bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic and Molecular Orbital Electronegativity Models Based on the Transition State and Transition Operator Approaches
Authors: Schmidt Peter C. , Böhm Michael C. 
Published: July 2012

AbstractOrbital electronegativities χi of atoms A, χi(A), and organic molecular radicals G, χi(G), have been determined by means of transition state (TS) calculations for atomic systems as well as by means of the transition operator (TO) method in the molecular domain. The theoretically determined χi(A) values are compared with “experimentally” deduced electronegativities and the correlation between χi(A) and χi(G) and measured nuclear quadrupole coupling constants C = e2qQ/h in ACl and GCl systems have been studied. In all examples an increase of the electronegativity is accompanied by an increase of the absolute value to C(35Cl). It is found that a linear relation C ∼ χi holds for a series of similar compounds in those cases, for which one active orbital i describes the bonding mechanism between G and Cl satisfactorily. In these systems the calculation of χi based on the TS and TO methods is a helpful tool to analyze coupling constants, and thus to rationalize the nature of the chemical bonds. ‐ On the other hand for systems where the bonding mechanism is of larger complexity, and where one specific active orbital is not a suitable model for the representation of the heterobonds AX or GX, the interplay of different one‐electron states has to be taken into consideration. For atomic systems an additional problem occurs, e.g. an appropriate active valence state has to be defined, which describes the bonding mechanism in AX compounds quantitatively.
The Bond Indium‐Halogen in Isomorphous Complexes A2InX5 · H2O (A = K, NH4, Rb, Cs; X = Cl, Br). A 35Cl, 79,81Br, and 115In NQR study
Authors: Yamada Koji , Weiss Alarich 
Published: July 2012

AbstractThe isomorphous series of complexes A2InX5 · H2O (A = K, NH4, Rb, Cs; X = Cl, Br) was investigated by 35Cl, 79,81Br, and 115In nuclear quadrupole resonance spectroscopy. For the bromine compounds the temperature dependence of the NQR spectra was studied in the range 77 ≦ T/K ≦ 380. Solid state phase transitions are found for K2InBr5 · H2O at T = 145.5 K and for (NH4)2InBr5 · H2O at T = 82 K. The 81Br NQR frequencies are observed between 65 and 80 MHz. At room temperature the 35CI NQR frequencies are found in the range 9.8 ≦ ν (35Cl)/MHz ≦ 11.6. The nuclear quadrupole coupling constants /e2 ϕzzQh−1 (115In)/in the compounds vary between 60 MHz and 115 MHz. There is a marked dependence of /e2 ϕzzQh−1 (115In)/on cation radius rA and temperature. /e2 ϕzzQh−1 (115In) /(increases with increasing rA, and such a dependence is observed for ν(81Br), too. As a function of temperature, n(115In) goes through 1. On the basis of the semiempirical MO model of Townes and Dailey the covalent character of the bond In‐Halogen is estimated. From this the increase of /e2 ϕzzQh−1 (115In)/and of ν(81Br) is understood to be due to small changes in the bond character with rA and with temperature.
Kohärente Kurzzeit‐Strukturen und momentane Brechzahl‐, Dichte‐ und Temperaturprofile in einer n‐Hexan‐Tankflamme
Authors: Brötz W. , Schönbucher A. , Lucas R. , Schieß N. 
Published: July 2012

AbstractCoherent short‐time structures of a n‐hexan pool flame were shown as a 1000 exposures/sec picture‐sequence using a holographic real‐time synchronous interferometer. These coherent structures have eddies, thermal boundary layers as well as luminous flame fronts. Also gaschromatographically measured concentration profiles of 18 stable molecules of the flame gas mixture were considered. ‐ As a result, the refraction index profiles and also the density and temperature profiles were determined up to 60% by the chemical composition of the pool flame. In the upper flame plume as well as mainly within the thermal boundary layer the density profiles are solely determined by the temperature field. ‐ The quasi‐instantaneous density and temperature profiles are NON‐Gaußian distributed. Within the visible flame field quasi‐instantaneous temperature maxima reach values up to about 2000°C, whereas maximal temperatures within the instantaneous flame neck come up to about 900°C. – This big difference between the maximal flame temperatures can be explained by the momentary number of eddies responsible for the heat and matter exchange. The maximal flame temperatures in the plume are much higher in case of less eddies being in this range than in the neck.
Unstetigkeiten im Abbrandverhalten angeströmter Kohlenstoffoberflächen
Authors: Adomeit G. , Hocks W. , Henriksen K. 
Published: July 2012

