bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and Mechanism of Hydrogen Diffusion in Hydrides of Titanium, Zirconium and TiNi0.5
Authors: Brauer E. , Gruner R. , Rauch F.
Published: July 2012

Hydrides of titanium and zirconium formed during cathodic polarization in acid solutions were investigated by the15N nuclear reaction method. Hydrogen depth profiles obtained in this way give informations about the hydrogen concentration in the metal, allowing to determine diffusion coefficients and therefrom to study the absorption of hydrogen by the metal lattice and the kinetics of the hydride layer growth. The mechanism was studied using Ti single crystals. The hydrogen diffusion was found to depend on the crystal orientation.
The Approach to Stationary States of Autocatalytic Systems in the Continuous‐flow Stirred Tank Reactor
Authors: Gray P. , Scott S. K.
Published: July 2012

The relaxation times characterizing the growth or decay of small perturbations from a stationary‐state established under continuous‐flow, well‐stirred conditions are derived for the autocatalytic sequences A + n B → (n + 1) B, with n = 1 or 2. The results show how as the flow‐rate is varied, relaxation times may gradually become very long compared with the mean residence‐time of the system. This lengthening is accompanied by a change in the mathematical form, from an exponential to an inverse dependence on time. This is not, however, a critical phenomenon, nor are infinite values possible.
Self‐Diffusion in Water‐Alcohol Mixtures. Part I. Water‐Methanol Solution of NaI
Authors: Hawlicka E.
Published: July 2012

The self‐diffusion coefficients of components in methanol‐water‐NaI system at 298.2 K have been investigated using open‐end capillary method. The influence of NaI concentration on methanol and water self‐diffusion coefficients has been studied. The dependences of self‐diffusion coefficients of sodium and iodide ions on NaI concentration have been determined. In methanol‐water‐NaI system the methanol self‐diffusion coefficient is greater than in pure methanol‐water mixture. The water self‐diffusion coefficient in the presence of NaI does not exhibit the minimum and in methanol rich mixtures is equal to the self‐diffusion coefficient of sodium ion.
Chemical Exchange and Raman Line Broadening. The Rate of Protolysis of Nitric Acid
Authors: Strehlow H. , Wagner I. , Hildebrandt P.
Published: July 2012

The influence of chemical exchange on the line shape in Raman spectroscopy is investigated. A theory, covering also the „fast case”︁ is derived. The results are compared with the similar but not identical equations valid for the kinetic line broadening in NMR spectroscopy. — The Raman line broadening technique is applicable only to extremely fast reactions with life times of the involved species shorter than about 10−11 s. — A practical application is given for the protolysis of nitric acid and the formation kinetics of ion pairs of NaNO3 both in highly concentrated solution. The rate constants obtained are higher than the rate constants for diffusion controlled reactions as calculated with the Smoluchowski‐Debye theory [1]. An explanation is proposed. The pK of nitric acid is reevaluated to be (−0.9 ± 0.3).
Arrhenius Parameters for the Reactions of O Atoms with Some Alkynes in the Range 300–1300 K
Authors: Homann K. H. , Wellmann Ch.
Published: July 2012

The rates of the reactions of oxygen atoms with acetylene (1), propyne (2), 1–3‐butadiyne (3), 1‐buten‐3‐yne (4), and 1‐butyne (5) in a discharge flow system have been measured in the temperature range 300 <T< 1300 K. — The Arrhenius expressions for the respective bimolecular rate constants are

There is a correlation between the activation energies and the ionization potentials of the alkynes.
Group Additivity for the Band Strength of the CF‐Chromophore for IR‐Photochemistry
Authors: Quack M. , Thöne H. J.
Published: July 2012

Integrated band strengths for rovibrational absorption in the frequency range of the CF‐chromophore (800 to 1300 cm−1) have been obtained from vapour phase IR‐spectra of twelve fluoroalkanes containing one or more CF groups. It is found that the chromophore band strength is about 1.7 (pm)2 for each CF group with some minor variations due to neighbouring substituents at the CF carbon atom. These variations can be accounted for by a simple, empirical equation. The results are discussed in relation to the chromophore principle in IR‐photochemistry. The frequency distribution of the chromophore absorption for primary, secondary, and tertiary alkyl fluorides is considered. The primary CF‐chromophore (R ‐ CH2 ‐ F) is suggested to be a particularly useful general chromophore for CO2‐laser pumping. The foundations of the group additivity for chromophore band strengths and some further applications are discussed as well.
Concentrated Aqueous Sodium Chloride Solutions from 200 to 600°C and to 3000 bar. — Phase Equilibria and PVT‐Data
Authors: Gehrig M. , Lentz H. , Franck E. U.
Published: July 2012

The specific volume of aqueous sodium chloride solutions with 6, 10, and 20 weight percent salt was measured from 200°C to 600°C and from 100 bar to 3000 bar. The uncertainty of the data is below 0.5%. Data are given of temperature, pressure, volume and composition at 24 points on the two‐phase boundary surface. About 230 values for the one‐phase region are presented. The critical curve for the binary system runs from 374°C and 220 bar for pure water to 500°C and nearly 600 bar for a solution with 12% salt. The specific volume at this point is 2.0 cm3 g−1. At 600 °C, 3000 bar and 20% salt a volume of 1.163 cm3 g−1 was found. The apparatus and procedure, which uses an autoclave with variable volume and sapphire window is described.
Time Resolved Visible and UV Absorption Spectroscopy of Bromine Clusters in Argon Matrices
Authors: Raffel B. , Wolfrum J.
Published: July 2012

