bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of Adsorption of Methanol on Metal Dopant/Active Carbon Systems
Authors: Afzal M. , Mahmood F. , Saleem M.
Published: July 2012

Adsorption 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

The 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

Ultrasonic 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

We 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

The 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

Metal 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

We 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

It 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

The 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

After 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

Proton 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

Core 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

The 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

Evaporation 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

Sulfur 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.
Electronic Structure of LinHn Clusters
Authors: Dugourd Ph. , Rayane D. , Vezin B. , Chevaleyre J. , Broyer M. , Labastie P.
Published: July 2012

The LinHm clusters are produced in a seeded molecular beam. The lithium vapor is expanded in the vacuum with a mixture of 99% of argon and 1% of H2. The formed clusters are analyzed by a time of flight mass spectrometer and the clusters electronic structure is probed through ionization potential measurements. The electronic structure of LinH and LinH2 may be interpreted by assuming that the bonding of one hydrogen atom localizes one electron of the lithium atoms and that the other electrons remain delocalized.
Theory for the Polarization Interaction between an Excess Electron and a Cluster of Polar Molecules
Authors: Stampfli P. , Bennemann K. H.
Published: July 2012

The polarization interaction between an excess electron and a cluster of polar molecules is discussed in a microscopic model and related to the dielectric continuum model. We obtain that the polarization of the bound electrons strongly reduces the strength of the interaction between the excess electron and the molecules by an effective screening. Previous calculations of the electronaffinity of clusters of polar molecules have used pair‐potential interactions, which neglect these screening terms. Thus the attractive polarization energy has been overestimated, resulting in much larger vertical detachment energies than observed in the experiment.
Photoelectron Spectroscopy of Clusters and Adsorbates on Clusters
Authors: Cha Chia‐Yen , Ganteför Gerd , Eberhardt Wolfgang
Published: July 2012

The electronic and geometric structure of free metal cluster anions is studied by photodetachment. The cluster anions are produced in a PACIS (Pulsed Arc Cluster Ion Source). From mass separated bunches of anions electrons are detached by a UV‐laser pulse. Photoelectron spectra of the detached electrons are measured with a “magnetic bottle” type time of flight spectrometer. First data on Ga clusters are presented and compared to similar measurements on Al clusters. At the high resolution (∽ 30 meV) accessible with this experimental set up comparison of the data with calculations delivers new insights into the geometric structure of the particles. A first application of this technique to molecules adsorbed on metal clusters is presented.
Complex Electron Affinity Processes in Clusters of S and Si
Authors: Von Niessen W. , Zakrzewski V. G.
Published: July 2012

Vertical and in some cases adiabatic electron affinities are calculated for the clusters S4 and Sin, n = 3 – 7 with large basis sets. The effects of electron correlation are taken into account by CI and Green function techniques. The clusters show a complex behaviour upon electron attachment. The isomers of 84 show normal electron capture processes as well as electron attachment with shake‐up. The Si clusters show multiple affinity states resulting from capture of an electron into different orbitals: Si3 C2v has at least three, Si4 D2h four, Si5 D3h two, Si6 D4v one, Si6 C2v three and Si7 D5h two affinity states (vertical processes: Sin + e− ± Sin + hν). For the Sin clusters in some cases shake‐up affinities are calculated which are positive. The effects of electron correlation on the electron affinities are extremely large for the Si clusters in particular. In several cases the differences between the adiabatic and vertical electron affinities are very large amounting up to 1.5 eV.
Theory for the Magnetic Properties of a Free Metal Cluster Ensemble
Authors: Jensen P. J. , Bennemann K. H.
Published: July 2012

