bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isomerization of Meta‐Xylene Over Pentasil‐Type Microporous Gallosilicates
Authors: Richter M. , Kosslick H. , Tuan Vu Anh , Richter‐Mendau J. , Parlitz B. , Ehrhardt K. , Vorbeck G. , Szulzewsky K. 
Published: July 2012

AbstractThe isomerization of meta‐xylene under normal pressure was studied in the temperature range 570–770 K on three catalyst series, viz. (i) gallosilicates with a constant Si/Ga ratio of 50, but different synthesis times ranging from 5 to 96 h, (ii) gallosilicates with a higher (100) and lower (25) Si/Ga ratio after 48 h and 96 h crystallization time, and (iii) a series that included a ZSM‐5 zeolite, a gallosilicate, and a ferrisilicate, all with comparable concentrations of Brønsted acid sites. The characterization of the catalysts is based on XRD, electron microscopy (TEM, SEM), ammonia thermodesorption, thermoanalysis and n‐hexane adsorption. Synthesis products that were characterized by X‐ray diffraction to have 100% crystallinity, acquire further acidity when the synthesis time is prolonged. This effect is due to an additional insertion of gallium in framework positions from a reservoir of nonframework gallium species. — The isomerization on gallosilicates proceeds with negligible disproportionation to toluene. The activity is intermediate, compared to the ZSM‐5 zeolite and to the ferrisilicate. The shape selectivity of the gallosilicates is inversely related to the crystallinity. — The kinetics of the isomerization can be described by a parallel two step model, in good agreement with experimental results. The significance of internal mass transport effects is discussed.
Electronic Spectra of 1,4‐Diketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole in the Solid State
Authors: Mizuguchi Jin , Rihs Grety 
Published: July 2012

AbstractThe title compound (DPP) is a new red pigment based on the diketopyrrolopyrrole chromophore. The evaporated film of DPP has a vivid red whose absorption spectrum is very similar to the molecular spectrum in solution. When exposed to acetone vapor, the film turns orange, and changes in photoelectrical properties take place. Electronic spectra of DPP have therefore been investigated mainly in evaporated films from the standpoint of π‐π interactions along the stacking axis. Special attention has been paid to the temperature dependence of the absorption spectra in connection with lattice contractions. The effective overlap of π‐electrons between molecular planes strongly influences the electronic system and perturbs the molecular‐like spectrum in the solid state. Several solid state spectra can arise from DPP, depending on the extent of the π‐π interactions.
Electronic Properties of 1,4‐Dithioketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole in Solution and in the Solid State
Authors: Mizuguchi Jin , Rochat Alain Claude , Rihs Grety 
Published: July 2012

AbstractThe near IR optical absorption of the title compound (DTPP) is of practical importance for laser printers and information storage applications based on GaAs laser diodes. Electronic properties of DTPP have been investigated in solution and in the solid state from the standpoint of deprotonation and intermolecular hydrogen bonding. The electronic state of the dithioketopyrrolopyrrole chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group. The deprotonation (= N−) in solution leads to increased electron density on the nitrogen atom. As a consequence, there is more overall electron density in the chromophore which contributes to a large bathochromic displacement. A similar increase in electron density is also operative in the solid state through the inter‐molecular hydrogen bonds between the NH group of one DTPP and the sulfur of the neighboring molecule. This is responsible for the large bathochromic shift of DTPP from the solution to the solid state. The visible absorption in the solid state is attributed to transitions along the molecular plane. On the other hand, the strong near IR absorption is interpreted as being due to interplanar π — π interactions along the stacking axis perpendicular to the molecular plane.
TiO2 Thin Films Prepared by Pulsed Beam Chemical Vapor Deposition from Titanium Tetraisopropoxide and Water
Authors: Döring H. , Hashimoto K. , Fujishima A. 
Published: July 2012

AbstractTiO2 thin films were deposited by pulsed beam chemical vapor deposition from titanium tetraisopropoxide and H2O vapors. Each reactant gas was introduced to a chamber alternately using commercial automobile electric fuel injectors as beam sources. These thin films, deposited at various substrate temperatures, were characterized by measuring optical absorption spectra, X‐ray diffractions and X‐ray photoelectron spectra. Their properties were compared with those of TiO2 films deposited by electron beam evaporation.
Electrochemical and Thermodynamic Aspects Controlling the Iron‐Hexacyanoferrate Redox System in Ethylene Glycol‐Water Mixed Solvent
Authors: Hilal N. H. , El‐Shazly Sh. A. , Bekheet A. M. , Badawy W. A. 
Published: July 2012

