bluuebunny/crossref_metadata_2025_split huggingface dataset:
Weak Collision Effects in the Reaction CH3CO → CH3 + CO
Authors: Bencsura A. , Knyazev V. D. , Slagle I. R. , Gutman D. , Tsang W. 
Published: July 2012

AbstractRate constants for the unimolecular decomposition of CH3CO have been obtained as a function of temperature (420 ‐ 500 K) and helium density (3 ‐ 18 · 1016 atom cm−3), conditions which are in the second order region of the fall‐off curve. An Arrhenius expression for the low‐pressure limit unimolecular rate constant was obtained from the results, k1±(He) = (6.7 ± 1.8) · 10−9 exp[(‐6921 ± 126 K)/T] cm3 molecule−1 s−1. Using a Master Equation formalism to calculate values of k1, a set of the two energy parameters needed in the calculations, E± and ΔE)down (including its temperature dependence), was found that is within the range of expected values (including a temperature dependence in the case of ΔEdown), which, when incorporated into the Master Equation, provides calculated rate constants which agree well with the measured ones. They are E± = 65.3 ± 4.0 kJ mol−1 and ΔEdown = 65.6 + 0.271 T cm−1 (the latter, a parameterized expression, is valid only in the temperature range of this study). A transition state model for the unimolecular decomposition of CH3CO was produced which provides high‐pressure limit rate constants for this reaction (k1±(CH3CO ± CH3 + CO) = 2.50 · 1013 exp(‐8244 K/T) s−1 and k−1±(CH3 + CO ± CH3CO) = 7.64 · 10−13 exp(‐3073 K/T) cm3 molecule−1 s−1) and k(E) values for solving the Master Equation for reaction conditions that are in the fall‐off region. Fall‐off behavior of k1 and k−1 reported by others for several different bath gases was reproduced within the uncertainty limits of the experimental results using the Master Equation formalism incorporating the transition state model, the energy parameter E± given above, and reasonable values for ΔEdown for the different bath gases used. This Master Equation formalism and transition state model should provide unimolecular rate constants for reaction (1, ‐ 1) in the fall‐off region for additional bath gases using reasonable estimates of ΔEdown (e. g., values obtained for this energy‐transfer parameter for collisions between other polyatomic radicals and the bath gases of interest).
Shock Tube Measurements on the Thermal Decomposition of COS
Authors: Woiki D. , Roth P. 
Published: July 2012

AbstractThe thermal decomposition of carbonyl sulfide was studied behind reflected shock waves by direct measurements of the time‐dependent S(3P) atom concentration using atomic resonance absorption spectroscopy (ARAS). The experiments were performed in highly diluted mixtures of Ar with relative concentrations of COS between 4 to 100 ppm in the temperature range 1750 K ≤ T ≤ 2990 K at pressures between 0.5 bar and 1.5 bar. In reaction systems with very low concentrations (4 – 30 ppm COS in Ar) the initial reaction magnified image was found to dominante the initial slope of the measured S(3P) atom concentration profiles. The rate coefficient obtained results in: magnified image In reaction systems with higher initial concentrations of 100 ppm COS the measured S(3P) atom concentration profiles were additionally affected by secondary reactions consuming sulfur atoms. The most probable reaction is magnified image which has an influence on S(3P) at later reaction times. A rate coefficient for reaction (R2) of magnified image was determined from the present experiments by fitting calculated S(3P) atom profiles to measured ones. The given mean value is to be valid for temperatures near 2000 K.
Direct Measurement of the Rate Constant for CH3 + OH Recombination at 290 K
Authors: Hughes Kevin J. , Richard Pereira A. , Pilling Michael J. 
Published: July 2012

