bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Fe2+ –Mg2+‐Interdiffusion in Olivine (II)
Authors: Nakamura A. , Schmalzried H. 
Published: July 2012

AbstractInterdiffusion experiments have been performed in the quasibinary system Fe2SiO4–Mg2SiO4. Interdiffusion coefficients D̄ have been evaluated for polycrystalline (FexMg1‐x)2SiO4 between 1050°C < T < 1280°C and compositions x ranging from 0.9 to 0.1. It was found that D̄, at given T and po2, increases almost exponentially with composition x in (FexMg1‐x)2SiO4, in accordance with other oxide solid solutions. For x > 0.3, a po21/5‐dependence is found. For smaller x‐values, D̄ is rather proportional to po21/5.5. It is also found that the oxygen pressure dependence of D̄, and of the vacancy concentration in the sublattice of the divalent cations, is the same. This means that indeed a vacancy mechanism is operative in the interdiffusion process. The strong composition dependence of D̄ is almost entirely due to the strong composition dependence of the vacancy concentration. Various other olivine solid solution systems (where Me2+ = Ni2+, Co2+, Mn2+) can be shown to behave similar to the iron‐olivine. It is also found that DFe > DMg. The meaning of D̄ is discussed in terms of the selfdiffusion coefficients DFe and DMg.
Ellipsometry During the Growth of Electrochemically‐Formed Mercury Nuclei
Authors: Greef R. 
Published: July 2012

AbstractMercury can be deposited electrochemically from mercurous nitrate solutions onto glassy carbon in conditions which allow the number density and radius of the growing nuclei to be estimated. This system can be taken as a model for a surface of controlled roughness. In this paper the ellipsometric response of the system is described, and a simple graded‐film model is presented that accounts for the salient features of the results.
Photochemistry of Colloidal Metal Sulfides 6. Kinetics of Interfacial Reactions at ZnS‐Particles
Authors: Henglein A. , Gutiérrez M. , Fischer Ch.‐H. 
Published: July 2012

AbstractZnS sols containing alcohol or formate as reactants for positive holes and nitrous oxide or carbon dioxide as reactants for electrons were illuminated and the yields of the various products determined. Alcohols are oxidized via a one‐hole mechanism, the product being an 1‐hydroxyalkyl radical which undergoes reaction in the bulk solution. Carbon dioxide is exclusively reduced to formic acid via a two‐electron mechanism. Formate is mainly (77%) oxidized to CO2 in a two‐hole process and less frequently via one‐electron transfer, i.e. formation of intermediate CO2− which reacts with other radicals in the bulk solution. A possible role of intermediate zinc atoms in the two‐electron reductions is discussed. In the presence of two reactants for one kind of charge carrier, the yields of the products can often be described by conventional competition kinetics. A scavenger for electrons influences the yield of the reaction of the scavenger for positive holes and vice versa. This influence is described for various pairs of scavengers (such as strong h+ and weak e− scavenger; strong h+ and strong e− scavenger etc.).
Mobility and Self‐Diffusion Coefficient of Higher Valent Co‐Ions in Ion Exchange Membranes
Authors: Chakravarti A. K. , Schlögl R. 
Published: July 2012

AbstractDonnan concentration, self‐diffusion coefficient, and mobility of SO4− ‐ co‐ion in phenolsulphonic acid membrane have been determined using 0.0005 to 0.5 M MgSO4 as external electrolyte solutions. At lower external electrolyte concentrations (<0.25 M) the experimentally determined Donnan concentrations are higher than the corresponding theoretically calculated values; the discrepancy is larger at lower concentrations. Both the true self‐diffusion coefficient and the mobility decrease (although not appreciably) with increase in external solution concentration, but they increase with increasing temperature at a particular concentration (viz., 0.05 M).
Penning, Photo and Electron Impact Ionization of Argon Clusters
Authors: Birkhofer H. P. , Haberland H. , Winterer M. , Worsnop D. R. 
Published: July 2012

AbstractMass spectra of argon clusters from a supersonic expansion measured by electron impact or photo ionization are similar to those obtained by Penning ionization. Associative ionization of clusters is not observed. This allows a determination of the condensed fraction in the beam. The mean cluster size is compared to data of other authors and heavy fragmentation of the clusters upon ionization is found. The ionized atom in a cluster will react very rapidly to a dimer ion, whose large binding energy of about 1 eV will lead to cluster fragmentation. A time table of events happening in a rare gas cluster after ionization is conjectured.
Multiphoton Ionization of Ammonia Clusters with a Tunable Laser
Authors: Echt O. , Morgan S. , Dao P. D. , Stanley R. J. , A. W. Castleman  
Published: July 2012