AbstractThe effect of ethylene glycol on the electrochemical behaviour of the Au‐rde in the iron‐hexacyanoferrate redox system was studied. A standard potentiostatic technique was used to trace the kinetic parameters controlling the anodic and cathodic processes occurring at the electrode/electrolyte interface. The thermodynamic parameters of the ethylene glycol‐water mixed solvent were evaluated. The results revealed that the presence of ethylene glycol in the solvent mixture retards the diffusion processes and enhances the charge transfer kinetics. The rate of the anodic process was found to be entropy controlled and the isokinetic temperature of the cathodic process was fairly close to the experimental temperature indicating the presence of compensation effects between the entropy and enthalpy changes.
Melt‐Spinning of AB5.5‐Type Hydride‐Forming Compounds and the Influence of Annealing on Electrochemical and Crystallographic Properties
Authors: Notten P. H. L. , Daams J. L. C. , Einerhand R. E. F. 
Published: July 2012

AbstractNon‐stoichiometric almost single‐phase AB5.5 materials were prepared using the melt‐spinning technique. Characteristic of these materials is the anisotropically deformed crystal lattices (decreased a‐axis and increased c‐xis), resulting from the excess of B‐elements incorporated in the hP6‐CaCu5 structure. These materials show (i) an excellent long‐term stability during electrochemical cycling in alkaline solution, indicating that the oxidation resistivity strongly depends on the extent of the crystal lattice deformation and (ii) a relatively poor electrocatalytic activity which can be attributed to the absence of highly catalytic second‐phase alloys. Annealing of the as‐prepared samples induces the deformed crystal lattice to relax by secreting the excess of B‐elements. As a consequence, double‐phase materials are formed, consisting of hydride‐forming compounds with compositions close to the AB5 stoichiometry and second‐phase alloys. These double‐phase materials combine a relatively poor long‐term cycling stability with a high electrocatalytic activity.
Studies of Polymer Solvation by Dielectric Relaxation Spectroscopy V: Polyvinylpyrrolidone in Pyrrolidone
Authors: Rohmann M. , Stockhausen M. 
Published: July 2012

AbstractThe dielectric spectrum of PVP 1200 in pyrrolidone solution is measured between 2 MHz and 72 GHz at temperatures of 20, 40, and 60°C. Polymer concentrations are up to a monomole fraction of 0.5. The results are described in terms of Debye type components. For pure pyrrolidone two components are required which are probably caused by associated and monomeric solvent. Additional low frequency components ascribable to the polymer appear with PVP solutions. Here the solvent contributions can be distinguished into unaffected, loosely affected and tightly bound solvent. As a peculiar feature there is direct evidence of the interchange of solvent‐solvent to solvent‐polymer interaction.
The Vaporization of Cesium/Antimony Alloys under Equilibrium and Nonequilibrium Conditions
Authors: Hartmann Andreas , Weil Konrad G. 
Published: July 2012

AbstractWe evaporate cesium/antimony alloys either from a Knudson cell or from a Langmuir source. The compositions of the resulting molecular beams are determined mass spectrometrically. Using a quartz microbalance, we can determine total evaporation rates of the alloys. In all cases the alloys evaporate incongruently, antimony is enriched in the vapor. Comparison of Knudsen data with those obtained from Langmuir evaporation enables us to calculate evaporation coefficients for the individual evaporating species. The intermetallic molecules have evaporation coefficients in the order of magnitude of 0.1–0.5, while atomic cesium has an evaporation coefficient of about 0.01. From this we conclude that adsorbed neutral cesium is not a precursor for the formation of the intermetallic molecules.
Thermodynamics of Adsorption of Methanol on Metal Dopant/Active Carbon Systems
Authors: Afzal M. , Mahmood F. , Saleem M. 
Published: July 2012