AbstractPreliminary rate data for reaction magnified image under pseudo‐first‐order conditions of excess CH3, are reported at 290 K, covering a 7 – 700 Torr pressure range. The radicals were generated by laser flash photolysis of CH3COCH3 and HNO3 at 193 nm and detected by absorption (216.36 nm, CH3) and laser induced fluorescence (excitation at 282 nm and detection at 308 nm, OH). The rate constants were determined by fitting to a 3 parameter analytical expression and to a 15 reaction model by numerical integration. The two techniques gave results in good agreement. The pressure dependence of the rate constant was fitted using inverse Laplace transformation to obtain microcanonical rate constants which were incorporated in a chemical activation master equation model. The limiting high pressure rate constant obtained at 290 K is (7.6 ± 0.8) · 10−11 cm3 molecule−1 s−1, where the error limits represent ±2σ. Combining the experimental data with those of Oser et al. at lower pressures suggests that there is an incompatibility between these results, those of W. Hack et al. and the enthalpy of formation of 1CH2.
Absolute Temperature Fields in Flames by 2D‐LIF of OH Using Excimer Lasers and CARS Spectroscopy
Authors: Arnold A. , Lange B. , Bouché T. , Heitzmann T. , Schiff G. , Ketterle W. , Monkhouse P. , Wolfram J. 
Published: July 2012

AbstractA tunable KrF‐excimer laser was used to obtain temperature fields in a laminar, premixed atmospheric pressure flame by 2D‐LIF of OH. Relative temperatures were obtained first from the intensity ratio of two sequentially excited rotational lines of the OH (A2Σ+ – X2H) transition in the (3–0) band near 248 nm. Because the ν' = 3 level is predissociative, this excitation scheme is less sensitive to collisional quenching than lower vibrational levels of OH (A2Σ+). Fluorescence from lower lying, non‐predissociative vibrational levels of OH (populated by vibrational transfer) was effectively suppressed by narrow spectral filtering of the (3–2) band of OH. Absolute temperatures were determined by calibration at one point with broadband CARS measurements; the excellent agreement of LIF and CARS profiles suggests that for these conditions and at the present level of accuracy no further corrections are needed. The uncertainty in the 2D‐LIF measurements of 7% (for a spatial resolution of 300 μm) is due mainly to shot‐to‐shot fluctuations of the beam profile. Based on the photon shot noise contribution (less than 1%), we estimate that, provided the beam energy and profile are accounted for, single‐shot measurements should be feasible with a spatial resolution of 300 μm and a precision of 2%.
Two‐Dimensional LIF Approaches for the Accurate Determination of Radical Concentrations and Temperature in Combustion
Authors: Meier U. , Kienle R. , Plath I. , Kohse‐Höinghaus K. 
Published: July 2012

AbstractLaser‐induced fluorescence (LIF) techniques for the quantitative, point‐wise measurement of radical concentrations and temperature were developed and applied in laboratory‐scale combustion systems. Currently, the potential of similar measurement strategies for accurate two‐dimensional, single‐pulse experiments is being investigated. The sensitivity of typical LIF approaches for the determination of temperature and concentration to several parameters, especially to collision processes, is examined. Instantaneous two‐dimensional two‐species fluorescence imaging is demonstrated in a turbulent H2 diffusion flame. Implications for the quantitative interpretation of these results are discussed in view of single‐pulse multi‐species spontaneous Raman measurements under similar conditions.
Comparing Laser‐Induced Fluorescence Measurements and Computer Models of Low Pressure Flame Chemistry
Authors: Jeffries Jay B. , Smith Gregory P. , Heard Dwayne E. , Crosley David R. 
Published: July 2012

AbstractLaser‐induced fluorescence measurements in low pressure flames, including hydrogen atom profiles, are examined as crucial tests of models of combustion chemistry. Both absolute and relative spatial profiles of reactive intermediate concentrations are useful for comparison. Careful temperature measurements for use as model input are emphasized. Radial OH LIF profiles in flames below 10 torr show an expanding flame which must be properly treated in model calculations. Diluted flames at pressures above 30 torr provide a preferred one‐dimensional fluid flow.
Emissionsminderung bei Braunkohlefeuerungen
Authors: Hein Klaus R. G. 
Published: July 2012