The magnetization and the deflection profiles of an ensemble of free magnetic metal clusters in an inhomogeneous external magnet field are calculated. If a weak lattice anisotropy is present, as expected for 3d‐transition metal clusters, one obtains superparamagnetic behavior. If strong anisotropy is present, as might be the case for rare earth metal clusters, a smaller magnetization compared to superparamagnetism is obtained. A symmetric deflection profile is obtained for the case of vanishing anisotropy, but gnerally no longer if an anisotropy is present. Effects due to a low cluster Curie temperature comparable to the cluster temperature and cluster rotation are also discussed.
The Ferromagnetism of Iron and Nickel Clusters in a Molecular Beam
Authors: Becker J. A. , De Heer W. A.
Published: July 2012

The magnetic properties of small FeN and NiN clusters are studied in a molecular beam by their Stern Gerlach deflections. The magnetization of the particles is measured as a function of applied magnetic field H, size N and vibrational temperature Tvib (≈︁ 200‐1300 K). The intrinsic magnetic moments per atom μ at T ≈︁ 300 K are 2.2 μB for Fe130 and 0.5 μB for Ni560. A bulk‐like magnetization curve is found for Ni560 and for Fe130 at Tvib ≈︁ 1000 is found to be only slightly reduced compared with its low temperature value. The results are compared with the Heisenberg model. Anomalously low magnetization for strongly cooled FeN clusters (N = 120‐140) is found to be related to the rotational speeds. The distinct roles of rotational and vibrational temperatures for the ferromagnetism of isolated Fe clusters are rationalized in a model.
Electronic Spectra. Experimental vs. Semiclassical Electronic Spectra of Spectra of Naphthalene · Arn van der Waals Clusters
Authors: Troxler Thomas , Leutwyler Samuel
Published: July 2012

Classical molecular‐dynamics and Monte Carlo simulations were employed to study the structures, dynamics, vibrational power spectra and electronic spectra of naphthalene · Arn clusters. Theoretical electronic absorption spectra were calculated using the spectral density formalism of Mukamel et al.; a brief review of the formalism is given together with a simple application example for the naphthalene · Ar2 complex. The experimental R2PI spectra for the series of naphthalene · Arn clusters with n = 13 – 15 are discussed on the basis of the calculated spectra. The system is shown to undergo a wetting/nonwetting transition.
Impurity Doped Simple Metal Clusters: Optical Response
Authors: Koretsky Geoffrey M. , Dahlseid Tina A. , Pollack Stuart , Chris Wang C. R. , Alameddin George , Hunter Joanna , Cameron Douglas , Liu Shengzhong , Kappes Manfred M.
Published: July 2012

Existing and future measurements of the optical response properties of monodoped simple metal clusters are discussed.
Structure, Energetics, Dynamics. Structure and Dynamics of Size Selected Molecular Clusters
Authors: Buck Udo
Published: July 2012

By combining the method of size selection of clusters by momentum transfer in a scattering experiment with atomic beams with the absorption of infrared photons from a laser, the photodissociation spectra of weakly bound clusters have been measured as a function of cluster size. From the measured lineshift and linewidth, which depend sensitivily on the cluster size, the excited mode and the investigated species detailed information on the structure and the decay dynamics is obtained by accompanying calculations. Results are presented for clusters of methanol and acetonitrile as case studies.
Theoretical Treatment of Sodium Chloride Clusters
Authors: Ahlrichs Reinhart , Ochsenfeld Christian
Published: July 2012

Results of a systematic study of structure and energetics are reported on the SCF level and with inclusion of electron correlation (MP2 and CPF). The stoichiometric systems NanCln for n = 1–6, 8, 9, 12, 15, 18, 32, and the sodium excess systems Na14Cl13 and Na18Cl17 were considered in detail. The stoichiometric systems prefer geometric arrangements as in the solid state lattice whenever possible. The sodium excess systems show an electron at an anion defect location (F‐center) or localize the electron at a sodium atom (no surface states), in either case preferably in a corner position.
Associates, Clusters, Intermolecular Complexes, Supramolecular Systems: Van der Waals Species
Authors: Hobza Pavel , Zahradnik Rudolf
Published: July 2012

