bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Temperature Reaction Rate for H + O2 = OH + O and OH + H2 = H2O + H
Authors: Frank P. , Just Th. 
Published: July 2012

AbstractShock heating together with atomic resonance absorption spectrometry (ARAS) was used to record simultaneously H‐ and O‐atom concentration profiles in the post‐shock region behind reflected shocks. The dissociation of N2O together with the reaction O + H2 = OH + H was used as a source of H and OH for the reactions H + O2 = OH + O and OH + H2 = H2O + H. The test gas mixtures consisted of argon with relative concentrations of a few ppm N2O and 100 to 500 ppm H2 and O2. The experiments were conducted in the temperature range of 1700 to 2500 K at total densities of 6 · 10−6 to 1.3 · 10−5 mol cm−3. The following rate coefficients were deduced:

For temperatures below 2500 K nearly complete agreement with the value for the rate coefficient of reaction R1 as recommended by Baulch [1] was obtained. For reaction R2 a rate coefficient was deduced which is close to the value as given by Gardiner et al. [23].
Diffusion Controlled Atom Recombination and Photolytic Cage Effect of Halogens in Compressed Gases and Liquids
Authors: Hippler H. , Otto B. , Schroeder J. , Schubert V. , Troe J. 
Published: July 2012

AbstractPhotolysis quantum yields and atom recombination rate constants were measured for iodine and bromine at pressures of up to 7 kbar in both the dense gas and liquid phase employing a variety of solvents. The results are analyzed in terms of a simple model which uses empirical parameters to describe cage break‐out, competition between diffusive separation of atom pairs and cage energy relaxation, and stabilization in halogen molecule‐solvent clusters. This enables us to single out the dominant processes governing escape versus recombination efficiencies in the different density regimes.
Kinetics of OH(v = 0 and 1) and OD(v = 0 and 1) Studied by Time‐Resolved Laser‐Induced Fluorescence
Authors: Smith Ian W. M. , Williams Martin D. 
Published: July 2012

AbstractCoupled with pulsed photochemical generation of OH (and OD), laser‐induced fluorescence has been used to study the kinetics of OH(v = 0 and 1) and OD(v = 0 and 1) with HCI, DCI and CO.
Study of OH Reactions at High Pressures by Excimer Laser Photolysis — Dye Laser Fluorescence
Authors: Schmidt V. , Zhu G. Y. , Becker K. H. , Fink E. H. 
Published: July 2012

AbstractReactions of hydroxyl radicals have been studied up to total pressures of 1 atm and in the presence of strongly quenching gases by using excimer laser photolysis of H2O2 or HNO3 for the generation and pulsed dye laser fluorescence for monitoring the concentration of the radicals as a function of reaction time. Results are reported of a study of the effects of molecular oxygen on the reactions of OH with acetylene and with some sulfur containing compounds (e.g. CS2).
The Reaction of OH with C2H2 at Atmospheric Conditions Investigated by CW‐UV‐Laser‐Longpath‐Absorption of OH
Authors: Wahner Andreas , Zetzsch Cornelius 
Published: July 2012

AbstractA sensitive CW‐UV‐laser absorption method at 308 nm has been used to investigate the pressure dependence of the kinetics of OH reactions with C2H2. OH radicals are generated by excimer laser photolysis of H2O at 193 nm or of H2O2 at 248 nm. Using an absorption light path of 151 m and accumulating 50 decay curves, OH concentrations in the range from 1010 down to 107 cm−3 can be detected in the presence of N2 at 10–1000 mbar. The experimental data on the pressure dependence of the rate constant for the reaction of OH with C2H2 in N2 yield the limiting values (at room temperature):

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The Study of Reactions of HO2 Radicals by Mid‐Infrared Laser Spectroscopy
Authors: Salmon T. M. F. , Thrush B. A. , Tyndall G. S. 
Published: July 2012

AbstractIn principle, infrared lasers provide specific methods for detecting all reactive species in the gas phase, except for free atoms. This paper compares the use of tunable diode lasers and mid‐infrared laser magnetic resonance in the study of reactions of HO2 using its v3 band at 1100 cm−1.
Laser Induced Fluorescence Studies on C2O and CH Radicals
Authors: Bauer W. , Becker K. H. , Meuser R. 
Published: July 2012

