bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Thermal Behavior of Freely‐Suspended and Transferred Films Composed of a Single Compound, the Liquid Crystal 707PP
Authors: Decher G. , Maclennan J. , Reibel J.
Published: July 2012

We have recently introduced a new method for the preparation of ultrathin smectic films on solid supports by transferring freely‐suspended liquid‐crystalline films [1, 2]. Here we report on the preparation, structural properties and thermal behavior of freely‐suspended and transferred films of 2‐(4'‐Heptyloxyphenyl)‐5‐heptylpyridine (707PP). Freely‐suspended and transferred films were investigated using optical microscopy and X‐ray diffraction. Both types of films exhibit reversible phase transitions comparable to bulk values.
Photoelectrochemical Investigations of Molecular Semiconductors: Characterization of the Conduction Type of Various Substituted Porphyrins
Authors: Schlettwein D. , Jaeger N. I. , Wöhrle D.
Published: July 2012

The charge transfer from thin film electrodes (thickness ≈ 130 nm) of the zinc(II) complexes of phthalocyanine (1), 2,3,9,10,16,17,23,24‐octacyanophthalocyanine (2), tetrapyrido[2,3‐b; 2′,3′‐g; 2″,3″‐1; 2′″,3′″‐q]‐5,10,15,20‐tetraazaporphyrin (3) and tetrapyrazino[b;g;l;q]‐5,10,15,20.tetraazaporphyrin (4) to oxygen or EDTA dissolved in an aqueous electrolyte was investigated. Illumination with visible light results in photocurrents which are characteristic for each of the studied compounds. The observations are discussed in terms of the band model suitable for molecular organic semiconductors. From the observed predominant direction of the photocurrent a trend in the band positions and the conduction type of the materials 1, 2, 3 and 4 is established. The transformation of a p‐type into a n‐type porphyrin solid can be achieved by appropriate chemical substitution in the ligand system.
Anodic Dissolution of Metallophthalocyanine Layers and Their Intrinsic Oxidation
Authors: Jansen Rolf , Beck Fritz
Published: July 2012

Voltammetric measurements at a PtRRDE, where vacuumdeposited MePc‐layers (70–700 nm) are present at the disc, were performed in 0.1 M LiClO4 in acetonitrile. Any dissolved MePcz+‐species can be rereduced at the ring. Anodic dissolution was found to be the only process in the case of FePc and CoPc at relatively negative potentials. The cations dissolve layer by layer. For NiPc and CuPc, three different anodic processes can be distinguished: I) Anodic insertion of anions into the solid without any dissolution of cationic species. II) A further insertion of anions at more positive potentials, which is accompanied by a slow dissolution of the material. This is indicated by a relatively weak cathodic ring current. Lattice dynamics in the course of the anodic insertion of anions leads to a destabilization of the solid. III) A strong ring current shows the anodic dissolution of the whole MePc‐layer at even more positive potentials. It is accompanied by a chemical dissolution to release the anions, which were inserted in the course of steps I and II. The consequences with respect to the long term stability of MePc are discussed.
Photophysical Properties of Heterogeneous AgBr Layers
Authors: Böttcher Horst , Räbisch Mathias , Schreiber Kerstin , Siegel Jörg
Published: July 2012

By Multi Source Physical Vapour Deposition (MS‐PVD) the preparation of mixed thin layers consisting of different inorganic or organic substances is possible. By this method it was investigated which effect admixture of different metal halides (NaX, PbX2) had on structure and photosensitivity of evaporated AgBr layers. Unexpectedly the mixed layers revealed a considerable increase in photosensitivity in the range between 20 and 60 vol‐% metal halide admixture as compared to pure AgBr.—The results of photo‐EMF and microwave photoconductivity measurements are indicative of an effective charge carrier separation at the segregated crystallite phase boundaries.
On Coulombic and Solvophobic Liquid‐Liquid Phase‐Separation in Electrolyte Solutions
Authors: Weingärtner Hermann , Merkel Thomas , Maurer Ulrich , Conzen Jörg‐Peter , Glasbrenner Heike , Käshammer Stefan
Published: July 2012

