bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isomerization and dissociation in competition — The two‐component dissociation dynamics of energy‐selected C3H6O2+ isomers
Authors: Baer Tomas , Mazyar Oleg A. , Keister Jeffrey W. , Mayer Paul M. 
Published: July 2012

AbstractThe dissociation dynamics of three C3H6O2+ isomers (methyl acetate, acetol, and ethyl formate) are compared. Photoelectron photoion coincidence (PEPICO) mass spectrometry is used to energy select these ions above their dissociation limits. The dissociation rates are derived from the ion time of flight distributions. All three ions dissociate via two‐component decay rates which provides proof that these ions dissociate by competitive isomerization and dissociation steps. In each case a number of lower energy isomers are involved in the dissociation mechanism. However, it is interesting that these three ions do not share a common set of lower energy isomers. The conditions necessary for the observation of two‐component decay are described and the shapes of the resulting ion TOF distributions are illustrated.
Fluorescence lifetimes of jet‐cooled trans‐stilbene and its (1:1)‐van der Waals complexes with n‐hexane: Cluster effects in photoisomerisation
Authors: Lienau Christoph , Schroeder Jörg , Troe Jürgen , Wack Karsten 
Published: July 2012

AbstractThe excess energy dependence of the fluorescence decay of jet‐cooled trans‐stilbene in the vicinity of the photoisomerisation threshold is compared with k (E,J) as calculated from an optimized RRKM model. Van der Waals 1:1‐complexes between trans‐stilbene and n‐hexane are generated in a supersonic jet and identified by rotational coherence spectroscopy. A comparison of the fluorescence lifetimes of isolated trans‐stilbene and the 1:1‐complex in the excess energy range 0 < Eex > 2500 cm−1 provides evidence for a competition between the isomerisation of stilbene in the bound complex and fragmentation of the complex accompanied by internal energy loss in trans‐stilbene. The threshold energy for isomerisation in the 1:1‐complex is found to be approximately 300 cm−1 lower than for the isolated stilbene molecule.
Raman scattering from optically levitated microdroplets: Influence of input resonances on output resonances
Authors: Popp J. , Hartmann I. , Lankers M. , Trunk M. , Kiefer W. 
Published: July 2012

AbstractIn this paper we consider in detail the influence of input resonances (incident electromagnetic field is in resonance with the cavity) on the output resonances in Raman spectra (scattered Raman field is in resonance with the cavity) of optically levitated microdroplets. Dependent on the kind of input resonance the output resonances show spectral shifts. We explain that these shifts are the result of a temperature increase, due to an input resonance and weak absorbance of the microparticle. The main intention of this paper is to describe the dependence of these temperature increases on the kind of input resonance.
Salt effects on the proton transfer equilibria in the 3,5‐dinitro‐2‐hydroxybenzoic acid/ammonia system: A T‐jump study
Authors: Sánchez Antonio , Pérez Francisco , Galán Manuel 
Published: July 2012

AbstractA thermodynamic study of the proton transfer equilibria involved in the system 3,5‐dinitro‐2‐hydroxybenzoic acid/ammonia has been undertaken in LiClO4 and NaClO4 aqueous solutions at different ionic strengths. The enthalpy for the different equilibria involved was measured by T‐jump techniques, while the free energies were determined spectrophotometrically.The different thermodynamic magnitudes, ΔG, ΔH and TΔS, are functions of the nature and concentration of the salt. However, the MSA provides a reasonable explanation for the experimental trends in most of the cases, although in this model only one parameter, the radii of the ions, is used to reproduce the mean ionic activity coefficients of electrolyte solutions at high ionic strengths.The extrapolated values at infinite dilution were also compared with the MSA prediction, and a good agreement was found.
Transferring freely suspended liquid‐crystal films on top of one another: A new method for the study of liquid‐crystal interfaces
Authors: Lucht R. , Bahr C. H. 
Published: July 2012

AbstractWe report a new experiment which consists of the transfer of a freely suspended liquid‐crystal film on the top of a second freely suspended liquid‐crystal film. Thereby a well defined interface between two liquid‐crystal materials and phases is produced.
Adsorption from binary solution in slit shaped pores
Authors: Borówko M. , Borówko P. , Rz̀ysko W. 
Published: July 2012

