bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photodissociation of HNCO: Three competing pathways
Authors: Droz‐Georget TH. , Zyrianov M. , Sanov A. , Reisler H. 
Published: July 2012

AbstractThe unimolecular decomposition of expansion‐cooled isocyanic acid (HNCO) via channels (1) 3NH + CO, (2) H + NCO, and (3) 1NH + CO [where 3NH and 1NH denote NH(X3σ−) and NH(a1 Δ), respectively] has been investigated following photoexcitation to the S1(1A ) state in two energy regimes: (i) in the region of the 1NH + CO threshold (41 700–45 500 cm−1; 240–220 nm), and (ii) ˜ 3200 cm−1 above D0(1NH + CO), at around 46000 cm−1 (217.6 nm). Several complementary experiments are presented: NCO, 3NH and 1NH photofragment yield spectra and relative 1NH/3NH branching ratios are obtained by laser induced fluorescence (LIF); photo‐fragment ion imaging is used to record CO angular recoil distributions, and 1NH rotational distributions correlated with specific CO (v, J) levels, HNCO excited to S1 undergoes complex dynamics reflecting simultaneous decomposition on several potential energy surfaces, and including internal conversion (IC) and intersystem crossing (ISC). In energy region (i), a progressive loss of structure in the 3NH yield spectrum is observed above the opening of channel (3), and is interpreted as the imprint of short‐time dynamics characteristic of the ISC step. State selectivity in the photodissociation is revealed by comparing the photofragment yield spectra of the three channels. In region (ii), product state distributions for channel (3) exhibit clear dynamical signatures, as expected for dissociation on S1. At low excess energies channel (2) derives from dissociation on S0, but the respective roles of S0 and S1 at higher energies are not well established yet. The results are discussed in terms of vibronic levels of mixed electronic character coupled directly or via radiationless decay to the various continua. The competition between the different processes depends sensitively on photolysis energy and excitation conditions.
Unimolecular dynamics in bimolecular ion‐molecule reactions
Authors: Craig Stephen L. , Brauman John I. 
Published: July 2012

AbstractWe have measured the translational energy dependence of a series of chloride exchange reactions in the gas phase. The translational energy dependence varies with the changes in the potential energy surfaces across the series of reactions in a manner that is consistent with the predictions of statistical reaction rate theory. These results indicate that despite reports of non‐statistical behavior in simple SN2 reactions, the assumptions of unimolecular reaction rate theory (strong coupling, energy randomization) are valid for the complexes formed in many bimolecular ion‐molecule collisions.
Trajectory studies on the collisional relaxation of highly excited benzenes by mono‐ and polyatomic colliders
Authors: Lenzer T. , Luther K. 
Published: July 2012

AbstractCollisional energy transfer (CET) of highly vibrationally excited benzene and hexafluorobenzene molecules has been investigated by quasiclassical trajectory calculations. Influences of the intramolecular potential reflected in molecular parameters are studied systematically in collisions with argon. It is found that the lower the vibrational frequencies the more efficient is CET. Intermolecular potential effects are investigated. At larger well depths (for benzene+argon) the first moment of energy transfer <ΔE> scales with ε and is not very sensitive to details of the interaction. However at small well depths ε (for benzene + helium) energy transfer is dominated by the exact shape of the intermolecular potential, especially of the repulsive part. Benzene‐benzene collisions are studied as an example for CET between polyatomics and large colliders. Excellent quantitative agreement with experiment is found for <ΔE> and its energy dependence. The results suggest that vibrational energy loss of the excited molecule is dominated by V‐V transfer and that the rotation is heated up more strongly with increasing ε, an effect also present for noble gas colliders.
Quantum scattering studies of collisional energy transfer from highly excited polyatomic molecules: A bend‐stretch model of He + CS2
Authors: Lendvay György , Schatz George C. 
Published: July 2012