We have performed a systematic study of liquid‐liquid phase equilibria in aqueous and non‐aqueous solutions of tetraalkylammonium salts up to about 500 K, covering a large number of hydrogen‐bonding, dipolar aprotic and non‐polar solvents. There appear to be two different types of liquid‐liquid phase equilibria resulting from long‐range Coulombic and from short‐range specific forces, respectively. These may be denoted as Coulombic and solvophobic unmixing. Coulombic unmixing is observed in solutions of 1:1‐electrolytes in solvents of low dielectric constant, as is exemplified for solutions in hydrocarbons and long‐chain alcohols. It appears to be closely related to a general instability of ionic fluids at low reduced temperatures. Increase of the dielectric constant results in complete miscibility, as is demonstrated for salts dissolved in short‐chain alcohols and some common dipolar aprotic solvents. Solvophobic unmixing occurs if salts with large cations and anions are dissolved in water. A phenomenological analysis shows that this phase separation results from those thermodynamic pecularities which are usually attributed to the hydrophobic nature of the cations. Some cation‐anion association appears also to play a role. Similar immiscibilities have been observed with other hydrogen‐bonding solvents of high cohesive energy density, namely glycerol, ethylene glycol, 1,3‐propanediol, formamide and monoethanolamine, suggesting the existence of a more general solvophobic unmixing effect.
Internal Solid State Reactions of the Type A + B = AB: Diffusion‐Controlled Formation of AB from A and B Dissolved in a Crystalline Host Matrix
Authors: Backhaus‐Ricoult M. , Schmalzried H. , Tarento R. J.
Published: July 2012

A and B diffuse from opposite sides into a finite slice of solid C. After a certain diffusion time the solubility product of a product phase, AB, may be reached and AB precipitates. The location of the first nuclei formation is calculated as a function of the solubilities and the diffusion coefficients of A and B in the matrix C, and of the solubility product. Chemical diffusion coefficients of A and B, which are either constant or proportional to their own concentration, or proportional to the concentration of the other diffusing species are considered. For some sets of typical system parameters the diffusion profiles are calculated and the time and coordinate for first precipitation are shown.—Further growth of small nuclei is given by further diffusion of A and B into the matrix C and to the precipitate, which constitutes a sink for A and B. The precipitate grows in the diffusion field with a preference for certain directions. These directions and the initial growth rate of the precipitate depend on the transport properties of both the matrix and the precipitate, as well as on the thermodynamic conditions of phase coexistence of precipitate and matrix. Limiting cases of an infinitely fast or negligible material transport inside the precipitated phase are considered and the initial growth of a single precipitate in the diffusion field and its shape evolution during growth are calculated.—The global morphology of the assembly of AB precipitates for long diffusion times is discussed by considering the morphological evolution of an intermediate AB layer.
Electroreduction of 1‐and 2‐naphthylhydrazonodimedones in DMSO
Authors: Vasudevan D. , Venkatachalam C. S. , Kalidas C.
Published: July 2012

A detailed investigation on the reduction of 2‐(1‐naphthylhydrazono)dimedone (1‐NHD) and 2‐(2‐naphthylhydrazone)dimedone (2‐NHD) in 0.1 M TEAI‐DMSO was made using various electroanalytical techniques. Each of the two compounds gave two well‐defined polarographic waves/cyclic voltammetric (CV) peaks. The first one‐electron diffusion‐limited wave/peak arises out of the formation of the corresponding anion radical and has been characterised to be of oxy type from in‐situ EPR studies. However, the second wave/peak is attributed to an EC reaction involving a fast reverse disproportionation reaction by which the anion radical is regenerated, as confirmed from CV studies and also from the non‐integral n value obtained for the second wave from microcoulometry. Macroscale CPE experiments carried out at the limiting regions of the first and second polarographic waves of 1‐NHD and 2‐NHD afforded the corresponding naphthylamines as the major product. Based on these results, a plausible mechanism for the electroreduction of 1‐NHD and 2‐NHD in DMSO has been proposed.
Concentration Dependent far Infrared Absorption Spectra of the Mixtures FURAN/CS2, FURAN/CCl4, FURAN/C6H6
Authors: Haritopoulou M. , Samios J. , Zoidis E. , Dorfmüller Th.
Published: July 2012

