bluuebunny/crossref_metadata_2025_split huggingface dataset:
DISQUAC behaviour close to critical points application to methanol + alkane mixtures
Authors: Gonzalez Juan Antonio , De La Fuente Isaias Garcia , Cobos Jose Carlos 
Published: July 2012

AbstractInteractions present in binary mixtures of methanol + alkanes have been previously characterized in terms of the DISQUAC group contribution model. It was shown that DISQUAC is a reliable tool to represent thermodynamic properties such as molar excess functions: Gibbs energies, GE, enthalpies, HE, or heat capacities at constant pressure, CEP. In this work, we examine the ability of the model to represent liquid‐liquid equilibria, LLE, for the whole series of methanol + n‐alkanes mixtures, as well as for methanol+cyclohexane, + cycloheptane, or + cyclooctane. Up to now, we had only considered LLE of those solutions involving n‐hexane, n‐heptane, or cyclohexane.Using the interaction parameters previously reported for methanol + n‐alkanes mixtures, which are independent of the non‐polar compound, DISQUAC predicts UCSTs (upper critical solutions temperatures) of the methanol + n‐alkanes mixtures which are lower than the experimental values for those systems containing the longer n‐alkanes. This is in contradiction with the critical exponents theory. The possibility of improving results by modifying only the third interchange coefficients is discussed. So, two groups of these parameters are given depending on n, hereafter the number of carbon atoms in the n‐alkane (n ≤ 7; n ≥ 8). The coordinates of the critical points are then fairly well represented. Nevertheless, the shape of the LLE curves (the experimental ones being much flatter than those calculated) is rather poorly described, mainly for mixtures containing the longer n‐alkanes. The new interaction parameters are tested predicting vapor‐liquid equilibria, VLE, at very high temperatures (up to 473.15 K) and at moderate pressures (up to 40 atm) of methanol + n‐alkanes mixtures. It is noteworthy that DISQUAC correctly predicts the formation of azeotropes for systems with the lower n‐alkanes, and the absence of azeotropes for mixtures with the longer n‐alkanes (from n‐nonane).Properties of mixtures containing cycloalkanes are more difficult to represent because these compounds do not form an homologous series in terms of the c‐CH2 groups. Nevertheless, it has been shown that the interaction parameters of 1‐alkanols (# methanol)+cyclohexane systems can be applied to calculate HE of mixtures with other cycloalkanes. In the case of LLE of methanol + cycloalkanes mixtures, different first dispersive parameters are needed for each cycloalkane. The quasichemical parameters are, as usually, independent of the n‐alkane. The LLE coexistence curves are better represented than in the case of solutions including n‐alkanes.The possibility of modifying the scaling temperature (equal to 298.15 K in DISQUAC) in order to improve LLE results is also briefly examined.As usually, the experimental HE curves are much flatter than the calculated ones at temperatures close to the critical. Results for methanol+ n‐propane, or + n‐heptane are shown in order to complete information previously given.
Intramolecular vibrational redistribution and unimolecular reaction: Concepts and new results on the femtosecond dynamics and statistics in CHBrClF
Authors: Beil Andreas , Luckhaus David , Quack Martin , Stohner Jürgen 
Published: July 2012

AbstractWe present the conceptual background for intramolecular vibrational (rotational) redistribution (IVR) in polyatomic molecules and its analysis from high resolution spectra. We illustrate some of the basic concepts relating to the use of effective and real molecular hamiltonians for IVR with examples drawn from our previous spectroscopic investigations of the chiral molecule CHFClBr. The importance of the initial state for the dynamics is shown, demonstrating that simple intuitive concepts of survival probabilities for some arbitrary chromophore (“zero order bright”) state are insufficient for a quantitative understanding of IVR. An approximate (C3‐like) symmetry prevents relaxation towards quasi‐equilibrium in highly excited C1‐asymmetrical CHFClBr. The coherent infrared multiphoton excitation of CHFClBr at the CH‐stretching frequency leads to coherent vibrational states with a very wide energy distribution corresponding to short time oscillatory behaviour of the CH‐stretching motion with a period of 11–12 fs. On longer time scales between 50 and 500 fs substantial vibrational motion is found in the CH‐bending coordinates. For modest excitation energies both the initial vibrational angular momentum quantum number (l = 0) and a' symmetry of the wavepacket are well conserved for 1–2 ps. At higher excitations and longer times (2–4 ps) these approximate symmetries are lost. These results are briefly discussed in relation to a general classification of IVR mechanisms and in relation to reactive processes in CHFClBr.
The rovibrational dynamics of hydroxylamine
Authors: Luckhaus D. 
Published: July 2012

