentally by thermogravimetry covering the stability range of magnetite between 900 and 1400 °C. A cation deficit is observed at high and a cation excess at low oxygen activities corresponding to cation vacancies and iron interstitials as the predominant point defects, respectively. An overexponential temperature dependence occurs for the defect concentrations in stoichiometric magnetite.
The Fluorescence Lifetime of Trans‐Stilbene and its Variation with Temperature
Authors: Good Hans P. , Wild Urs P. , Haas E. , Fischer E. , Resewitz E.‐P. , Lippert E. 
Published: July 2012

AbstractThe fluorescence lifetime of trans‐stilbene in solution was measured in the temperature range 300–80 K by three different methods. The decay was found to be mono‐exponential throughout, but prone to falsification by impurities, which may be responsible for the bi‐exponential decays reported by some authors. At room temperature τF is 80–130 ps, increasing to 1200–1400 ps at 77 K.
Chlorine NQR on Hemiacetals of Chloral, Cl3CCH(OH)OR
Authors: Hashimoto M. , Weiss Alarich 
Published: July 2012

AbstractThe 35Cl NQR spectra of 22 hemiacetals of chloral, Cl3CCH(OH)OR, were studied. Most of these hemiacetals with R = unbranched aliphatic group, show a three line 35Cl NQR spectrum having a regular splitting pattern; two lines around vL = 38.6± 0.1 MHz and the third line at vH = 39.0 ± 0.1 MHz. It is assumed that the difference between vL and vH is due to “chemical splitting”. Completely irregular splitting pattern are found for the hemiacetals carrying bulky branched aliphatic groups. Moreover the magnitudes of these splittings are relatively large. A deformation of the molecules due to intramolecular steric hindrance seems to be responsible for this large splitting. The frequency shift in these compounds due to the steric effect is estimated to be 1 MHz or less. A peculiar temperature dependence of the 35Cl NQR line intensity was found for chloral n‐butylhemiacetal. An intramolecular bifurcated hydrogen bond between CCl3 and OH groups is proposed to be responsible for the phenomenon. For p‐chlorobenzylalcohol at ca. 226 K a phase transition was observed.
Photoelectrochemical Investigations of Pyranthrone in Aqueous Electrolytes
Authors: Ahuja R. C. , Hauffe K. , Schumacher R. , Schindler R. N. 
Published: July 2012

AbstractThe present paper reports the results of investigations on the photoelectrochemical properties of pyranthrone. The used samples were of the type SnO2/pyranthrone/aqueous electrolyte and Au/pyranthrone/aqueous electrolyte. They were prepared by vacuum evaporation of pyranthrone on SnO2 and Au substrates. Under illumination, both samples showed anodic as well as cathodic currents. It was found that the potential at which the anodic photocurrent crosses over to the cathodic, depends on pH and additives introduced into the electrolyte. The magnitude of photocurrents is also dependent on pH, biasing conditions and the presence of additives. The results are discussed, treating the pyranthrone as photosemiconductor. The observed photocurrents thus arise, because of the reaction of photogenerated charge carriers with H+/OH− ions in the aqueous electrolyte. The pyranthrone layer was found to be stable especially under conditions where cathodic photocurrents flow. The observed quantum yield was ca. 10−3 e/incident photon. Using redox potential data, the position of energy bands of pyranthrone at pH 13 were determined to be: Ev = −5.35 eV and Ec = −3.40 eV with respect to the vacuum level.
Messungen dielektrischer Eigenschaften bei hohen Drücken und tiefen Temperaturen III: Die statische und komplexe Dielektrizitätszahl von Cyclopentanol
Authors: Würflinger A. 
Published: July 2012

