bluuebunny/crossref_metadata_2025_split huggingface dataset:
Raman Spectrometric Study of the Composition of Sulfur Vapor at Temperatures up to 700°C
Authors: Lenain Pascal , Picquenard Eric , Corset Jacques , Jensen Detlef , Steudel Ralf 
Published: March 2014

AbstractSulfur vapor has been investigated by Raman spectroscopy in a wide temperature and pressure range (300 to 900°C, 0.05 to 0.5 MPa for overheated vapor and 0.007 to 1.65 MPa for saturated vapor). At least eight different species have been observed through their characteristic Raman lines. Well separated Raman lines have been selected for the observation of the change in vapor composition with temperature: symmetrical bending modes for the cyclic species S8, S7, and S6 and stretching modes for the chain‐like species S3 and S2. There are indications for the presence of two conformational isomers of S4, and in addition a new species has been discovered by its resonance Raman line at 635 cm−1 which is tentatively assigned to chain‐like molecules Sn (n > 4) of helical conformation. Several relationships between the thermodynamic properties of the vapor and the Raman measurements are proposed, e.g., the determination of the temperature at which the molar fraction xi is maximum for the overheated vapor at constant pressure; estimation of the xi/x8 ratios using solution measurements of the Raman cross section for the molecules S8, S7, S6. A careful comparison of these results with the values deduced from Rau's model results in good agreement for the behavior of most of the species apart from S7 which is underestimated in Rau's model. S7 is the dominating species in saturated sulfur vapor above 600 K until S2 takes over at ca. 1000 K.
Evidence for Spinodal Decomposition in a Single Component Fluid
Authors: Klein H. , Schmitz G. , Woermann D. 
Published: March 2014

AbstractExperimental conditions are reported under which scattering patterns characteristic for spinodal decomposition have been observed in a single component fluid, sulfur hexa‐fluoride (SF6). Analysis of the data shows that the development of the ring shaped patterns is consistent with the requirements of spinodal decomposition within the accuracy of the measurements.
Effect of Pressure on the Hydrogen‐Bond Formation III. Phenol‐Tertiary Amines and ‐Acetates in n‐Hexane
Authors: Sawamura S. , Taniguchi Y. , Suzuki K. 
Published: March 2014

AbstractThe effects of pressure on the hydrogen‐bond (H‐bond) formations between phenol as a proton donor and tertiary amines (Et3N, n‐Pr3N, and n‐Bu3N) or acetates (MeOAc, EtOAc, n‐PrOAc, and n‐BuOAc) as proton acceptors in n‐hexane were studied by means of the UV absorption spectroscopy up to 640 MPa at 25°C. The reaction volumes (ΔV) for H‐bond formations at 0.1 MPa were −10.7, −7.7, −8.0, −3.5, −4.2, −1.1, and −2.5 cm3 mol−1, respectively. These observed ΔV values were related to the theoretical ΔVest calculated by the extended Hamann's method. The method is applicable to the determination of the ΔV for the other molecular complex formations.
Liquid‐Liquid Extraction of Copper by Terdodecylthioglycolic Acid. Structures for the Extracted Species
Authors: Beneitez P. 
Published: March 2014

AbstractThe extraction of Cu(II) from nitrate medium by dodecylthioglycolic acid and the influence of buffered medium on that extraction have been studied at 293 K. Distribution of the metal ion in a wide range of pH and carboxylic acid concentration has been measured. Experimental data, treated by a graphical method have been interpreted by assuming the presence in the organic phase of the species CuDTG2 · HDTG2 and CuDTGAc · HDTG2. Characterization and structure of the solid compounds isolated from the extract have been discussed on the basis of elemental analysis, thermal gravimetric analysis, IR spectra and measurement of magnetic susceptibility.
Zur unimolekularen β‐Spaltung großer n‐Alkylradikale
Authors: Olzmann M. , Scherzer K. 
Published: March 2014

AbstractThermal fall‐off curves for ethylen split‐off from higher alkyl radicals are calculated on the basis of RRKM theory and an empirical representation of weak collision effects. It is shown that rate constants under conditions of industrial pyrolysis do not reach their high pressure limit.
Measurements of Dielectric Permittivity Near the Consolute Critical Point of Methanol‐Cyclohexane Mixture
Authors: Orzechowski Kazimierz 
Published: March 2014