AbstractIn the present work the ignition and quench phenomena of the combustion of a carbon surface in oxidizing cross flow is investigated theoretically. For certain values of moisture content and of heterogeneous reaction rates, multiple ignition and quench phenomena are observed together with non‐monotonous dependence of the burning rate upon the surface temperature. These phenomena occur in the region of transition from the reaction controlled to the transport controlled regime. In dependence upon reaction rates this regime extends from 1300 K to about 2000 K.
The Photochemistry of 1,3‐Diphenyltriazene in Various Media. II: Solid State Photolysis
Authors: Baro J. , Dudek D. , Luther K. , Troe J. 
Published: July 2012

AbstractSolid 1,3‐diphenyltriazene (DPT) has been photolyzed at 290 nm and 360 nm. The distribution of the photoproducts showed that recombination of the radicals produced after photochemical excitation was governed by a “cage effect” favouring a minimum of motion of the recombining radicals. In many details the results differ from observations on the photochemistry of DPT in liquid solutions. The photolysis of DPT in polymethylmethacrylate films, however, resembles the photochemistry of DPT in liquid solutions.
Molecular Dynamics Calculations of a Second Order Kinetic Phase Transition in an Open System (CSTR)
Authors: Heinrichs M. , Schneider F. W. 
Published: July 2012

AbstractWe performed Molecular Dynamics calculations (MD) for a few hundred reacting molecules in a continuous flow stirred tank reactor (CSTR), in order to assess the significance of fluctuations in particle numbers at the point of a second order kinetic phase transition. The latter occurs in the following mechanism A + B → C; C + B → D + B, D → 2B (net: A + 2B → 3 B) under given conditions of in‐flow of A and B into the reactor at the critical flow rate. All molecules are represented by hard spheres and periodic boundary conditions are assumed. The MD calculations for ∼500 particles show deviations from the deterministic steady states particularly at the critical flow rate where the distribution function of B particles is found to display about two maxima (MD) instead of one (Poisson distribution for the deterministic case). The magnitude of the concentration fluctuations is enhanced at low frequencies at or near the critical flow rate as exemplified by a Fourier transformation from the time to frequency domain for the MD results in analogy to the phenomenon of critical slowing down in the deterministic CSTR calculations. We conclude that the macroscopic rate laws for first and second order reactions may be applied with confidence to only a few hundred reacting molecules if one is willing to accept some scatter in the rate constants. This conclusion does not apply to the point of a kinetic phase transition in the CSTR which shows a qualitatively different behavior in the low number limit, because of the large and “slow” fluctuations at that point. We present a new approach to the MD treatment of second order rate constants. Kinetic processes in biological cells or on biological membranes may be realistically simulated by MD calculations.
Die photochemische Valenzisomerisierung 9‐alkylsubstituierter Anthrazene zu 9,10‐Dewarisomeren
Authors: Jahn B. , Dreeskamp H. 
Published: July 2012

AbstractOn light absorption in the long wavelength 1La‐band 9‐alkyl‐substituted anthracenes in fluid solutions isomerise with low quantum yield (about 0.016 at 300 K) to the 9,10‐Dewarisomer, provided the substituent is sufficiently spacefilling (t‐butyl or t‐pentyl). On increasing the viscosity and/or reducing the temperature the quantum yield of this valence isomerisation decreases while the quantum yield of fluorescence and the vibrational structure of the fluorescence emission increases. From spectroscopic, caloric and kinetic data an energy diagram of the ground and first excited states is constructed for this photo‐ and thermoreversible reaction in which the folding along the 9,10‐axis of the anthracene sceleton serves as the main reaction coordinate. Steric interaction of the bulky substituent effects a folding of the anthracene sceleton along the 9,10‐axis already in the ground state, which was confirmed by an X‐ray analysis. Thereby a transition from the excited state to a hypersurface is facilitated on which a transformation in low yield to the Dewarisomer and mainly to the starting compound occurs.
Interfacial Phenomena of Some Titanate Photoanodes
Authors: Lam R. U. E. 'T , Janssen L. H. J. M. , Schoonman J. 
Published: July 2012

AbstractTwo types of titanate photoanodes are discussed, viz. mechanically polished n‐TiO2: Nb and hydrogen‐reduced n‐SrTiO3: Nb surface‐doped with LaCrO3. The anodes are investigated in acidic as well as in basic solutions. In addition the influence of ultraviolet irradiation is examined. Detailed equivalent circuits are proposed for both types of cells. Mott‐Schottky plots indicate the presence of a severely disturbed space‐charge region for both photoelectrodes. In the case of the mechanically polished n‐TiO2: Nb anode, the disturbance is attributed to surface roughness effects, whereas for the hydrogen‐reduced n‐SrTiO3: Nb, LaCrO3 anode, the existence of a nonuniform donor level is suggested.
Clustering in Free Jets — Aggregation by Dispersion
Authors: Ryali S. B. , Fenn J. B. 
Published: July 2012