AbstractA theoretical model for adsorption of a binary solution in a slit shaped pore is proposed. The classic lattice model of the solution is used. Adsorption systems exhibiting complete mixing are considered. The theoretical results are compared with Monte Carlo simulations in the grand canonical ensemble. An influence of pore size and non‐ideality of the liquid mixture on adsorption and selectivity is analysed.
Vapor‐Liquid equilibria of binary mixtures of n‐heptane with 1,1‐dimethylpropyl methyl ether and 1,1‐dimethylethyl methyl ether
Authors: Mößner Frank , Coto Baudilio , Pando Concepción , Renuncio Juan A.R. 
Published: July 2012

AbstractVapor‐liquid equilibrium data are reported for the binary mixtures formed by n‐heptane and the branched ethers 1,1‐dimethylpropyl methyl ether (tert‐amyl methyl ether or TAME) and 1,1‐dimethylethyl methyl ether (tert‐butyl methyl ether or MTBE). A Gibbs‐Van Ness type apparatus was used to obtain total vapor pressure measurements for n‐heptane‐MTBE and n‐heptane‐TAME mixtures at 298.15 and 308.15 K. The systems show very small positive deviations from Raoult's law with a nearly ideal behavior. Results are analyzed in terms of the Peng‐Robinson equation of state and the Wong‐Sandler mixing rule, the Lattice‐Fluid (LF) model, the UNIQUAC model, and several versions of the UNIFAC model.
Influence of the zeolite matrix on the optical properties and the stability of hosted PbS nano‐particles
Authors: Wark M. , Jaeger N. I. , Lutz W. , Tkachenko O. P. 
Published: July 2012

AbstractThe formation of PbS nano‐particles with narrow size‐distribution in zeolite X is reported. By control of the degree of ion exchange the mean diameters of the particles can be varied between 3 and 8 nm. Particles exceeding the dimension of the zeolitic supercages are hosted in intra‐zeolitic mesopores which are formed in dependence on the growth of the particles.It is demonstrated that for zeolite‐hosted PdS nano‐particles the width of the optical band gap depends on size‐quantiation effects and on interactions between the particles and the host. As a consequence of its anionic character the zeolite framework generates extra charges (defect electrons) in the particles leading to an optical Burstein shift. From XPS it can be concluded that the polarisation of the Pb‐S bonds is the more pronounced the smaller the particles are. This results also in a decrease of their thermal stability.
Formation of amalgam particles in bimetallic silver and mercury colloids
Authors: Su Dangsheng , Katsikas Lynne , Giersig Michael 
Published: July 2012

AbstractWe report results gained in the transmission electron microscopy studying of silver and mercury colloids in an attempt to find the alloying behaviours of the two metals in the solution. Amalgam particles are formed, but aggregate and recrystallize to participates. While a large amount of mercury ions are reduced the small silver particles in the solution “disappear”. Then only relative large amalgam particles exist which sediment after some hours.
Synthesis and structural characterisation of Si and SiOx particles of nanometer sizes
Authors: Hofmeister H. , Ködderitzsch P. , Gösele U. 
Published: July 2012

AbstractThe possibilities of various gas phase processes for fabrication of nanosized Si and SiOx particles have been explored in a comparative Study. Conventional and high resolution electron microscopy was used to investigate in detail agglomeration, size, shape, crystallinity, surface roughness and internal structure of the particles, respectively. Accretions of nearly spherical crystalline Si particles of 2‐8 nm size mostly embedded in amorphous matrix were prepared by means of a gas evaporation cluster source. Their structural characteristics depend on the aggregation conditions applied. Inert gas are evaporation of silicon yielded single crystalline, spherical Si particles 4‐16 nm in size being completely free of defects. These particles, agglomerated into chains and tangles, are covered entirely by a thin amorphous oxide layer. Thermal evaporation of solid SiO in an inert gas atmosphere produced highly agglomerated, nearly spherical amorphous SiOx, particles 8‐24 nm in size with a considerable surface roughness. Upon annealing at 900°C the formation of 3‐6 nm sized Si crystallites in the interiro of these particles were observed.
Switching of optical properties in zeolitic nanocomposites
Authors: Marlow Frank , Hoffmann Katrin 
Published: July 2012

AbstractThe guest molecule azobenzene is aligned nearly perfectly by the channels of the molecular sieve AlPO4‐5. After irradiation with light of the wavelength 360 nm the configuration and the orientation of the molecules are changed. This results in changes of the refractive index. It turns out that this reaction is reversible (back reaction by irradiation with 436 nm) and that the change of the birefringence can be very large (δn' = 0,033). It is demonstrated that a crystal of a thickness of 13 μm is sufficient to be switched between a λ‐plate and a λ/2‐plate. This is an example of an opto‐optical microswitch.
Interfacial effects on the dynamics of cooperatively rearranging regions
Authors: Streck C. , Yan X. , Richert R. 
Published: July 2012