AbstractIn compliance with the Large Furnace Order (GFAVO) in Germany, existing power stations had to be retrofitted with emission control devices. For brown coal fired boilers the emission reduction is achieved for SO2 by applying the wet scrubber technique using limestone and for NOx by modifying the combustion process.
Direct Detection of an Attractive Interaction between Anions and Hydrophobically Hydrated Unpolar Groups
Authors: Holz Manfred , Sörensen Martin 
Published: July 2012

AbstractThere exist some indirect hints that in multicomponent aqueous electrolyte solutions anions are attracted to hydrophobically hydrated alkyl groups and it seems that this phenomenon is of general nature. In order to detect for the first time directly such an attractive interaction we have determined intermolecular dipole‐dipole relaxation rates (1/T1)inter of protons residing on the hydrophobically hydrated species dimethylformamide (DMF) and dimethylacetamide (DMA), respectively, in aqueous solutions containing as probe ions either tetraphenylborate (Ph4B−) or tetraphenylarsenate (Ph4As+) ions. We have also measured the translational diffusion coefficients D of DMF, DMA and the ions in the solutions DMF/D2O + phenyl salt (NaPh4B or Ph4AsCl) and DMA/D2O + phenyl salt in function of the salt concentration. This allowed the determination of the so‐called Aij‐parameter with respect to the amide‐ion interaction. This Aij‐parameter is connected with an integral over the pair correlation function and the results clearly show that there is a stronger attractive interaction between the hydrophobically hydrated CH3‐groups and anions than with cations. In a simple model we explain this peculiar attraction by preferentially oriented water molecules at the hydrocarbon‐water interface.
In‐situ Study of the Defect Structure of Wüstite Fe1‐xO by Diffuse Elastic Neutron Scattering
Authors: Schweika W. , Hoser A. , Martin M. 
Published: July 2012

AbstractIn‐situ diffuse neutron scattering experiments were carried out to investigate the defect structure of wüstite Fe1‐xO. The data were collected at various temperatures from room temperature to 1150°C and at deviations from stoichiometry, x, from 0.05 to 0.13. Diffuse peaks were found at Q = 2π/a (1.66, 0, 0) and Q = 2π/a (0.83,0.83, 0.83). Within the stability field of wüstite the intensity of these diffuse maxima scales with the defect concentration. Neither the 13:4 defect clusters proposed from earlier X‐ray experiments, nor a simple vacancy defect with a spherical displacement field (as found in Mn1‐xO) are compatible with our observations.
Metal‐Rich Sulfides of Mixed Tantalum and Niobium: A New Chemical Concept
Authors: Yao Xaioqiang , Marking Greg , Franzen Hugo F. 
Published: July 2012

AbstractThe structures of the metal‐rich sulfides of Nb and Ta are briefly reviewed, and it is suggested that the differences between the structures containing Nb and those containing Ta indicate the possibility of novel ternary compounds. The existence of four unique compounds of this type and their structures are discussed. The interplay of first‐order bonding energy and configurational entropy are shown to lead to a plausible explanation for the formation of the unsual materials. The explanation is supported with extended Hückel calculations and consideration of metal‐metal interactions scaled by the Pauling bondorder equation.
Ordering Phenomena and Demising in the Quasiternary System HgTe/CdTe/Ga2Te3
Authors: Zeppenfeld Astrid , Leute Volkmar 
Published: July 2012

AbstractThe phase diagram of the quasiternary system Hg(3–3k‐3l)Cd3lGa2kTe3 for the temperature range 600 < T/K < 1000 was investigated by X‐ray diffraction, by DTA and DSC measurements, and by electron microprobe analysis. It is shown that ordered structures are formed at special concentrations of structural vacancies. Depending on temperature and concentration, continuous order‐disorder transitions can be detected. Beside a spinodal miscibility gap, several structural miscibility gaps and a three phase region occur.s
Effective Pair Interactions in Transition Metal Carbides
Authors: Klíma J. , Weinberger P. , Herzig P. , Neckel A. 
Published: July 2012