The far infrared absorption spectra of furan in liquid solutions with carbon disulphide, carbon tetrachloride and benzene, are to the first time presented, along with the absorption spectra of neat furan at three different temperatures. The spectral behaviour of the absorption curves is studied for each solvent at three mole fractions of furan. The results are qualitatively discussed in terms of the intermolecular geometry in the solution, as determined by the structure characteristics of the non‐polar solvents, and also in terms of the interaction between solvent and solute, producing under certain circumstances an interaction induced contribution to the permanent dipole moment of the furan molecule.
Surface Ionization of Dipalmitoylphosphatidylcholine as Detected by the pH Dependence of the Phase Transition Temperature of Liposomes
Authors: Fernández Marta S. , Calderón Estela
Published: July 2012

The surface ionization of lecithin phosphodiester has been studied following the effect of bulk pH on the increment in the gel to liquid‐crystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine (DPPC) liposomes, induced by incorporation of protonated stearylamine. At constant pHb, the increment (Δtm is a monotone increasing function of stearylamine concentration which deviates from linearity, toward lower Δtm values, at high proportions of additive. From plots of Δtm as function of the stearylamine proportion in DPPC liposomes at different pHb values, the initial slopes, as stearylamine concentration approaches zero, is obtained and interpreted as a potentiality for tm elevation of DPPC bilayers. The slope value, seems to be related to the ionization degree of the phosphate group since it increases with bulk pH and levels off above pHb 4 i.e., for zwitterionic lecithin. If the titration curve resulting from normalization of those slope values, is attributed to ionization of lecithin phosphate, an apparent pK of 1.3 is obtained. The consistency of the data analysis is supported by the good fitting found between the experimental results and a theoretical curve based on Henderson‐Hasselbach, Boltzmann, and Gouy‐Chapman equations. Best fit is obtained when the intrinsic interfacial pK, which is the pK in the absence of surface electrostatic effects, is set equal to 4. Such a high intrinsic pK value is explained in terms of the effect of the reduced dielectric constant of the lipid‐water interface, on the ionization of the phosphate group which is a molecular acid and, as such, will be stabilized in a low polarity region.
Multiprocessed Simulation of Competing Folding Pathways in RNA: The Shaping of the Catalytic Site for Splicing
Authors: Fernández Ariel
Published: July 2012

The open problem in RNA catalysis we focus on is how to predict which mitochondrial mRNA introns belonging to group I will splice exclusively in vivo. We have simulated competing folding pathways by a parallel distributed process in order to prove that early base‐pair disruptions ultimately cause the internal guiding sequence (IGS) to function as intramolecular adaptor in an otherwise‐inert structure. In this way, the participation of the IGS‐3′exon pairing in promoting splicing in vivo is elucidated. The case of the YC4 intron is chosen as an illustration. Our approach requires implementing parallel‐processed Monte‐Carlo simulations to monitor the effect of base‐pair disruptions, leading to competing folding pathways. The search for active structures is subject to time constraints characteristic of the assembling of pre‐mRNA's.
An Investigation of the Methanol Decomposition Behind Incident Shock Waves
Authors: Dombrowsky Ch. , Hoffmann A. , Klatt M. , Gg. Wagner H.
Published: July 2012

The pyrolysis of methanol was investigated behind incident shock waves at temperatures and densities between 1400 and 2200 K and 1 · 10−6 and 5 · 10−6 mol/cm3, respectively. Narrow band‐width laser absorption for OH radicals and ARAS technique for H atoms was used to determine the decomposition channels. For the experimental conditions described above the direct OH‐formation is found to be the main channel of about 80% of the decomposition rate. The channel leading to H and CH2OH is found to be less than 5%. There remains the possibility of channels leading from methanol to 1CH2 + H2O or to CH2O + H2.
Rate Constants for the Reactions of N2(A3Σu+,v′) with O3(X̃1A1)
Authors: Böhmer E. , Hack W.
Published: July 2012