AbstractClusters of ammonia, formed by adiabatic expansion, were subjected to analysis in a time‐of‐flight mass spectrometer following multiphoton ionization. All cluster ions had the composition (NH3)n · H+ (with n ranging up to approximately 65) and none corresponding to (NH3)n·+ were detected with the exception of n = 1. An unusually stable species (NH4+)(NH3)4 was produced under all expansion and ionizing conditions investigated; it is attributed to an especially stable ion structure. Well resolved rotational structure for the β and c̄ states of a cold monomer beam were obtained and rotational assignments are presented for the c̄' band. A search for resonances in the ammonia clusters failed to reveal any well resolved structure, although isotope shifts in the monomer spectra were found through use of deuterium substitution.
Supersonic Metal Clusters
Authors: Morse Michael D. , Smalley R. E. 
Published: July 2012

AbstractRecent developments in laser and molecular beam technology have now made it possible to produce supersonic beams of metal clusters of virtually any metal in the periodic table. The availability of these clusters for study in the gas phase provides an opportunity to investigate in detail the physics and chemistry of economically important and scientifically interesting metal cluster species. Initially, studies have involved the investigation of the metal‐metal bond in transition metal dimers, including Cr2, Mo2, V2, and Ni2 through resonant twophoton ionization spectroscopy. These studies have demonstrated the importance of 3d (and 4d) electrons in the metal‐metal bond in Cr2, Mo2, and V2. A comparison of V2 and Cr2 illustrates the importance of the 3d contraction with increasing nuclear change, and this is found to be of central concern in Ni2, where no 3d contribution to the chemical bond is found. Finally, Cu3 is investigated, providing the first gas‐phase spectrum of a triatomic transition metal cluster. Electronically, Cu3 is analogous to Na3 and other alkali trimers, so it is not surprising that the observed spectrum is best explained as arising from a Jahn‐Teller distorted 2E' state (in D3h symmetry), as has been calculated for Li3. The observed transition in Cu3 is assigned to be 2E”←2E', with both upper and lower states undergoing Jahn‐Teller distortions.
Electronic Structure and Properties of Small Al and Ge Clusters
Authors: Pacchioni Gianfranco , Koutecký Jaroslav 
Published: July 2012

AbstractStabilities, geometries and electronic structures of Aln (n = 3–5) and Gem (m = 3–6) clusters have been determined by means of pseudopotential MRD CI calculations. Most stable Al clusters are characterized by high spin multiplicities and can be considered as deformed sections of the Al fcc crystal lattice. On the contrary, most favoured Ge clusters have singlet ground states and geometrical structures which cannot be identified as parts of the diamond‐like Ge crystal lattice. – The differences in the properties of Al and Ge clusters can be rationalized on the basis of their respective electronic structures.
Interaction of Accelerated Cluster Ions of Hydrogen with Gas Targets
Authors: Henkes P. R. W. , Pfeiffer U. 
Published: July 2012

AbstractHydrogen cluster ions of 800 keV were passed through an H2O gas target. The production and destruction of charged fragments was followed as a function of the target thickness. The comparison of the experimental results with those of a model calculation shows that the dominant process for fragment production is most probably the evaporation of H2 molecules.
Mass Spectrometric Study of Sodium Clusters under Equilibrium Conditions with a Knudsen Cell
Authors: Hilpert K. 
Published: July 2012

AbstractThe vaporization of Na(l) was studied under equilibrium conditions by the high‐temperature mass spectrometric method with a Knudsen cell. The atomization enthalpies of Na2(g) and Na3(g) were determined as 71.8 ± 4.0 and 103 ± 12 kJ mol−1 respectively. Knudsen cells developed for the study of alkali metals are described.
The Preparation of Metal Clusters and Molecules by Means of the Gas Aggregation Technique
Authors: Schulze W. , Frank F. , Charlé K.‐P. , Tesche B. 
Published: July 2012

