bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas‐Phase Chemistry of Isolated Metal Ions: Are Predictions on Catalytic Properties Possible Based on the Study of Simple Model Reactions?
Authors: Eller Karsten , Schwarz Helmut 
Published: March 2014

AbstractThe reactions of Ti+ through Zn+ with isopropyl isocyanate have been studied using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Cr+ –Zn+, in analogy to simple pyrolysis, afford only loss of propene and HNCO while Ti+ and V+ mainly give rise to a combined decarbonylation/demethanation to form acetonitrile complexes. The latter is strictly analogous to the heterogeneously catalyzed reaction of i‐PrNCO on Nix/Cα which presumably proceeds via surface‐bound nitrenes. Deuterium labeling is used to show that in the gas phase nitrenes are most likely also involved as reaction intermediates. It is proposed that the binding energies (BE's) of the metal ions to the intermediate nitrenes determine the course of the reaction as only metal ions with high D0(RN = M+) binding energies (Ti+, V+) arc able to produce CH3CN. Transcribed into heterogeneous catalysis this would imply that catalysts with high BE's to surface nitrenes should work out best in the formation of acetonitrile.
Activation Energies of the Proton‐exchange Reactions in Water Measured with the 1H‐NMR Spin Echo Technique
Authors: Pfeifer R. , Hertz H. G. 
Published: March 2014

AbstractFrom the pH‐dependence of the transverse relaxation‐time T2 of protons in 17O‐enriched water we have determined the rate constants k1 und k2 of the two proton‐exchange processes (I) and (II)magnified imagein the temperature range from +5°C to +60°C. – Modified Bloch equations including exchange between the different states of the proton‐septett are used to fit the experimental data yielding directly the rate constants k1 and k2. Classical and quantum mechanical relations connecting the limiting ionic equivalent conductivities λH+ and λOH− with the rate constants k1 and k2 are discussed.
Multiphoton Dissociation of Organic Molecules: Step by Step Investigation with Laser Tandem Mass Spectrometry
Authors: Boesl U. , Weinkauf R. , Walter K. , Weickhardt C. , Schlag E. W. 
Published: March 2014

AbstractMultiphoton ionization of molecules is connected with strong multiphoton dissociation of the molecular ions for high enough laser intensities. By varying the laser intensity, the degree of dissociation can be tuned from very soft (no fragmentation) to extremely hard. In earlier work we proposed and proved the “ladder‐switching” model to explain this process for excitation with nanosecond laser pulses. Recently, we developed a new laser tandem mass spectrometric technique which allows to investigate the fragmentation paths due to the “ladder‐switching” mechanism step by step. We applied this method to benzene cations and could verify the proposed tree of fragmentation pathways. Also a wavelength dependence of the fragmentation pattern has been detected and explained. Our new technique includes (i) a two stage ion source with laser ionization and second order space focus, (ii) secondary laser excitation and dissociation in this space focus and (iii) a reflectron time‐of‐flight analyzer.
Kinetik der Gasphasenreaktion NH2 + NO im Temperaturbereich 294–1025 K
Authors: Atakan B. , Wolfrum J. , Weller R. 
Published: March 2014

AbstractAbsolute rate coefficients for the reaction NH2 + NO were measured by time resolved observation of the OH radical formation at temperatures 294–1025 K in a heatable quartz reactor by means of the laser photolysis/laser induced fluorescence technique. The data can be represented by the expression: k1 = (7.9 ± 1.0) · 1015 T−(1.17 ± 0.25) cm3/mol s. The branching ratio β into the OH product channel was determined to be 0.1 ± 0.025 at 300 K; β increases with increasing temperature and reaches a value of 0.19 ± 0.05 at 1000 K.
Quenching of I(2P1/2) by O3
Authors: De Vöhringer Cecilia M. , Badini Raúl G. , Argüello Gustavo A. , Staricco Eduardo H. 
Published: March 2014

AbstractThe quenching of the spin‐orbit excited state of iodine atoms (I*) by ozone was measured in a flash photolysis system monitoring the resonant absorption of I* at 206.2 nm. A quenching rate constant of (1.1 ± 0.1) · 10−11 cm3 s−1 was obtained at 300 K. This high value implies a reactive channel leading to the production of IO + O2. Indirect experimental observations confirm the presence of the latter species after the flash. A comparison of the present results with the reaction involving the fundamental state of atomic iodine is made. A strong spin‐orbit effect is found. The rate constant for the quenching by O2 was also measured yielding a value of (2.7 ± 0.3) · 10−11 cm3 s−1.
LIF‐Measurements of the Dynamics of the Reactions HT (2.57 eV) + NO → OH + N and HT (1.86 eV) + O2 → OH + O
Authors: Jacobs A. , Schuler F. M. , Volpp H. R. , Wahl M. , Wolfrum J. 
Published: March 2014