AbstractThe dielectric permittivity as a function of temperature and frequency for a near critical methanol + cyclohexane mixture was investigated. A low frequency dispersion (fr = 150 kHz) was found which is usually interpreted in terms of the Maxwell‐Wagner polarization. The “static” dielectric constant was measured at 2000 kHz, and a decrease of the |dϵ/dT| value close to Tc was observed. The critical properties of the ϵ · v product (where ϵ is the static dielectric constant, and v is the specific volume) was described in terms of the Sengers et al. model. The results yield the critical exponent 1 – α = 0.89, rather than 2β = 0.65. Neglecting the specific volume anomaly leads to a slight decrease of the obtained exponent value.
Defect Structures in Membranes: Routes for the Permeation of Small Molecules
Authors: Lawaczeck R. 
Published: March 2014

AbstractTransient defect structures in thermodynamic equilibrium with the membrane lattice are considered to be major pathways for the passive permeation of small and neutral (with the possible exception of protons) molecules. Results on the water permeation and on the transfer of protons across erythrocyte membranes are discussed. The inhibition/stimulation of transport rates is interpreted in terms of specific or global actions of the inhibitory/stimulatory molecules on lipid/protein and protein/protein assemblies.
Interaction of Ganglioside and Glycoprotein Carbohydrates with Membrane Surfaces
Authors: Ollmann M. , Tampé R. , Winter A. , Wohlfart P. , Galla H.‐J. 
Published: March 2014

AbstractElectron spin resonance techniques were employed to investigate the interaction of sialic acid bearing carbohydrates covalently bound to gangliosides or glycophorin with membrane surfaces. In phosphatidylcholine membranes it was found that gangliosides induce a rigidification. This hydrophobic effect is partially compensated by a hydrophilic interaction with the membrane surface. In phosphatidylethanolamine membranes ganglioside GD1a is the only one that reduces the lipid phase transition temperature. We assume a special oligosaccharide conformation, that strongly disturbs the hydrogen bond network of the PE host membrane. The results are further supported by experiments with reconstituted glycophorin containing membranes. In a phosphatidylcholine matrix we observed the formation of an immobilized lipid domain that surrounds the protein. Phosphatidylethanolamines within a phosphatidylcholine membrane are excluded from such a domain. This is also interpreted by the formation of hydrogen bonds between sialic acid groups of the protein and the amino functions of the lipid headgroups.
Structural Fluctuations of Polypeptides in Lipid Membranes
Authors: Vogel Horst , Nilsson Lennart , Rigler Rudolf , Voges Klaus‐Peter , Jung Günther 
Published: March 2014

AbstractTime‐resolved fluorescence anisotropy (FA) measurements are reported for five helical, bilayer spanning heneicosapeptides, each containing one Trp at sequence position 1, 6, 11, 16, and 21, respectively. The FA decay reflects two molecular processes in all cases, local internal fluctuations of the Trp side chain with a relaxation time of 200–500 ps and motions of the whole polypeptide molecule with a relaxation time of 9–10 ns. Concomitant molecular dynamics calculations indicate a correlation between the fast FA decay and conformational fluctuations within the helix.
Light Stimulated Ion Fluxes Across the Plasma Membrane of Photoreceptors
Authors: Rüppel H. , Cieslik J. 
Published: March 2014

AbstractIn vertebrate photoreceptors the main step of signal transduction process occurs at the plasma membrane of the outer segments. In darkness Na+‐ and Ca++‐ions are passing this membrane. There is an influx of Na+ but no net flux of Ca++‐ions. After a light pulse the Na+‐current is transiently reduced and the outer Ca++‐concentration increased. By diffusion the Ca++‐ions are rapidly distributed
Studies on the Intrinsic Membrane Proteins of Photosystem II from Spinach
Authors: Irrgang K.‐D. , Hanssum B. , Renger G. , Vater J. 
Published: March 2014

AbstractThe key reactions of photosynthetic water oxidation by visible light take place in photosystem II. Here we report on our recent results about functional studies on a transmembrane pigment‐protein complex of photosystem II. Using O2‐evolving PSII membrane fragments from spinach we isolated the intrinsic membrane proteins and investigated the effect of solubilization with three different non‐ionic detergents, β‐dodecylmaltoside (β‐DM), Triton X‐100 and β‐N‐octylglycopyranoside (β‐NOGP), on two parameters:
77 K fluorescence emission and II. PSII electron transport (DPC → DCIP). The following results were obtained:
All the detergents dramatically modified the 77 K fluorescence emission spectra at/or near their critical micelle concentrations (CMC).
The yield per flash or rate of DCIP‐reduction as an indicator of electron transport activity markedly depended on the type and concentration of the detergent. β‐NOGP caused a decrease of the electron transfer already below its CMC, whereas β‐DM and Triton X‐100 did not reveal a distinct modification at submicellar concentrations. In the case of β‐NOGP the half‐maximum activity is observed at about 20 mM.
On the basis of a simple model assuming an apparent equilibrium between only two stable states (non‐solubilized and β‐NOGP‐solubilized PSII intrinsic membrane proteins) we calculated an apparent equilibrium constant Keq to 48.2 and a free solubilization energy of ΔGsol = −9.6 kJ/mol.