AbstractWe present the results of an accurate quantum scattering study of collisional energy transfer in a bend‐stretch model of the He + CS2 system, considering energies up to 45 kcal/mol. These results are generated using a coupled channel method, with vibrational eigenfunctions obtained from a discrete variable representation method. Detailed comparisons with the results of classical trajectory' calculations are performed so as to assess classical/quantum correspondence for energy transfer moments, and for the energy transfer probability distribution function. We find good agreement of the energy averaged first moments over a wide range of molecular vibrational energies. The second moments, as well as <ΔE>up and <ΔE>down show less quantitative agreement. The quantum energy transfer distribution functions show considerable mode‐specific behavior, but the overall envelope is approximately exponential at large ∥ ΔE∥ with a broad spike near ∥ΔE∥ = 0. We analyze this behavior in terms of contributions from individual state‐to‐state transition probabilities. The corresponding classical distribution functions are very similar, showing better correspondence than was found for other models with smaller state densities.
Solvatochromism in binary solvent mixtures: Effects of the molecular structure of the probe
Authors: Novaki Luzia P. , El Seoud Omar A. 
Published: July 2012

AbstractThe solvatochromic behavior of 2,6‐diphenyl‐4‐(2,4,6‐triphenyl‐1‐pyridinio)‐1‐phenolate (RB), 1‐methyl‐8‐oxyquinolinium betaine (QB), sodium 1‐methyl‐8‐oxyquinolinium betaine‐5‐sulphonate (QBS), and 1‐methyl‐3‐oxypyridinium betaine (PB) was studied spectrophotometrically in mixtures of cyclohexane‐THF and cyclohexane‐1‐butanol. It was also studied in mixtures of water with acetone, acetonitrile, 1,2‐dimethoxyethane (DME), 1,4‐dioxane, and THF. Empirical parameters of solvent polarity, ET (in kcal/mol), were calculated from the position of the longest‐wavelength absorption band of the respective solvatochromic probe, and they were then correlated with the mole fraction of the more polar component of the binary solvent mixture (THF, 1‐butanol, or water). Although the non‐aqueous solvent mixtures behave ideally, plots of ET versus the mole fraction of THF, or 1‐butanol, are not linear for all probes, due to nonspecific (e.g., dipolar) interactions and specific solute‐solvent interactions (e.g., H‐bonding). The contribution of each type of interaction has been quantified and correlated with the structure of the solvatochromic probe molecule. For RB in cyclohexane‐THF mixtures, the deviation from linearity of the above mentioned plot is due to nonspecific probe dipole/solvent dipole interactions. For cyclohexane‐1‐butanol binary mixtures, both nonspecific and specific interactions contribute to the observed solvatochromism. For RB in binary aqueous mixtures, plots of ET versus the mole fraction of water are generally sigmoidal, and follow closely the changes of solvent structure, particularly in the microheterogeneous domain. The same plots for PB show a positive deviation from linearity, because this probe forms its own water‐rich solvation shell, whose composition is relatively insensitive to the nature of the organic co‐solvent. In all binary solvent mixtures, the solvatochromic behavior of QB is more or less similar to that of PB.
Gas phase addition kinetics of the tert‐butyl radical to oxygen
Authors: Dilger Herbert , Stolmár Martina , Tregenna‐Piggott Philip L.W. , Roduner Emil , Reid Ivan D. 
Published: July 2012

AbstractThe kinetics of the addition reaction of O2 to the tert‐butyl radical has been investigated at 1.5 bar as a function of temperature (241–462 K) using the muon spin relaxation technique in longitudinal magnetic fields. The data are represented by kch = 43+88‐26 X 10−10T−0.96±0.21 cm3 molecules−1 s−1, or alternatively by an Arrhenius activation energy of −2.4(0.7) kJ mol−1 and an apparent frequency factor of 68(19)x10−13 cm3 molecules−1 s−1. The results of these temperature‐dependent measurements agree well with an experimental literature value at room temperature, but disagree with a more recent estimate by a factor of six.
Surface‐embedded oxygen: Electronic structure of Ag(111) and Cu(poly) oxidized at atmospheric pressure
Authors: Schedel‐Niedrig Th. , Schlögl R. , Bao X. , Muhler M. 
Published: July 2012