AbstractThe nature of free jet expansion is reviewed with emphasis on those features that are important in the clustering process. Thermodynamic and kinetic aspects are examined. The importance of nozzle geometry is discussed along with some of the implications of the newly developing pulsed flow technique. Some problems relating to free jet sampling into vacuum from high pressure are identified.
Electron Localization and Electron Induced Cluster Formation in Dense Polar Vapors
Authors: Krebs Peter 
Published: July 2012

AbstractWe discuss the mobilities of electrons photoinjected in dense sub‐ and supercritical polar vapors (NH3, H2O) as a function of vapor density and temperature. With increasing density they show a transition from the quasi‐free to the localized electron state. The density range where the onset of this transition is observed obeys the Ioffe‐Regel principle. At this density large radius orientational fluctuations of the dipole molecules as precursors of dense clusters are important for electron localization. Electron cluster formation is strongly supported by the observed temperature dependence of the electron mobility in low density H2O vapor. These results are discussed in context with optical absorption measurements on excess electrons in sub‐ and supercritical D2O and ND3. In NH3 gas around the critical density the electron mobility shows an anomalous density dependence. It is concluded that there occurs a further transition: the electron localized in a dense orientational cluster obviously turns over to an electron localized in a cavity (solvated electron).
Para‐ and Diamagnetic Polyhalide Anions in Liquid CsI – I2
Authors: Nakowsky B. , Nicoloso N. , Freyland W. 
Published: July 2012

AbstractWe have measured the concentration and temperature dependence of the magnetic susceptibility in liquid CsI–I2 mixtures. At low iodine concentrations we have also investigated the EPR and optical absorption spectra. From these results we deduce that localized paramagnetic states similar to V centers exist in CsI rich solutions. With increasing I2 concentration these transform in equilibrium with diamagnetic polyiodide anions like I2n+1− A conduction mechanism via bond fluctuations within iodine clusters is suggested which accounts for the unusual transport properties of these solutions.
Fast Photocurrent Transients in Photoelectrochemical Cells with Semiconductor and Insulator Electrodes
Authors: Willig F. , Bitterling K. , Charlé K.‐P. , Decker F. 
Published: July 2012

AbstractPhotocurrent transients have been measured with better than 1 nanosecond time resolution in photoelectrochemical cells with insulator and semiconductor electrodes. The shape of the transients observed with semiconductor electrodes in the time window of several nanoseconds can be deduced from a simple equivalent circuit. The transient observed in the external circuit consists of two contributions, the first is the time integral and the second is directly proportional to the actual photoresponse. At low light intensity good semiconductor electrodes show only the first contribution. There is no direct influence of charge carrier discharge or of the Helmholtz‐layer as such on the fast transient in the nano‐second range.
Kinetics of the Reactions of HCO with HCO and O2
Authors: Temps F. , Wagner H. Gg. 
Published: July 2012

AbstractThe reactionsmagnified imageandmagnified imagehave been studied at room temperature in an isothermal flow reactor using helium in the pressure range 1 mbar ≤ p ≤ 5 mbar as carrier gas. The concentrations of HCO‐, HO2‐ and OH‐radicals were measured by laser magnetic resonance. The reaction F + H2CO → HF + HCO served as radical source. The experiments yielded the resultsmagnified imageFor the conditions used here HO2 + CO are found to be the only products formed in the reaction of HCO‐radicals with O2.
Rate Constants for the Reactions of OH‐Radicals with CH2O and HCO
Authors: Temps F. , Wagner H. Gg. 
Published: July 2012

AbstractThe rate constants for the reactionsmagnified imageandmagnified imagehave been determined at room temperature in an isothermal discharge flow reactor using laser magnetic resonance to monitor OH‐ and HCO‐radicals. For the study of reaction (1) low initial OH concentrations were used, so that stoichiometry corrections were negligible. By varying the surface to volume ratio of the flow reactors employed, wall effects were carefully controlled. From pseudo first order analysis of the OH‐decay a rate constant of k1(296K) = (4.9 ± 1.0) · 1012cm3/mol · s was obtained. The rate constant for reaction (2) was determined relative to k1 yielding k2(296K) = (1.1 ± 0.4) · 1014 cm3/mol·s.
Termination Rates by Time‐Resolved ESR. The N‐Hydropyridinyl Radical in Solution and the Influence of Non‐Uniform Radical Concentration on the Apparent Rate Constant
Authors: Leuschner Rainer , Krohn Holger , Dohrmann Jürgen K. 
Published: July 2012