The results are discussed with special emphasis on two questions: a) To what extent have the polypeptide subunits and the pigment and redox group arrangement the same structure and configuration in detergent‐solubilized state as in the thylakoid membrane and PSII membrane fragments, respectively? b) How can we interprete the solubilization properties of the different detergents on the basis of their physical and chemical features and the structural architecture of the PSII membrane fragments?
Reactions of Ba Atoms with NO2, O3 and Cl2: Dynamic Consequences of the Divalent Nature of Barium
Authors: Davis H. Floyd , Suits Arthur G. , Hou Hongtao , Lee Yuan T. 
Published: March 2014

AbstractThe role of the divalent nature of barium atoms in chemical reactivity was explored using crossed molecular beams. Angular and velocity distributions of products from reactions of Ba(1S) with NO2 and O3 indicate the existence of long lived collision intermediates despite very large reaction exothermicities. The existence of these intermediates results from barriers to transfer of the second electron necessary to form ground state products. Although BaO was the dominant product in both reactions, two previously unknown channels were observed: Ba + N02 → BaON + O and Ba + O3 → BaO2 + O. We obtained bond dissociation energies of D0(Ba–ON) = 270 ± 80 kJ/mol and D0(Ba – O2) = 500 ± 80 kJ/mol for these molecules. The dependence of the cross sections for the ion channels, Ba(1P) + Cl2 → Ba+ + Cl−2 and Ba(1P) + Cl2 → BaCl+ + Cl− on Ba(1P) orbital alignment and collision energy was used to probe the course of the reaction through intersections between the ionic and covalent potential energy surfaces.
Theoretical Studies of Collision‐induced Energy Transfer in Electronically Excited States
Authors: Alexander M. H. , Berning A. , Esposti A. Degli , Joerg A. , Kliesch A. , Werner H.‐J. 
Published: March 2014

AbstractSome recent theoretical studies of collision‐induced energy transfer in electronically excited states are reviewed. Using accurate ab initio electronic wavefunctions potential energy surfaces have been computed for OH(X2Π, A2Σ+) + He and Ar, Li2 (A1Σu+) + Ne, N2+ (X2Σg+, A2Πu) + He, and CN (X2Σ+, A2Π) + He and used in quantum scattering calculations of cross sections and rate coefficients for rotational, vibrational, and electronic energy transfer processes. In cases where comparison with accurate experimental data is possible, the theoretical and experimental data agree within 20–30 percent.
Molecular Reaction Dynamics – Subdoppler and Polarization Spectroscopy –
Authors: Comes F. J. 
Published: March 2014

AbstractPhotofragmentation spectroscopy, – the study of “half‐collisions” with polarized light of subdoppler band width – opens a window to look into the structure of molecules. A pictorial view of the intermediate state is provided by the analysis of fragment vector properties. The forces which make the fragments fly apart or rotate can be “seen” from the line shapes. Information is gained from the stable products of the fragmentation reaction long after the parent has dissociated. – Hydrogenperoxide as a model example is treated and a complete picture of its fragmentation in the uv is given by the discussion of the various vector correlations. The method is further applied to the fragmentation of hydrazoic acid which shows to have a fairly complex dissociation process.
Size Distribution Studies of Sputtered Transition Metal Cluster Ions by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Authors: Selinger A. , Schnabel P. , Wiese W. , Irion M. P. 
Published: March 2014

AbstractMass spectra of various metal cluster ions, mainly of transition metals are presented. These clusters were sputtered by an external 20 keV Xe+ ion source and detected with a Fourier transform mass spectrometer (FT‐MS). Cluster ions could be efficiently trapped in the ion cyclotron resonance cell (ICR‐cell). In the case of indium, for instance, clusters containing more than 100 atoms could be observed. The sensitivity of our instrument was sufficient to even detect Au+85 cluster ions with mass 16745 u. “Magic numbers” are observed in the cluster cation distributions of indium and the d10S1 metals copper, silver and gold.
Nucleophilic Substitution Reactions in Mixed Organic Clusters after Resonant Two Photon Ionization
Authors: Eggert J. , Janes C. , Wassermann B. , Brutschy B. , Baumgärtel H. 
Published: March 2014