AbstractThe combination of overtone spectroscopy and detailed quantum mechanical modelling of rovibrational dynamics provides an unique tool for investigating many aspects of intramolecular dynamics such as dynamical symmetries, coupling hierarchies, and the separation of time scales, which control the intramolecular energy flow at high excitations relevant for unimolecular reactions.Hydroxylamine NH2OH, which plays an important role in N/O/H chemistry in general, provides an intriguing example for the interplay between high frequency stretch‐bend motions and low frequency torsion/inversion tunneling. This paper discusses the dynamical analysis of its high resolution infrared absorption spectrum up to the visible range on the basis of up to five‐dimensional ab initio models using vibrational DVR grids of several million points.The torsion‐inversion process is found to follow a consecutive mechanism with very slow (≥ 1 μs) inversion tunneling below the trans‐cis isomerisation barrier (2673 cm−1 at MP2/TZ2P). The metastable cis isomer shows localised zero point and fundamental level eigenfunctions. From the overtone spectrum fast energy redistribution is deduced within the OH and NH2 manifolds, respectively, on time scales below 100 fs. A direct coupling between the two moieties leads to a slow decay of OH stretching excitation within 3 ps. Further significant contributions to the effective homogeneous broadening observed in high OH stretch overtones are predicted from the 1,2‐H shift leading to ammonia oxide NH3O with a barrier around 18200 cm−1 (CASPT2) and a NH3O well depth exceeding 1 eV.The spectroscopic characterisation of the metastable isomers of hydroxyl amine, cis‐NH2OH and NH3O, by stimulated emission pumping experiments is suggested on the basis of ab initio calculations for electronically excited states.
Predissociating resonances of Cs2 — Theory and experiment
Authors: Lee Sungyul , Kim Bongsoo , Yoshihara Keitaro 
Published: July 2012

AbstractWe present the experimental observation and detailed quantum mechanical analysis of the complex resonances occurring through multiple predissociation pathways. The complex features in the photodissociation spectrum of Cs2 are well reproduced by the close‐coupling calculation including three channels. A very narrow resonance with a linewidth of ˜2×10−7cm−1 is predicted. It is shown that q‐reversal can occur in predissociation with only two channels involved.
Isomerisation of deuterated cyclopropanes — The possibility for stereochemical control
Authors: Bolton Kim , Hase William L. , Doubleday Charles 
Published: July 2012

AbstractThe direct dynamics technique, based on an AM1 semiempirical Hamiltonian modified with specific reaction path parameters, has been employed to study the constant energy and thermal isomerisation of S,S‐trans‐cyclo‐propane‐1,2‐d2 and cyclopropane‐1,2,3‐d3. At a classical energy of 48.25 kcal mol−1 above the conrotatory saddle point, the dynamics is mode specific. This raises the possibility of stereochemical control in this energy regime. The sensitivity of the reaction mechanism to the character of the excited normal mode eigenvector is also apparent under thermal conditions at 695 K. Similar product branching ratios are obtained for the d2 and d3 species at this temperature, when the trajectories are initialised at the conrotatory saddle point.
Photofragment vector correlations as a probe of K‐scrambling in unimolecular dissociation
Authors: North Simon W. , Hall Gregory E. 
Published: July 2012

AbstractWe discuss the relationship between fragment‐rotational polarization and the extent of K‐mixing in an energized molecule undergoing unimolecular dissociation at fixed energy and angular momentum. Accurate measurements of the second Legendre moment of the v · j angular correlation are presented for the CN fragments produced in the photoinitiated dissociation of NCCN at 193 nm. as determined by Doppler spectroscopy using a transient frequency modulation technique. The strength of the correlation significantly exceeds what would be observed if all K states of the dissociating molecule were equally represented.
Models for the analysis of rate data for radical decomposition and multichannel radical‐radical reactions
Authors: Pilling Michael J. , Gang Jun , Robertson Struan H. , Zeng Guang 
Published: July 2012