AbstractThe glass‐forming liquid 2‐methyltetrahydrofuran is particularly well described by the theory of Adam and Gibbs as regards the coupling between molecular dynamics and configurational entropy near the glass transition temperature at Tg = 91 K. Therefore, the underlying physical picture of cooperatively rearranging regions captures the temperature dependence of orientational dynamics for the bulk liquid on the basis of the configurational entropy. We demonstrate that geometrical confinement of such a liquid to nanopores gives rise to a dynamical coupling of the liquid to the rigid pore wall resulting in a non‐ergodic regime for long time, whereas the short time dynamics remain unaffected.
A spectroelectrochemical study of the slow relaxation in polyaniline and its acceleration in composite films with poly(o‐phenylenediamine)
Authors: Malinauskas Albertas , Holze Rudolf 
Published: July 2012

AbstractThe kinetics of the slow relaxation, or “first cycle effect”, observed during the cathodic reduction of a polyaniline film, were investigated with UV‐vis spectroelectrochemistry. It was shown, that the slow cathodic reduction of a polyaniline layer, present initially in its emeraldine state, can be accelerated by placing an additional layer of poly(o‐phenylenediamine) between the substrate electrode and the polyaniline film. Furthermore, it was found, that the anodic oxidation of the leucoemeraldine form of polyaniline is also favoured by the inserted film of poly(o‐phenylenediamine). The observed acceleration of the slow relaxation by the intermediate film is discussed in the framework of a previously presented model, which takes into account anion movement in the polymer film proceeding during the redox processes in opposite directions for both polymers studied here.
Aggregation of cationic surfactants in D2O: A proton NMR study on effects of the structure of the headgroup
Authors: Bazito Reinaldo C. , El Seoud Omar A. , Barlow Graham K. , Halstead Tom K. 
Published: July 2012

AbstractAggregation of the following surfactants in D2O has been studied by 1H NMR spectroscopy at 500.13 MHz, 298 K: series I, dodecyltrialkylammonium bromides, alkyl group = methyl, ethyl, n‐propyl, and n‐butyl; series II, dodecyldimethyl (2‐hydroxyethyl)ammonium bromide, dodecylmethyl bis(2‐hydroxyethyl)ammonium bromide, and dodecyl tris(2‐hydroxyethyl)ammonium bromide. Chemical shifts of the surfactant discrete groups were measured at concentrations below and above the surfactant critical micelle concentration, c.m.c., whose value was determined by conductance measurements in H2O. Plots of observed chemical shifts versus [surfactant]are sigmoidal, and were fitted to a model based on the mass‐action law. Excellent fits were obtained for the discrete groups of all surfactants. The parameters determined by these fits were: the equilibrium constant for micelle formation, K, c.m.c., and the chemical shifts of the monomer, δmon and the micelle, δmic. 1H NMR‐based c.m.c. values are in excellent agreement with those which we determined by conductance measurements. Values of K increase as a function of increasing the size of the headgroup of series I surfactants, but the incremental contribution to the Gibbs free energy per CH2 group at the interface is small, its value increases from 0.13 kJ (moles of CH2)−1 to 0.29 kJ (moles of CH2)−1 in going from the trimethyl‐ to the tri‐n‐propyl, and the tri‐n‐butyl analogue, respectively. Micellization affects the chemical shifts of the groups at, or near to, the interface mainly because of differences in hydration of the surfactant molecule in its monomeric and aggregated forms. This conclusion is supported by comparing (δmic ‐ δmon) with (δCDCl[Text is not clear]‐δmon), where δCDCl3 is the chemical shift of the surfactant in CDCl3, i.e., in absence of hydration. For series II surfactants, the chemical shifts versus [surfactant]plots are qualitatively similar to those for series I, this shows that substitution of the 2‐hydroxyethyl group for the ethyl group in the hydrophilic part of the surfactant does not seem to change the properties of the formed aggregate.
Interfacial wetting transitions in ionic and metallic fluid mixtures
Authors: Freyland W. , Nattland D. 
Published: July 2012