AbstractWe investigated the surface electronic structure of an oxidized Ag(111) single crystal and a polycrystalline Cu foil prepared under conditions of pressure and temperature (1000 mbar and 900 K) far beyond those used in usual UHV studies. It has recently been shown that a strongly bound oxygen species (Oγ) apart from oxygen atoms chemisorbed on the surface (Oα) or oxygen atoms dissolved in the bulk (Oβ) can be prepared on silver surfaces. Using core‐level photoemission we show these three atomic oxygen species, Oα, Oβ and Oγ, exhibit characteristic spectral properties. X‐ray absorption spectroscopy at the O K‐edge indicates that the formation of the strongly bound Oγ species is accompanied by a strong hybridization between O2p and Ag4d states and that also the Ag5sp states are important for the metal‐to‐oxygen covalent interaction. The reaction with methanol was used to selectively remove the surface‐embedded atomic species and to study the effect of the strongly bound oxygen Oγ species on the valence electronic structure of silver. This separation of the oxygen species did not work for the more reactive copper‐oxygen system. The chemical bonding interaction of the novel Oγ species with silver is discussed in terms of the ligand‐field theory emphasizing the covalent character of the interaction. For copper, the spectroscopic analysis is complicated by the existence of a stable oxide Cu2O with similar bonding properties of the oxygen than postulated for the surface‐embedded species in silver.
Optical spectroscopy on Se8 clusters and Se chains embedded in zeolite matrices
Authors: Goldbach A. , Saboungi M.‐L. 
Published: July 2012

AbstractIncorporation of Se into the supercages of zeolite Y leads to formation of Se8 rings and distorted Se chains with a ratio which is dictated by the nature of the zeolitic counter cations. Both rings and chains give rise to characteristic Raman and UV/vis absorption bands. In particular low frequency Raman bands are attributed to phonon localization in ordered segments of distorted chains.
Pore condensation in novel highly ordered mesoporous silica
Authors: Groß Stephan , Findenegg Gerhard H. 
Published: July 2012

AbstractThe pore condensation of SF6 in two novel ceramic silica materials, obtained by templating lyotropic phases of nonionic surfactants and of amphiphilic block copolymers, has been investigated over a temperature range from below the triple point up to the critical point of the fluid. One of the materials represent an ordered array of cylindrical pores (mean pore size 29 Å); the sorption isotherms for this material exhibit no hysteresis in the entire experimental temperature range. For the other material, which is believed to constitute a more complex pore system (mean pore size 34 Å), a pronounced hysteresis loop is seen near the triple point temperature but not at higher reduced temperatures. For both materials pore condensation disappears well below the bulk critical temperature. The experimental isotherms are used to determine the coexistence curve and the critical temperature of the fluid in the confined pore space.
Inelastic light scattering and phonon‐confinement in nanocrystalline Y2O3
Authors: Bruch Ch. , Krüger J. K. , Unruh H.‐G. , Krauss W. , Zimmermeier B. , Beck Ch. , Hempelmann R. 
Published: July 2012

AbstractNanocrystalline powders of Y2O3 with grain sizes in the range between 7 and 40 nm were prepared by the micro‐emulsion technique and by condensation from an inert gas atmosphere. The cubic respectively monoclinic powders were examined by means of Brillouin scattering (consolidated samples) and micro‐Raman scattering (powders and consolidated samples).Measurements of the elastic properties of quasi‐isotropic pellets yield a longitudinal modulus reduced down to 25% compared with that of the monocrystal and point to optical inhomogeneities in the range of the wavelength of the light. With decreasing dimensions of the crystallites a shift of the characteristic Raman lines to lower frequencies and a distinct broadening of the lines are observed. A trial is made to interpret these features by the phonon‐confinement model of Richter et al. [1]. A possibility to characterize the nanocrystalline powders by means of Raman spectroscopy is discussed.
Investigation of the complex conductivity of nanocrystalline Y2O3‐stabilized zirconia
Authors: Mondal P. , Hahn H. 
Published: July 2012