This is an article summarizing theoretical studies carried out recently in our laboratory on van der Waals (vdW) species. In contrast to classical molecules, theoretical structure elucidation of vdW molecules nearly always represents a challenge for computational chemists. Results on molecule‐molecule complexes (e.g., (H2)2, benzene and benzyne complexes with rare gas atoms, benzene dimer, purine‐pyrimidine complexes) and ion‐molecule complexes (e.g., H, radical cations of dimers of alkyl halogenides and of alkylated and arylated water) are reviewed. The importance of study of the intersystem vibrational degrees and the role of molecular dynamics in the field of vdW systems in outlined.
Study of Electron Correlations in Pb‐Clusters
Authors: Pastor G. M. , Reindl S. L.
Published: July 2012

The ground state properties of Pb‐clusters are investigated using a many‐body Hamiltonian with intra and inter‐atomic Coulomb interactions. By solving the model exactly we obtain that Pb is metastable (lifetime τ > 1040s) and that it has isosceles geometry (bondangle Θ ≃ 124°). The importance of electron correlations for the stability of doubly charged clusters is discussed. By comparison between the exact solution and several variational approaches we particularly show that both the metastability and isosceles shape of Pb result mainly from antiferromagnetic quantum spin‐fluctuations.
Rapid Approximate Calculation of Numbers of Quantum States W(E,J) in the Phase Space Theory of Unimolecular Bond Fission Reactions
Authors: Olzmann M. , Troe J.
Published: July 2012

A facile and rapid approximation for counting numbers of quantum states W(E,J) is described for application in the phase space theory of unimolecular bond fission reactions. The method accounts for J‐conservation. It is based on an empirical interpolation between analytical expressions of W(E,J) in the low J‐ and high J‐limits, and it is checked by extensive accurate state counting for sets of representative model molecules.
The Use of a Flashlamp‐Pumped Dye Laser for Single‐Pulse Spontaneous Raman Scattering in Flames
Authors: Prucker S. , Meier W. , Plath I. , Strieker W.
Published: July 2012

A Raman scattering system based on a commercially available, high power flashlamp‐pumped dye laser is presented. Single‐pulse measurements of the temperature and major species concentrations in a stable laminar methane/air flame and in a weakly turbulent H2/air diffusion flame have been performed to assess the measuring precision and detection efficiency of this system. The problem of spatial resolution is discussed and — in this context — the advantages of combined Raman/2D LIF measurements are demonstrated.
The Anodic Growth and the Stability of Thin Passive Films on Titanium Electrodes
Authors: Müller A. , Popkirov G. S. , Schindler R. N.
Published: July 2012

The growth of thin passive oxide films on titanium was investigated in 1 M sodium hydroxide and in 0.5 M sulphuric acid solution. Potentiodynamic and galvanostatic experiments were carried out with simultaneous microbalance measurements to follow mass changes associated with the processes at the electrode. In addition ac impedance data were collected at different stages of the oxidation in a wide frequency range. — In alkaline electrolyte oxide growth leads to the expected mass gain of the electrode due to oxygen ion incorporation. Also the total impedance of the electrode decreases continously with increasing film thickness. In acidic environment oxide electroformation is accompanied by different dissolution processes, one of which is a potential independent chemical dissolution. The initially observed mass gain of the electrode during oxidation switches over at potentials of oxygen evolution to a total mass decrease. This effect is also reflected in the impedance measurements by a pronounced change in the total capacitance Ct plotted as function of the oxidation potential. It is suggested that this electrochemical behaviour is related to changes in the thin oxide film structure and/or composition. The results are discussed in the context of observations obtained in experiments using other experimental techniques.
tert‐Butanol as an OH‐Scavenger in the Pulse Radiolysis of Oxygenated Aqueous Systems
Authors: Piechowski Magnus Von , Thelen Marie‐Anne , Hoigné JüRg , Bühler Rolf E.
Published: July 2012