The gas phase reaction of N2(A3Σu+) with O3(X̃1A1) was studied in a fast flow reactor. N2(A) was prepared by the energy transfer reaction of N2(X) with Ar* and detected by laser induced fluorescence (LIF) in the first positive system. From the depletion of N2(A,v′) as a function of the reactant concentration under pseudo‐first order conditions [N2(A)]0 < [O3], the overall rate constants of the reaction N2(A,v′ = 0,1,2, and 3) + O3(X̃1A1) → products for the specific vibronic states were determined to be: k(v′ = 0) = 2.5, k(v′ = 1) = 2.5, k(v′ = 2) = 4.8, k(v′ = 3) = 6.1 (in 1013 cm3/mol·s) at T = 298 K.—The products NO(X2Π) and O(3P) formed in the elementary reaction (1) were detected by LIF via the transition (A2Σ+ – X2Π) and by resonance absorption (RA), respectively.
Catalytic CO Oxidation over La1‐xSrxMnO3 at High CO Partial Pressures
Authors: Jaenicke S. , Chuah G. K.
Published: July 2012

The catalytic CO oxidation over polycrystalline LaMnO3 exhibits a bistability at high CO concentration. Under atmospheric pressure, the regime of bistability extends from 200 to 220°C and widens with increasing CO concentration. A systematic study of the solid solution system La1‐xSrxMnO3 which crystallizes in the perovskite structure, shows that the width of the bistable regime decreases with an increasing amount of strontium substitution and no bifurcation was observed for x > 0.2. A model is proposed to explain the bistability, based on a CO‐driven reconstruction of the reduced surface, leading to pairs of Mn2 ions with a Mn‐Mn distance comparable to the spacing in the metal. These pairs provide reactive sites for CO oxidation and oxygen chemisorption. Such metal‐metal pairs are not found in the perovskite lattice but are a structural feature of the closely related hexagonal 4‐layered packing which is the normal crystal structure of SrMnO3. The rate of change back to the “oxidized” surface is found to correlate with the lattice oxygen mobility. With low oxygen mobility, the transition from the active into the less active state becomes slow and hysteresis may result. Strontium substitution increases the number of defects in the oxygen lattice and leads ultimately to an oxygen deficiency (reductive nonstoichiometry). The catalytic activity of the system peaks at x = 0.2, indicating the influence of both the oxygen mobility and the oxygen nonstoichiometry on the catalytic oxidation reaction.
Suspension Structures of Deionized Colloidal Silica Spheres As Studied by the Reflection and Transmission Spectroscopy
Authors: Okubo Tsuneo
Published: July 2012

Structural distributions of colloidal silica spheres are studied from the reflection and transmitted‐light spectrum measurements. The crystal‐like structures are suppressed when the sphere size is small and/or monodispersity index (standard deviation of the diameters divided by the mean diameter) is large; monodisperse (0.05 to 0.13 in monodispersity index) and large spheres (100 to 192 nm in diameter) give sharp peaks in the reflection and transmitted‐light spectra, which supports the existence of the crystal‐like structure in the suspensions. When the suspensions are diluted, phase transition toward liquid‐like distribution occurs. On the other hand, the deionized suspensions of polydisperse (0.20 and 0.21 in monodispersity index) and large spheres (133 to 148 nm in diameter) display the amorphous solid‐like distributions, and crystal‐like structures are not observed at any concentrations examined. By dilution the structure is transformed to the liquid‐like one. The crystal‐like and amorphous solid‐like distributions are melted out into the liquid‐like structures by the addition of a small amount of sodium chloride. The intersphere distances (D) decrease in the course of the melting. The transmitted‐light spectra for the suspensions of small spheres (45 nm in diameter) show the single broad peak, which supports liquid‐like distribution of the spheres. The D‐values of both crystal‐like and amorphous solid‐like structures agree with the mean distances calculated assuming that the spheres distribute homogeneously throughout the suspension. These results are consistent with the effective hard‐sphere model.
Reactivity of HO2· Radicals in Alcohols
Authors: Keszler Ágnes , Irinyi György , Héberger Károly , Gál Dezsö
Published: July 2012

Photoinitiated liquid phase oxidation of 1‐phenyl ethanol and benzyl alcohol have been investigated in the temperature range of 50–70°C using the intermittent illumination (rotating sector) technique. The rate of oxidation was followed by gas chromatography while the rate of initiation was determined by the inhibitor method. Results were explained by assuming HO2· radicals to be the main chain carriers, supported by comparison of the results with literature data. – The termination rate constant of HO2· was calculated from the average lifetime of radicals in both alcohols:

2kt = 9.91 · 1012 exp(–29.2 kJ · mol−1/RT) in 1‐phenyl ethanol and

2kt = 8.98 · 1012 exp(–31.3 kJ · mol−1/RT) in benzyl alcohol.