AbstractEffective pair interactions (EPI) up to 4th nearest neighbour (NN) have been calculated for TiCx and NbCx as a function of vacancy concentration using the KKR‐CPA implementation of the generalized perturbation theory (GPT). Results are compared to experimentally determined EPIs and the agreement is discussed.
New Copper Phosphates as Ionic or Mixed Conductors
Authors: Warner T. E. , Milius W. , Maier J. 
Published: July 2012

AbstractAs part of a search for solid‐state copper ion conductors, new copper phosphate compounds of the Nasicon or alluaudite type structure were synthesized. Compounds with the former structure are reported here in more depth. CuTiZrP3O12 and the previously prepared compound CuTi2P3O12 were found to be copper ion conductors with a relatively low electronic contribution, and comparable both in structure and in conductivity behaviour to both CuZr2P3O12 and the NaZr2P3O12 end‐member of the classical Nasicon composition range. In contrast to the Cu(I) halide conductors these phases are stable under ambient conditions. Partial substitution of Zr by Sc, or Ti by Cr (rather than Si for P) results in a new Cu‐rich compound Cu2ZrScP3O12, together with the previously prepared compound Cu2TiCrP3O12, both showing expectedly very high Cu+ conductivity comparable to Nasicon compounds with a similar charge carrier concentration. A new related phase CuTiCrP3O12 was also synthesized. Magnetic measurements, Wagner‐Hebb polarization and e.m.f. measurements performed to elucidate partial conductivity contributions and valence states are discussed. The e.m.f. results obtained with Cu‐activity cells reveal a predominant ionic conductance together with a minor but not negligible electronic contribution resulting in a fast copper diffusion. Cu–Fe and Cu–Mg phosphates were also prepared for the first time as first examples of quaternary compounds in the Cu–Fe–P–O and Cu–Mg–P–O system respectively. These materials, Cu1,3Fe3P3O12 and Cu2Mg3P3O12 were found to be of the alluaudite structure type, with predominant electronic conductivity at high temperature.
Electronic Structure of B2‐NiTi and ‐PdTi
Authors: Bihlmayer G. , Eibler R. , Neckel A. 
Published: July 2012

AbstractThe electronic structure of B2‐phase NiTi and PdTi is determined by means of the self‐consistent Linearized Augmented Plane Wave (LAPW) method. The bandstructures, local densities of states and electron densities for the two compounds are compared and the differences analyzed. The calculated broadened DOS show close resemblance with measured photoelectron spectra. Accurate calculations of the Fermi surface and some Fermi surface‐related properties are also presented. We investigate the topology of the Fermi surface and calculate the generalized susceptibility of non‐interacting electrons and, approximately, the electron‐phonon contribution to the dynamical matrix of phonons, in order to estimate the influence of nesting regions on the electron‐phonon coupling, thus establishing a relation between the electronic structure and the martensitic transformations of these compounds. The calculations suggest that the appearance of “bottle‐necks” in the Fermi surface of PdTi may be responsible for the different transformational behaviour of these two alloys.
Defect Model Applied to the Diffusion in the Intermetallic Phases ε‐(Ag, Sn) and ε‐(Cu, Sn)
Authors: Schwitzgebel G. , Rupp R. 
Published: July 2012

AbstractA substitutional defect model of binary hexagonal closed packed structures is developed based on interactions of nearest neighbours and on the configurational entropy of randomly distributed deviations from stoichiometry. The dependence of the thermodynamic quantities on composition can be expressed within the homogeneity range by an order parameter. – With the thermodynamic data of ε‐(Ag, Sn) and ε‐(Cu, Sn) the order parameters of Ag3Sn and Cu3Sn were determined (523 K–623 K) and used for calculating Sn‐activity curves of the the phases. By the help of these curves chronoamperometric diffusion experiments could be evaluated. The contributions of the bulk material and the grain boundaries to diffusion are given by volume and grain boundary diffusion coefficients.
7Li‐NMR Study of Diffusion‐Induced Spin‐Lattice Relaxation in Glassy and Crystalline LiAlSi2O6
Authors: Franke W. , Heitjans P. 
Published: July 2012