The application of tert‐butanol as an OH scavenger in aqueous, oxygenated solutions was studied by pulse radiolysis and computer simulation of the entire reaction mechanism. In such systems, the initially produced tert‐butanol radical (· Rtb) reacts with O2 with a rate constant of k = 1.4 · 109 M−1 s−1. The UV absorption‐spectrum of the resulting tert‐butanol peroxy‐radical, · OOR,tb, was determined. The rate constant for its dimerization, 2 · OORtb RtbO4Rtb, is k = 1.8 · 108 M−1 s−1. The formation of HO2 from the decay of RtbO4Rtb has often been neglected in earlier studies. Our reinvestigation showed a yield of 5 ± 2%. In deoxygenated systems we confirmed the rate constant for · Rtb dimerization to be k = 6 · 108 M−1 s−1.

The UV spectrum of · Rtb was determined to be slightly different from literature data.
Phase Transitions in Dimethylammonium Tetrafluoroborate and Molecular Motions in Its Ionic Plastic Phase Studied by 1H and 19F NMR, Thermal Measurements, and X‐Ray Powder Diffraction Techniques
Authors: Ishida Hiroyuki , Iwachido Tadashi , Ikeda Ryuichi
Published: July 2012

Three solid phases of (CH3)2NH2BF4 were found between 200 K and the melting point (375 K) by differential thermal analysis, differential scanning calorimetry, and 1H and 19FNMR measurements. The highest‐temperature solid phase obtainable above 283.5 K was shown to be an ionic plastic phase, where the cations as well as the anions perform rapid translational self‐diffusion and isotropic reorientation about their center of gravity. The crystal in this phase was revealed to form a CsCl‐type cubic structure with α = 5.35 Å at ca. 290 K by powder X‐ray diffraction. The two phase transitions, from the lowest‐temperature phase to the intermediate one and from the intermediate phase to the highest temperature phase, successively occur at nearly the same temperature of 283.5 ± 0.5 K. The intermediate phase could be clearly observed as an undercooled state.
TEM/EDX‐Microanalysis of Ferrite/Titanate Interfaces
Authors: Haberkern M. , Nicoloso N. , Brook R. J.
Published: July 2012

Ferrite/titanate interfaces, prepared by the co‐sintering (1400 K; 2 h) of laminates formed from tape cast (Ni,Zn)Fe2O4 and MgTiO3, have been investigated by combined TEM and EDX‐analysis. Reaction between the starting materials leads to a < 3 μm thick layered interface consisting of a cation exchanged spinel phase Mg1+xFe2‐2xTixO4, x = 0.66, and a pseudobrookite phase, MgxFe2‐2xTi1+xO5 phase with x = 0.75. As expected for this sintering time and temperature, the interface constitution is controlled by the appropriate thermodynamic relationships, favouring solid solution.
Towards a First‐Principles Thermodynamics of Solids Plenary Lecture
Authors: De Fontaine D. , Wolverton C
Published: July 2012

Total energy density‐functional methods have made it possible to calculate, from first principles, such important properties as cohesive energies, lattice constants and elastic moduli for elemental crystals and perfectly ordered compounds. Real solids are imperfect, however, so that lattice vibrations and compositional disorder lead to entropy contributions, vibrational and configurational. When these effects are included in an appropriate manner, properties of real crystals can be computed ab initio as a function of temperature and concentration. Consequently, it is possible to obtain, virtually from the knowledge of atomic numbers alone, such basic thermodynamic properties as free energies, entropies, heats of formation, and lattice parameters for stable and metastable phases, leading, for example, to the successful computation of certain classes of phase diagrams. Recent progress in field will be reviewed.
Structure and Electronic Properties of Complex Solids
Authors: Freeman A. J.
Published: July 2012