AbstractThe gas aggregation technique has been brought up to the point, where metal clusters can be produced continuously in the size range from 105 atoms per cluster down to molecules. The knowledge of the parameters controlling the cluster growth allows the shift of the mean cluster size within the above given size range with reasonably narrow size distributions of the Gauss‐type. The cluster size down to 10 Å in diameter is measured by electron microscopy; the existence of smaller particles can be monitored by optical spectroscopy. – The cluster source can be stabilized for hours. Thus a sufficient amount of clusters can be accumulated and stabilized in matrices, allowing, e.g. EXAFS and IR measurements.
Cluster Ion Formation in Free Jet Expansion Processes at Low Temperatures
Authors: Beuhler R. J. , Friedman L. 
Published: July 2012

AbstractAn experimental high voltage post‐acceleration facility for the detection of high molecular weight cluster ions is described. A summary of results obtained with this facility in studies of high molecular weight water and argon cluster ions is presented. Results on studies of hydrogen cluster ion formation in the expansion of pure weakly ionized hydrogen gas are also presented. Attempts to limit cluster ion formation in hydrogen to quasi equilibrium conditions inside the ion source with source apertures as small as 0.00125 cm were inconclusive. These studies indicated that approximately 25–33 cluster‐ion hydrogen molecule collisions could serve to stabilize the growing cluster ions.
Mass Spectra of Negatively Charged Water and Ammonia Clusters
Authors: Haberland Hellmut , Schindler Hans‐Gerg , Worsnop Douglas R. 
Published: July 2012

AbstractSlow electrons are mixed into a heavily clustered supersonic expansion of water and ammonia. The resulting negatively charged cluster ions are mass analyzed. Mass spectra for (H2O)n−, (D2O)n−, and (NH3)n− are presented. The smallest cluster ions observed contain 11, 12, and 36 water, heavy water and ammonia molecules per clusters, respectively.
Mass Spectral and Electric Deflection Study of Acetic Acid Clusters and Sulfur Trioxide/Water Clusters
Authors: Keesee R. G. , Sievert R. , Castleman A. W. 
Published: July 2012

AbstractA beam of the clusters of interest was produced and analyzed with respect to polar nature via passage through an electric quadrupole focusing field. Subsequently, the beam was ionized using electron impact and the resulting distribution of ions determined with a quadrupole mass spectrometer. Acetic acid clusters containing up to twelve molecules were produced. The polarity and ionizing fragmentation of the clusters were investigated by the effect of stagnation conditions and electrostatic focusing on the intensity of the detected fragment ions. Both the dimer and tetramer were found to be nonpolar while the trimer was polar. Evidence that some larger clusters have polar structures was also found. For the SO3/H2O experiment, beside protonated water clusters, a less abundant series of ions of the form SO3(H2O)nH+ was observed. Focusing experiments indicated that any SO3 · H2O adduct which is formed becomes rapidly isomerized to sulfuric acid. The precursor neutral to the ions HSO3+ and H2SO4+ were strongly focused, but the neutral clusters giving rise to the larger cluster ions were defocused.
Spectroscopy of Neutral and Charged Metal Clusters
Authors: Delacrétaz G. , Fayet P. , Wöste L. 
Published: July 2012

AbstractThe technique of supersonic molecular beams is used to investigate alkali clusters by means of resonant Two‐Photon‐Ionization (TPI). Under specific stagnation conditions the clusters are sufficiently cooled to exhibit well resolved vibrational structures. The interpretation of highly excited Rydberg states permits a determination of the molecular constants of the related cluster ions. All excitation and ionization processes, however, exhibit strong fragmentation channels. With growing particle size, therefore, a proper assignment of the observed spectra to the original unfragmented particle becomes more and more difficult. For this reason an experiment was established, which allows the spectroscopic investigation of single size particles.
Electronic Structure of Small Metal Particles: Self‐Consistent Spherical Jellium Background Model
Authors: Ekardt W. 
Published: July 2012

AbstractGround state properties of small metal particles are investigated with the use of the local density approximation applied to the spherical jellium background model. Large quantum size effects are obtained for the work function, in strict analogy to those obtained for thin metal films. The convergence of the various physical properties to their value of a semi‐infinite half‐space is investigated. The static polarizability of small metal particles is obtained and compared both to the classical result and to the Thomas‐Fermi approximation. The importance of self‐consistency is discussed.
Metal Halide Clusters
Authors: Martin T. P. 
Published: July 2012

AbstractThe mass spectra of clusters of NaCl, CsI and CuBr are very similar, whether the clusters are formed by quenching the vapor in He gas or by bombarding a solid surface with high energy ions. This fact is quite surprising when one remembers that these materials condense into three distinct crystal structures; rock salt, CsCl‐type and zinc blende, respectively. We present evidence that all of these materials seem to prefer the rock salt structure in their early stages of growth.
Transport and Magnetic Properties of Assemblies of one Dimensional Metallic Particles Produced by Irradiation of Organic Conductors
Authors: Zuppiroli L. 
Published: July 2012