Matrix deposition was observed by a laser interference technique at deposition rates of 0.1 – 0.2 mmol/h at T = 10 K up to a matrix thickness of 1.1 · 10−4 m. Absorption spectra of Br2/Ar matrices (1 : 1000 – 1 : 300) examined quantitatively at λ = 300 nm and 415 nm showed an increase of molar bromine absorptivity with increasing Br2‐concentration. The increase of absorptivity may be explained by formation of Br2‐dimers during matrix deposition. Br2/Ar matrices were exposed to laser pulses at λ = 490 nm and showed a transient increase of absorption in the near UV (λ < 370 nm), a spectral region mainly due to Br2‐dimers. This increase presumably depends on laser excitation of Br2‐molecules situated in dimers into the B3π(O) state followed by deactivation into the ground state X1Σ. At least three exponentials are necessary to fit the transient signals with the lifetimes t1 = 3.5 μsec, t2 = 64 μsec, t3 = in the order of some msec.
Second Derivative UV Spectroscopy Study of the Thermal and Photochemical Reaction of NO2with SO2and SO3
Authors: Penzhorn R.‐D. , Canosa C. E.
Published: July 2012

The rate constants for the thermal reaction of NO2with SO2(k9= (1.4 ± 0.1) · 10−5l/mol · s) and SO3(k10= 88 ± 8 l/mol · s) have been determined employing second derivative UV spectroscopy. This technique was shown to be adequate to solve the problem of light scattering by aerosols always present in these systems. NOHSO4and H2O were found to strongly catalyze the NO2– SO2reaction. – The quantum yields of O2production and NO2depletion as well as the NO yield from the photolysis of NO2in the presence of SO2and/or CO2were determined at 366 nm as a function of SO2and CO2partial pressure at room temperature. The results were satisfactorily correlated with a reaction mechanism. – The relevance of the above reactions in urban aerosol formation are briefly commented.
Experimental Investigation on the Thermal Stability of Metallic Glasses
Authors: Bergmann H. W. , Brokmeier U. , Fritsch H. U.
Published: July 2012

There are many instances in practice of phase changes in which the initial phase e.g. a homogeneous melt is not replaced by one or more thermodynamic stable phases but rather by metastable phases. Knowledge of systems in which metastable phases can form has increased considerably in recent years. Rapid quenching increases the tendency to form metastable phases including ultimately for appropriate compositions the amorphous metallic glasses. In any discussion about metastable phases there arises the question of the conditions under which they form and their stability which depends on temperature, pressure and composition. In the present work some attempts to describe the thermal stability of metallic glasses and the experimental means of measuring it are discussed.
Thermodynamic Properties of Pt — B Solid Solutions
Authors: Brodowsky H. , Sagunski H.
Published: July 2012

The activity coefficients of B in Pt were determind at 1200 and 1300 K by equilibrating Pt with B2O3in a controlled H2– H2O atmosphere and measuring the weight gain. The partial molar excess Gibbs energies at vanishing B concentration are –44 and –43 kJ/ mol, respectively. The atomic fractions at the solidus line are 0.036 and 0.031. A relative lattice contraction of the solid solutions prepared at 1200 and 1300 K of (1/a)(∂a/∂xB) = −0.042 and of −0.035 ± 0.002 was observed. This dependence of the lattice constant on the temperature of preparation suggests a mixed occupation of lattice and interstitial sites, with the majority of B atoms on lattice sites.
Statistical Properties of Non‐Equilibrium Effects in Turbulent Diffusion Flames
Authors: Peters N.
Published: July 2012

It is shown that the interaction between non‐equilibrium chemistry and turbulence in non‐premixed combustion depends essentially on two parameters: the conserved scalar and the instantaneous scalar dissipation rate. The previously favoured assumption of statistical independence between these two parameters is discussed. It is argued that the assumption must be questioned in the early part of jet flames where a comparatively regular flow field exists. A semideterministic model, the mixing layer ensemble model is developed on the basis of a statistical assumption about the stretching of the surface of stoichiometric mixture.
Thermal Decomposition of Ethylbenzene in Shock Waves
Authors: Brouwer L. , Müller‐Markgraf W. , Troe J.
Published: July 2012

The thermal decomposition of ethylbenzene has been investigated under high dilution by Ar in incident and reflected shock waves in the temperature range 1250–1600 K. At 4 · 10−6 ≤ [Ar] ≤ 2.4 · 10−4 mol cm−3 the reaction was found to be in the fall‐off regime of the unimolecular reaction. At the highest experimental density a first order rate constant k = 1017.1 ± 0.3 exp(–340 ± 10 kJ mol−1/RT) s−1

has been derived. Based on observations of the UV spectra of the primary dissociation fragment and the final product styrene, as well as the kinetics of formation and consumption of the intermediate species, a dominant formation of benzyl radicals can be excluded. Instead it was shown that the dissociation starts with a C–H bond split.
Graphite Oxidation Phenomena During Massive Air Ingress Accidents in Nuclear High Temperature Gas Cooled Reactors with Pebble Bed Core
Authors: Moormann Rainer
Published: July 2012

Air ingress into the mainly on graphite consisting core of a High Temperature Gas Cooled Reactor leads to graphite oxidation phenomena. The computer code REACT/THERMIX developed for safety analyses on reactor accidents connected to significant graphite corrosion processes, is briefly described. Calculations for massive, hypothetical air ingress accidents have shown, that severe safety endangering consequences do not occur; one of the main reasons for this behaviour is, that the small graphite/oxygen reaction front is not locally fixed during the accident but migrates through the core parallel to the cooling flow.
Kopplung von Stoffaustausch mit chemischer Kinetik beim Abbrand von Kohlepartikeln
Authors: Specht E. , Jeschar R.
Published: July 2012