Dramatic advances in computational chemistry and materials science have generated an excitement, enthusiasm and fervor among its practitioners not seen for many decades. There has now been achieved a high level of reliability concerning predictions of physical and chemical properties and phenomena – thanks in large part to the continued rapid development and availability of computing power (and its easy accessibility) and the new computational methods/algorithms which this permitted to be generated. A prime area continues to be electronic structure theory where new computational/theoretical methods have been developed that permit highly precise solutions of complex many body systems at the level of the local density approximation. This talk illustrates some aspects of the present state of the field by means of several examples, notably aluminum intermetallics and semiconductor heterojunctions.
Host Lattice Electronic Properties of Hydrated Layered Intercalation Compounds Studied by Solid State 1H NMR
Authors: Lobert M. , Müller‐Warmuth W. , Katzke H. , Schöllhorn R.
Published: July 2012

Solid state 1H NMR methods have been applied to study local magnetic fields at the proton sites of water molecules intercalated together with alkali cations in layered transition metal dichalcogenides. The chemical shift anisotropy of the Ax(H2O)y[MX2] compounds (A = Na, K; M = T1, V, Nb, Mo, Ta, W; X = S, Se) depends greatly on M and on the reduction degree x. It appears to be proportional to the anisotropic Pauli paramagnetic susceptibility and to the host material density of states at the Fermi level. For the intercalation compounds of TiS2 and NbS2 the structure of the d band has been determined. The “rigidband model” could be confirmed. Exceptional results for TaS2 and MoS2 host lattices are discussed.
Application of the Zintl‐Concept to Equilibrium Gaseous Molecules
Authors: Poth Lutz , Weil Konrad G.
Published: July 2012

We report on mass spectrometric investigations of the equilibrium vapor of intermetallic compounds or over heterogeneous mixtures of metals and salts. We give examples for intermetallic gaseous compounds which are representatives of the following classes of Zintl molecules: Molecules containing polyanions, molecules with Zintl anions, and molecules with Zintl cations. The latter are found in the systems antimony/tellurium/chlorine and antimony/tellurium/bromine. Details about the experiments in which the cation containing molecules are detected are given.
Investigation of the Electronic Structure of Oxocuprates by Photoelectron Spectroscopy
Authors: Adler P. , Simon A.
Published: July 2012

The oxocuprates Y2BaCuO5 and Bi2CuO4 the crystal structures of which contain discrete CuO5 and CuO4 units, respectively, have been investigated by angle integrated photoelectron spectroscopy. The Cu 2p core level and Cu L3VV Auger spectra are analysed within a simple cluster configuration interaction model. The experimental data and model parameters, namely the charge transfer energy Δ, the transfer integral T, and the correlation energy U as well as the main valence band features are similar as for oxocuprates with extended copper oxygen network.
Correlation between the Electrostatic Potential and the Occupation of Interstitial Sites by Hydrogen in Metallic Systems
Authors: Philipp Sabine , Leiberich Ricarda , Schmidt Peter C. , Weiss Alarich
Published: July 2012

The electrostatic crystal potentials V(r) of the cubic metals Pd, V, Nb, Ta, and the intermetallic phases FeTi and XEr, X = Cu, Ag, Au, have been determined by the full potential augmented‐plane‐wave method (FP‐APW). Furthermore, to study the electronic states in dilute metal‐hydrogen‐systems the partial densities of states have been calculated by the supercell procedure using the augmented‐spherical‐wave method (ASW) for PdH1/32. The results are compared with the values for PdH1/4, PdH, and Pd. – A relation is found between the depth of the host lattice electrostatic potential and the occupation of interstitial lattice sites by hydrogen in the metal‐hydrogen α‐phases. For bcc V, Nb, and Ta the crystal potential “seen” by a proton has its deepest minimum at the tetrahedral site, for fcc Pd the minimum occurs at the octahedral site and in FeTi (B2‐type) the minimum of Vproton(r) is found for the octahedral site surrounded by 2 Fe atoms and 4 Ti atoms. In all these cases the calculated site of the minimum is in accordance with the location of hydrogen in the respective α‐phases found experimentally by neutron scattering. For XEr. X = Cu, Ag, Au, a preferred occupation by hydrogen is predicted.
Magnetic Properties of Iron(II)‐Cyclo‐Tetraphosphate Fe2P4O12
Authors: Gunßer W. , Röhl B. R. , Schütze A. , Gmelin E. , Wiedenmann A.
Published: July 2012