AbstractThe rate constants (2 k) for the second‐order self‐termination reaction of the N‐hydropyridinyl radical have been measured by time‐resolved ESR during intermittent UV photolysis of pyridine in various solvents containing propanol(‐2). The frequency factor and the activation energy are (1.8 ± 0.4) · 1010 M−1 s−1 and (10.7 ± 0.4) kJ · mol−1, respectively, in propanol(‐2)/acetone (1:1 by volume) as obtained from the Arrhenius plot of 2 A: in the temperature range between 293 and 230 K. The rate constants at 285 K are (7 ± 1) · 108 M−1 s−1 in H2O/propanol(‐2)/acetone (2:1:1 by volume), independent of the pH value (7.5 – 13.7), and (6 ± 1) · 108 M−1 s−1 in neat propanol(‐2), the latter value being essentially diffusion controlled. The rate constants measured in propanol(‐2)/acetone (1:1) containing various amounts of water correlate with Kosower's solvent polarity parameter. The self‐termination reaction ultimately leads to the destruction of the pyridine ring. Finally, a model is presented for the correction of the influence of non‐uniform radical concentration on apparent values of second‐order rate constants as determined by time‐resolved ESR during intermittent photolysis.
Rate Constant of the Reaction HO + CO in the Presence of N2 and O2
Authors: Hofzumahaus A. , Stuhl F. 
Published: July 2012

AbstractThe kinetics of the reaction HO + CO was studied in the presence and in the absence of O2 using VUV flash photolysis of H2O and kinetic absorption spectroscopy of HO. In the absence of O2, the value of the rate constant was found to vary from 1.4 · 10−13 cm3 s−1 at low total pressures to (2.30 ± 0.16) · 10−13 cm3 s−1 at atmospheric pressure of N2. In the presence of traces of O2, a complex reaction mechanism is necessary to explain the HO decays. With recent rate data, the mechanism allows us to reinterpret the experimental data of Biermann et al. [9] which were significantly influenced by secondary reactions thus simulating the previously reported O2‐effect.
Photochemistry of Colloidal Metal Sulfides. 7. Absorption and Fluorescence of Extremely Small ZnS Particles (The World of the Neglected Dimensions)
Authors: Weller H. , Koch U. , Gutiérrez M. , Henglein A. 
Published: July 2012

AbstractExtremely small colloidal ZnS particles (diameter ∼ 1.7 nm) were made by either photo‐degradation of 3 nm particles or rapid precipitation in phosphate containing solution at pH = 7‐−8. The absorption spectra of these particles are different from that of macrocrystalline ZnS, and the changes are regarded as an indication for the transition from semiconductor ZnS to polymolecular ZnS with decreasing particle size. – The dependence of the intensity of the fluorescence on particle size, temperature, photoanodic corrosion and the quenching of fluorescence were investigated for colloids on a silicon dioxide carrier, in phosphate solution, and without a stabilizer. Photo‐anodic corrosion strongly improves the fluorescence properties. – One adsorbed Cd2+ ion per colloidal particle is sufficient for efficient quenching of the fluorescence. However, a new fluorescence band appears which is explained by the formation of a layer of 1:1 co‐colloid at the surface of the ZnS particles. – Methylviologen was also found to be a very efficient quencher. The decay of the fluorescence is wavelength dependent, i.e. the fraction of long‐lived fluorescence is greater at longer wavelengths. – A mechanism is discussed, where the fluorescence centers are anion vacancies, and fluorescence is emitted when electrons trapped in states of different energies and exhibiting different life‐times tunnel to the localized positive holes.
Negative Ions in the Gas Phase Observed in Electron Transmission and Electron Attachment Spectroscopy
Authors: Heni Martin , Kwiatkowski Georg , Illenberger Eugen 
Published: July 2012

AbstractA new electron transmission spectrometer is applied to study the formation of negative ions in ethylene and the fluoroethylenes. It is found that the electron attachment energy in the fluoroethylenes observed in electron transmission completely coincides with the energy of the resonances associated with the formation of F− (and various other stable negative fragments) observed in dissociative electron attachment. This demonstrates that the combination of electron transmission and dissociative electron attachment spectroscopy yields information on the formation and decomposition of molecular negative ions in the gas phase.
On the Determination of the Fractionation Factors of Aqueous Bromide and Iodide Ions by Proton NMR
Authors: El Seoud Monica I. , El Seoud Omar A. 
Published: July 2012