AbstractTranslationally “hot” H atoms from photolysis of HBr and HCl at 193 nm, were used to investigate the reaction dynamics of H + NO → OH + N and H + O2 → OH + O. Nascent OH rotational and fine structure distributions were measured by LIF. For both reactions, a high degree of rotational excitation was found. Spin‐orbit states Π1/2 and Π3/2 were found to be equally populated. The lambda‐doublet distributions show a preference for the symmetrical OH‐Π:(A′) component. With a calibration method using H2O2 photolysis as a well defined source of OH radicals, absolute reactive cross sections at translational energies of 2.57 eV and 1.86 eV, respectively, could be determined: σH + NO = (0.01 ± 0.005) Å2 and σH + O2 = (0.34 ± 0.20) Å2.
The Reactions of the Cyclic Hydrocarbon Radicals c‐C3H5, c‐C5H9, and c‐C6H11 with O Atoms in the Gas Phase
Authors: Heinemann‐Fiedler P. , Hoyermann K. , Rohde G. 
Published: March 2014

AbstractThe production of the cyclic hydrocarbon radicals c‐C3H5, c‐C5H9, and c‐C6H11 by the reactions of c‐C3H6, c‐C5H10, and c‐C6H12 with F atoms and the reactions of the cyclic hydrocarbon radicals with O atoms were studied at low pressure (around 1 mbar) and low temperature (290–300 K) using the discharge flow method. Stable and labile species were detected by mass spectrometry combined with molecular beam sampling. The rate constants of the reactions c‐C3H5 + O (4), c‐C5H9 + O (5), and c‐C6H11 + O (6) were determined: k4 = 1.4·1014, k5 = 1.7 · 1014, k6 = 1.4 · 1014 cm3/mol · s. One main reaction route is interpretated by the formation of a highly excited adduct, decomposing to H + oxygen containing ring products; at high strain energy (reaction (4)) total ring cleavage, at low strain energy (reaction (6)) partial ring cleavage was observed. A second reaction route leads to OH + alkene. The rate constant for the reaction F + c‐C6H12 (3) was found as k3 = 5.7 · 1013 cm3/mol · s.
Comparison of the Reactions of Mono‐ and Polycyclic Aromatic Hydrocarbons with Oxygen Atoms
Authors: Frerichs H. , Tappe M. , Wagner H. Gg. 
Published: March 2014

AbstractNewly obtained rate data for the reactions of the polycyclic aromatics biphenyl, methylnaphthalenes and phenanthrene with O (3P) are compared with the results of previous measurements for monocyclic aromatic hydrocarbons. These reactions were studied in an isothermal low pressure discharge flow system with mass spectrometric detection in the temperature range 298 K to 870 K, in an excess of O atoms over hydrocarbon. The obtained Arrhenius expressions and especially the activation energies for the reactions of mono‐ and polycyclic aromatic hydrocarbons with O atoms fit together well and strongly support as main reaction channel the addition of the electrophilic species to the aromatic ring
Interferometric Determination of the Rate Constant of the Isomerization of Cyclopropane to Propene in the Temperature Range between 690 K and 750 K
Authors: Hohm Uwe , Kerl Klaus 
Published: March 2014

AbstractThe thermally induced isomerization of cyclopropane (C) to propene (P) was studied for the first time with an interferometric technique, using HeNe‐laser radiation of vacuum‐wavelength λ = 632.99 nm. The investigations have been performed in the temperature and pressure ranges between 690 K and 750 K and between 7 · 104 Pa and 9 · 104 Pa, respectively. By recording the isothermal and nearly isobaric increase of the refractive index nM (t) and therefore of the polarizability αM (t) = xC(t)αC + xP(t)αP of the mixture with increasing reaction time t, one can obtain the mole fraction xC(t) = (αM(t) – αP)/(αC – αP) = exp(–k ∞ t) of cyclopropane. Assuming that the high pressure limit of this reaction is already achieved, a usual Arrhenius plot ln(kx/s−1) = ln(A/s−1) – EA/RT with the high‐pressure rate constant kx yields for the frequency factor ln(A/s−1) = 34.32(60) and for the activation energy EA = 267.5(3.6) kJmol−1. These values, also somewhat smaller, are in fair agreement with data published in the literature.
Influence of the Density of Surface Hydroxyl Groups on TiO2 Photocatalytic Activities
Authors: Kobayakawa Koichi , Nakazawa Yoshitake , Ikeda Masato , Sato Yuichi , Fujishima Akira 
Published: March 2014