Polycrystalline samples of iron(II)‐cyclo‐tetraphosphate were prepared and the magnetic properties were investigated using magnetic susceptibility, magnetization and heat capacity measurements. The Curie‐Weiss law is obeyed down to ca. 240 K and a paramagnetic Curie temperature Θp of 28 K was obtained. Susceptibility‐ and heat capacity mesurements revealed a Curie‐temperature TC of 17 K. Furthermore, the heat capacity experiments indicate that the compound does not exhibit low dimensional magnetism. The results show that no simple antiferromagnetic order can be assumed.
Ungewöhnliche paramagnetische Zentren in Markasitkristallen
Authors: Siebert D. , Dahlem J. , Doll M.
Published: July 2012

In natural single crystals of marcasite we could detect Mn2+ on iron site by EPR in the low‐spin configuration with S = 1/2, and Cu2+ within a compressed ligand octahedron. The unusual EPR parameters are considered to be tue to the strongly covalent bonding. Further resonances were assigned to Au0, presumably also on iron site, (SF)2‐, and S−, alltogether centers with spin S = 1/2.
ESR‐Investigations on the Superionic Behaviour of Doped β‐PbF2
Authors: Ten Eicken J. , Gunsser W. , Chernov S. V. , Murin I. V.
Published: July 2012

ESR results of low concentrated systems Pb1‐x{Gd,Sc}xF2+x at temperatures up to 775 K are reported. At room temperature, ESR‐spectra of single crystals and polycrystalline samples show three sets of lines which are correlated to different Gd‐sites. The observed shift of the line positions with increasing temperature is caused by the decreasing crystal field interaction. There is no temperature dependence of the differential linewidth until about 600 K. At higher temperatures we observed a drastic increase of the linewidth, correlated to the faster relaxation upon transition to the superionic state.
IR‐ and XRD‐Investigations on Isomorphous Substituted ZSM‐5 Zeolites
Authors: Kosslick H. , Tuan V. A. , Fricke R. , Peuker Ch.
Published: July 2012

Ge–ZSM‐5 zeolites are characterized by XRD and IR Spectroscopy in the spectral range of lattice and hydroxyl vibrations. XRD data confirm the high crystallinity of hydrothermally synthesized Ge–ZSM‐5 samples. The incorporation of germanium into the ZSM‐5 framework is proven by the increase of the unit cell volume from 5342 Å3 (silicalite I) to 5390 Å3 (Ge–ZSM‐5, Si/Ge = 4). At the same time the wavenumber of the asymmetric T–O–T stretching vibration band is decreased from 1102 to 1090 cm−1 and the intensity of the double ring vibration band at 550 cm−1 is decreased and losses its structure. In the hydroxyl vibration spectra a new absorption band at ca. 3670 cm−1 is observed the intensity of which increases with growing germanium content. This new absorption band is assigned to terminal Ge–OH groups in the zeolite structure.
Electrochemical Hydrogen Charge Characteristics of Metal Hydride Electrodes
Authors: Sakamoto Y. , Kuruma K. , Naritomi Y.
Published: July 2012

A model for the cathode potential vs. time relationship during the galvanostatic charge process for metal hydride electrodes has been derived on the basis that the adsorbed hydrogen produced at the electrode surface by charge transfer of the Volmer reaction diffuses through the bulk electrodes, i.e., α, (α+β) and β phases during the charge process, and after the absorbed hydrogen concentration in the electrodes attains a saturation value for hydrogen solution, the electrode kinetics is followed by the chemical Tafel reaction and/or the electrochemical Heyrovsky reaction. The calculated electrode potential vs. time curves are in a reasonable agreement with the experimental results of Pd hydride electrodes.
Vanadia Supported on Titania Prepared by Grafting: Influence of Support Properties on the Structure and Activity of Vanadia for the Selective Catalytic Reduction of NO by NH3
Authors: Handy Brent E. , Gorzkowska Irena , Nickl Julius , Baiker Alfons , Schraml‐Marth Matthias , Wokaun Alexander
Published: July 2012