AbstractTwo models are described for use in the analysis of experimental rate data for dissociation and association reactions. The first is a method for calculating partition functions and densities of states for molecules and radicals with asymmetric internal rotors. Its application to calculation of the heat capacity of butane and to analysis of pressure‐dependent rate data for the dissociation of 2‐C4H9 are described. The second technique is the use of the master equation to analyse rate data for multichannel radical‐radical reactions. It is applied to the CH3 + OH reaction.
The gas phase reactions of benzyl radicals with O, O3, and NO3: Rate, mechanism, and unimolecular decomposition of the chemically activated benzoxy radical
Authors: Hoyermann K. , Seeba J. , Olzmann M. , Viskolcz B. 
Published: July 2012

AbstractThe reactions of the benzyl radical with O, O3, and NO3 are investigated in a discharge flow‐reactor with mass spectrometric detection. For the rate coefficients of the latter two reactions, we obtain values of 2.8·1013 and 1.93·1012 cm3 mol−1s−1, respectively (T≈300 K, P ≈ 2 mbar). The main products for all three reactions are C6H6 and C6H5CHO with relative yields of 0.60/0.40 (M. Bartels, J. Edelbüttel‐Einhaus, and K. Hoyermann, 22nd Int. Symp. on Combustion, p. 1041, The Combustion Institute. Pittsburgh 1988), 0.37/0.66, and 0.23/0.77, respectively. These branching fractions are interpreted in terms of the unimolecular decomposition of an intermediarily formed benzoxy radical, using statistical rate theory. The molecular data needed are calculated by quantum chemical methods. The verification of the experimental branching fractions requires the assumption of a direct reaction channel leading from C6H5CH2O to C6H6. The nature of this channel is still uncertain.
Complex‐forming bimolecular reactions of metastable NH(a1Δ) with H2O(X̃1A1) and H2O2(X̃1A)
Authors: Hack W. , Jordan R. 
Published: July 2012

AbstractThe elementary reactions:
equation image
and
equation image
were studied in a quasistatic laser photolysis cell at a pressure of 20 mbar in the temperature range 295 ≤ T/K ≤ 523 and at room temperature respectively. NH(a1Δ, v) was produced by excimer laser photolysis of HN3(X̃) and detected by laser‐induced fluorescence (LIF). A variable delay time between photolysis and detection pulse brought about the time resolution. The NH(a) depletion yielded the following rate constants:k1(T = (3.5±0.8)1013(T/295 K)−(1.5±0.2)cm3/molsk2(v = 0) = (7.5±1.4)1013cm3/molsk2(v = 1) = (7.1±0.9)1013cm3/molsThe reaction products of reaction (1) are NH2(X̃) + OH(X). For reaction (2) NH2(X̃) radicals were detected (24%); the quenching channel was found to be unimportant kq < 7.5 · 1011 cm3/mol s. The reaction mechanism is discussed. The reaction NH(a) + H2O(X̃) is compared to the reaction NH(X) + H2O(X̃).
Dynamics of charge‐transfer state formation in supercritical fluid solvent
Authors: Kajimoto O. , Sekiguchi K. , Nayuki T. , Kobayashi T. 
Published: July 2012

AbstractThe rate of the intramolecular charge‐transfer state formation has been determined for 4‐(N, N‐dimethylamino)‐benzonitrile (DMABN) in supercritical CF3H by means of a time‐correlated single‐photon counting technique. The rate constant increases rapidly with increasing CF3H density, indicating the importance of the polar environment offered by the CF3H molecules which are clustering around a DMABN molecule. With increasing clustering number, the activation barrier is lowered and hence the rate increases exponentially. The observation is semiquantitatively interpreted on the basis of a molecular dynamics simulation of clustering in supercritical solutions.
Description of solvent effect on the visible absorption spectrum of fluorenone radical anion
Authors: Wagner‐Czauderna E. , Lipka R. , Kalinowski M.K. 
Published: July 2012

AbstractThe solvatochromic shift of the most intensive band of fluorenone radical anion (FN*‐) in the visible region has been examined in 10 polar formally aprotic media. It has been found that this shift depends on the solvent acceptor number (AN) and static dielectric constant (D) according to planar regression:

It is suggested that the ground state of FN*‐ is relatively stabilized in a solvent with a high acceptor number and the dipole moment of the solute increases during an excitation.
Coherent interference patterns of optical second‐harmonic waves from substrate‐free ultrathin poly(methyl methacrylate) films asymmetrically incorporating amphiphilic dyes
Authors: Yamada Sunao , Shimada Yoshihisa , Kawazu Mitsuhiro , Matsuo Taku 
Published: July 2012