AbstractRecent experimental investigations of interfacial wetting phenomena in binary liquid mixtures characterized by Coulomb or screened Coulomb short range interactions are discussed. Wetting transitions occurring at the fluid‐wall and the fluid‐vapour interface are considered focusing on the examples of fluid alkalimetal‐alkalihalide mixtures and liquid gallium‐based binary alloys at elevated temperatures. Different spectroscopic methods have been employed to probe the respective interfaces, spectroscopic ellipsometry and second harmonic generation (SHG). In the case of K‐KCl solutions the SHG results exhibit changes characteristic of a prewetting transition in metalrich solutions implying a first order wetting transition at coexistence. A wetting transition is observed for liquid Ga‐Bi and Ga‐Pb alloys approaching the monotectic point at coexistence.
The influence of charge centres separation in complex structure ion on ionic‐strength dependence of equilibrium constants in aqueous solution
Authors: Sadofeev Igor G. , Mironov Igor V. 
Published: July 2012

AbstractThe acid‐base equilibria of oxalic, malonic and succinic acids, ethylenediamine, diethylenetriamine and glycine were studied potentiometrically (glass electrode) in NaClO4 (for polyamines also in NaCl) solution of various concentrations (0.01‐3 M), at 25°C. The dependence of the change of equilibrium constants with ionic strength on the distance between charge centres in ion is discussed. This dependence more markedly exhibits for ions with the shortest distances between charge centres. No differences in observed effects for different classes of ions were found. The simulation of the medium effects for the systems involving ions with separated charge centres was carried out on the basis of electrostatic notion with the data on the ion structure and the magnitudes of charges on atoms.
Kinetics of the reactions of bromine atoms with a series of aliphatic aldehydes at 298 K
Authors: Szilágyi I. , Imrik K. , Dóbé S. , Bérces T. 
Published: July 2012

AbstractThe kinetics of the reactions of Br(2P3/2) with selected aldehydes, i.e. ethanal (l), propanal (2). 2‐methyl‐pro‐panal (3), 2,2‐dhethyl‐propanal (4) and trichloroacetaldehyde (5) were studied at 298±2 K. Rate constants for overall reactions were measured using the fast flow technique with resonance fluorescence detection of Br. Complementary determinations were carried out by the laser flash photolysis method. The following rate constants were obtained in the kinetic measurements (±2σ): k1=(2.1±0.2)×1012, k2=(4.3±0.4)×1012, k3=(6.3±1.4)×1012, k4=(8.5±0.8)×1012, k5≤1×109 all in cm3 mol−1 s−1 units.The probable mechanism for the reactions of bromine atoms with aliphatic aldehydes has been discussed.
Quantized aggregation phenomena in II‐VI‐semiconductor colloids
Authors: Ptatschek V. , Schmidt T. , Lerch M. , Müller G. , Spanhel L. , Emmerling A. , Fricke J. , Foitzik A. H. , Langer E. 
Published: July 2012

AbstractHighly concentrated 0.5 M II‐VI semiconductor quantum dot solutions for coating applications can be synthesized employing chalcogenolysis and condensation of functionalized cluster‐like cadmium and zinc ethoxy‐acetates. Furthermore, in nucleation studies on CdSe solutions, new magic clusters between 0.42 and 1.7 nm in size were found exhibiting sharp HOMO‐LUMO resonances (lowest absorption features) in the optical absorption spectra. High resolution small angle X‐ray scattering (SAXS) measurements performed on 1.7 and 3.4 nm CdSe clusters corroborate the size. Information on the intra‐cluster structure was hard to derive with respect to the small cluster size. These species could be Koch pyramids with a fractal dimension Df=2 as well as non‐fractal zincblende pyramids (additionally checked by XRD and HRTEM). In any case rather chain‐like (Df= 1) aggregates are formed. It further will be shown that in alcoholic CdSe sols the initially nucleated “seeds” are highly reactive. Their sharp HOMO‐LUMO transitions are found to be strongly modified by externally induced chemical reactions. For example, aminosilane capped 1.7 nm clusters decompose rapidly upon exposure to phosphines. After a period of few hours, they begin to re‐grow to their original size or they reorganize to give smaller 0.85 nm subunits depending on the P/N ratio. In contrast, 0.85 nm phosphine‐capped clusters double their size if exposed to amines. The last process liberates cadmium ions into the solution as found in complementary polarographic measurements.
UHV Model experiments of the semiconductor/electrolyte interface: Adsorption of I2on n‐ and p‐doped WSe2(0001)
Authors: Henrion O. , Jaegermann W. 
Published: July 2012