AbstractNanocrystalline ZrO2‐ and Y2O3‐powders with grain sizes from 5‐20 nm were prepared by the Inert Gas Condensation method. The powders were mixed in different fractions, pressed into green bodies and sintered to ceramic samples with 35‐49 nm average grain size. The phase, grain size and specific surface area of the powders and ceramic samples was characterized by X‐ray diffraction and nitrogen adsorption. Densities from 82 to 93% of the single crystal density were determined using the Archimedes principle. The complex conductivity was measured for frequencies ranging from 20 Hz to 3 MHz at temperatures between 80 and 1100 K. The lattice relaxation, grain boundary relaxation and the contact process could be resolved and identified. The dc‐conductivity for the lattice and the grain boundaries were deduced from the data. The activation energies for dc‐conductivity were determined for the lattice and the grain boundaries as 0.85 ± 0.05 and 1.0 ± 0.1 eV, respectively.
Corrosion of gold by alkane thiols
Authors: Edinger K. , Grunze M. , Wöll Ch. 
Published: July 2012

AbstractSTM images of self assembled alkanethiol films on gold surfaces show holes which have been identified as vacancies in the topmost gold layer. We show that this vacancy formation is accompanied by a corrosion process of gold in ethanolic thiol solutions. The amount of dissolved gold from polycrystalline substrates as a function of immersion time, thiol concentration, chain length and solvent has been investigated by Atomic Absorption Spectroscopy (AAS). The results suggest that the thiol molecule itself is the active oxidant. In case of a 1 mmol solution of docosanethiol in ethanol a gold concentration corresponding to 6% of a gold monolayer has been detected after an immersion time of 24 h. By using hexane as a solvent the amount of dissolved gold is reduced to less than 0.2%, indicating a strong solvent (e.g. polarity) dependence for the corrosion process. The kinetics of the corrosion process have been measured and compared to kinetic data related to the formation of an ordered thiol film.
Hydrogen solubility and thermodynamics of dissolved hydrogen in Pd1‐xTbx(x = 0.05 and 0.08) solid solution alloys
Authors: Narayanan S. Shankara , Ramaprabhu Sundara 
Published: July 2012

AbstractThe hydrogen absorption and the thermodynamics of dissolved hydrogen in Pd1‐xTbx(x= 0.05 and 0.08) solid solution alloys have been determined from the pressure‐composition‐temperature relation in the ranges 5 ßP/mbar ß 1000 and 473 ßT/K ß 873 using a pressure reduction method. The hydrogen solubility is found to increase with increase of xTb.The partial molar enthalpy of hydrogen solution at infinite dilution (ΔH°H) and the partial molar excess entropy of dissolved hydrogen at infinite dilution (ΔSEH°) decrease with increase of terbium content. The chemical potential of dissolved hydrogen at infinite dilution (ΔH°H) decreases with increase of xTbindicating that the stability of dissolved hydrogen increases with increase of xTb. The Pd1‐xTbx‐H systems fall on the correlation between the ionic diameter (dRE) of the substitutent RE metals when in solution in Pd and the exothermicity of hydrogen absorption for the Pd1‐xREx‐H (RE = Er, Ho, Dy, Y, Gd and Sm;x= 0.05 and 0.075) systems.
Detection, Quantification, and Propagation of Uncertainty in High‐Throughput Experimentation by Monte Carlo Methods
Authors: Osberghaus A. , Baumann P. , Hepbildikler S. , Nath S. , Haindl M. , von Lieres E. , Hubbuch J. 
Published: July 2012