AbstractThe photocatalytic activities of titanium dioxide for the reduction of silver ions and the oxidation of isopropanol were evaluated by using titanium dioxide with the various amount of surface hydroxyl groups per unit surface area. The photocatalytic activities increased with increasing concentration of the surface hydroxyl groups on the catalyst and then decreased from an inflection point. The mechanism was discussed from the stand point of the surface hydroxyl radical formation and their interaction.
Thermodynamic Studies of the Absorption of Hydrogen by Pd – Ti(Zr) Solid Solution Alloys
Authors: Sakamoto Y. , Miyagawa U. , Hamamoto E. , Chen F. L. , Flanagan T. B. , McNicholl R.‐A. 
Published: March 2014

AbstractThe solubility of hydrogen in Pd – Ti and Pd – Zr solid solution alloys containing up to 6.0 at.% Ti and Zr has been measured at temperatures between 273 K and 433 K and hydrogen pressures up to 1000 Torr. The relative partial molar enthalpy, ΔH0H, at infinite dilution for Pd – Ti alloys shows a minor minimum around 4 at.% Ti, in spite of the Pd lattice contraction on Ti substitution. For Pd – Zr alloys the ΔH0Hvalues increase in exothermicity regularly with Zr content. The relative partial molar entropy, ΔS0H, at infinite dilution in both alloy series decreases with the solute contents. The apparent H‐H attractive interactions,g1, in Pd – Ti(Zr) alloys decrease with alloying metal content, and the trend of theg1value with Ti content is dissimilar to those found for other lattice contracted alloys. The stability of the β‐phase hydride in Pd – Ti alloys decreases with Ti content and the β‐phase hydride in Pd – Zr alloys also becomes less stable with Zr content, albeit by a small amount, despite being a lattice expanded alloy system. Solvus compositions at the αmaxphase boundary in both Pd – Ti and Pd – Zr alloys are almost equal at the same alloying compositions of each alloy series, although increasing with alloying metal content in both cases.
Copper Catalyzed Aryl Dehalogenation Reactions and their Inhibition
Authors: Lippert Th. , Wokaun A. , Lenoir D. 
Published: March 2014

AbstractThe aryl coupling reaction of halobenzenes over alumina‐supported copper catalysts has been studied by FTIR spectroscopy. Time‐dependent changes in the spectra were recorded after stepwise addition of bromobenzene to the carrier gas stream. The coupling product, biphenyl, as produced by the copper‐catalyzed “Ullmann type I” reaction, as well as phenol and phenolate species, have been observed. It was found that the thermal pretreatment of the supported catalyst has a pronounced influence on the rate of the catalytic bromobenzene conversion, and on the distribution of side products observed. Novel approaches to inhibit the catalytic dehydrogenation of aryl halides by ethanolamine addition to the catalyst have been studied for the investigated model reaction. The inhibitory action is due to both site blocking and irreversible deactivation of the copper surface due to nitride formation.
Ultrasonic Attenuation of an Isobutyric Acid/Water Mixture of Critical Composition
Authors: Belkoura L. , Calenbuhr V. , Müller‐Kirschbaum Th. , Woermann D. 
Published: March 2014

AbstractUltrasonic attenuation data (frequency range 10 MHz < f < 45 MHz) of a binary isobutyric acid(COOH)/H2O mixture and a pseudo‐binary isobutyric acid(COOH)/H2O, D2O mixture of critical composition are analyzed in terms of the Ferrell‐Bhattacharjee attenuation function F(Ω). The system specific parameter ω0 necessary to calculate the temperature and frequency dependence of the universal reduced variable Ω is determined by static and dynamic light scattering experiments. It is found that F(Ω) fails to describe the ultrasonic attenuation in both systems. The data do not scale as expected theoretically and indicate a temperature and frequency dependent background attenuation caused by chemical processes. The background attenuation (α/f2)b,T reaches considerable values at frequencies f < 20 MHz and at temperatures away from the critical ((α/f2)b,T/(α/f2)T of the order of 0.1). The chemical background attenuation reflects parts of the broad spectrum of low frequency relaxation processes (frequency at the principle relaxation time f1 ≃ 2 MHz) found by Kaatze et al. (J. Chem. Phys. 93, 4955 (1989)) in a broadband ultrasonic attenuation study in a critical isobutyric acid(COOH)/H2O mixture.
Dynamic Investigation in a Nematic Mixture with High Glass‐Transition Temperature
Authors: Kresse Horst , Ernst Sabine , Wedler Wolfgang , Demus Dietrich , Kremer Frieder 
Published: March 2014