The boundary layer of a burning particle in an air flow was investigated. It is illustrated, that at high temperatures the combustion is a two‐step mechanism: heterogeneous gasification at the solid surface area and homogeneous combustion of carbon monoxid in the boundary layer. The diffusion controlled burning rate can be calculated from the Sherwoodfunction according to the particular circumstances multiplied by the factor 2, which is confirmed by experiments. At high Reynoldsnumbers the burning rate becomes controlled by the chemical kinetics. The range of particle size in which the chemical kinetics influences the burning rate, is shown in dependence on temperature and air velocity.
Electrochemical Studies on the Electron Disorder in Cuprous Selenide
Authors: Mostafa S. N. , Seliman S. A.
Published: July 2012

The ratio of copper‐to‐selenium in cuprous selenide has been determined as function of the copper activity in the selenide at 435°C with the help of coulometric titrations. At 435°C the homogeneity range of cuprous selenide extends from a Cu/Se ratio of 1.998 to a value lower than 1.860. Analysis of the experimental data shows that the change of the chemical potential of copper by a change of the composition is only given by a change of concentration of the defect electrons or of the quasifree electrons. From these studies, the energy gap in coprous selenide is at least 0.37 eV.
Novel Effect of Man‐Made Molecular Assemblies on Photoinduced Charge Separation. 4. Synthetic Bilayer Membrane of Amphipathic Viologen as an Efficient Electron Collector in Photosensitized Redox Reactions
Authors: Nagamura Toshihiko , Tanaka Koji , Takeyama Naoki , Matsuo Taku
Published: July 2012

Addition of synthetic bilayer membrane formed by a new type of amphipathic viologen containing two hexadecyl groups to aqueous solution of zwitterionic propylviologen sulfonate (PS2 – V2+) remarkably increased the yield of viologen photoreduction as sensitized by tris(2,2'‐bipyridine)‐ruthenium complex, Ru(bpy), in the presence of triethanolamine. Zwitterionic viologen was confirmed to shuttle as an efficient electron mediator between bulk aqueous solution and the interface of the bilayer membrane with a viologen head group. The quantum yield of viologen cation radicals was close to the net cage‐escape yield of photogenerated Ru(bpy) ‐ PS2‐V+ ion pair. The electrostatic field of positively charged interface of bilayer membrane was concluded to attract PS2‐Vc which transports electron to viologen head groups of bilayer membranes. Remarkable (500‐fold) suppression of the reverse electron transfer reaction was attained by the addition of viologen bilayer membrane. It was attributed to Coulombic repulsion between Ru(bpy) and positively charged interface of bilayer membranes. Relevance of the present system to chemical conversion of solar energy is discussed.
Broken Symmetry in Excited States of 9,9′‐Bianthryl
Authors: Rettig Wolfgang , Zander Maximilian
Published: July 2012

The dual fluorescence in polar solvents of 9,9′‐bianthryl (BA) and of the electronically perturbed BA‐derivatives 10‐chloro‐BA (BACl), BA‐10‐carboxaldehyde (BAA) and N‐(9‐anthryl)‐carbazole (C9A) as well as of N‐(4‐cyanophenyl)‐carbazole (CBN) is analysed and interpreted in terms of a simplified microstructural solvent interaction model. Dipole moments μT relative to μT (CBN) of the fluorescent charge transfer state have been derived from the solvatochromic band shifts in nitrile and alcohol homologous solvent series and are similar for BA, BACl and C9A. This implies that the charge transfer in the excited state occurs to a maximum degree even in the symmetric molecule BA. – QCFF/PI‐potential energy curves have been calculated and are used to discuss these findings. BAA fluoresces in alcohols only, μT‐compared to the other compounds studied being somewhat smaller probably because of specific H‐bond interactions with the solvent. – Using relative fluorescence quantum yields and energetic considerations the dependence of the excited states equilibrium on both solvent polarity and solute perturbation is discussed.
The Influence of Three‐Body Forces on the Lifetime and Stability of Rare Gas Clusters
Authors: Polymeropoulos E. E. , Brickmann J.
Published: July 2012

The formation of clusters in compressed argon and xenon gases is studied with the molecular dynamics simulation technique using two‐body Lennard‐Jones and three‐body Axilrod‐Teller interaction potentials. It is shown that the effect of three‐body interactions is a function of the temperature of the system and increases with decreasing temperature. The occurrence of clusters corresponding to the “magic‐number” n = 13 for xenon is explained in terms of the dispersion forces inherent in the Axilrod‐Teller potential. Computer generated images of stable and unstable Xe13 clusters are presented.
The Thermal Conductivity of n‐Hexane and n‐Octane at Pressures up to 0.64 GPa in the Temperature Range 34—90°C
Authors: Li S. F. Y. , Maitland G. C. , Wakeham W. A.
Published: July 2012