AbstractIn order to study the effect of structural disorder on the diffusion of mobile ions, both the glass Li2O · Al2O3 · 4SiO2 and its crystalline counterpart (β‐spodumene) were investigated by 7Li‐NMR. The spinlattice relaxation (SLR) time T1 of 7Li was measured as a function of temperature T from 150 K to about 960K in the glass (glass transition temperature) and 1300 K in the polycrystalline sample. The frequency ν was varied in the range 10 MHz to 100 MHz. Both in the glass and the crystal a diffusion‐induced peak in T1−1(T) was observed. Comparison of the positions of the maxima and the slopes of the low‐T sides of log T1−1 vs 1/T curves shows that the Li+ jump rate in the glass is higher and the activation energy is lower than in the crystal. In both cases the ν and T dependences of the diffusional SLR rate strongly deviate from the BPP model. In particular, the ν dependence of T1−1 on the low‐T sides is sublinear or, at most, linear. The activation energies obtained from the temperature regime above the maximum and those below at various frequencies are briefly compared with corresponding values from a.c. impedance measurements on the same samples.
Magnetic and EPR Spectroscopic Investigations on a Ferromagnetic Coupled Trinuclear Cu(II) Complex
Authors: Fleischhauer P. , Gehring S. , Haase W. 
Published: July 2012

AbstractMagnetization measurements and X‐band EPR investigations on the trimeric exchange coupled Copper(II)‐complex [(Cu3(C6H5CO2)4{(C)2NC2H4O}2(CH3OH)2] are reported. The field dependence of the magnetization at 3.7 K is consistent with a quartet ground state and proofs that ferromagnetic exchange coupling is operative between adjacent Cu(II) – centres in the trimeric molecule. – A strong temperature dependent variation of the g value from geff ≈︁ 4.3 at liquid helium temperature to geff ≈︁ 2.6 at room temperature was observed in the EPR experiment. Different explanations for the g shift are discussed.
Ein Verfahren zur Berechnung der temperaturabhängigen Suszeptibilität itineranter Systeme aus Grundzustandsgrößen
Authors: Kirchner B. , Weber W. , Voitländer J. 
Published: July 2012

AbstractThe temperature dependence of magnetic properties of itinerant electron systems is predominated by the excitation of spin fluctuations. To describe the energy of the spinfluctuation field, we use a functional, which treats the fluctuation modes only in the static limit and which includes the energy of the coupling between different modes in a local, i.e. wavevector‐independent way. Along the lines of the Murata‐Doniach approach we derive formulas for the free energy and the susceptibility of the system, using a variational principle. Except for the approximations mentioned above our energy functional is quite general, going beyond the Ginzburg‐Landau expansion. It is possible to deal with arbitrary fluctuation amplitudes. Furthermore the energy functional can be completely derived from first principle calculations for the ground state of the system. Thermodynamic properties may thus be traced back to details of the bandstructure. We apply our method to the calculation of the temperature dependent susceptibility of Pd metal and PdAg with very small Ag concentrations.
Lateral Interaction between Adsorbates at Ionic Surfaces: Theoretical Investigation of the CO Vibrational Frequency Shift at MgO(001)
Authors: Neyman Konstantin M. , Rösch Notker 
Published: July 2012