The selective catalytic reduction (SCR) of NO by NH3 has been investigated over vanadia/titania catalysts prepared by grafting of vanadyl alkoxides onto three titania supports which differed in their morphologies (surface area, phase composition) and concentrations of impurities. Neutron activation analysis revealed the presence of chlorine and potassium as major impurities in the titania carriers. The supported catalysts were prepared by the reaction of VO(OR)3 (R = i‐C3H7, i‐C4H9) with support surface hydroxyl groups. Attention was paid to the influence of various preparation parameters (vanadia precursor, support pretreatment, impurities) and their relation to the amount, reducibility and activity of the vanadia deposited. Thermal analysis, X‐ray diffraction and Raman spectroscopy revealed that pre‐conditioning the titania supports before the grafting, if not carried out under mild conditions, results in partial transformation of the anatase phase to rutile. Potassium impurities appear to stabilize the anatase phase with regard to this transformation. For titania containing potassium as impurity, the rutilization occurs at a significantly higher temperature than observed with titania containing chlorine as impurity. Raman spectroscopy showed that within the series of titania supports investigated, the vanadia loading is the most important factor that determines the structure of the immobilized vanadia surface species. Small clusters and ribbons prevail at low coverages (∼ 2μmol V5+/m2). At higher coverages, the catalytically most active two‐dimensional vanadia layers are prevailing. The maximum level of NO turnovers is achieved at coverages exceeding ∼ 3μmol V5+/m2. This behaviour was observed for vanadia deposited on all three titania carriers, irrespective of the largely different BET surface areas and contaminant levels of the supports.
Volumes, Dilution Enthalpies and Dielectric Polarization of Water‐Sulpholane Mixtures at Different Temperatures
Authors: D'Aprano Alessandro , Capalbi Antonio , Bonicelli Maria Grazia , Ceccaroni Gian Franco
Published: July 2012

Densities and dielectric constants of water‐sulpholane mixtures have been measured at 25, 30 and 40°C over the complete mole fraction range. Excess molar volumes and apparent molar volumes of the two components were derived from density data. The temperature and concentration dependences of these quantities are discussed in terms of the structural modification of water imposed by sulpholane. Dielectric constant data, analyzed in terms of Kirkwood theory, show that the short range intermolecular interactions between the components in the mixtures are conform to the depolymerization of the water hydrogen bonded network promoted by the mixing with sulpholane. The changes of the water structure have been further investigated by measuring the enthalpies of dilution of the sulpholane at 30°C. The data were analyzed with a polynomial equation to derive the relative apparent molal enthalpies. The resulting values of these quantities are in good agreement with the volumetric and dielectric constant results.
Pressure Dependence of ortho‐Positronium Lifetimes in Molecular Liquids
Authors: Kobayashi Y.
Published: July 2012

Effect of external pressure on annihilation of ortho‐positronium (o‐Ps) hi molecular liquids has been studied for benzene, toluene, isooctane, n‐hexane and carbon disulfide. In all cases the o‐Ps lifetime becomes shorter as pressure is increased. The shorting of the lifetimes in the case of the former four liquids is found to be almost in agreement with the prediction of a simple bubble model. The change of the lifetime in carbon disulfide is, however, much larger than that expected from the model and the discrepancy can be explained by assuming some attractive interaction between Ps and the surrounding carbon disulfide molecules. Some discussion is given on the effect of pressure on Ps yields.
Selective Counterion Binding to Linear Polyelectrolytes in Aqueous Solutions
Authors: Cametti C. , Di Biasio A.
Published: July 2012