AbstractAn ultrathin poly(methyl methacrylate) film, as prepared by a casting‐on‐water method, emitted optical second harmonic (SH) light in association with asymmetric alignment of an amphiphilic dye. Coherent interference due to SH waves from a pair of films in parallel afforded a periodic pattern with the film, and the pattern was 180° phase‐shifted on flipping either one of the films. These observations were ascribed to asymmetric orientation of the dye in the film and negligibly small thickness of the film in comparison with the coherence length. Overall orientation of dyes in the film could be estimated from the experiments.
Partitioning of some combination di‐ and tripeptides in aqueous two‐phase systems of poly(ethylene glycol) and Di‐potassium hydrogen phosphate at 293 K: Experimental results and predictions
Authors: Tintinger Ralf , Zhu Jiandung , Großmann Christoph , Maurer Gerd 
Published: July 2012

AbstractAqueous two‐phase systems are effective extraction systems for separating peptides and enzymes from aqueous phases. Such extraction processes are based on the finding that peptides and enzymes show different preferences for the coexisting phases. Methods to calculate and predict the liquid‐liquid phase equilibrium in those systems can only be developed when an extensive experimentally determined data base is available. The present contribution contributes to that goal by presenting experimental data for the partitioning of small amounts (micrograms solute per kilogram of solution) of low molecular‐weight combination peptides of glycine, 1‐glutamic acid, 1‐phenylalanine, and 1‐lysine in aqueous two‐phase systems of di‐potassium hydrogen phosphate and poly(ethylene glycol) of molecular mass of about 6000 and 35000 at about 293 K. A group‐contribution model for the excess Gibbs energy is used to predict liquid‐liquid phase equilibrium. A preliminary set of binary interaction parameters was taken from the literature. These model parameters were determined using experimental results for the partitioning of single amino acids and some of their peptides in the same aqueous two‐phase system. No experimental results for the partitioning of combination peptides had been used for parameter estimation, i.e. those peptides were products of condensation reactions of molecules of a single amino acid. Therefore, partition coefficients calculated for combination peptides are predictions. For some peptides predicted and measured partition coefficients agree within experimental uncertainty. In a few cases predicted partition coefficients deviate from experimental results by a factor of about two. However, the model always correctly predicts which phase (polymer‐rich or salt‐rich) is preferred by the peptide.
On the production of different carbon forms by electric arc graphite evaporation
Authors: Belz T. , Find J. , Herein D. , Pfänder N. , Rühle T. , Werner H. , Wohlers M. , Schlögl R. 
Published: July 2012

AbstractWe report results gained in the operation of a fullerene‐generating graphite evaporator in an attempt to evaluate its suitability for a rationally designed production of different new forms of carbon. The effects of varying experimental conditions on the composition of the products as well as on observable properties of the carbon arc have been examined. The primarily produced fullerene blacks and electrode deposits were characterized by powder X‐ray diffraction, transmission electron microscopy and oxidation experiments monitored by TGA/DTA. Yield and composition of the soluble fullerenes were determined gravimetrically and by HPLC, respectively. Furthermore, the arc plasma was investigated by UV/VIS emission spectroscopy under varied conditions to detect possible correlations of the fullerene yield with properties of the hot plasma.
Constitution and thermodynamics of Cu‐Y alloys
Authors: Abend U. , Schaller H.J. 
Published: July 2012

AbstractThe thermodynamic properties of Cu‐Y alloys were determined between 973 and 1073 K by emf measurements on galvanic cells using CaF2 single crystals as solid electrolytes. Results yield a complete set of thermodynamic functions for the intermetallic phases (Cu), Cu6Y, Cu4Y, Cu7Y2, Cu2Y, and CuY, as well as information on the phase relations. The system is characterized by moderate negative deviations from ideality. A comparison with analogous systems indicates the influence of the electronic structure of the components on thermodynamic functions. The phase relations of the Cu‐Y system were additionally investigated by DTA and X‐ray diffraction.The present results as well as literature data on the thermodynamics and phase diagram of the Cu‐Y system were used as a basis for a thermodynamic optimization of the system using a computer program based on the least squares method. Optimized and experimental data turned out to be in good agreement.
The kinetics of structural changes in anionic adlayers on stepped Au(111)s electrodes from sulfuric acid solutions
Authors: Dretschkow T. H. , Wandlowski T. H. 
Published: July 2012