AbstractThe static permittivity ε of liquid and solid cyclopentanol has been determined as a function of temperature (+ 50 to ‐ 80 °C) and pressure (up to 3 kbar). From these and PVT data the Kirkwood correlation factor g has been calculated. Plots of g as a function of temperature intersect at g = 2.6 and at the “cross‐over‐temperature” of 30 °C. The calculations have also been extended to the plastic phases (SI, SII) of cyclopentanol, because their permittivity (especially that for SII) exceeds that for the liquid considerably. There is a drastic decrease of ε to values about 2.5 at a lower SII/SIII transition. The increase of ε at the freezing point is larger as should be expected according to the Onsager equation. The temperature dependence of g at constant volume is negative. Also the dielectric relaxation has been studied for the plastic phases of cyclopentanol up to frequencies of 10 MHz. The complex permittivity has been evaluated with the help of the Cole‐Cole equation, showing only a small deviation from a simple Debye‐mechanism (α ≤ 0.05). The relaxation times τ about 1000 bar vary from 10−5 s (‐70°C) to 3 · 10−8 s (‐ 10°C) in solid cyclopentanol, τ being discontinuous at the SI/SII transition. Activation volumes (5–7 cm3 mol−1) and activation energies (40 kJ mol−1) have been derived from the pressure and temperature dependence if τ.
Theoretical Study of Intermolecular Proton Transfer between Equivalent Molecules in Solution: Diffusion Induced Tunneling
Authors: Klöffler Martin , Brickmann Jürgen 
Published: July 2012

AbstractThe mechanism of intermolecular proton transfer AH + A ⇋ A + HA in solution is studied in terms of a model in which the motion of the molecule A is treated as a classical random motion while the proton behaves quantum mechanically. The proton moves in a symmetrical double well potential which is stochastically time dependent. The energy splitting due to the coupling of the AH stretching vibration in different molecules is assumed to depend only on the distance between diffusing molecules but not on their relative orientation.—Using a first order perturbation approach the transfer rate is found to be inversely proportional to the diffusion coefficient. The proton transfer rates are calculated for two limiting cases corresponding to a WKB type and a Franck Condon type coupling term.
A Semi‐Empirical Investigation into the Trans‐Cis Photoisomerisation of Stilbene
Authors: Olbrich Gottfried 
Published: July 2012

AbstractPotential curves of the eight lowest singlet and eight lowest triplet states for the isomerization reaction of stilbene have been calculated by CI including triply excited configurations. The CI was based on MO's evaluated by a CNDO method. A ground state activation energy of the isomerization of 259 k J/mol was calculated. The lowest excited singlet state has a minimum at the perpendicular geometry and an activation energy of 50 kJ/mol for the trans cis isomerization in this state was found. It is shown, that this activation energy originates from an avoided crossing with a higher lying singlet state. Isomerization in the triplet manifold should occur preferentially via the lowest triplet state.
A Proton Magnetic Resonance Study of Ligand Exchange on Tetrakis (N,N‐Dimethylacetamide) Beryllium(II) and its N‐Methylacetamide, and N,N‐Dimethylformamide Analogues
Authors: Lincoln Stephen F. , Tkaczuk Michael N. 
Published: July 2012

AbstractA 1H (90 MHz) NMR study shows that ligand (L) exchange on [BeL4]2+ is characterised by the rate law: exchange rate = 4(k1 + k2[L]free)[BeL2+4] when L = O = CMe(NMe2), O = CMe(NHMe), or O = CH(NMe2) in the non‐coordinating solvents CD3NO2 and CD3CN, and also in CD2Cl2 in the case of O = CH(NMe2). The kinetic parameters observed for these systems are exemplified by those characterising [Be(O = CMe(NMe2))4]2+ in CD3NO2 solution which are: k1 (340 K) = 7.3 ± 0.7 s−1, ΔH#1 = 56.9 ± 1.5 kJ mol−1, ΔS#1 = −62.1 ± 4.6 J K−1 mol−1, k2 (340 K) = 10.5 ± 1.0 dm3 mol−1 s−1, ΔH#2 = 66.7 ± 2.6 kJ mol−1, and ΔS#2 = −30.1 ± 7.4 JK−1 mol−1. The k1 and k2 rate constants are interpreted in terms of dissociative (D) and associative (A) (or interchange (I)) ligand exchange mechanisms and are discussed in conjunction with previously reported data for other beryllium(II) systems.
Colloidal TiO2 Catalyzed Photo‐ and Radiation Chemical Processes in Aqueous Solution
Authors: Henglein A. 
Published: July 2012