AbstractSubstitution reactions in mixed van der Waals aggregates, consisting of halobenzenes and polar molecules are studied by resonant two‐photon ionization (R2PI). From the optical fingerprints in the ion‐yield curves of the product ions we are able to assign their neutral precursors. The ipso substitution reactions have been found to depend both on the number and type of solvent molecules and on the halogen present and are discussed by an addition‐elimination mechanism. Dissociative electron transfer is found to play an important role in the reaction mechanism and in the size dependence of the reactivity.
Model Calculations on Laser Induced Dissociation of Bromine with Control of Electronic Product Excitation
Authors: Hartke B. , Kolba E. , Manz J. , Schor H. H. R. 
Published: March 2014

AbstractAfter a short survey of different methods to control electronic product excitations in laser‐induced unimolecular dissociations we develop an alternative strategy, adapted to interfering exit channels with potential energy curve crossings, and implement it for the bromine system. In a reference case with zero potential couplings optimal initial population of the competing dissociative states leads to complete product selectivity. In the real system, however, the electronically excited molecules pass the potential energy curve crossing of the B 3Πo + u and 1Π1u states on their way to dissociation, and Landau‐Zener‐type diabatic transitions establish the final product distribution. For this case we discuss the possibility to refine the electronic product distribution by a second, intense laser pulse applied after the curve crossing. Based on these results inversion of experimental product distribution data may be used to determine the curve crossing parameters, thus extending the short range information obtained from Raman scattering. Simulation of laser controlled dissociation is achieved by FFT (fast Fourier transform) propagation of representative wave packets.
Bond‐selective Photoion Correlations (“Memory Effects”) in Molecules from Site‐Specific 1s Excitation Using Synchrotron Radiation
Authors: Jung Rolf , Staub Ralf , Baiter Hermann , Reiser Georg , Habenicht Wieland , Müller‐Dethlefs Klaus 
Published: March 2014

AbstractWe observe bond‐selective photoion‐photoion correlations in the molecules CF2 = CH2 and CF3–CH3 upon site‐specific C (1s) excitation at either the CF or the CH atom. The observed double photoion correlations can be interpreted as a chemical “memory effect” where the fragmentation process memorizes the initial site of energy deposition. A new “Zero Kinetic Energy Photoelectron”‐photoion‐photoion coincidence technique incorporating a high transmission mass spectrometer and a multi‐stop time‐to‐digital converter is employed. The excitation is carried out by monochromatized X‐ray synchrotron radiation from BESSY.
Critical Examination of the Calculus Convolution Kinetics: The Influence of Nonstationary Diffusion on Excimer Formation with Dissociation
Authors: Vogelsang J. , Hauser M. 
Published: March 2014

AbstractIf time dependent rate coefficients (TDRC) appear in reactions, ordinary rate equations (RE) fail. The calculus convolution kinetics (CK) provides consistent results in these cases, but its appliance is quite unfamiliar. For rate coefficient(s) (RC) that are time‐independent the results of CK are analytically identical with those of RE, though being obtained on a completely different way. – In this paper the failure of the RE method will be briefly demonstrated with an example. Furthermore the concept of CK will be presented in short and applied on excimer formation. On the level of synthesis data a comparison of the result of the rate equations' treatment with √t‐term obtained numerically, the CK result and measuring data will be carried out. For this the time resolved decay curves of “single photon counting” – measurements and synthesis data of both methods convoluted by flash will be graphically laid on top of each other. It turns out that curves from CK represent the measuring graph better than data of the RE calculated with the same parameters. Larger differences appear in the initial part of the curves with both methods. To explain these differences a new mechanism of excimer formation will be brought into discussion, but also the uncompletness of the Smoluchowski approximation for nonstationary diffusion will be taken into account. – The kinetical treatment given below is an example of excited state kinetics [1]; but CK is not limited on this kind of kinetics.
Statistical and Kinetic Approach to Plasmachemical Reactions
Authors: Haberlandt R. , Stiller W. 
Published: March 2014

AbstractIn order to treat reactive and transport processes in dilute and dense gaseous plasmas a quantum‐statistical formalism is given leading to generalized expressions for reaction rate coefficients. For diluted gaseous plasmas with binary collisions the common Boltzmann equation formalism can be derived; for higher order collisions the pair distribution function has to be considered. – In the framework of the Boltzmann equation formalism for multi‐component diluted gaseous plasmas equations for a reactive Lorentz gas are derived. With the help of the calculus electron‐molecule reactions (electron capture) and reactions between small ions and molecules in rare gases can be treated.
Solvent Dynamic in Electron Transfer Reactions: An Application of Kramers Theory to Homogeneous Organic Electron Self Exchange
Authors: Grampp Günter , Harrer W. , Hetz G. 
Published: March 2014