The selective counterion condensation induced by a charged cylindrical polyelectrolyte in aqueous solution containing different mono‐ and di‐valent ions was investigated by means of the numerical solutions of the non linearized cylindrical Poisson‐Boltzmann equation. The critical charge fraction fc, above which the condensation predicted by the Manning theory occurs, has been evaluated in some selected cases of relevance in biopolyelectrolyte systems and a selective binding of counterions has been shown to occur. To take into account the effects of different types of mono‐ and di‐valent salts, an extension of the Manning theory recently proposed by Paoletti et al. and based on Gibbs free energy minimization, was considered. Discrepancies between the charge distribution of bound ions calculated by means of numerical solutions of Poisson‐Boltzmann equation and those predicted by the extended Manning theory, were found.
Dependence of Mass Density and Selfdiffusion in Liquid Binary Systems n‐Alkane/Tetramethylsilane on Temperature and Pressure
Authors: Brüsewitz Michael , Weiss Alarich
Published: July 2012

The selfdiffusion coefficients Di, of the spherical molecule tetramethylsilane, TMS, and of n‐alkanes have been studied in three binary systems of n‐alkane/TMS in the temperature‐ und pressure range 253.15 ⩽ T/K ⩽ 368.15; 0.1 ⩽ P/MPa ⩽ 200. The mol fractions of TMS in the mixtures were chosen as xTMS = 0, 0.1, 0.9, and 1; the n‐alkanes were n‐hexane, n‐nonane, and n‐dodecane. Measurements of the mass densities at the chosen xTMS‐values were done in the P,T‐range given above. – The results of the Di measurements can be rationalized by a polynomial Di = f(P,T). The molar volumes found from the mass density measurements are described by VM = f(p,T) for the range covered by the experiments; they are described by a polynomial, too. Activation energies for the selfdiffusion process have been determined. – Di at constant P,T decreases in the sequence n‐hexane, TMS, n‐nonane, n‐dodecane. For the pure substances as well as for the components in the mixtures (Di)max/(Di)min = 3.5 to 4. – The interpretation of the results relays on the “Free Volume” model [1]. From the data Di = f(P,T) the selfdiffusion coefficients at constant volume have been extrapolated and their dependence from T1/2 is discussed. The results of the measurements are interpreted by assuming folded conformations of the n‐alkanes in the mixtures with TMS. In the mixtures one component can be regarded as the solvent, dominating the properties of the solvent cage.
Self‐Reaction of Benzylperoxy Radicals in the Oxidation of Toluene. A Chemiluminescence and Product Study
Authors: Vasvári G. , Gál D.
Published: July 2012

The CL study of the oxidation of toluene initiated by AIBN has shown that both triplet and singlet benzaldehyde is formed (T/S ≈︁ 10.5). The lifetimes in toluene are: τ5 ≈︁ 4 · 10−9 s and τT ≈︁ 1.9 · 10−7 s. – In the presence of DPA the kinetic curve of the CL light shows a maximum at [DPA] > 10−4 M. The CL spectrum of the oxidation of toluene lacks both the fluorescence and phosphorescence peaks of the excited benzaldehyde (due to the very low efficiency of photon emission and very strong quenching by O2 and toluene). – Analysis of product distribution by HPLC revealed the formation of benzaldehyde, benzylalcohol, benzylhydroperoxide and benzoic acid. A small amount of H2O2 was also detected by spectrophotometry. Since the ratio of aldehyde/alcohol is always higher than unity detailed study of all circumstances led us to the conclusion that benzylperoxy radicals terminate both by the Russell‐mechanism and by the transition state containing two five‐membered rings suggested by Bennett and Summers. – The activation energy of hydrogen abstraction from toluene by benzylperoxy radicals is 53 kJ/mol and the rate constant of this reaction does not differ essentially from the same reaction of ethylbenzene. The kinetic chain length of oxidation calculated from the analytical data is equal to 2±0.2 (75–90°C).