AbstractSince the efficiency and speed of computing has increased significantly in the last decades, in silico‐approaches, e.g., quasi‐experimental analyses based on mechanistic simulations combined with Monte Carlo (MC) methods, are on the rise for uncertainty analyses and estimation of uncertainty propagation. The power and convenience of these approaches for high‐throughput processes will be demonstrated with a case study including miniaturized screenings on robotic platforms: a binding study for lysozyme on the adsorbent SP Sepharose FF in 96‐well format. All relevant uncertainties during the experimental preparations and automated high‐throughput experimentation were identified, quantified, and then embedded in a simulation algorithm for the calculation of uncertainty propagation based on MC sampling. A proof‐of‐concept for this approach is then followed by the simulation‐based analysis of various case scenarios. The MC‐based approach can easily be transferred to uncertainty analyses in other high‐throughput processes.
Hydrodynamics and Mass Transfer in Gas‐Liquid Flows in Microreactors
Authors: Sobieszuk P. , Aubin J. , Pohorecki R. 
Published: July 2012

AbstractOver the last ten to fifteen years, microreaction technology has become of increased interest to both academics and industrialists for intensification of multiphase processes. Amongst the vast application possibilities, fast, highly exothermic and/or mass transfer‐limited gas‐liquid reactions benefit from process miniaturization. Recent studies of hydrodynamics and mass transfer in gas‐liquid microreactors with closed and open microchannels, e.g., falling‐film microreactors, are reviewed and compared. Special attention is paid to Taylor or slug flow in closed channels, as this regime seems to be most adapted for practical engineering applications.
Simulation of a Compact Multichannel Membrane Reactor for the Production of Pure Hydrogen via Steam Methane Reforming
Authors: Vigneault A. , Elnashaie S. S. E. H. , Grace J. R. 
Published: July 2012

AbstractA steady‐state 2D model is developed for a multichannel membrane reactor (MCMR) to produce pure hydrogen. The model includes one reforming channel coupled with a PdAg membrane to produce H2 and one combustion channel to generate the heat needed for the reforming. Both isothermal and non‐isothermal simulations are applied in designing a laboratory‐scale proof‐of‐concept reactor. Isothermal sensitivity analysis indicates parameter adjustments practically available to improve reactor performance. In non‐isothermal simulations, catalyst layer thickness and kinetic pre‐exponential factor are varied along the reactor length. Predictions indicate that the reforming methane conversion increased from 74 % to 91 %, while avoiding hot spots. Compared with other membrane reactors, the MCMR has the potential for one to two orders of magnitude higher H2 production per reactor volume and per mass of catalyst.
Enhancement Factor for Gas Absorption in a Finite Liquid Layer. Part 3: Instantaneous and Second‐Order Reactions in a Liquid in Laminar Flow
Authors: Yue J. , Rebrov E. V. , Schouten J. C. 
Published: July 2012

AbstractNumerical analysis on gas absorption accompanied by an instantaneous reaction or a second‐order reaction into a liquid layer of finite thickness in laminar flow is presented. A similar influence of the reactant diffusivity ratio, the Fourier number, and the Hatta number on the enhancement factor is reported compared to the ideal situation in which the liquid layer is in plug flow motion. Approximate enhancement factor expressions are developed for both reaction cases by analogy to the plug flow situation, where the predictions according to the original penetration theory tend to give erroneous results in the enhancement factor at Fourier numbers above 0.1. The developed expressions in the case of a second‐order reaction can be extrapolated for estimating the enhancement factor in the more general case of a (1, n)‐th‐order reaction.
ChemInform Abstract: Structural Characterization of Moganite‐Type AlPO4 by NMR and Powder X‐Ray Diffraction.
Authors: Kanzaki Masami , Xue Xianyu 
Published: July 2012

AbstractA new high‐pressure AlPO4 phase obtained at 5 GPa and 1500 °C is characterized by synchrotron powder XRD and MAS NMR spectroscopy.
ChemInform Abstract: X‐Ray Diffraction and Raman Spectroscopy Studies of Temperature and Composition Induced Phase Transitions in Ba2‐xSrxZnWO6 (0 ≤ x ≤ 2) Double Perovskite Oxides.
Authors: Manoun Bouchaib , Ezzahi A. , Benmokhtar S. , Ider A. , Lazor P. , Bih L. , Igartua J. M. 
Published: July 2012