New, absolute measurements of the thermal conductivity of liquid n‐hexane and n‐octane are reported. The measurements have been carried out within the temperature range 34—90°C and over the pressure range 1.8 — 640 MPa in a transient hot‐wire instrument. It is estimated that the experimental data have an uncertainty of ±0.3%. The density dependence of the thermal conductivity of n‐hexane and n‐octane may be satisfactorily represented by means of an equation whose form is based upon an heuristic modification of the Enskog theory for transport processes in dense fluids. The optimum correlations for n‐hexane and n‐octane are slightly different from those which have been found to be universal among normal alkanes with an odd number of carbon atoms. This behaviour is predominantly attributable to the superior accuracy of the present experimental data, resulting from an improved treatment of radiative heat transport in the measurement.
Simultaneous Time‐Resolved ESR and Optical Absorption Spectroscopy. The Photolysis of 4‐Acetylpyridine in Propanol(‐2)
Authors: Lauschner Rainer , Dohrmann Jürgen K.
Published: July 2012

A novel technique is described for the simultaneous in situ measurement of ESR and optical transients from intermediates produced by intermittent photolysis in solution. The technique has been applied to the photoreduction (λ ca. 300 ± 30 nm) of 4‐acetylpyridine (AP) in propanol(‐2) at room temperature. The measurements gave the absorption spectrum and the molar extinction coefficients of the intermediate 1‐hydro‐4‐acetylpyridinyl radical (·APH) in the 300 — 550 nm range as well as the ratio of the quantum yields for formation of · APH and disappearance of AP. Absolute values of the quantum yields at 300 nm have been determined by additional ESR and spectrophotometric measurements under steadystate conditions. The various results are discussed in terms of a mechanism proposed for the photoreduction of AP in propanol(‐2).
Rate Coefficients of Elementary Steps in the Inhibited Oxidation of Ethylbenzene, II. Interaction between Hydroperoxide and Alcohol Molecules
Authors: Héberger K. , Hubert Noszek E. , Gál D.
Published: July 2012

The decomposition of 1‐phenylethyl‐hydroperoxide assisted by 1‐phenyl‐ethanol has been investigated in the presence of 2,6‐di‐tert‐butyl‐4‐methyl‐phenol (ionol). Ethylbenzene was used as solvent, the temperature range was 115–130°C. The inhibition period was measured as a function of alcohol concentration (and inhibitor concentration as well). The activation parameters of hydroperoxide decomposition assisted by alcohol have been determined:

kHROOH + HROH = 1.13 · 107 exp(94.9 kJ mol‐1/RT) s‐1
Excess Gibbs Function of the Binary Liquid Mixtures Formed by Acetonitrile with Pentyl Acetate, n‐Butanol, n‐Propanol, and Carbon Tetrachloride at 25°C
Authors: Masegosa R. M. , Prolongo M. G. , Hernández‐Fuentes I. , Horta A.
Published: July 2012

Light scattering and differential refractometry at 546 nm have been used to determine Rayleigh ratios, depolarization factors, and refractive index increments in the title systems, at 25°C. The activity coefficients and the excess Gibbs function (GE) have been calculated from these measured magnitudes. The results of GE together with literature values of HE are used to discuss the importance of interactions and of order in these systems. The mixtures here studied are cosolvent of polymers. The present results should be useful for a better understanding of such phenomenon of cosolvency.
The Effect of Pressure on the Self‐Association of Dyes in Aqueous Solutions Studied by Cable Temperature‐Jump Relaxation Spectroscopy
Authors: Ohling W.
Published: July 2012

Equilibrium and rate constants of the self‐association of methylene blue and pyronine G in aqueous solutions (water and water/methanol mixtures) are reported for pressures up to 200 MPa at T = 20°C and 30°C. The kinetic measurements were performed in a high pressure cable temperature‐jump apparatus. The volumes of reaction determined from the pressure dependence of the association constants are negative (–9.0 to –13.5 cm3 mol−1) for all reactions. From the pressure dependence of the rate constants the volumes of activation are found to be slightly negative for the forward reaction (±0 to –5.3 cm3 mol−1) and positive for the reverse direction (+ 4.3 to + 13.3 cm3 mol−1). The volumes of reaction of the two intermediate steps of the self‐association (i.e. formation of the encounter complex and rearrangement of the complex to form the dimer) are calculated by using the theory of diffusion controlled reactions. The resulting volume profiles of the reactions are discussed in view of the specific role of water as solvent.
Interactions of Methylbenzenes with Aluminium Bromide
Authors: Erb H.‐P. , Felbecker H. , Bluhm Th.
Published: July 2012

Proceeding from the chemical shifts of the 13C and 27Al atoms, the thermodynamic properties were calculated for the simultaneous formation of the complexes arene · Al2Br6 (C) and arene · AlBr3 (D) in liquid binary mixtures of methylbenzenes with aluminium bromide. Other stoichiometric models, that take into account the formation of only one complex (C or D) at a time, could only be eliminated by including the 27Al NMR data.– We conclude from the effects of concentration on the chemical shifts, that the aromatic π‐electrons transfer charge to the aluminium bromide, which is oriented above or below the aromatic plane.
The Influence of the Electronic Structure on the Dimerization of Phenthiazonium Cations in Aqueous Solution
Authors: Ruprecht J. , Baumgärtel H.
Published: July 2012

The association of different aminophenthiazonium cations in aqueous solution has been investigated and correlated with the distribution of π‐electron density in the cations. The 3,7‐disubstituted cations with their cyaninelike π‐system dimerize in contrast to aminophenthiazonium cations with noncyaninelike distribution of π‐electron density.
On the Nature of the Bonding of Lone Pair Ligands to Small Metal Clusters
Authors: Bagus P. S. , Hermann K. , Bauschlicher C. W.
Published: July 2012