AbstractWörterDielectric measurements have been performed on oriented samples of a nematic mixture with a glass‐transition temperature of about 285 K in a frequency range between 0.1 and 106 Hz and on unoriented, quenched samples of this mixture from 156 K up to 300 K. Rotations around the short and long molecular axis gave a Vogel‐Fulcher‐Tammann‐behaviour; the seperate rotation of polar end‐groups caused the appearance of a high‐frequency‐Arrhenius‐like mechanism which was observable at very low temperatures.
Electrostatic Interactions of Bodies Bearing Thin Double‐Layers II. Exact Numerical Solutions
Authors: Adamczyk Z. , Belouschek P. , Lorenz D. 
Published: March 2014

AbstractA new numerical algorythm was used to calculate the electrostatic interaction forces between regularly shaped particles bearing thin double‐layers immersed in an arbitrary electrolyte. Our numerical procedure enabled the solution of the nonlinear one‐dimensional Poisson‐Boltzmann (PB) equation in which the excluded volume effect is quantitatively considered for an arbitrary surface charge. These one‐dimensional solutions (parallel‐plate system) were then integrated according to the modified Derjaguin summation method giving the electrostatic force between bodies either convex or concave in the vicinity of their contact area. Calculations were performed for plates and particles bearing similar surface charge (homointeractions) for simple electrolytes and electrolyte mixtures with constant charge and constant potential boundary conditions. From these solutions the range of validity of previously derived analytical approximations (Part I [16]) was estimated. It was shown that the excluded volume effect plays a significant role for β > 10−2 increasing the surface potential of plates (constant charge model) at all separations as well as the absolute value of the interaction force. At the critical separation h̄* the force remains finite in accordance with our previous analytical equations. A significant role of trace amounts of higher valency electrolytes decreasing considerably the interaction force was confirmed.
High‐Frequency Dielectric Dispersions in Dilute Water‐in‐Oil Microemulsions
Authors: Cametti C. , Codastefano P. , Tartaglia P. 
Published: March 2014

AbstractA set of measurements of the dielectric constant of a three‐component microemulsion system sodium bis (2‐ethylhexyl) sulfosuccinate‐water‐decane as a function of frequency (106 to 109 Hz) and temperature (5 to 35°C) and for two values of the volume fraction of the dispersed phase (0.025 and 0.050) has been made. The frequency dependence of the dielectric constant clearly shows a low‐frequency dispersion and a high‐frequency one, both describable in terms of a Cole‐Cole type relaxation. The high‐frequency dispersion is characterized by a relaxation time of the order of 10−9 s and a dielectric increment of few units, both largely independent of temperature and composition. We try to identify the origin of the high‐frequency dielectric dispersion and to relate it to the dynamics of the surfactant polar heads within the single droplet.
Ergodic and Nonergodic Relaxation Timescales for Metastable RNA Folding
Authors: Fernández Ariel , Belinky Alejandro 
Published: March 2014

AbstractWe investigate the relaxation of metastable RNA secondary structure in the limit of very long random chains. We make use of a Monte‐Carlo simulation which handles nonequilibrium refolding events occurring as a random uncorrelated primary sequence is being generated by sequential incorporation of nucleotides. We provide evidence confirming the existence of two different relaxation timescales with rates of divergence identical respectively to the ergodic and nonergodic relaxation timescales for spin glasses approaching the thermodynamic limit. These results substantiate the concept of substate in biopolymer folding, as introduced previously in the context of proteins.
New Possibility for Metastable RNA Folding of Biological Significance: A Physico‐Chemical View at Biological Regulation and Control
Authors: Fernández Ariel 
Published: March 2014