AbstractC2O and CH radicals were quantitatively analysed by LIF in the reaction systems C3O2 + O + H and C2H2 + O + H. The measurements of rate constants and products of the reaction C2O + O as well as C2O + H have been carried out by excimer laser pulse photolysis for the production and by LIF for the detection of the radicals. The results give a basis of a new interpretation of the C2H2 + O + H atom flame system.
A Direct Study of the Reactions of CH2 (X̃ 3B1)‐Radicals with Selected Hydrocarbons in the Temperature Range 296 K ≤ T ≤ 705 K
Authors: Dóbé S. , Böhland T. , Temps F. , Wagner H. Gg. 
Published: July 2012

AbstractThe kinetics of the reactions of CH2 (X̃ 3B1)‐radicals with five selected organic compounds has been studied in an isothermal discharge flow system in the temperature range 296 K ≤ T ≤ 705 K. Ground state CH2‐radicals have been generated via the reaction O + CH2CO and monitored with a far infrared laser magnetic resonance spectrometer. The experimental results are described by the following Arrhenius expressions:

Two basic reaction mechanisms, either direct H‐atom abstraction by 3CH2 or thermal excitation of 3CH2 to the low lying ã 1A1 state followed by consecutive reactions of 1CH2, are of importance. For acetaldehyde, isobutane, and propane direct H‐atom abstraction by 3CH2 predominates. After separation of the small contribution attributed to the singlet reaction the following rate constants for the reactions of CH2 (X̃3B1) with acetaldehyde, isobutane, and propane are obtained:

Presuming the reactions of 1CH2 with hydrocarbons are fast the thermal excitation mechanism dominates the reaction system in the cases of methane and ethane. The activation energy of EA (CH4) = 40 ± 8 kJ/mol measured for methane is concluded to he determined by the singlet‐triplet energy splitting in CH2.
p,T,c‐Dependence of 2H Spin‐Lattice Relaxation Rates in Supercooled LiCl‐D2O Solutions
Authors: Lang E. W. , Lüdemann H.‐D. 
Published: July 2012

AbstractLong‐ranged structural correlations develop within the random, transient hydrogen‐bonded network of liquid water at low temperatures and cause characteristic anomalies in the physical properties of supercooled water. Hydrostatic pressure suppresses these anomalies and turns liquid water into a normal viscous liquid. The addition of salt‐is considered another mean to suppress long‐ranged density‐density correlations, hence the pressure‐, temperature and composition dependence of deuterium (2H) spin‐lattice relaxation times (T1) is reported for supercooled LiCl‐D2O solutions over a large range of concentration (c ≤ 11 molal), pressure (p ≤ 226 MPa) and temperature (180 K ≤ T ≤ 283 K). The anomalous pressure dependence of the spin‐lattice relaxation times becomes weaker with increasing salt concentration
Dispersed Systems ‐ Recent Developments
Authors: Ottewill R. H. 
Published: July 2012

AbstractDirect methods for determining the electrostatic force of interaction between molecularly smooth mica plates are compared with a less direct method (osmotic pressure) of determining the forces between particles (flat plates) in a colloidal dispersion. It is shown that macroscopic surfaces and particles exhibit similar behaviour the common link being the range of the interaction forces; the range is very large in low salt concentrations compared with atomic size. For concentrated dispersions of spherical particles small angle neutron scattering can be used to determine the nature of the interaction forces. In addition this enables the structure of the system to be determined in terms of the pair distribution function g(r). From the latter and the interaction pair potential it becomes possible to predict the bulk properties of the system.
Morphology of Complex Boundaries
Authors: Richter Peter H. , Peitgen Heinz‐Otto 
Published: July 2012

AbstractThe dynamics of physical or mathematical systems may follow simple rules and yet unfold in enormous complexity. Thanks to computer graphical experimentation we are beginning to detect universal scenarios some of which are reviewed here. The emphasis is on the formation of boundaries between different modes of behavior, or between basins of attraction in systems with competitive dynamics.
Visualization of Organized Structures in Buoyant Diffusion Flames
Authors: Schönbucher A. , Brötz W. , Balluff Ch. , Riedel G. , Kettler A. , Schieß N. 
Published: July 2012