AbstractAdsorption of methanol on active carbon and metal doped carbons (Ni, Cu, Zn and Cd) has been studied as a function of temperature. From adsorption data, differential heats and molar entropies of adsorption were calculated as a function of coverages. The values of isosteric heats of adsorption are found to be higher for metal doped carbons which may be due to the chemisorption of methanol molecules on metal sites present on the surface of active carbon. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated from virial isotherm expression and interpreted therefrom. It is observed that metal dopant/active carbon systems are synergic, exhibiting more adsorption affinity for methanol than the sum of its constituents. Results show that an increase in adsorption affinity for metal doped carbons is not due to configurational factors affecting the entropy of adsorption but because of large exothermicity in the enthalpy of adsorption.
Mechanistic Studies on Uranyl Ion Initiated Photopolymerization of Acrylamide
Authors: Burrows Hugh D. , Faria Isabel M. D. , Formosinho Sebastião J. , Miguel Maria Da Graça M. , Martins Luis J. A. , Mailhot Gilles , Bolte Michèle 
Published: July 2012

AbstractThe mechanism of the uranyl ion photoinitiated polymerization of acrylamide has been studied in aqueous solutions and in acetone. Steady‐state and dynamic luminescence quenching studies show that initiation proceeds through a thermally activated bimolecular interaction between *UO22+ and monomer involving electron or charge transfer. Results from various studies show that the mechanism previously suggested for this process, involving energy transfer, is incorrect. ESR studies suggest that initiation involves formation of a uranium(V)‐radical pair. Polymerization then proceeds through a radical mechanism in both solvents. With the exception of the chloride, the yields do not depend upon the counter‐ion. Polymer is frequently produced with adsorbed uranyl ions, which can be separated by dialysis. In agreement with previous studies, photopolymerization proceeds without significant overall reduction in the uranyl concentration. It is shown that this is probably due to any intermediate uranium(V) being reoxidized by monomer, with concurrent thermal initiation of polymerization.
Ultrasonic Studies of Rotational Isomerism and P,V,T Data of 2‐Methylbutane at Elevated Pressures
Authors: Walter Thomas , Bardelmeier Ute , Würflinger Albert 
Published: July 2012

AbstractUltrasonic velocity and attenuation have been measured in 2‐methylbutane from 203 to 253 K and pressures up to 100 MPa. P,V,T data are determined in the temperature range from 210 to 290 K up to pressure of 300 MPa. Both activation and equilibrium parameters are derived from the temperature and pressure dependences of the relaxation frequency and the maximum of absorption. P,V,T data enable us to treat the rotational isomerism under isochoric conditions. Activation volumes of the order 4–8 cm3 mol−1 are observed, increasing with increasing temperature. The isochoric activation energy is of the order of 15–18 kJ mol−1, decreasing with increasing density. This finding is in reasonable accordance with the negative volume change associated with the rotational isomerism.
Nuclear Spin Dynamics (I = 1/2) under the Influence of Random Perturbation Fields in the “Strong Collision” Approximation
Authors: Bauer W. R. , Schulten K. 
Published: July 2012

AbstractWe investigate the relaxation of a spin 1/2 system by random perturbation fields in the strong collision approximation. In contrast to prior studies no assumptions are made about the fluctuation frequency or about the magnitude of the perturbation fields. A general result for the Laplace transform of the spin lattice and phase relaxation is derived. We discuss the result for phase relaxation induced by a perturbation field with only two opposite modes along the x, y and z axis. Using the method of the general moment approximation we demonstrate how the spin lattice relaxation can be approximated by a sum of exponentials, and we discuss approximations by a single exponential and a bi‐exponential function.
Polarizability α (ω, T, ρ) of Small Molecules in the Gas Phase
Authors: Kerl Klaus , Hohm Uwe , Varchmin Hartmut 
Published: July 2012

AbstractThe dependence of the mean dipole polarizability α(ω,T, ρ) of small molecules in the gas phase on electromagnetic radiation frequency ω, temperature T, and molar density ρ is discussed. Experimental results are presented for the noble gases, the molecular gases H2, N2, O2, CO2, CH4, C(CH3)4, CH3OH, CF2Cl2, and the gas mixture air. Hints to some rather unusual effects concerning α(ω,T, ρ) are given, too. In each case α(ω,T, ρ) was derived from precise interferometric measurements of the refractive index n(ω,T, ρ) of the gas in the visible (VIS) frequency range.
Chemical Reactivity. Chemical Reactions of Metal Cluster Cations in a Fourier‐Transform ion Cyclotron Resonance Mass Spectrometer
Authors: Irion Manfred P. , Schnabel Patrick 
Published: July 2012