(in 1 · mol−1 · s−1, the uncertainties given by the covariance matrix, see in the text.) – The rate constants for hydrogen abstraction by HO2 from the substrate molecules have also been determined in the case of both alcohols:

kp = 4.61 · 108 exp(–52.0 kJ · mol−1/RT) in 1‐phenyl ethanol,

kp = 1.04 · 109 exp(–54.3 kJ · mol−1/RT) in benzyl alcohol,

(in 1 · mol−1 · s−1, uncertainties see in the text.)
Photoinduced Back Electron Transfer within Geminate Radical Ion Pairs. Observation of the Marcus Inverted Region in the System Thionine with Several Aromatic Donors
Authors: Grampp Günter , Hetz Gabriel
Published: July 2012

The Marcus “Inverted Region” is found for back electron transfer reactions within geminate radical pairs consisting of triplet‐thionine and several aromatic donors. Measurements were performed in buffered methanol (pH = 8.6) at 295 K. The standard free energy change ΔG−et0 ranges from –54.0 to –150.5 kJ/mol by varying the donors from N,N,N′,N′‐tetramethyl‐p‐phenylendiamine, p‐phenylendiamine, p‐aminodiphenylamine, 1‐naphthylamine, diphenylamine, 9,10‐dimethylanthracene, 1,2,4‐trimethoxybenzene to 9‐methylanthracene. The rate constants start at 3.3 · 107 s−1, reach a maximum at 1.0 · 109 s−1 for 1‐naphthylamine and decrease to 1.7 · 108 s−1 for highly exergonic reactions.
Mass Spectrometric Study of Volatile Products During the Carbochlorination of Zirconia
Authors: Pasquevich Daniel M. , Amorebieta Valentín T.
Published: July 2012

The reaction of chlorine with zirconium oxide in the presence of carbon was studied by mass spectrometry. Volatile reaction products were measured at different temperatures and traces of oxygen were detected. We also observed that the CO2/CO ratio increases with increasing reaction temperature. The role of the Boudouard reaction in the carbochlorination process is discussed and a reaction mechanism based on chlorine atoms is suggested.
Study of Forces of Inertia Acting on the Aqueous Pore Fluid of Polyelectrolyte Gels with Negatively Charged Fixed Ionic Groups
Authors: Röttger H. , Woermann D. , Rickert H. , Kappelhoff Th.
Published: July 2012

It is demonstrated that pulses of the inertia‐electromotive force can be generated during the deceleration of stiff rods of water containing Polyelectrolyte gels with negatively charged ionic groups covalently bound to the gel matrix. The counter ions of the fixed charges are silver ions. Two types of gels are used for the experiments. The concentration of the fixed ionic groups of gel type 1 is larger than that of gel type 2. The value of the ratio (m/e)exp (m, e, mass and charge of one silver ion respectively) calculated from the experimentally determined voltage puls ∫ U dt (U, inertia‐electromotive force; t, time) during the deceleration with gel type 1 is nearly a factor of 4 larger than the corresponding value calculated from corresponding experiments with solid ionic conductors (e.g. RbAg45). For the gel type 2 this factor has a value of about 20. The larger values of (m/e)exp found with the gels are attributed to a larger effective mass of the silver counter ions. During deceleration, the aqueous pore fluid together with hydrated mobile silver ions is shifted relative to the hydrated stiff matrix of the gel. This situation is different from that encountered in ion conductors in which the naked mobile silver ions are shifted relative to the rigid lattice formed by the anions during deceleration.
The Role of the Microstructure of Copper Deposits During Electroless Plating in Formaldehyde Containing Alkaline Baths. Comparison of Fourier Transform Impedance Spectroscopy and Surface Enhanced Raman Spectroscopy
Authors: Bittner Alexander , Wanner Michael , Weil Konrad G.
Published: July 2012