AbstractA number of free radical reactions was observed upon the illumination of TiO2 sols with light of the near UV. Cl−, Br−, and I− were oxidized to yield the radical anions Cl−2, Br−2, and I−2, respectively. Propanol‐2 was oxidized to yield the 1‐hydroxy‐1‐methyl ethyl radical. These intermediates were identified by their optical absorptions or their reaction with tetranitromethane or acrylonitrile. The quantum yields were measured as a function of the substrate concentration. The effects are explained by the formation of electron‐hole pairs in illuminated colloidal TiO2, rapid diffusion of these charge carriers to the surface of the colloidal particles, and reaction with adsorbed acceptors. Most of the charge carriers, however, disappeared by recombination, the largest quantum yield observed being 0.16. The lifetime of the charge carriers was less than 30 ns.—Acidic TiO2 sols containing propanol‐2 were also γ‐irradiated. In these sols, 1‐hydroxy‐1‐methyl ethyl radicals were formed which attacked the colloidal particles. The overall reaction consisted of the dissolution of the colloid. At short irradiation times, the sols became blue, and this color slowly disappeared upon further irradiation. The color centers had an absorption coefficient of 1 · 104 M−1 cm−1. They were very sensitive towards oxygen. Their formation is connected with the electron transfer from the organic radicals to the colloidal particles. A mechanism is proposed according to which the energy of dissolution of colloidal TiO2 is supplied by the overall disproportionation of the radicals.
Influence of the Solvent on the Electrochemical Stability of a Semiconductor Electrode
Authors: Sculfort Jean‐Lou , Gautron Jacques , Lemasson Philippe , Herlem Michel 
Published: July 2012

AbstractThe influence of the supporting electrolyte on the decomposition mechanisms of an electrode (n‐ZnSe) whose behaviour is well‐known in aqueous media has been investigated in liquid ammonia (‐60 °C) and in liquid ammoniate of sodium iodide (room temperature). In each case, the flat band potential of the ZnSe‐electrolyte junction was determined unambiguously giving the following values: −2.3 V/MSE in acidic aqueous medium; −2.2 V/SRE (‐60°C) in liquid ammonia and −2.2 V/SRE in neutral ammoniate. For low concentrations of residual water (CH2O ≤ 10−2 M), a cathodic mechanism of decomposition is evidenced. In liquid ammonia, it takes place below −2.0 V/SRE (‐60°C) and in neutral ammoniate below −2 V/SRE. In the latter solvent, when CH2O increases, this decomposition is changed for the reduction of water. At positive potentials, in the dark and under illumination, whereas the semiconductor decomposes in aqueous medium, in liquid ammonia and in ammoniate it is the solvent which decomposes, the electrode remaining unmodified.
A Photoelectrochemical Investigation of the n‐Semiconductors α‐HgS and α‐HgS1‐xSex Solid Solutions
Authors: Repenning D. , Sprünken H.‐R. , Schindler R. N. 
Published: July 2012

AbstractPhotoclectrochemical investigations are described with solid solution HgS1‐xSex electrodes of the compositions x = 0, 0.01, 0.03, and 0.06. The electrodes were prepared by a sublimation and a vapor phase technique, respectively. The semiconductor electrodes were characterized by their current‐potential dependence and their spectral response as function of illumination time.—No corrosion currents were observed in an aqueous electrolyte of pH 2.5 in the potential vs. SCE region −0.45 to +0.9 V in the dark. Upon illumination only the electrode with the highest selenium content corrodes noticeably. Bandgaps of Eg = 2.1 eV with x = 0 and Eg = 1.7 eV with x = 0.06 are determined from wavelength dependent photocurrent spectra. The results indicate that the transition of the hexagonal α‐ to the cubic β‐structure is more hindered in the solid solution electrodes than in the pure α‐HgS system.
Kinetics of Phase Separation in Binary Lutidine/Water Mixtures Using a Fast Temperature Jump Technique
Authors: Strey R. , Wagner J. , Woermann D. 
Published: July 2012

AbstractTemperature jump experiments with a characteristic heating time of 0.5 ms are carried out with lutidine/water mixtures of off‐critical composition. The system is brought from an equilibrium state in the one fluid phase region into a metastable state in which formation of a second fluid phase occurs. The temperature jumps are produced by discharging a high voltage capacitor through the electrically conducting sample.—The light intensity scattered by the sample at an scattering angle of 90° is monitored as function of time after triggering the temperature jump. The scattering intensity versus time curves show consecutive maxima. They can be interpreted by Mie‐scattering of growing droplets of the new emerging phase. The growth rate is calculated as function of the overheating temperature and supersaturation respectively. The data indicate diffusion controlled growth. — The experimentally determined upper and lower limits of metastability are discussed in terms of the classical (Becker‐Döring) nucleation theory and the Langer‐Turski model of nucleation.
Kinetics of the Reaction NH2 + 1,3‐Butadiene
Authors: Hack W. , Schröter M. R. , Gg. Wagner H. 
Published: July 2012