AbstractMetal cluster cations are generated in an external ion source by sputtering the respective metal foil with 20 keV Xe+ primary ions and are then injected by a series of electric lenses into the analyzer cell of a home‐built Fourier‐Transform Ion Cyclotron Resonance Mass Spectrometer (FT‐ICR MS). There, they are trapped in a magnetic field of 7 T for several tens of seconds through electrostatic deceleration and pulsed addition of a bath gas. Collisions serve to remove excess kinetic as well as inner energy and cool them to nearly room temperature. By the application of a radio frequency (RF) ejection pulse, one specific ion mass may be isolated. – Chemical reactions of the stored metal cluster ions may be studied by admitting a reactive gas with a continuous leak valve. We have investigated a variety of combinations metal/gas and found often surprising size‐specific effects. For some systems, the reactivity as a function of cluster size changes in an abrupt way whereas for others it varies smoothly. Transition metal clusters predominantly show dehydrogenation reactions, the degree of which depends on the nature of the metal as well as on cluster size. In addition, it is demonstrated that naked gas phase metal cluster ions may possess catalytic activity: Fe4+ ions bind up to four molecules of ethene under hydrogen elimination and liberate benzene through collision‐induced dissociation at low energy. The assertion of catalysis is proven by a complex sequence of five consecutive mass spectrometry steps (an (MS)5 experiment), in which the originally trapped Fe4+ clusters actually do initiate the synthesis of benzene twice.
Reactions of Fe Ions (3 ≤ n ≤ 12) with ethane, ethylene and acetylene – reaction paths and rate constants –
Authors: Schnabel Patrick , Irion Manfred P. 
Published: July 2012

AbstractWe report on measurements of absolute rate constants of the reaction Fe + M → Fen(M–2H)+ + H2, with M = ethane, ethylene, and acetylene. The clusters were prepared by sputtering and the reactions took place in the ICR cell of a FT mass spectrometer. With acetylene, all clusters with 4 ≤ n ≤ 13 react and the rate constants do not display any significant size dependence. With ethylene Fe and Fe react, but the latter with a markedly smaller rate. Only Fe shows a detectable rate with ethane. Fe4H+ does not, however, react with ethane. The addition of H to iron cluster ions can also have the opposite effect; with acetylene Fe3H+ reacts, while Fe does not. – It appears that pronounced size specificities are more likely the more saturated the reacting molecule is. This statement is corroborated by results of earlier work with other molecules.
Shell Dependent Chemical Reactivity of Large Sodium Clusters
Authors: Lange T. , Göhlich H. , Näher U. , Martin T. P. 
Published: July 2012

AbstractIt has been shown in the past that sodium clusters possess an electronic shell structure characteristic of a nearly spherical, finite Fermi system. For this reason they might be expected to behave like giant atoms. In fact, closed shell clusters are known to have particularly high ionization energies. In this paper, we report variations in the reactivity of Nan for 100 ≤ n ≤ 800 with molecular oxygen. Clusters with completely filled electron shells are found to be relatively unreactive.
Gas‐Phase Reactivity of Sulphur Cluster Cations and Anions by FT‐ICR Investigations
Authors: Schindler Thomas , Berg Christian , Niedner‐Schatteburg Gereon , Bondybey Vladimir E. 
Published: July 2012

AbstractThe gas phase reactions of sulphur cluster cations S (n = 2,…,8) and anions S (n = 2,…,6), have been studied by means of a Fourier‐Transform‐Ion‐Cyclotron‐Resonance (FT‐ICR) mass spectrometer. While with several simple gases no reactions, besides some fragmentation, were observed, some of the clusters were found to be reactive towards NO, NH3 and particularly NO2. Where product ions were detected, relative and absolute rate constants were extracted from the data, while only upper limits could be estimated for those systems which do not yield observable amounts of products. We discuss in most detail the reactions of NO2 which reacts with both the anions and cations. By comparing the reactivities of clusters of differing charge we try to deduce the influence of charge versus structure.
Chemical Reactions in Mixed Molecular Clusters, Studied by Resonant Two‐Photon Ionization
Authors: Brutschy Bernhard 
Published: July 2012