AbstractIn pool fires of liquid hydrocarbons static equidensitometric structures (2 types) and dynamic radiance structures (18 types) are obtained from flame photograms evaluated with an image analysis computer system. A third kind of structures, the dynamic synchronous structures (9 types) are visualized with a holographic real‐time interferometry method. ‐ The control parameters of the observed structures are the pool diameter, the height above the fuel surface, the density of the fuel vapor and the volumetric fuel flow rate. ‐ The dynamic radiance structures have 4 monoperiodic subprocesses with a frequency of 12 Hz (n‐hexane pool fire, d = 4.6 cm) which depend strongly on the pool diameter and show 18 statistical characteristics. The dynamic synchronous structures of the same pool fire show a quasiperiodic region I with 7 sub‐processes at 11, 13 and 3 Hz. In a quasiperiodic region II, 8 sub‐processes exist at the frequencies 11, 12, 13, 39 and 41 Hz. In addition there are 17 statistical characteristics. ‐ The effects of the observed dynamic structures on turbulent exchange processes in pool fires are calculated and lead to turbulent Prandtl‐, Schmidt‐ and Lewis‐numbers between 0.3 and 1.
Non‐Linearities in Chemical Reactions. Temporal and Spatial Structures; Efficiency
Authors: Ross John 
Published: July 2012

AbstractExperiments and theory are reviewed on systems with multiple stable states, stabilization of unstable stationary states, oscillations, inverted Hopf bifurcations, the velocity and structure of chemical fronts and waves including the constancy of the profile in time, and structure formation in precipitation processes. Reduction of dissipation is shown possible in nonlinear systems compared to stationary state operation, by means of external periodic perturbations or oscillatory conditions, and is illustrated with thermal and biochemical engines (glycolysis).
Effects of Global Constraints on Permissible Local Behavior
Authors: Noyes Richard M. 
Published: July 2012

AbstractIf two composition variables X and Y are sufficient to define both the thermodynamic and dynamic states of a system with acceptable accuracy, any such state can be represented by a point in a bounded region of the positive quadrant of the X‐Y plane. Any stationary state within that region must belong to one of seven behavior classes, one of which is a double degeneracy that will probably never the encountered. The other six behavior classes are illustrated by well established models. Assignment of behavior class for a specific system can be made from the dynamic parameters for local behavior by using the signs and relative magnitudes of the trace and determinant of the secular equation. An entirely equivalent assignment can be made if two of the rate constants are replaced by the directions of the X and Y nullclines at the intersection which generates the stationary state. Although the secular equation is based solely on local behavior, the use of nullcline directions permits that local behavior to be impacted by global thermodynamic constraints. Such considerations show that the Lotka model with irreversible steps does not satisfy the thermodynamic constraints for a real chemical system, and only a very fortuitous combination of rate constants would permit the steady state to become the conservative center generated by the irreversible mechanism. The irreversible Brusselator model also fails to satisfy the thermodynamic constraints on a real chemical system, but the difficulty can be resolved by inclusion of reversibility. The irreversible Oregonator and Berlinator models satisfy the global constraints even with virtually no attention to reversibility.
The Development of a Model for the Cooperative Behavior of Palladium Crystallites During the Catalytic Oxidation of CO
Authors: Jaeger N. I. , Möller K. , Plath P. J. 
Published: July 2012

AbstractThe complex product oscillations in the catalytic oxidation of carbon monoxide on a zeolite supported palladium catalyst are analyzed by reconstructing the time series in 3‐dimensional phase space. A mathematical model is proposed based on a cellular automaton corresponding to a discrete version of the Sierpinsky‐gasket.
Slow Fluctuations between Attractors in a Forced Chemical Oscillator: The Belousov‐Zhabotinsky Reaction in the CSTR
Authors: Freund A. , Buchholtz F. , Schneider F. W. 
Published: July 2012

AbstractLongtime measurements in a isothermal CSTR over 25–30 residence times (100 oscillations) showed that at least two oscillators (attractors) exist together with their combination bands in the Fourier spectrum of the unperturbed (constant in‐flow) Belousov‐Zhabotinsky (BZ) oscillations. Slow and large fluctuations in successive power spectra were observed. They are due to transitions between attractors and do not represent chaos. Such slow fluctuations were also observed in the quasi‐periodic region but not in the entrained state of the sinusoidally perturbed BZ reaction. From previous experiments we show entrainment of order 2 (superharmonic) and 1/2 (subharmonic) as examples. The extreme sensitivity of the Fourier spectra with respect to slight changes in the forcing period (0.2–0.3%) is noteworthy.
The Diversity of Biochemical Time Patterns
Authors: Hess Benno , Markus Mario 
Published: July 2012