AbstractThe deuterium‐protium fractionation in aqueous solutions of KBr, NaBr, KI, and NaI was studied by 1H NMR. The fractionation factor of the bromide ion (ϕBr‐), and that of the iodide ion (π1‐) were determined from the dependence of the chemical shift of the water protons on the concentration of the solubilized salts, and on the deuterium content of the solvent. The values of the fractionation factors were: ϕBr‐ = 0.96 ± 0.05 and ϕ1‐ = 0.97 ± 0.04. These are practically the same as the one recently determined for the aqueous chloride ion. The present work is in good agreement with the results of other studies which demonstrated that the structure of the water in the solvation shells of these halide ions is only slightly disturbed.
New Developments in the Field of High‐Pressure Extraction of Natural Products with Dense Gases (Invited Lecture)
Authors: Stahl Egon , Quirin K. W. , Glatz A. , Gerard D. , Rau G. 
Published: July 2012

AbstractA short historical review is followed by a survey of more recent work, some of it still unpublished. Solubility determinations in the pressure range up to 3000 bar and at temperatures up to 80°C yielded new surprising results for the substance classes of the triglycerides, wax esters and sterols. The difficult problem of the high pressure extraction of flexible viscous masses, such as crude lecithin and similar pastes and slimes, could be elegantly solved by the continuous high pressure jet procedure. In the field of separation of substances of high vapour pressure, e.g. essential oils, new paths were opened up. We succeeded in separating selectively undesirable fatty oils, waxes and colouring matter. The procedure for the continuous deterpenation for the recovery of high quality concentrated flavours is also new. We could further show the possibility of removing lipophilic pesticides from plant material, e.g. DDT, γ‐HCH from sennae leaves and ‐pods.
Thermal Conductivity in Supercritical Fluids
Authors: Le Neindre B. , Garrabos Y. , Tufeu R. 
Published: July 2012

AbstractNow it is well established that the thermal conductivity of a fluid shows a strong enhancement in its critical region. Several experimental results are reported on the thermal conductivity of various fluids in their critical region. A tentative method is given to predict the thermal conductivity excess of any kind of pure fluid in its supercritical region. Results of the calculation are compared with experimental data of some fluid solvents.
1H NMR Studies on the Dynamics of Planar [C(NH2)3]+ Cations in the Crystal of Various Guanidinium Salts
Authors: Gima Shin‐Ei , Furukawa Yoshihiro , Nakamura Daiyu 
Published: July 2012

AbstractThe temperature dependences of 1H NMR spin‐lattice relaxation times and 1H NMR second moments were observed for guanidinium chloride, bromide, iodide, thiocyanate, nitrate, and perchlorate. The results of the NMR experiments carried out with the crystals of these compounds except the last one can be interpreted in terms of the C3 reorientation of the cation about its symmetry axis. The solid‐solid phase transition at 454 K reported for guanidinium perchlorate could be resolved into two phase transitions taking place successively at 450 and 452 K. In the low temperature phase of this salt, the C3 reorientation of the cation is activated. The occurrence of cationic self‐diffusion in the high temperature phase was confirmed by the measurements of 1H NMR relaxation times. The NMR motional parameters are evaluated for these cationic motions in the present salts. The phase transition temperature of guanidinium iodide was strongly depended on the grain size of the sample employed. Guanidinium bromide yielded a single 81Br NQR line at room temperature indicating that all bromide ions in the crystal are crystallographically equivalent in agreement with the results of X‐ray analysis.
Measurements of the Volumetric Properties for Perfluoro−2‐methylpentane in the Range of Temperatures 333 to 473 K up to 5.7 MPa
Authors: Momoda K. , Uematsu M. , Watanabe K. 
Published: July 2012

AbstractThe PVT properties and vapor‐pressures for 2‐CF3C5F11 have been measured in the range of temperatures 333 to 473 K and of pressures 0.1 to 5.7 MPa, which corresponds to density variation from 115 to 1368 kg/m3, by using a constant‐volume spherical piezometer. The experimental uncertainty of the temperature, pressure and density measurements were estimated to be less than 10 mK, 1.5 kPa and 0.12%, respectively. The temperatures of orthobaric densities were determined graphically based on the present measurements. The critical parameters were proposed to be ρc = 635 ± 6 kg/m3, Tc = 455.3 ± 0.3 K and Pc = 1.923 ± 0.012 MPa.