AbstractThe adsorption of CO molecules at the MgO(001) surface is investigated by the LCGTO‐LDF cluster method for the low‐coverage limit as well as for a monolayer coverage. A static adsorbate‐adsorbate contribution to the partial red shift of the C–O vibrational frequency with increasing surface coverage is calculated in agreement with experiment. This red shift is related to a small adsorbate‐to‐substrate σ charge transfer which modifies the electrostatic field on the surface and thus is a “solvent” effect. No transmission of the donated charge through the substrate is found. Both the low‐coverage and the monolayer models predict an approximate doubling of the C–O vibrational intensity as compared to free CO. This intensity enhancement derives to a large extent from a change of the π component of the CO dynamical dipole moment due to a Pauli repulsion between the adsorbate and the nearest‐neighbour surface anions.
Crystal Chemistry and Magnetic Behavior of Compounds RE3Mn4Sn4, RE = La, Ce, Pr, Nd, Sm and MM (Mischmetal)
Authors: Weitzer F. , Hiebl K. , Rogl P. , Noël H. 
Published: July 2012

AbstractNovel ternary stannides RE3Mn4Sn4 have been synthesized by the arc melting technique, starting from the pure elements. All compounds with the early and large rare earth metals (RE = La, Ce, Pr, Nd, Sm) and mischmetal (MM) were found to be isotypic with the Gd3Cu4Ge4‐type (space group, Immm‐D2h25, No. 71; Z = 2). The crystal structure of the Gd3Cu4Ge4‐type stannides is a combination of structural slabs RESn2 of the AlB2‐type and slabs RE4Mn2Sn2, common to the ThCr2Si2type. The (Ce, Pr, Nd, Sm)3Mn4Sn4 compounds exhibit antiferromagnetism. For (Pr, Nd)3Mn4Sn4 an onset of a spinflip process is indicated at a magnetic field Hcrit > 2.5 Tesla. La3Mn4Sn4 as well as Ce3Mn4Sn4 show broad maxima of the susceptibility at T ∼ 300 K, possibly due to demagnetizing effects caused by valence instabilities. The manganese atoms carry localized effective moments of 3 μB and 5 μB, respectively.
Structure, Photoabsorption and Reversible Reactivity of Faujasite‐Supported Dispersions of CdO and SnO2
Authors: Wark M. , Schwenn H.‐J. , Schulz‐Ekloff G. , Jaeger N. 
Published: July 2012

AbstractHigh dispersions of CdO and SnO2 in a faujasite matrix are obtained by consecutive ion exchange, alkaline precipitation and calcination. The particle sizes in the range 5 to 20 nm are inferred from electronic spectra, transmission electron microscopy and X‐ray diffraction. The correlation between the blue shift of the absorption edge and the particle size is described by the effective mass approximation. The reactivity of CdO dispersions for the formation of carbonate increases with decreasing particle size.
Influence of Incorporated Copper on the Formation, Solid State Structure and Electrochemical Properties of γ‐FeOOH
Authors: Schneider M. , Stratmann M. 
Published: July 2012

AbstractIt is well known, that the rate of the atmospheric corrosion of iron is slowed down considerably, if the metal is alloyed by small amounts of Cu. This effect is specifically pronounced during those times, when the metal surface is covered by thin electrolyte layers. As then the oxygen reduction is rate determining for the corrosion rate, the kinetics of the oxygen reduction is slowed down on Cu‐containing steels with respect to pure iron. On pure iron oxygen is reduced within the oxide scale at electron conducting oxide crystals. Such oxides contain high amounts of Fe2+ states and result from an electrochemical reduction of γ‐FeOOH. Therefore it is quite likely, that on Cu‐containing steel the solid state properties of the oxide scale are changed such, that the electronic conductivity decreases. – In this study model electrodes of Cu‐doped γ‐FeOOH are investigated. The morphology of the scale is analysed by SEM, the chemical state of Cu and Fe by XPS and the structure of the scale using FT‐IR spectroscopy. The results clearly show, that the morphology of the Cu‐doped oxide is changed significantly and XPS data suggest, that the reducibility of the doped oxide is much less than the one of undoped γ‐FeOOH.