AbstractThe title compounds are characterized by powder XRD and Raman spectroscopy.
ChemInform Abstract: NaEu3(GeO4)2(OH)2: A High‐Pressure‐Stable Photoluminescent Lanthanide Germanate.
Authors: Zhao Xinguang , Yan Tingting , Wang Kai , Yan Yan , Zou Bo , Yu Jihong , Xu Ruren 
Published: July 2012

AbstractThe title compound is hydrothermally synthesized from a mixture of Eu(NO3)3, GeO2, NaOH, and H2O (autoclave, 230 °C, 7 d).
ChemInform Abstract: High Pressure in situ Differential Thermal Analysis of Na0.5Bi0.5TiO3 Phase Transitions up to 5 GPa.
Authors: Xu Chao , He Duanwei , Wang Haikuo , Liu Chunmei , Yin Shuai , Wang Kaixue , Guan Junwei , Peng Fang , Kou Zili 
Published: July 2012

AbstractPhase transitions of the title compound are investigated by high pressure in situ DTA up to 5 GPa.
ChemInform Abstract: Synthesis and Properties of New Multinary Silicides R5Mg5Fe4AlxSi18‐x (R: Gd, Dy, Y, x ≈ 12) Grown in Mg/A Flux.
Authors: Ma Xiaowei , Chen Banghao , Latturner Susan E. 
Published: July 2012

AbstractThe compounds Ln5Mg5Fe4Al12Si6 (Ln: Gd, Dy, Y) are synthesized by reaction of Fe, Si, and Ln in an equimolar Mg/Al flux (750 °C, 24 h).
ChemInform Abstract: Highly Enantioselective [4 + 2] Annulations Catalyzed by Amino Acid‐Based Phosphines: Synthesis of Functionalized Cyclohexenes and 3‐Spirocyclohexene‐2‐oxindoles.
Authors: Zhong Fangrui , Han Xiaoyu , Wang Youqing , Lu Yixin 
Published: July 2012

AbstractBy employing isatin‐derived alkenes, the cycloaddition yields spirocyclohexene‐2‐oxindoles (V), a framework of biological significance.
ChemInform Abstract: Coinage Metals Catalyzed Cascade Reactions of Aryl Alkynylaziridines: Silver(I)‐Single vs. Gold(I)‐Double Cyclizations.
Authors: Kern Nicolas , Blanc Aurelien , Miaskiewicz Solene , Robinette Michelle , Weibel Jean‐Marc , Pale Patrick 
Published: July 2012

AbstractIn the presence of Ag(I) salts, the substrates undergo efficient rearrangement to aminoallenylidene isochromans, isoquinolines, and tetrahydronaphthalenes.
ChemInform Abstract: Pd(II) Catalyzed Transformation of Schiff Bases in Complexes of the Type trans‐[PdCl2(NH2Ar—X)2] (X: H, CH3, Cl): Reactivity with Aldehydes and Heck Coupling Reaction.
Authors: Kumari Niraj , Yadav Vinod Kumar , Zalis Stanislav , Mishra Lallan 
Published: July 2012

AbstractAniline‐palladium complexes of the type trans‐[PdCl2(H2N‐Ar)2] are synthesized, which efficiently catalyze the Heck reaction of bromobenzene with functionalized olefins (II).
ChemInform Abstract: Novel Basic Ionic Liquid Based on Alkylammonium as Efficient Catalyst for Knoevenagel Reaction.
Authors: Zhou Shuai , Liu Lu , Wang Bo , Ma Mingguo , Xu Feng , Sun Runcang 
Published: July 2012

AbstractThe novel basic ionic liquid exhibits excellent catalytic activities for Knoevenagel condensation [→(III)] and marked catalytic activities in Claisen—Schmidt [→(VI)], Michael [→(VIII)], aldol [→(X)] and epoxidation reactions.