The microstructure of copper deposits was in‐situ investigated by impedance measurements and by surface enhanced Raman scattering. The simultaneous determination of the copper deposition rate with a quartz microbalance and the mixed potential under electroless plating conditions allows to separate the two partial processes copper deposition and formaldehyde oxidation. Due to this combination of investigation techniques we are able to correlate responses of the partial processes e.g. caused by variation of the bath components on changes of the surface microstructure of the copper deposit. A microstructure with amplitudes of an atomic scale is only maintained during the electroless deposition process and is a specific catalyst for formaldehyde oxidation. The overall process is found to be a complex heterogeneously catalyzed system, which can be understood in synergetic terms as a selforganizing process.
Phase Behavior and Light Scattering of the System Dodecyldimethylaminoxide, n‐Hexanol and Water in the Very Dilute Region
Authors: Platz G. , Thunig C. , Hoffmann H.
Published: July 2012

Solutions of Dodecyldimethylaminoxide (DDMAO), n‐hexanol and water show a phase behavior which is found to be typical for many surfactant‐alcohol‐water systems with lamellar phases. Three types of lamellar phases and three types of isotropic low viscous clear phases which exhibit extreme flow birefringence (L3‐phases) are found at room temperature. Both a hexanol‐rich (Lαh) and a hexanol‐poor lamellar phase (Lαl) can be diluted to iridescent solutions with bright colors. The iridescent Lαh phase is of low viscosity and forms quickly, the higher viscous Lαl phase needs 600 hours until the iridescence can be observed. — UV‐Vis and classical light scattering measurements show that the interlamellar structures or spacings of the Lαl phase are strongly and those of the Lαh phase are weakly fluctuating. The Lαh phase is much more sensitive to added electrolyte than the Lαl phase. The Lαl phase seems to be the type of iridescent phases which can be found with some ionic surfactant‐water systems. — An intermediate lamellar phase exists between the Lαh and the Lαl phase with a second order or kinetically controlled phase transition. At the lower concentration limit (DDMAO concentration around 50 mmol/l) this intermediate phase needs several months for the formation. — The Lαh phase is accompanied at some higher hexanol concentration by a L3 phase. This phase transforms quickly to an iridescent phase immediately after shear stress. Depending on concentration and temperature this iridescent phase remains stable for a few minutes to several hours. The second isotropic phase with extreme flow birefringence exists below the Lαl phase. Dilution of the intermediate lamellar phase leads to an intermediate phase of type L3 which is not in a thermodynamic equilibrium state. — The Lαl phase and the intermediate lamellar phase give slow torsion waves whose propagation can be observed between crossed polarizers. The rheologic behavior which leads to these shear waves is discussed.
Investigation of 22Na Tracer Diffusion Through a Cation‐Exchange Membrane Using a Coincidence Counting Method
Authors: Daniel Thomas , Löhr Helge , Seidel Wolfhart , Sattler Ernst Ludwig , Seibold Georg
Published: July 2012

By means of e+ pair annihilation radiation the diffusional transport of 22Na ions through a poly‐phenol sulfonate (PPS) membrane was observed continuously using a coincidence counter device. Compared to usual tracer methods the present one has several advantages, e.g. appreciable smaller amount of solution and less total time for an experiment. — For different salt concentrations the apparent self diffusion coefficient of 22Na+ ions was determined.
Excimer and Isomer Mediated Reactions in Ionized van der Waals Clusters
Authors: Märk T. D. , Foltin M. , Grill V. , Rauth T. , Walder G.
Published: July 2012

Electron impact ionization of rare gas clusters Rn (Nen, Arn) has been found to result via multiple collisions of the incoming/outgoing electrons in the production of cluster ions R containing R excimers. Radiative decay of these excimers leads to violent fragmentation of the respective cluster ions. Energetics, kinetics and dynamics of these reactions will be discussed. Moreover, a new technique – cluster autoscavenging spectroscopy – based on the excitation of neutral electronic states in the production process of mixed cluster anions (e.g. (XeSF6)−, (ArO4)−, (ArO3)−) will be introduced. Finally, a novel metastable decay reaction – observed for ionized hydrocarbon clusters of propane and butane – originating from an isomerization reaction of a single ion constituent within the cluster (e.g. C3H7+ and C4H7+ respectively) will be presented.
Chemical Reactions in Molecular Cluster Ions
Authors: Stace A. J.
Published: July 2012