AbstractOrganic conductors are molecular crystals composed of conducting stacks of molecules. Their electronic properties are quasi‐one‐dimensional. Submitted to irradiation by ionizing particles, these assemblies of parallel metallic chains are transformed in assemblies of metallic segments, bounded by strong defects. The transport and magnetic properties of a large variety of irradiated organic conductors have been measured; all these experimental results are interpreted very simply within the framework of models based on the electronic properties of one‐dimensional metallic particles: the magnetic susceptibility reveals the presence of unpaired spins on a half of the metallic segments, as expected; the longitudinal and transverse conductivities of such assemblies are dominated by the hopping of electrons between metallic segments, controlled by the differences in the level structure between neighbouring segments of different lengths; the electron spin resonance linewidth decreases exponentially with the lengths of the segments due to the confinement of spins within the metallic particles. – It is demonstrated that most of the electronic properties of the non magnetic metallic clusters, which are difficult to observe experimentally in three dimensional clusters, are very easy to study in one dimension.
Experiments on Simulated Circumstellar Clusters
Authors: Donn Bertram 
Published: July 2012

AbstractSolid grains in a gas cloud ejected from a star condense in a hot gaseous medium with all elements present in their cosmic abundances. A study of this phenomena requires knowledge of the initial clusters that form from a multielement refractory system. Experiments on SiO, Mg + SiO and Fe + SiO clusters in a nitrogen matrix have been performed. Much of the results for the first two systems have been reported. These will be summarized and the iron silicate experiments described. A flow system with a quadrupole mass spectrometer detector has been built to study the temperature dependence of clusters in the gas phase. The systems to be studied are various combinations of Si, O, Mg, Fe and ultimately Ca and C. These six elements constitute the major fraction of refractory cosmic species.
Raman Measurements of Matrix‐Isolated Small Metal Clusters
Authors: Froben F. W. , Schulze W. 
Published: July 2012

AbstractSmall clusters of Group Ia, Ib, IIIa, IVa and Va homonuclear metals are measured in rare gas matrices. The results for Lix, Nax and Kx and problems concerning the identity of the species are discussed together with some theoretical predictions.
ESR‐Spectroscopic Investigation of the Homogeneous Electron Transfer Reactions between Substituted p‐Phenylenediamines and Quinonediimines, and the Validity of Marcus' Theory. II. Temperature Dependence and Activation Parameters
Authors: Grampp Günter , Jaenicke Walther 
Published: July 2012

AbstractUsing ESR‐line broadening the rate constants of electron self exchange between five substituted p‐phenylenediamines, semiquinonediimines, and quinonediimines in six aprotic solvents are measured in the temperature range 230 K < T < 360 K. A linear dependence of ln k on the solvent parameter γ = 1/n2 ‐ 1/ϵ (n = refractive index, ϵ = permittivity) is observed for each temperature as expected from Marcus' theory, also a linear dependence of ln kT−1/2 on T−1 for each solvent. The experimental surface ln k(γ, T), however, is not in agreement with Marcus' theory, the resulting activation energies and ‐entropies being proportional to γ and increasing from negative values at low γ (extrapolated) to positive at high γ. The deviations are explained by a temperature‐dependent reaction distance and a preceding association between the radical cations and the counterions which increases strongly with decreasing polarity of the solvent.
A LEED and RHEED Investigation of Cu on Au(111) in the Underpotential Region
Authors: Nakai Y. , Zei M. S. , Kolb D. M. , Lehmpfuhl G. 
Published: July 2012

AbstractThe structure of Cu adsorbates, deposited electrochemically up to one monolayer onto Au(111) at underpotentials, has been investigated using LEED and RHEED after transfer of the gold electrode from the electrochemical cell into an UHV chamber. Before electrochemical deposition, the gold surface was thoroughly cleaned in the UHV‐chamber by argon bombardment and subsequent annealing. The Cu adsorbate is then found to yield a (√3 × √3)R30° superstructure at medium coverages, which is in clear contrast to the growth behaviour for Cu evaporated in UHV onto a bare Au(111) surface, where pseudo‐morphic growth is observed from the very beginning.
Thermal Desorption and Photoelectron Spectroscopy of NO Adsorbed on ZnO(1010)
Authors: Zwicker G. , Ranke W. , Jacobi K. , Pöss D. 
Published: July 2012