AbstractThe gas‐phase reaction of free NH2 radicals with 1,3‐butadiene has been investigated in an isothermal discharge‐flow system under pseudo‐first‐order conditions. NH2 was produced in the fast reaction to fluorine atoms with ammonia and its concentration was monitored by laser‐induced fluorescence. For the room temperature measurements at 2 mbar a rate coefficient of 6.7 · 109 cm3 mol−1 s−1 was derived. Temperature and pressure conditions were varied in the range of 230–360 K, and 2–10 mbar, respectively. The temperature dependence can be described in the Arrhenius expression k(T) = 3.8 · 1011 exp(‐1140 K/T) cm3 mol−1 s−1. An effect of the total pressure on the rate constant was not observed.
Polarized Absorption Spectrum of Biphenylene: The Origin of the Intensity of the First Band System and the Vibrational Analysis for the Second Band System
Authors: Hoshi Toshihiko , Yamamoto Hiromasa , Miyauchi Toru , Mori Shoji , Kobayashi Michio , Tanizaki Yoshie 
Published: July 2012

AbstractA polarized absorption spectrum of biphenylene was measured at a low temperature using a stretched polymer film technique. The polarizations of the bands positioned at 253 and 200 nm were determined to be long‐axis and short‐axis polarized, respectively. A mechanism is proposed in which the intensity of the first symmetry forbidden band system is induced merely by coupling with the vibration of a b2u skeletal deformation without borrowing the intensity from the nearby band. The vibrational analysis for the second band system was also examined in views of the polarized spectrum using the stretched polymer film.
Molecular Beam Studies of Bimolecular Reactions: F + H2 and Li + HF
Authors: Lee Yuan T. 
Published: July 2012

AbstractUsing reactions of F + H2 → HF + H and Li + HF → LiF + H as examples, the application of the crossed molecular beams method in the investigation of dynamics of bimolecular chemical reactions is described. Most of the discussions are centered on the angular distributions of reaction products and their implication to the relation between potential energy surface and reaction dynamics.
H3 and H3+: Correlations of Theory and Experiment
Authors: Porter Richard N. 
Published: July 2012

AbstractA survey of calculations of the properties of H3 and H3+ with particular emphasis on those in which the author has been involved is given. Correlations with hot‐atom experiments and spectroscopic observations are discussed. A preview of new work on the predissociation of quasistable upper‐sheet Jahn‐Teller states of H3 is presented.
Reactive Scattering Studies on Oriented Molecules
Authors: Stolte Steven 
Published: July 2012

AbstractThe state of the art of reactive scattering with oriented molecules is presented. The alignment and orientation achieved with laser methods and deflection fields are compared to each other. They can be described very well with a short Legendre series. The steric reactive scattering phenomena turn out to be large and are closely connected to the configuration of the transition state. In a few cases a deconvolution to a steric reaction probability function can be carried out. The concept of azimuthal steric dependence is introduced.
Stochastic Trajectory Studies of Chemical Processes at Surfaces
Authors: Tully John C. , Muhlhausen Carl W. , Ruby Leah R. 
Published: July 2012

AbstractClassical trajectory studies have been carried out of the dynamics of simple chemical processes at surfaces. Empirical potential energy hyper‐surfaces were employed. The motion of only a few (5 or 6) atoms in the immediate vicinity of the reactive event was followed explicitly. The effects of the remaining surface and bulk atoms were replaced by friction and random forces (with memory), constructed from experimental phonon spectra. Among the systems studied are inelastic scattering of N2 from Ag(111), and recombination of O with C on Pt(111). Particular attention was paid to the mechanisms of energy transfer and to the specificity of energy disposal in surface reactions.
Cyanine Dyes as Sensitizers of the Photopolymerization of Diacetylenes in Multilayers
Authors: Bubeck C. , Tieke B. , Wegner G. 
Published: July 2012