AbstractThe kinetics of structural changes in anionic adlayers on stepped Au(111)s electrodes has been investigated in sulfuric acid solutions by potential step experiments. The experimental transients obtained with “quasi‐ideal” (miscut <0.5°) surfaces could be modelled with the exponential law of nucleation in combination with 2D surface diffusion‐controlled growth which is preceded by an adsorption process. The semi‐quantitative analysis was restricted to i vs. t‐traces, which revealed significantly different time constants of these two processes. The current transients with higher miscut angle showed (i) a systematic increase of the nucleation rate with increasing step density and (ii) a decrease of the macroscopically detectable charge density associated with the nucleation and growth process. The latter could be parameterized within a first approximation employing the general Avrami‐ansatz in combination with an adsorption process. In‐situ STM experiments showed that increasing step density of the substrate surface is accompanied with decreasing domain size of the ordered (√3 X √7) (hydrogen) sulfate adlayer patches. Respective correlations with the kinetic data obtained will be discussed.
Applied laser spectroscopy in technical combustion systems
Authors: Dreizler Andreas , Sick Volker , Wolfrum Jürgen 
Published: July 2012

AbstractSeveral laser‐based diagnostic techniques for nonintrusive measurements of species concentrations and temperatures were developed during recent years and have become valuable tools to study technical combustion processes. Data gained from such experiments are the basis for a comparison with detailed mathematical modelling of chemical processes in laminar and turbulent flows including heat and species transport. Examples for the application of laser‐induced fluorescence (LIF), laser‐induced thermal grating spectroscopy (LITGS), Rayleigh scattering (RS), differential absorption (DIAL) and emission in the infrared in ignition processes, internal combustion engines, municipal waste incinerators, and pressurized fluidized bed reactors are described.
Electric conductivity of supercritical cesium‐cesium hydride mixtures at high temperatures and pressures
Authors: Keller E. , Franck E. U. 
Published: July 2012

AbstractAbove a critical temperature of 665° liquid cesium and nonmetallic ionic liquid cesium hydride are completely miscible. This has been demonstrated previously with high pressure phase equilibrium measurements. An equilibrium hydrogen pressure belongs to each temperature and mixture composition and is used to prepare a desired sample composition. An autoclave for high pressure hydrogen is described into which electric conductance cells can be placed. With the cylindrical cell A the sample resistance is measured parallel to the thin stainless steel walls. With cell B, the resistance is determined between two tantalum electrodes separated by alumina.Conductances have been measured along seven isotherms from 550 to 800°. To cover mole fractions x (CsH) from 0.01 to 0.98, hydrogen pressures up to 1000 bar had to be applied. In the cesium‐rich, “metallic”, region conductances between 3000 and 9000 Ω−1 cm−1 were observed with negative temperature derivatives. In the cesium hydride‐rich, “ionic”, region conductances between 20 and 100 Ω−1 cm−1 were found with positive temperature coefficients. For the metallic region the conductance is discussed with the Mott “nearly free electron” (NFE) model in comparison with cesium‐gold and cesium‐halide systems. The NFE region extends down to 1300 Ω−1 cm−1 for the hydride systems. The metallic‐nonmetallic transition region extends from 1300 to 250 Ω−1 cm−1. At the critical consolution point (665°, x(CsH) = 0.68, p(H2) = 157 bar) the conductivity is 830 Ω−1 cm−1.
Formation of carbynoid structures by chemical dehydrohalogenation of poly(vinylidene chloride). A 13C solid‐state NMR study
Authors: Evsyukov S. E. , Paasch S. , Thomas B. , Heimann R. B. 
Published: July 2012

AbstractThe products of the interaction of poly(vinylidene chloride) (PVDC) powder with a mixture of alcoholic KOH solution and tetrahydrofuran were studied by solid‐state 13C NMR spectroscopy. The reaction was found to be a complex process involving dehydrochlorination as a target reaction and some side reactions, viz., nucleophilic substitution, cross‐linking, and secondary transformations of intermediate and final products. The endproducts are “carbynoid‐type” polymeric materials containing short carbyne fragments along with various defect links such as alkoxy‐ and hydroxy groups, carbonyl species, as well as cross‐links. The reasons for the concurrent formation of both polyyne and cumulene structures, and the nature of side reactions are discussed.