The promotion and observation of chemical reactions in molecular cluster ions is discussed in terms of results from three recent experimental studies. The presence of “magic numbers” in cluster ions of the type Arn · X+, where X is either a reactant or fragment ion, provides evidence of molecules occupying sites on or close to the surface of a cluster. Results from experiments on excitation transfer are used to discuss the possibility that a single chemical reaction in an ion Y+, could be promoted through the selective excitation of a host cluster of the form XnY+. Finally, results are present from a new experiment designed to study laser‐induced chemical reactions in mass‐selected cluster ions. Preliminary data are given for photoinduced reactions in cluster ions of 1,3‐butadiene.
The Structure of Mixed Reactive Aggregates Studied by the Combination of IR Depletion and Resonant Two‐photon Ionization (R2PI) Spectroscopy
Authors: Riehn Ch. , Lahmann Ch. , Wassermann B. , Brutschy B.
Published: July 2012

We report on a molecular beam experiment combining the methods of IR depletion and resonant twophoton ionization (R2PI) spectroscopy. Mixed molecular aggregates of fluorobenzene (FB) and methanol (MeOH), viz. (FB)(MeOH) and (FB)(MeOH)2, are characterized. After photoionization these clusters show size‐dependent reaction channels. By comparing our IR depletion spectra with those of free methanol aggregates an assignment of the neutral precursors is feasible. For the system in question, the (1:2) aggregate is identified as the neutral precursor for both, the fragmentation product (1:1)+ and the reaction product anisole+.
Correlated‐Pair Fragmentation and Charge‐Transfer of CO2 Clusters from Atom‐Specific 1s Core Level Excitation
Authors: Dietrich H.‐J. , Jung R. , Waterstradt E. , Müller‐Dethlefs K.
Published: July 2012

Correlated pair fragmentation processes, for C 1s core level excitation of free CO2 molecules and CO2 clusters, have been investigated by “Zero Kinetic Energy” (ZEKE) electron spectroscopy and a (triple) ZEKE electron‐ion‐ion coincidence technique. For free CO2, the main fragmentation channels observed are the correlated ion pairs C+/O+, O+/O+, O+/CO+. These correlated pairs of cations originate from fragmentation of a CO2 dication which is formed by Auger‐type relaxation of the primary 1 s−1 core hole state. Surprisingly, for CO2 clusters this fragmentation channel is quenched, and correlated pair formation between intact cluster ions, i.e. CO2+/CO2+, CO2+/(CO2)2+ and (CO2)2+/(CO2)2+, become the dominant channels. This observation is explained by a fast charge transfer within the cluster, leading to redistribution of the two positive charges. For excitation to the CO22πu(π*) resonance, a possible mechanism for this intra‐cluster charge transfer is the participator valence Auger process following Auger core hole relaxation.
Decay Kinetics and Binding Energies of Benzene Clusters
Authors: Krause Harald , Ernstberger Bernhard , Neusser Hans Jürgen
Published: July 2012

Dissociation energies for monomer evaporation from small (n ≤ 4) neutral and ionized molecular clusters are experimentally determined from the measured ionization potentials and the appearance potentials of the respective metastable decay channels of each cluster ion. The results strongly support a sandwich structure for benzene dimer and trimer ions. For larger benzene cluster ions up to n = 23 the dissociation energies are deduced from the measured intensities of their metastable decay applying the evaporative ensemble model combined with a restricted RRKM formalism. The dissociation energies are discussed as a function of cluster size and interpreted in terms of the interaction mechanism and the structure of the complex.
Electronic Structures and Related Properties. Electron Impact Ionization Potentials of Gold and Silver Clusters Men, n ≤ 22
Authors: Jackschath C. , Rabin I. , Schulze W.
Published: July 2012

Small noble metal clusters were produced by a gas aggregation technique and were investigated mass spectrometrically using electron ionizing energies ranging from 100 eV down to the threshold region. For energies above approximately 20 eV electronic effects are displayed, that characterize a stable cationic distribution, i.e. enhanced stability is found for odd numbered clusters posessing an even number of electrons, furthermore, shell closing appears at n = 3, 9, 21… On the other hand, the electronic effects found while investigating the threshold energy region have to be attributed to neutral clusters, i.e. even numbered clusters are more stable.–The vertical ionization potentials in this region clearly demonstrate the manifestations of shell effects as well as distinct even‐odd oscillations. For both Ag and Au a dramatical drop in the ionization potential is observed from dimer to trimer. The overall size‐dependence of the ionization energies differs from that of alkali clusters due to the presence of d‐electrons.
Electronic Supershells in Metal Clusters
Authors: Genzken O. , Brack M. , Chabanat E. , Meyer J.
Published: July 2012