We analyse the interaction and bonding between CO, NH3 and PF3 molecules and a Cu5 cluster in detail. From a constrained space orbital variation (CSOV) study, we are able to determine the energetic importance of different contributions to the metal‐ligand interaction, such as intra‐unit, Cu5 and ligand, polarization and inter‐unit donation. The results show that the Cu5–NH3 bonding is determined to a large part by the electrostatic interaction between the units with little charge transfer. The Cu5–CO bonding is characterized mainly by a metal to ligand π donation. The Cu5–PF3 bonding has metal to ligand π and ligand to metal s̀ donation of comparable importance. The free PF3 dipole leads to a repulsive interaction with the Cu5 and this affects the intra‐unit polarization.
Surface Enhanced Raman Scattering (SERS) at Matrix Isolated Metal Clusters of Ag, Na and K
Authors: Schulze W. , Breithaupt B. , Charlé K.‐P. , Kloss U.
Published: July 2012

Surface‐enhanced Raman spectra of various molecular gases adsorbed on colloidal matrix isolated silver, sodium and potassium clusters of about 100 Å diameter are reported. For CO adsorbed on silver clusters the strongest enhancement is observed in the region of considerable surface plasmon absorption of the metal colloid (electromagnetic enhancement). N2 and O2 adsorbates on silver colloid on the other hand show much weaker SERS‐signals. Furthermore the frequency shift of the adsorbate relative to the condensed free molecule as well as the line broadening is much weaker than for CO, indicating a weaker chemical interaction. – The importance of surface plasmon excitation for getting SERS signals is additionally proven by using colloids of sodium and potassium. On these more reactive metal colloids chemical reactions can even be monitored at low temperatures.
The Optical Properties of Silver Microcrystallites in Dependence on Size and the Influence of the Matrix Environment
Authors: Charlé K.‐P. , Frank F. , Schulze W.
Published: July 2012

The surface plasmon absorption band of small metal particles or large clusters (diameter ≤ 100 Å) is known to shift and to broaden with decreasing diameter. It is argued and experimentally proven at Ag‐colloids that this size effect depends sensitively on the microscopic surface properties of the clusters, which are influenced by the interaction with the embedding matrix.
Reactivity of Fluorochloromethanes with Desert Sands
Authors: Benzoni L. , Garbassi F.
Published: July 2012

Desert sand reactivity with halocarbons like CCl3F (F11), CCl2F2 (F12) and CHCl2F (F21) has been proved. Reactivity increases in the sense: F12 ⩽ F21 < F11 and is favoured by temperature and short activation of samples at 673 K. For F11, the main reaction products are CCl4 and COCl2, but some transformation to F12 has been observed too. An influence of the desert sand origin (i.e. of its phase composition) has been also found. — X‐ray photoelectron spectra of samples after reaction show the presence of F and Cl on their surface, mainly as calcium halides, and in direct proportionality with reactivity.
The Transition Between Regular and Chaotic Dynamics and Its Influence on the Vibrational Energy Transfer in Molecules After Local Preparation
Authors: Brickmann J. , Pfeiffer R. , Schmidt P. C.
Published: July 2012

The classical as well as the quantum dynamics of two‐dimensional nonseparable oscillator systems is studied in order to investigate the influence of regular and chaotic motion on the nature of the intermode vibrational energy transfer after local excitation. Representative sets of initial conditions ‐ each element representing a single phase space cell — were chosen. For the classical problem one phase space point per cell was used while for the quantum problem minimum uncertainty wave packets (harmonic oscillator coherent states) with position and momentum expectation values corresponding to the classical values were taken as initial quantum states. For both types of motion information entropies were determined from time averaged probabilities. These entropies are compared with “ergodic limit entropies”. The latter correspond to a statistical preparation of the initial states. Although there is only a weak correspondence between single‐trajectory motion and wave packet dynamics, some general predictions about the quantum dynamics can be made from the classical results for a time scale of chemical interest. No sharp transition is found for the wave packet dynamics going from the classically regular to the irregular energy region. However, one can estimate the probability for an arbitrarily prepared local minimum uncertainty wave packet to possess statistical (RRKM) or non statistical (non‐RRKM) dynamics from the analysis of a sample of classical trajectories each starting in a phase space cell of the bound area of the Hamiltonian, i.e., the nature of unimolecular reactions can be roughly predicted from the potential energy surface and a sample group of classical trajectories.
Diffusion Coefficients and Thermal Diffusion Factors of Several Binary Systems of Carbon Monoxide and Oxygen with Noble Gases
Authors: Trengove R. D. , Robjohns H. L. , Dunlop Peter J.
Published: July 2012

Diffusion coefficients and thermal diffusion factors are reported for several binary systems of carbon monoxide and oxygen with noble gases. Using approximate spherical potential functions, most of which have been reported in the literature, the experimental results are compared with the predictions of the Chapman‐Enskog theory.
Direct Determination of the Rate Constant for the Reaction CH2 + H → CH + H2
Authors: Böhland T. , Temps F.
Published: July 2012

The reaction

magnified image

was investigated at room temperature in an isothermal discharge flow reactor with laser magnetic resonance detection of CH2 and CH. Direct measurements of the decay of CH2 in the presence of an excess of H‐atoms yielded a rate constant of

magnified image

Combined with the known rate constant for the reverse reaction CH + H2 + CH2 + H the heat of formation of CH2 was found to be

magnified image
On Complex Formation in Mixed Solvents
Authors: Strehlow H. , Busse G.
Published: July 2012