AbstractMultilayers of amphiphilic diacetylene fatty acids are prepared following the method of Langmuir and Blodgett. The photopolymerization of the diacetylene units can be sensitized for visible light by surface active cyanine dyes embedded in the multilayers. Using optical spectroscopy a high polymer yield is found. The yield is independent of the spectral range of the absorption and the concentration of the dyes, respectively, in the range between 0.02 and 3 mole percent. ‐ The quantum yield of the sensitized photopolymerization is low: the dye molecule must absorb about 1000 photons to sensitize the reaction of one monomer molecule. The fluorescence of the dyes is already quenched at low conversion. The origin is an energy‐ and electron transfer to the oligomer chain.
Rotational and Vibrational Relaxation in the Degenerate Vibrationsv24andv21of Cyclohexane in the Liquid State
Authors: Bien T. , Düge G. 
Published: July 2012

AbstractCorrelation functions ϕ(t) and correlation times were obtained by Fourier transformation of the degenerate fundamental bandsv24andv21of liquid cyclohexane. Reorientational correlation functions were calculated based on the Kubo line shape theory in order to extract the contribution of vibrational relaxation. Dephasing caused by short range interactions is a possible mechanism for vibrational relaxation at least forv21.
An NMR Study of the Dynamics of the Schlenk Equilibrium of 2‐Methylpropylmagnesium Bromide in Tetrahydrofuran
Authors: Allen Peter E. M. , Hagias Stan , Lincoln Stephen F. , Mair Clyde , Williams Evan H. 
Published: July 2012

AbstractA 90 MHz proton NMR determination of the activation and thermodynamic parameters of the Schlenk equilibrium of 2‐methylpropylmagnesium bromide in tetrahydrofuran is reported. The entropy of activation is consistent with bimolecular reactions of unassociated species proceeding through a transition state resembling a mixed‐bridge dimer. The quantitative data confirm accepted concepts of the solvation states of the species involved. — Association equilibria were explored in order to ensure that they were insignificant under the conditions of the kinetic measurements on the Schlenk equilibria. — The association of di‐2‐methylpropylmagnesium is strongly concentration‐dependent but almost temperature‐independent. The exchange rate is too slow to be measured by NMR methods and much slower than the Schlenk equilibrium. The associates are either cyclic or cluster compounds, or, if linear, have an average degree of polymerization of 10. — The field positions of the resonances of RMgBr and R2Mg reverse at low temperature.
Charge Transfer from the Solvent Radical Cation to Solutes Studied in Pulse‐Irradiated Liquid n‐Butyl Chloride
Authors: Mehnert R. , Brede O. , Naumann W. 
Published: July 2012

AbstractCharge transfer from n‐butyl chloride radical cations (BuCl+) to 11 solutes (S) (alkanes, alkenes, aromatics, and amines) was studied by pulse radiolysis. Using a mechanism proposed for radiation‐induced ionic processes in liquid n‐butyl chloride the rate constants of the reactionmagnified imagewere determined. At gas phase ionization potential differences ΔI = (IBuCl‐Is) smaller than 1.5 eV the rate constants increased rapidly with increasing ΔI and reached for larger ΔI nearly constant values of about 1010 dm3 mol−1 s−1. The dependence of the rate constants on the ionization potential differences k vs. ΔI is explained in terms of a two‐step process consisting of migration of solvent cations and electron transfer from the solute molecule to the solvent cation. The probability of the last step was calculated using the Franck‐Condon principle. In the framework of a simplified model taking into account vibrational stretching and deformation modes of the reactants and solvent modes in thermally averaged form a reasonable fit of the k vs. ΔI behaviour was obtained.
The Magnetic Susceptibility of Molten Bi — BiCl3, In — InCl3, and In — InBr3 Solutions
Authors: Itoh T. , Tashiro Y. , Uemura O. , Satow T. 
Published: July 2012

AbstractMeasurements of the magnetic susceptibility for Bi — BiCl3, In — InCl3, and In — InBr3 systems in the liquid state were made over a wide composition range. Total diamagnetic susceptibilities of molten Bi — BiCl3 system decrease with increasing temperature. On the other hand, little change of the susceptibility was observed against temperature in both molten In systems. Composition dependences of the magnetic susceptibility indicate that apparent paramagnetic contributions exist both in the metal rich and in the salt rich regions of the molten Bi — BiCl3 system, while an extreme electron localization occurs in the composition range between pure salt and 66.7 mol‐% In in the molten In systems. The valency of existing ions and the degree of electron localization are discussed using these experimental results.