We present selfconsistent calculations of the supershell structure of sodium, lithium, indium and aluminium clusters, by using the spherical jellium model in LDA and solving the Kohn‐Sham equations for up to N ≈︁ 3000 electrons. While the agreement with the experimental results is very good for alkali metal clusters (Na and Li), it is rather poor in the case of aluminium. We also present quantum‐mechanical calculations for a recently suggested phenomenological Woods‐Saxon potential for the valence electrons of aluminium clusters.
Theory for the Ionization Potential of Clusters of Rare Gas Atoms
Authors: Stampfli P. , Bennemann K. H.
Published: July 2012

We present a theory for the ionization potential of clusters of rare gas atoms. It accounts for the polarization of the rare gas atoms and the delocalization of the hole. Results for the vertical ionization potential are obtained for very large cluster sizes. A comparison with experiments indicates that a gradual size‐dependent transition from adiabatic ionization (for small clusters) to vertical ionization (for bulk and large clusters) has been observed.
High‐Resolution UV Spectroscopy of Molecular Complexes
Authors: Neusser H. J. , Sußmann R. , Smith A. M. , Riedle E. , Weber Th.
Published: July 2012

Information on the structure, the rigidity and the intermolecular potential of molecular complexes is essential to our understanding of the physical and chemical properties of molecular complexes. In this work we would like to demonstrate that rotationally resolved UV spectroscopy provides precise new information on these topics. In particular, the structure and van der Waals bond length of benzene‐X complexes (X = Ne, Ar, Kr, Xe, N2) have been experimentally determined. In the benzene‐N2 complex with its parallel‐stacked configuration, the two constituents, benzene and N2, can rotate against each other. Rotationally resolved vibronic van der Waals bands allow the clear assignment of the excited van der Waals vibrations. Their anharmonicity and the vibrationally averaged rotational constants provide basic information on the intermolecular potential. For the example of the benzene‐Ar2 trimer it is shown that isomeric structures exist that are rigid on the nanosecond time scale.
Kinetics of Formation and Vibronic Spectroscopy of H‐Bonded Clusters in Supersonic Jets
Authors: Wolf K. , Kuge H.‐H. , Schmitt M. , Kleinermanns K.
Published: July 2012

Mass‐selected two‐photon resonant ionization spectra of supersonically cooled p‐cresol · (H2O)n are reported. Cluster spectra with n = 1–4 water molecules attached can be unambiguously assigned. The excellent agreement between the experimental curves of cluster densities as function of H2O pressure and the corresponding calculated curves obtained from numerical integration of the master equation system assuming successive cluster formation further subsidizes the cluster size assignment.–The cluster spectra all lie on the red side of the monomer spectrum but exhibit an irregular red and blueshift relative to each other. Simple molecular orbital (HOMO‐LUMO) considerations based on ab initio calculations quantitatively show this to be due to the H‐bond induced change in the inductive effect of the phenolic O‐atom on the π*‐π transition. The oxygen atom of p‐cresol acts a proton donor in the n = 1 cluster and additionally as proton acceptor in the n = 2 clusters, while the H2O‐subunits in the n = 3 and 4 clusters form a cycle. These structures are further substantiated by extensive ab initio calculations and the measured H‐bond stretch frequencies in the S0 and S1‐state.
Weak Collision Effects in the Reaction CH3CO → CH3 + CO
Authors: Bencsura A. , Knyazev V. D. , Slagle I. R. , Gutman D. , Tsang W.
Published: July 2012

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

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

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

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

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

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

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

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

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

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

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

Effective pair interactions (EPI) up to 4th nearest neighbour (NN) have been calculated for TiCx and NbCx as a function of vacancy concentration using the KKR‐CPA implementation of the generalized perturbation theory (GPT). Results are compared to experimentally determined EPIs and the agreement is discussed.