AbstractThe WSe2(0001)/I2semiconductor/electrolyte interface was simulated in Ultra‐high‐Vacuum (UHV) by adsorbing I2onto the van der Waals plane of the layered substrate at 100 K. The interface was characterized by photoelectron spectroscopy and surface photovoltage measurements. The interaction proved to be non‐reactive and I2adsorbs as molecular species. The electric potential distributions measured by UPS und XPS are in reasonable agreement to semiconductor/electrolyte interfaces. Iodine behaves as electron acceptor inducing strong band bending only for n‐doped and not for p‐doped samples. After correcting for source‐induced surface photovoltage effects the 2σulevel (LUMO) of adsorbed I2is identified of being responsible for establishing electronic equilibrium.
CO adsorption and hydrogenation on crystalline YBa2Cu3Ox thin films
Authors: Chen L. , Lin J. , Chen H. Y. , Xu S. , Li K. , Ong C. K. , Tan K. L. , Li J. 
Published: July 2012

AbstractYBa2Cu3Ox (YBCO, x=6‐7) is shown to have catalytic activity for methanol synthesis from syngas in this work. In order to get more details about the nature of the reactive site and reaction mechanism, CO adsorption and hydrogenation on a high quality YBCO thin film were studied by using in situ Fourier transform infrared spectroscopy (FTIR), angle‐resolved X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD) and atomic force microscopy (AFM). Carbonate‐like species, aldehyde, formate and methoxy were detected as reaction intermediates. After the CO hydrogenation reaction Cu2+ ions were reduced to Cu1+, and the orthorhombic structures of YBCO was transformed to the tetragonal phase with the formation of carbonatelike complexes. The degradation of some YBCO to amorphous surface phases was also observed. Based on these studies, carbonate‐formate‐dioxymethylene‐methoxy (or carbonate‐aldehyde‐carnene‐methane) reaction scheme is proposed.
Chemical kinetics of phase boundaries in solids
Authors: Schmalzried H. , Janek J. 
Published: July 2012

AbstractThe kinetics of solid/solid interfaces is of major importance for the course of heterogeneous reactions in the solid state. Solid/solid interfaces are normally sources of elastic stress and thus may interact with outer surfaces. In addition, they can offer high diffusivity paths and thus represent two‐dimensional reaction media. Essential kinetic situations are defined and basic formal considerations are summarized. Corresponding experimental examples are presented in order to illustrate kinetic phenomena at static and moving boundaries. This includes questions of exchange fluxes, boundary‐controlled solid state reactions, morphology, nonlinear phenomena and reactions in boundaries.
NMR study of the dynamics and structure of a good glass former LiCl‐6H2O
Authors: Maurin P. O. , Jal J. F. , Dupuy‐Philon J. , Asahi N. , Kawamura J. , Kamiyama T. , Nakamura Y. 
Published: July 2012

AbstractThe temperature dependences of the self‐diffusion coefficient and the spin‐lattice relaxation time have been studied by NMR measurements performed on a good glass former LiCl‐6H2O. The spin‐lattice relaxation time can be separated into two relaxation processes, i.e., inter‐ and intramolecular processes. We have related these relaxation processes to the translational diffusion which corresponds to the primary or α‐relaxation and to the local motions which are related to the β‐relaxation in glass forming systems. The results throw some light to the evolution with temperature of these relaxation processes in the LiCl‐6H2O system over the normal liquid, supercooled liquid and glass sates.
Diffusion on simple heterogenous surfaces
Authors: Nieto F. , Uebing C. 
Published: July 2012

AbstractIn this work we use the well‐known bivariate trap model with random topography in order to study the effects of surface heterogeneities on surface diffusion. Utilizing Monte Carlo simulations we characterize how the tracer, jump and chemical diffusion coefficients depend on temperature and concentration of deep traps, θ. In order to calculate the chemical diffusion coefficient we apply the fluctuation and the Kubo‐Green methods. Both methods are in good agreement at large values of θ only. The discrepancies are discussed and explained. The effects of heterogeneities are largely pronounced at low total coverage and low temperatures, where most of the adatoms are trapped by the deep traps. At high coverages the mobility of adatoms adsorbed on shallow traps dominate the diffusion behavior.
Thermodynamics and statistical mechanics of ammonia in zeolite NaZSM5
Authors: Boddenberg B. , Rakhmatkariev G. U. , Viets J. 
Published: July 2012

AbstractThe adsorption isotherm and the differential heat of adsorption of ammonia in zeolite NaZSM5 (Si/Al=32) were measured over a wide range of equilibrium pressure at the temperature 303 K. The obtained data can consistently be interpreted to be due to the formation of s‐meric (s = 1 − 6) ammonia/sodium cation complexes residing in the intersections of the straight and zig‐zag channels of the zeolite structure. The energies of formation and the potential energies of the s‐mers are reported.