In a mixture of solvents S1 and S2 a cation Mz+ forms “solvatomers” of the type M(S1)i(S2)k‐iz+, where k is the coordination number of the cation and i = 0 to k. The rate of substitution of a solvating molecule by a ligand LzL depends in general on the specific solvatomer and on the solvent molecule being substituted. – Kinetic measurements are reported on systems with the cations Be2+, Al3+, and Ni2+, the ligands sulfate, rhodanide and acetate and the solvent pairs water‐dimethylsulfoxide, water‐N‐methylformamide, water‐hexamethylphosphoric triamide, water‐formamide and methanol‐dimethylsulfoxide. – Some rules concerning the kinetic behaviour of such systems have been developed. In particular, an explanation is presented for the different kinetics observed with tetrahedrally coordinated complexes (k = 4) and with octahedrally coordinated ones (k = 6).
The Solubility of Ethane in Water up to 473 K
Authors: Crovetto Rosa , Fernandez‐Prini Roberto , Japas Maria L.
Published: July 2012

The Henry constants for the dissolution of ethane in water have been determined with two experimental methods up to 473 K and with an overall precision of 2%. From this data it was possible to calculate the thermodynamic properties of the dissolution process and using the results of our previous study of the thermodynamics of dissolution of methane in water, it was possible to calculate the contribution of the so‐called hydrophobic effect over a wide temperature range. It is shown that a Percus‐Yevick plus Lennard‐Jones perturbation theory accounts reasonably well for the observed behaviour.
Kinetics of the Reaction of Solvated Electrons with Water in Liquid Ammonia
Authors: Telser Th. , Schindewolf U.
Published: July 2012

Solvated electrons (< 10−6 M) produced by flash photolysis in ammonia react with water according to the rate law d[e−]/dt = k · [e−] · [H2O] with the rate constant k = 0.16 ± 0.03 M−1 sec−1 at – 40°C. The rate law is compatible with the reaction e− + H2O → H + OH−, but the activation energy Ea (e−) = 6 ± 1 kJ/mol is too small for this endothermic process with ΔH0 = 52 kJ/mol. Therefore we conclude that in the rate determining step an unknown intermediate is formed which in turn recombines to molecular hydrogen. Evidence for this intermediate was given already 15 years ago in the pure aqueous system in which solvated electrons a few msec after their reaction could be regenerated by a photo flash too soft to photo‐generate them directly. – The reaction of very low concentrated metal ammonia solutions with water follows the same kinetics. But at higher concentrations (0.1 M) the relative reaction rate is very low. With sodium the reaction is slower than with cesium, in deutero‐ammonia it is slower than in normal ammonia. It is almost of zero order with respect to the metal and of one ha1f order with respect to water and has an activation energy Ea (Na) = 32 ± 3 kJ/mol (normal sodium‐ammonia solution). The observed kinetics suggest that the solvated electrons are still the only reactive species in these solutions; but their concentration is lower than the metal concentration by many orders of magnitude due to the well known spin pairing equilibrium, which must include a metal cation and a solvent molecule. The stability of the spin paired species increases with decreasing cation size and with increasing tendency of the solvent to form hydrogen bridges. The high experimental activation energy is partly due to the temperature dependence of the spin pairing equilibrium.
Calorimetric Investigations of Lipid Phase Transitions. II. The Heat of Transition
Authors: Knoll Wolfgang , Höhne Günther W. H.
Published: July 2012

Multilamellar liposomes of dimyristoylphosphatidylcholine in excess water have been investigated by differential temperature scanning calorimetry. The heat, ΔQ, that is exchanged between the environment and the sample at its main phase transition (fluid ↔ ordered) has been determined as a function of the sample volume, lipid concentration, and scanning rate. No variation of the transition heat is found for sample volumes ranging from 35 μl to 785 μl and for lipid concentrations ranging from 3 mM to 300 mM. For low scanning rates α(α ≤ 0.02 K · min−1) a constant transition heat of ΔQ = 23.4 kJ · mol−1 is found that increases around α = 0.1 K · min−1 to ΔQ = 27.2 kJ · mol−1 which remains constant for higher α. We interpret this finding as being evidence for non‐equilibrium transitions at high scanning rates due to relaxation process in the lipid‐water‐system that need minutes to be completed.
Phase Equilibria in Liquid Crystalline Systems Part II. Theory and Interpretation of Experimental Results
Authors: Ballauff M. , Flory P. J.
Published: July 2012

Characteristic temperatures T* have been evaluated for the oligomeric p‐oxybenzoates, C6H5CO(‐OC6H4CO)n‐2‐OC6H5 from the transition temperatures TNI presented in the preceding paper. For n = 3, 4 and 5 they are, respectively, 343, 316 and 306 K. These parameters that measure the intensities of the orientation‐dependent intermolecular interactions are correlated with the optical anisotropy Δα and the average intermolecular cohesive energy expressed by the characteristic pressure p*. The characteristic temperature T* decreases slightly with chain length. The lattice theory of nematic fluids is extended to include mixtures of rodlike molecules having different characteristic temperatures T* in order to treat binary and ternary mixtures of the p‐oxybenzoate oligomers. The wide biphasic gaps predicted for the several binary systems and the concomitant pronounced partitioning of the components between the nematic and isotropic phases are not confirmed by experiments. Compositions of the coexisting phases in ternary systems were found to be identical within limits of experimental determinations. These marked departures from theory are explicable on the premise that facile rotational diffusion of the nematogens here considered, which are of comparatively low chain length, leads to rapid generation of ordered domains of large dimensions. Subsequent diffusional transport over the required distances consequently is very slow. The transition temperatures observed in binary systems are in excellent agreement with calculations carried out in the “single component” approximation using mean values of the axial ratio and of T* for the mixture, these being taken to be the same in the two phases at equal concentrations.
Composition Dependent Electronic Conductivity and Hall Coefficient of β‐Ag2 + ΔS
Authors: Sohège J. , Funke K.
Published: July 2012