AbstractWe assess the importance of short‐lived nonequilibrium RNA folding in biological regulation. As an illustration, we explain the radical difference in pause site patterns during the synthesis of MDV‐1 RNA, depending on the nature of the process involved. The two situations of interest are: a) Replication by Qß‐replicase, a template‐instructed synthesis, and b) Transcription performed by E. Coli RNA polymerase. We start by establishing the possibility of soliton‐induced tautomerization of uracil which occurs exclusively in transcription. This tautomeric form of uracil forms base‐pairing with guanine and leads to a unique metastable folding of RNA. The assessment of this fact enables us to prove that in both replication and transcription, the pauses in the process are due to refolding events occurring in the replica chain as it is being synthesized and in the upstream portion of the template strand.
Ternary Diffusion and Onsager's Reciprocity Relations in Aqueous ZnCl2 + KCl and CdCl2 + KCl Revisited
Authors: Spallek M. , Hertz H. G. , Käshammer S. , Weingärtner H. 
Published: March 2014

AbstractWe report on e.m.f. data in the ternary electrolyte systems ZnCl2 + KCl + H2O and CdCl2 + KCl + H2O. In conjunction with diffusion data reported previously, these results enable a reassessment of a previous analysis of Onsager's reciprocity relations for ternary diffusion in these systems. The results eliminate contradictions to these relations observed in previous work.
The Determination of Rate Constants for the Reactions of Some Alkenes with the NO3 Radical
Authors: Benter Th. , Becker E. , Wille U. , Rahman M. M. , Schindler R. N. 
Published: March 2014

AbstractThe kinetics of the reaction of NO3 radicals with five alkenes was investigated at room temperature in a discharge fast flow system with mass spectrometric detection. NO3 radicals were produced by hydrogen abstraction from HNO3 with F atoms. The 1:1 stoichiometry of the reactions was confirmed. Rate constants were determined by measuring the decay of NO3 and/or of alkene under pseudo‐first‐order conditions. The following values of rate constants are reported: trans‐2‐butene (3.9 ± 0.3)·10−13, cis‐2‐butene (3.8±0.2)·10−13, iso‐butene (3.9±0.4)·10−13, 2‐methyl‐2‐butene (8.4±0.6)·10−12, 2,3‐dimethyl‐2‐butene (4.1±0.4)·10−11 in units of cm3 molecule−1 s−1. The results are compared with literature data.
In Situ Investigation of Duplex Semiconducting Films on Tin
Authors: Metikoš‐Huković M. , Šeruga M. , Ferina S. 
Published: March 2014

AbstractThe passive film on tin formed under dynamic conditions represents a duplex layer of the same oxidation state, with a stepwise concentration profile of two semiconducting or almost insulating oxide films in series. Their electrochemical properties are limited by their electronic properties. The electrode capacity (C) and photopotential (Eph) were measured in situ during oxide formation and reduction on tin in slightly alkaline solution. Analysis showed that the changing electronic properties of the oxide formed have a great impact on Eph and C. The formation of the inner SnO2 layer takes place homogeneously all over the surface with constant thickness. Schottky‐Mott type behaviour was found, indicating a surface donor concentration of 1015 cm−3 and a flat band potential vs. S.C.E., Efb, of −0.95V. For the outer layer the changes of electronic properties with increasing film thickness, as well as ageing processes, limit the validity of all electronic models with constant parameters. The oxide/hydroxide ratio increases with anodic polarization. The reaction is favoured by a free‐energy decrease. At higher potentials, especially under illumination, the electrode is covered with a very stable SnO2 species which is difficult to reduce.
Dynamic Behaviour of Ternary Microemulsions Consisting of Didodecyldimethylammoniumbromide, Water and Hydrocarbon
Authors: Lenz U. , Hoffmann H. 
Published: March 2014

AbstractTernary micromulsions containing water, dodecane and the surfactant didodecyldimethylammoniumbromide (DDABr) have been studied with flow and electric birefringence methods as well as with pressure jump relaxation techniques and conductivity measurements. Previous measurements had shown, that the isotropic L2‐phase can be subdivided into an area with spherical droplets and an area with interconnected water channels. Unexpectedly, a large birefringence was found within the region of the spheres and only small amplitudes in the other subregion. Kinetically measured relaxation times agree well with the rotation times which were determined from the birefringence methods. It is supposed that the water droplets are of ellipsoidal shape. The rotational diffusion time constants were determined from the birefringence signals. Both techniques gave the same results. The rotation time constants and the amplitudes of the birefringence signals increase with increasing water content. For large W/S ratios no large changes in the birefringence signals were observed in the percolation region of the conductivity. The measurements furthermore show that the lifetimes of both the globules and the channels are short and in the range of μs.