AbstractAfter a short overview on the different types of intracluster reactions, observed so far, this survey focuses on nucleophilic ipso‐substitution (SN) reactions in clusters consisting of one (1,n)‐chlorofluorobenzene cation with one (1:1) of two (1:2) ammonia molecules. The reaction efficiencies are compared with that in bimolecular ion‐molecule reactions as studied by Thölmann and Grützmacher. Two types of (SN2)‐reactions are observed, 1. abstraction of a chlorine radical, 2. abstraction of HX (X = Cl,F). The latter reaction is only observed in clusters but not in an ion‐molecule gas phase collision. For both channels different mechanisms are proposed. The Cl‐production strongly depends on the dipole moment of the neutral chromophore. It is rationalized in the framework of the theory of Shaik and Pross on polar reactions by an electron transfer as rate determining step. The HX formation channel, on the other hand is explained by a transition state with a concerted electron and proton transfer. It is strongly promoted by additional solvent molecules, probably due to bifunctional catalysis.
Proton Transfer in Mixed Molecular Clusters After Resonant Two Photon Ionization
Authors: Riehn Ch. , Lahmann Ch. , Brutschy B. , Baumgärtel H. 
Published: July 2012

AbstractProton transfer reactions in clusters of aromatic cations and polar molecules have been studied by resonant two‐photon ionization spectroscopy. Two types of protonation reactions have been observed. While cations of methylated derivatives of benzene may act as an acid, inducing a direct proton transfer to the solvent, cations of non‐methylated derivatives may be neutralised by electron transfer with the solvent moiety, followed by intrasolvent proton transfer. If the derivative contains different substituents (o‐chlorotoluene), proton transfer competes with nucleophilic substitution. The branching ratio of both channels depends on the number of solvent molecules in the cluster.
Excitation, Fragmentation and Decay Processes. Core Level Excitation in Molecular Clusters
Authors: Rühl Eckart 
Published: July 2012

AbstractCore level excitation in homogeneous molecular clusters is reported. Clusters of nitrogen and nitrous oxide are excited with monochromatized synchrotron radiation in the energy regime of the nitrogen K‐edge (390–460 eV). The near‐edge structure (NEXAFS) of mass selected cluster cations is compared to spectra of the isolated molecules and the condensed phase species. It is found that the photoionization efficiency curves of small cluster cations change their shape as the neutral cluster size is increased. Finally, the spectral shape becomes remarkably similar to ion yield curves of cations desorbing from the solid. This behavior is rationalized in terms of different fragmentation mechanisms, initiated by single and double ionization. Dissociative double ionization (Coulomb explosion) within molecular clusters is measured directly with the photoion‐photoion‐coincidence (PIPICO) technique. The fragmentation pathways are discussed in terms of electrostatic charge separation in doubly charged clusters. The results are consistent with the Knotek‐Feibelman mechanism for cation desorption from the solid.
Delayed Ionization of Photoexcited Niobium and Niobium Oxide Clusters
Authors: Athanassenas K. , Leisner T. , Frenzel U. , Kreisle D. 
Published: July 2012

AbstractThe delayed emission of electrons from hot refractory metal clusters can be regarded as the molecular equivalent of “thermionic emission”, which is well‐known for metal surfaces. Niobium clusters – generated via pulsed laser vaporization technique – were exposed to a 10 ns laser pulse, and the delayed emission of electrons from the clusters was recorded as a function of cluster size as well as time after the multiphoton excitation. A large yield of NbnOx+ (x = 0,1,2, and 3) cluster ions, which were born as late as microseconds after the laser pulse, has been detected for n > 5. The data are discussed in terms of a model based on the Richardson‐Dushman‐equation.
The Application of Thermal Kinetics to Carbon Ion Clusters
Authors: Sandler Pablo , Peres Tikva , Weissman Gabriel , Lifshitz Chava 
Published: July 2012

AbstractEvaporation of C2 from C, C and C has been studied experimentally through the respective kinetic energy release distributions (KERDs). A model‐free theoretical approach, due to Klots, which defines a transition state temperature T+ and a bath temperature Tb, has been applied to the experimental data to derive the C2 vaporization (i.e. binding) energies.
Ionization of SO2‐Clusters by Scattering from Surfaces
Authors: Christen Wolfgang , Kompa Karl‐Ludwig , Schröder Hartmut , Stülpnagel Heinrich 
Published: July 2012

AbstractSulfur dioxide clusters prepared in seeded, pulsed, supersonic molecular beams have been scattered from single crystal surfaces under ultrahigh vacuum conditions with the aim to investigate chemical changes (e.g. fragmentation) and cluster‐surface interaction with regard to certain experimentally accessible conditions (cluster size, kinetic energy, type and temperature of the surface). First measurements are reported which show that (SO2)n (n > 3) dissociation may occur yielding both, positively and negatively charged ionization products. Possible cluster‐surface interaction mechanisms are discussed.