AbstractExposure of the ZnO(1010) prism face to NO at 90 K leads to two molecularly adsorbed NO species. The weakly bound form desorbs at 110 K and the strongly bound form desorbs at 420 K for low exposure and at 300 to 450 K for high exposures. Adsorption of the strongly bound form is activated and slower than of the weakly bound NO. Simultaneously, NO reacts partly to N2O at 90 K. N2O desorbs at 140 K, oxygen desorption is not observed and it is concluded that the oxygen formed during the NO to N2O conversion diffuses into the substrate. After annealing to 190 K, the weakly bound NO and N2O desorb. After several cycles of reexposing and annealing to 190 K, N2O formation is completely suppressed due to accumulation of either oxygen or the strongly bound form of NO or both. The strongly bound NO increases, the weakly bound NO decreases the electron affinity χ. After saturation with the strongly bound form, the final increase of χ amounts to 1.2 eV.
A Laser Temperature Jump Investigation of the Interaction between Proflavine and Calf‐Thymus Deoxyribonucleic Acid at Low and High Ionic Strength Avoiding Electric Field Effects
Authors: Marcandalli B. , Winzek C. , Holzwarth J. F. 
Published: July 2012

AbstractWe have used our very fast “Iodine‐Laser Temperature‐Jump” technique with a time resolution between 10−10 and 100 s to investigate the intercalation of proflavine into calf thymus DNA. Salt concentrations between 10−2 and 1 M and temperatures from 290 to 320 K were used. The DNA concentration ranged from 10−3 to 10−5 M and was always in large excess of the proflavine concentration to avoid aggregation of the dye in solution as well as on the surface of DNA. Under all experimental conditions only a single relaxation time which varied between 10−4 and 10−3 s could be detected. This result is in contrast to all temperature jump experiments performed so far using “Joule‐heating” equipments. The reason for this behaviour is that our technique is the only one which avoids the electric field effects inevitably associated with the “Joule‐heating” T‐jump arrangements.
205Tl NMR in Molten TlCl ‐ Tl2S Mixtures
Authors: Nakamura Yoshio , Baba Kazuhiro , Shimoji Mitsuo , Shimokawa Shigezo 
Published: July 2012

AbstractNMR shifts and spectral linewidths of 205Tl in molten TlCl ‐ Tl2S mixtures have been measured as a function of composition. With increasing Tl2S content the chemical shifts increase toward the paramagnetic direction and the lines become broader. At the Tl2S‐rich end, no resolvable spectra were obtained due to anormally broad linewidth or rapid relaxation rate. This rapid relaxation rate may be attributed to the formation of the paramagnetic center Tl2+; their concentration and lifetime have been estimated from the present NMR data and electronic conductivity data.
Thermal Conductivity of Ammonia in a Large Temperature and Pressure Range Including the Critical Region
Authors: Tufeu R. , Ivanov D. Y. , Garrabos Y. , Le Neindre B. 
Published: July 2012

AbstractUsing a coaxial cylinder apparatus, the thermal conductivity coefficient of ammonia was measured up to 80 MPa along nine quasi‐isotherms in the supercritical regime and one quasi isotherm below the critical temperature. The thermal conductivity in the critical region was carefully investigated. The results are compared to previous data. A semi empirical equation is proposed to correlate the data in the supercritical regime.
Nonequilibrium Phase Transitions with Hysteresis in Solid Catalysts. The System Copper‐Oxygen‐Propene
Authors: Greger M. , Ihme B. , Kotter M. , Riekert L. 
Published: July 2012

AbstractThe rates of formation of acrolein, CO2and CO from propene and oxygen on oxides of copper as catalysts have been investigated atp= 50 mbar, 4 mbar ≤p≤ 200 mbar in a differential reactor at 645 and 735 K. Oxygen contents of the catalysts have been determined in situ by titration with H2at 713 K. Selectivity and rate of oxygen consumption at steady state of the catalyst arenotsingle valued functions of gas phase composition. Mainly the selectivity of acrolein formation follows a closed hysteresis‐loop over a finite interval ofp. This phenomenon can be understood as due to hysteresis in the phase transition between CuO and Cu2O under nonequilibrium conditions, which has been predicted by Wagner [1] on the basis of theoretical considerations. The results demonstrate that the steady state of a solid catalyst can be indeterminate for a given initial condition and a complete set of intensive variables describing the surroundings.