The electronic conductivity, σe, and the Hall coefficient, RH, of β‐Ag2 + δS are experimentally determined at temperatures T between 190°C and 320°C and at values of δ covering the entire stability range. The change of composition is achieved by in situ coulometric titration. At δ > 5 · 10−4, where β‐Ag2 + δS shows a metallic behaviour, the data are consistent with a parabolic conduction band and an electronic relaxation time which is proportional to T−3/2, but does not depend on the electronic energy. The same concept, plus number densities of defect electrons taken from the titration curves, is also used for an interpretation of σe and RH at smaller δ, where the metal‐semiconductor transition is observed.
ArF Laser (193 nm) Photolysis of HNO3. Formation of Excited Fragments
Authors: Papenbrock Th. , Haak K. K. , Stuhl F.
Published: July 2012

HNO3 was photolysed using an ArF (193 nm) excimer laser. Besides strong emission from OH(A2Σ+), weaker fluorescence from excited NO was observed in the investigated wavelength range 130‐−900 nm. The OH(A) emission is generated by absorption of two laser photons while the NO emission is produced by a one‐photon process. The rotational and vibrational populations of the OH fragments can be explained by a simplified impulsive model with additional contributions from the change of the OH bond length and by a slight bending motion of the parent molecule. Monitoring the strong OH emission appears to be a sensitive method to detect gaseous nitric acid in air in the ppb range.
A Generalized van der Waals Equation of State IV. Corrections for Medium and Low Densities for the Example of Methane
Authors: Móritz P. , Kohler Friedrich
Published: July 2012

An equation of state, recently developed for high densities, is extended to the whole density range and is compared to tabulated values of the thermodynamic data of methane. The agreement is very satisfactory. At subcritical temperatures, the parameters can be derived from second virial coefficient, vapour pressure, orthobaric liquid volume, and isothermal compressibility. At supercritical temperatures, the number of necessary p‐ν‐T measurements can be considerably reduced in comparison to conventional equations of state.
The Kinetic Behaviour of Polycrystalline Alloy Electrodes (σ‐(Fe, Zn))
Authors: Lang J. , Schwitzgebel G.
Published: July 2012

The equation for the impedance of alloy electrodes was developed on the basis of a model for diffusion in polycrystalline alloys by using Fourier transformation and was included in the total cell impedance. In order to obtain experimental confirmation, the magnitude and the phase displacement of the impedance of cells containing electrodes made of Γ(Fe,Zn) were measured with the aid of a special impedance spectrometer. The experimental results were very well represented by the theoretical equation in the frequency range from 0.3 Hz up to 7 kHz. The evaluation yielded the electrochemical parameters of the alloy electrode. Thus, the coefficients D(25 °C) = 2 · 10−16 cm2 s−1 of bulk and D' (25 °C = 5 · 10−8 cm2 s−1 of grain boundary diffusion, as well as their activation energies were determined.
Supercritical‐Fluid Extraction Calculations for High‐Boiling Petroleum Fractions Using Propane. Application of Continuous Thermodynamics
Authors: Cotterman Ronald L. , Dimitrelis Dimitrios , Prausnitz John M.
Published: July 2012

Supercritical‐fluid extraction is a useful process for upgrading heavy multicomponent mixtures such as high‐boiling petroleum fractions. Design‐oriented calculations are reported for an extraction process using propane to extract intermediate components from a petroleum fraction with molecular weights in the range 150‐−500. The composition of the heavy‐hydrocarbon mixture is described by two continuous distribution functions of molecular weight, one for paraffinic and one for aromatic components. Process calculations are based on a recently developed thermodynamic framework for mixtures with very many components, coupled with an equation of state of the van der Waals form. Particular attention is given to multicomponent phase equilibria in the retrograde region where solvent recovery is favorable. Quantitative results are given for solvent capacity and selectivity as a function of operating conditions.
Physicochemical Properties of Supercritical Solvents (Invited Lecture)
Authors: Franck E. U.
Published: July 2012

A survey is given of selected thermophysical properties of supercritical solvents which have been determined more recently and which may have technical interest. The static dielectric permittivity of water and of supercritical water‐benzene mixtures to 400°C and several 1000 bar is shown. The transport properties viscosity and thermal conductivity of water at high pressures and extending into the supercritical region are discussed. Of binary systems anthracene as a model solute in ten different highly compressed sub‐ and supercritical fluids is discussed and results presented as “enhancement” factors and virial coefficients B12. Critical curves of binary aqueous systems are shown and methods for calculations indicated. The binary systems water‐nitrogen and water‐oxygen were determined to 2000 bar and excess volumes of water‐methane and water‐benzene measured and calculated.
Chromatography with Mobile Phases in the Liquid and the Supercritical State
Authors: Schmitz Franz P. , Leyendecker Dietger , Klesper Ernst
Published: July 2012