AbstractThe effects of coupling of oscillating glycolysis and oscillating substrate supply are investigated with a two‐enzyme model using detailed two‐substrate rate laws for both enzymes. Under a sinusoidal substrate supply rate, a profusion of entrained, quasiperiodic and chaotic regimes is obtained. Periodic modulation of the sinusoidal supply rate may lead to a considerable enhancement of the degree of randomness in the chaotic regime. Up to four coexisting attractors are found in phase space for a given set of control parameters, having complicatedly interleaved basins of attraction. Switching between such coexisting attractors is accomplished by pulsed substrate fluctuations that drive the system from one basin of attraction to the other. The effect of a series of substrate fluctuations with randomly distributed amplitudes is investigated, allowing the following distinction of cases: 1. For small fluctuations, the system stays within a given basin thus preserving the initial time pattern. 2. For larger fluctuations, an evolution takes place by which the system reaches a basin that cannot be left, thus displaying a time pattern that is fittest to withstand the external stochasticity. 3. For even larger fluctuations, the system is driven back and forth between the basins, displaying an intermittent switching between time patterns. 4. For still larger fluctuations, the system is switched between the basins, staying always so far from the attractors that it can be considered as an amplifier of random fluctuations.
Dynamics of Evolutionary Optimization
Authors: Schuster Peter , Sigmund Karl 
Published: July 2012

AbstractGeneral criteria of selection are derived from the kinetic equations of polynucleotide replication. As an illustrative example we discuss replication in the continuously stirred tank reactor (CSTR). The total rate of RNA synthesis is optimized during selection. The conjecture that the rate of approach towards the stable steady state is a maximum can be easily disproved. It is possible, nevertheless, to derive a potential function for polynucleotide replication in the CSTR. Following a method first introduced by Shahshahani we define a non Euclidean metric on the space of polynucleotide concentrations. In this space with a Riemannian metric the systems follows the corresponding generalized gradient during the process of selection and, therefore, the rate of ascent is now maximum. Potential functions can be derived also for some second order autocatalytic systems which are of interest in evolution, for a multidimensional Schloegl model in the CSTR and, as originally has been shown by Shahshahani, for the Fisher‐Haldane‐Wright equation of population genetics. In the general case, however, second order autocatalysis is not compatible with the existence of a potential. The elementary hypercycle is discussed as one simple example of a reaction network whose dynamics cannot be described by means of a generalized gradient system. Finite population size introduces a stochastic element into the selection process. Under certain conditions fluctuations in particle numbers become extremely important for the dynamics of selection. Two examples of this kind are: kinetic degeneracy of rate constants and low accuracy of replication.
Dielectric Properties of Polyelectrolyte Solutions Behaviour of Aqueous Solutions of Carboxymethylcellulose with Different Univalent Counterions
Authors: Bordi F. , Cametti C. 
Published: July 2012

AbstractThe dielectric properties of Carboxymethylcellulose in various uni‐univalent electrolyte solutions in the frequency range from 1 KHz to 10 MHz have been measured by means of a conventional impedance bridge technique. — Two contiguous dielectric dispersions, due to different molecular mechanisms, have been observed, in accordance with the usual behaviour of linear, high‐charged polyelectrolytes. — The influence of the molecular weight, polyion concentration and different monovalent counterions (Na+, K+, Li+) has been examinated. — The results are analyzed in terms of rod‐like polyelectrolyte dielectric models taking into account the polarization due to the fluctuation in the counterion concentration.
The H2O/D2O Exchange Across Vesicular Lipid Bilayers. Lecithins and Binary Mixtures of Lecithins
Authors: Engelbert H.‐P. , Lawaczeck R. 
Published: July 2012

AbstractA new method to measure the water (D2O/H2O) permeation across vesicular lipid bilayers is described. The method is based on the solvent isotope effect of the light scattering which is a consequence of the different indices of refraction of D2O and H2O. Unilamellar lipid vesicles in excess of H2O are rapidly mixed with D2O or vice versa. As result of the H2O/D2O exchange across the vesicular bilayer the light scattering signal has a time dependent, almost single exponential component allowing the deduction of the exchange relaxation rate kex and, at known size, of the permeability coefficient, Pd. The experimental results are in accord with calculations from the Mie theory of light scattering for coated spheres. The method is applicable for large vesicles where the permeation is the rate‐limiting step. Size separations are performed by a flow dialysis through a sequence of pore‐membrane‐filters. For dimyristoyl‐lecithin bilayers the water permeability‐coefficient is 1.9 · 10−5 cm/s in the crystalline phase and increases by a factor of 10–100 in the liquid‐crystalline state. The temperature dependence of the permeation exhibits a sharp change at the phase transition. For binary mixtures of lecithins this sharp change follows the solidus curve of the non‐ideal phase diagram determined by spectroscopic techniques.
UCl4 Compound: Determination of High Temperature Phase Transitions from Electrical Conductivity and Calorimetric Measurements
Authors: Fouque Y. , Bros J. P. , Gaune‐Escard M. , Wisaniowski M. , Bogacz A. 
Published: July 2012