AbstractUsing ESR spectroscopy the rate constants of homogeneous electron self exchange in the TCNQ/TCNQ−., TCNE/TCNE−. and TTF/TTF+.‐couples (TCNQ = tetracyanoquinonedimethane, TCNE = tetracyanoethylene, TTF = tetrathiofulvalene) were measured in 14 different solvents at 293 K. The rate constants were expressed by the preequilibrium encounter model for adiabatic processes applying Kramers theory. “Friction” dependent preexponential factors expressed by the longitudinal relaxation time τL of the solvents are found. The solvent dependence of the rate constant is explained in terms of Marcus theory by using an outer‐sphere reorganization energy for ellipsoidal molecules. From these solvent dependencies the geometric term g(r̄,d′) = 1/r̄‐1/d′ is obtained leading to an experimental reaction distance d between both molecules in the transition state.
Automatic Generation of Reaction Mechanisms for the Description of the Oxidation of Higher Hydrocarbons
Authors: Chevalier C. , Warnatz J. , Melenk H. 
Published: March 2014

AbstractOxidation mechanisms even for rather simple hydrocarbons like heptane consist due to the occurrence of many isomeric structures of thousands of reactions of hundreds of species. The automatic generation of these reaction mechanisms using artificial intelligence means is described. Results are presented for n‐heptane‐air mixtures, where a hand‐written reaction mechanism tested against experimental data is available.
Determination of the Rate Constant Ratio for the Reactions of the Acetylperoxy Radical with NO and NO2
Authors: Kirchner F. , Zabel F. , Becker K. H. 
Published: March 2014

AbstractThe thermal decomposition of acetyl peroxynitrate was studied in a 420 1 DURAN glass reaction chamber in the presence of different initial [NO2]/[NO] ratios. From an analysis of the rate data, the following rate constant ratios k2/k1 for the reactions of CH3C(O)O2 radicals with NO (k1) and NO2 (k2) were derived at different temperatures and total pressures: 0.45 ± 0.05 (304 K, 1000 mbar), 0.41 ± 0.05 (321 K, 1000 mbar), 0.42 ± 0.02 (313 K, 1000 mbar) 0.39 ± 0.02 (313 K, 300 mbar), 0.28 ± 0.04 (313 K, 100 mbar), 0.25 ± 0.04 (313 K, 30 mbar). Using recent data on k2, a pressure independent rate constant k1 = (2.1 ± 0.5) · 10−11 cm3 molecule−1 s−1 was deduced from these ratios at 313 K.
IR‐Chemiluminescence from the Reactions of Atomic Fluorine with Ethyne and Butyne‐2
Authors: Schwanke U. , Heydtmann H. 
Published: March 2014

AbstractThe reactions F + C2H2 and F + C4H6 (2‐butyne) were studied in a low pressure flow system using the IR‐chemiluminescence technique. The vibrational‐rotational state distributions for the product molecule HF were determined for various conditions. For F + C2H2 only secondary reactions can lead to vibrational excitation of HF; with an excess of F‐atoms HF(ν ≤ 7) was observed. For F + C4H6 the primary abstraction yields the vibrational distribution N1:N2:N3:N4 = 26:36:32:7. With an excess of F atoms ν = 5 and ν = 6 are populated. The possible secondary steps are discussed on the basis of our observations.
1H‐CIDNP During the Reaction of Heavy Carbene Analogues R2M (M = Si, Ge, Sn; R = Me, n‐Bu) with Halides
Authors: Lehnig Manfred , Klaukien Heino , Reininghaus F. 
Published: March 2014

AbstractDuring the reaction of photochemically generated silylenes Me2Si: with PhCH2Cl, PhCH2Br, and Ph2CHCl, 1H‐CIDNP is observed in the products of insertion reactions into the C‐X bonds (X = Cl, Br) and in the abstraction products Ms2SiX2 indicating the occurrence of a radical abstraction‐recombination reaction. The silylenes react from singlet states. Me2Si: reacts with CH2 = CHCH2Cl without CIDNP phenomena in a concerted way. (n‐Bu2Sn)6 reacts with EtBr via a radical chain mechanism without the appearance of free stannylenes n‐Bu2Sn: as intermediates.