A comparative study on the chromatographic properties of the alkanes n‐pentane, n‐butane, iso‐butane, and propane in the liquid and the supercritical state has been performed using silica gel as the stationary phase and four condensed aromatic compounds as the substrates. At supercritical conditions, chromatographic parameters can be influenced by temperature and pressure to a greater extent than at liquid conditions. Both the capacity ratios and overall resolutions reach maximum values at supercritical state. The maxima become more pronounced with decreasing critical temperature of the mobile phase. The possibilities for optimizing a chromatographic analysis with supercritical eluents are considerable.
Experimental and Theoretical Investigations of the Second‐Order Zero Field Splitting Parameters of Mn(II) with Cl− as Ligand
Authors: Heming M. , Remme S. , Lehmann G.
Published: July 2012

Zero field splitting (ZFS) parameters for [MnCl6]4‐ in three Cd compounds were determined and the validity of the superposition model was demonstrated by the consistent values of the intrinsic ZFS parameter b̄2 in all three cases as well as by a detailed comparison of the experimental ZFS pattern for one compound with that calculated from the crystal structure data. Additional ZFS data for [MnCl6]4‐ from the literature are also shown to lead to only slightly variable values of b̄2. – The change of the intrinsic ZFS parameter b̄2 from a negative value for F− to a larger positive value for Cl− as ligand is shown by detailed calculations for the various mechanisms to be due to the superponable overlap and covalency contributions as a result of increased charge transfer and ligand spin‐orbit coupling constant. The reliability of such calculations is still limited by the lack of experimental data for the transferred spin densities.
The Structure of the Formic Acid Molecule in the Liquid State from Neutron Diffraction Measurements Involving Five Isotopically Different Species
Authors: Bertagnolli H. , Chieux P. , Hertz H. G.
Published: July 2012

Neutron diffraction experiments on liquid formic acid of the five isotopically different forms DCOOD, DCOOH, HCOOD, 0.36 DCOOD + 0.64 DCOOH, and 0.36 DCOOD + 0.64 HCOOD were performed. Inelastic scattering corrections had to be performed in a particularly careful way considering that H is a strongly incoherent scatterer. From the five corrected coherent cross sections and the corresponding weighted sums of pair correlation functions a first set of intramolecular structure data is derived. A suitable decomposition of the primary experimental material in selected groups of pair correlation functions served to work out further structural details which showed that formic acid in the liquid state is a molecule for which the OH group is rotated by about 50° out of the molecular plane.
Excess Molar Enthalpies, Excess Molar Heat Capacities and Excess Molar Volumes of (Fluorobenzene + an n‐Alkane)
Authors: Roux A. H. , Grolier J.‐P. E. , Inglese A. , Wilhelm Emmerich
Published: July 2012

A flow microcalorimeter of the Picker design was used to measure excess molar enthalpies HE at 298.15 K of {x1C6H5F + x2n‐ClH2/+2} for l = 6, 7, 8, 10, 12, 14 and 16. The calorimeter was used in the discontinuous mode. The actual mole fractions x1 were determined with the aid of a vibrating‐tube densimeter connected to the outlet of the mixing cell in conjunction with density data measured separately. The imprecision of the measurements is characterized by s(HE)/H < 0.005, where s(HE) denotes the standard deviation from a Redlich‐Kister type smoothing equation, and the subscript max indicates the maximum of HE with respect to composition. At the same temperature and for the same mixture, excess molar volumes VE were determined with a vibrating‐tube densimeter (flow conditions). With one exception (i.e. l = 6), s(VE)/V < 0.007. Another type of flow calorimeter was used to measure excess molar heat capacities C at constant pressure of mixtures belonging to the same series with l = 7, 8, 10, 12 and 14. In all cases s(C)/CP,minE < 0.013, where min indicates the minimum of C. A preliminary discussion of the results is presented in terms of the simplest version of the Guggenheim‐Barker‐Kehiaian group‐contribution theory.
Bone morphogenetic proteins regulate hinge point formation during neural tube closure by dynamic modulation of apicobasal polarity
Authors: Eom Dae Seok , Amarnath Smita , Fogel Jennifer L. , Agarwala Seema
Published: August 2012

BACKGROUND

A critical event in neural tube closure is the formation of median hinge points (MHPs) and dorsolateral hinge points (DLHPs). Together, they buckle the ventral midline and elevate and juxtapose the neural folds for proper neural tube closure. Dynamic cell behaviors occur at hinge points (HPs), but their molecular regulation is largely unexplored. Bone morphogenetic proteins (BMPs) have been implicated in a variety of neural tube closure defects, although the underlying mechanisms are poorly understood.

METHODS

In this study, we used in vivo electroporations, high‐resolution microscopy, and biochemical analyses to explore the role of BMP signaling in chick midbrain neural tube closure.

RESULTS

We identified a cell‐cycle–dependent BMP gradient in the midbrain neural plate, which results in low‐level BMP activity at the MHP. We show that although BMP signaling does not have a role in midbrain cell‐fate specification, its attenuation is necessary and sufficient for MHP formation and midbrain closure. BMP blockade induces MHP formation by regulating apical constriction and basal nuclear migration. Furthermore, BMP signaling is critically important for maintaining epithelial organization by biochemically interacting with apicobasal polarity proteins (e.g., PAR3). As a result, prolonged BMP blockade disrupts apical junctions, desegregating the apical (PAR3+, ZO1+) and basolateral (LGL+) compartments. Direct apical LGL‐GFP misexpression in turn is sufficient to induce ectopic HPs.

CONCLUSIONS

BMPs have a critical role in maintaining epithelial organization, a role that is conserved across species and tissue types. Its cell‐cycle–dependent modulation in the neural plate dynamically regulates apicobasal polarity and helps to bend, shape, and close the neural tube. Birth Defects Research (Part A) 2012. © 2012 Wiley Periodicals, Inc.