AbstractIn the course of a systematic investigation of some compounds of uranium (IV), several physico‐chemical methods have been applied to the salts of the series UX4 and M2UX6 (with X = Cl, Br, I and M = Li, Na, K, Rb, Cs). ‐ The results obtained in the present work refer to UCl4; they have been obtained by electrical conductivity measurements, by differential thermal analysis and by differential enthalpic analysis.
Ternary Diffusion of Carbon Dioxide in Alkaline Solutions of Aqueous Sodium Hydroxide and Aqueous Sodium Carbonate
Authors: Leaist Derek G. 
Published: July 2012

AbstractCarbon dioxide dissolved in alkaline solutions diffuses as bicarbonate and carbonate ions produced by the reactions CO2 + OH− = HCO−3 and CO2 + 2OH− = CO2‐3 + H2O. Ternary diffusion coefficients of the systems NaHCO3 + Na2CO3 + H2O and Na2CO3 + NaOH + H2O have been measured by a conductimetric technique at 298.15 K. The mixed electrolyte data are transformed by use of the solution equilibria to ternary diffusion coefficients of the systems CO2 + Na2CO3 + H2O and CO2 + NaOH + H2O. Unlike the binary diffusivity of CO2 in water (1.9 · 10−9 m2 s−1), the ternary diffusivity of CO2 in alkaline solutions is sensitive to concentration and varies from 0.9 · 10−9 to 3.5 · 10−9 m2 s−1 at 298.15 K. Expressions are derived to estimate the transport coefficients of the components from the concentrations and diffusion coefficients of the constituent ions. At high pH values hydroxide‐coupled transport leads to rapid diffusion of CO2 as CO2‐3. The results are consistent with the Onsager reciprocal relation for isothermal ternary diffusion.
Excess Molar Heat Capacity of (1,2‐Dichloroethane + Benzene) Revisited
Authors: Lainez A. , Grolier J.‐P. E. , Wilhelm Emmerich 
Published: July 2012

AbstractExcess molar heat capacities CEP at constant pressure were measured, as a function of mole fraction x1 at 298.15 K, for {x1 1,2‐C2H4Cl2 + x2C6H6}. Determinations in the regions x1 < 0.1 and x1 > 0.9 were emphasized. The instrument used was a Picker flow calorimeter. The new data corroborate our results of 1977 [2]: CEP shows only one minimum at about x1,min = 0.4595, and CEP (x1,min) = ‐ 1.165 J K−1 mol−1. The “inverted” W‐shaped composition dependence of CEP, as inferred by Baños et al. [9] from their measurements of excess enthalpies between 288.15 and 318.15 K, is thus shown to be untenable.
Aggregation of an Azo Dye in Aqueous Solution
Authors: Hamada Kunihiro , Kubota Hiroyuki , Ichimura Ayako , Lijima Toshiro , Amiya Shigetoshi 
Published: July 2012

AbstractThe investigation of the aggregation of a simple monoazo dye carrying fluorine atoms was performed by means of 19F nuclear magnetic resonance Spectroscopy. — As the concentration of the dye increased, the signals of the fluorine showed progressive shifts to the higher field. From the changes in shift it is concluded that the fluorine atoms are oriented above an adjacent aromatic nucleus. The results of the visible absorption Spectroscopy indicate that the dye solutions are a polydispersed system. The equilibrium constant of the aggregation was estimated dn the basis of an isodesmic model. A molecular model of the aggregates was proposed.
Picosecond‐Absorption Study of the Photoisomerization of Trans‐Stilbene in Compressed Gases and Liquids
Authors: Maneke G. , Schroeder J. , Troe J. , Voß F. 
Published: July 2012

AbstractThe photoisomerization of trans‐stilbene after picosecond excitation at 308 nm has been studied by picosecond absorption at 500 or 616 nm in ethane and propane. Experiments were performed in gaseous ethane (30–54 bar), liquid ethane (42–6000 bar), and liquid propane (9–4050 bar). The pressure dependence of the reaction is modelled from isolated molecule conditions in low pressure gases up to diffusion control in high pressure liquids. In dense media marked solvent shifts of the reaction threshold energy are postulated which can be described by simple cluster — and cage — solvent shift models. UV spectra show similar solvent shifts as isomerization rates.