bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Theoretical Studies on the Dielectric Field Effect of an Alamethicin‐like Peptide in a Lipophilic Medium
Authors: Schwarz Gerhard , Walther Peter 
Published: July 2012

AbstractA special resonance circuit technique is described which can be used to measure even very small changes of the dielectric constant of a poorly conducting liquid as they may be caused by a strong electric field. This is applied to an octanolic solution of trichotoxin A40, an antibiotic peptide which is known to form electrically sensitive pores in bilayer membranes. Experimental results at about 0.6 and 11 MHz, respectively, are reported and discussed in terms of a theoretical analysis based on the classical Debye‐Onsager approach. In particular, the frequency dependence of the normal dielectric saturation has been calculated in order to correct for the finite rate of dipolar orientation. It turns out that in addition to the normal dielectric field effect an anomalous effect occurs. The latter apparently arises from concentration changes of different dipolar species. These changes are attributed to a field induced displacement of the aggregational equilibrium which exists in the system.
Pair Configuration of Maximum Occurrence Probability in Liquid Formic Acid as Determined from Neutron Scattering and Proton Magnetic Relaxation Results
Authors: Bertagnolli H. , Hertz H. G. 
Published: July 2012

AbstractIntermolecular parts of thex→rFourier transform of the coherent scattering cross section of five isotopically different formic acids are presented and from these data four weighted sums of intermolecular atom‐atom pair distribution functions are determined. Very limited informations about the two (equal) hydrogen‐hydrogen correlation function is also given. From proton magnetic relaxation data available in the literature two possible pair configurations were proposed. From these pairs and one additional one the corresponding sets of intermolecular atomic distances were determined and examined whether these sets lead to agreement with the weighted sums of correlation functions. Agreement was found to be best for a pair with O=C vectors being close to but not exactly parallel, it was concluded that this is the correct molecular pair configuration of maximum occurrence probability.
The Kinetics and Mechanism of Reactions Between the Nitroprusside Ion and Secondary Amines
Authors: Casado J. , Mosquera M. , Rodr ÍGuez Prieto M. F. , Vázquez Tato J. 
Published: July 2012

AbstractThe kinetics of the reactions of the nitroprusside ion — pentacyanonitrosylferrate(II) — with various secondary amines have been studied in basic media. Two parallel reaction pathways are involved: (i) the reaction of the nitroprusside ion with hydroxyl ions to form Fe(CN)5NO4+2, in which NO−2 is then replaced by the amine; and (ii) the reaction of the nitroprusside ion with two molecules of amine to form the corresponding nitrosamine and the complex Fe(CN)5NHR3‐2. The corresponding rate equations have been obtained and explained by proposed reaction mechanisms. We propose a concerted mechanism for reaction (ii) in which the amine binds the nitrosyl group at the same time as the amine proton is removed by a base catalyst. The resulting nitrosamine complex subsequently undergoes substitution by the amine in a faster step.
Fluid Phase Equilibria in Quasi‐Binary Systems of Ethylene + n‐Eicosane + n‐Tetracontane
Authors: De Loos Th. W. , Foot W. , Perbal R. , Lichtenthaler R. N. 
Published: July 2012

AbstractVapour‐liquid equilibria in quasi‐binary systems of ethylene with mixtures of n‐eisosane and n‐tetracontane of fixed molar ratios of n‐eisosane to n‐tetracontane of 0.748:0.252, 0.700:0.300, 0.510:0.490 and 0.247:0.753 have been measured in the temperature range 325 to 450 K and at pressures up to 40 MPa. The results show a distinct influence of the mean molecular weight of the n‐alkane mixtures on these equilibria especially in the critical region. The phase behaviour of the quasi‐binary systems investigated is compared with the phase behaviour of binary systems of ethylene and n‐alkanes. — It is shown that except for the high‐pressure region the fluid phase equilibria of the quasi‐binary systems can be predicted reasonably well with the Peng‐Robinson equation of state using only pure component and binary data to determine the adjustable parameters.
Temperature Effect on the Positronium Formation in Organic Solutions
Authors: Alfassi Zeev B. , Ache Hans J. 
Published: July 2012

AbstractStudies of the temperature dependence of the rate constants for inhibition of o‐Ps formation in organic solvents show either zero or negative activation energies. This is additional evidence for the hypothesis that the experimentally observed inhibition rate constant k is the ratio of rate constants of two competing reactions, one being the reaction of the precursor of the thermalized o‐Ps with the solute (rate constant k), followed by annihilation and the second being the thermalization of this precursor (rate constant k2).
Dielectric Relaxation of 2‐Pyrrolidinone and Some N‐Substituted, Related Compounds in the Liquid State
Authors: Dachwitz E. , Stockhausen M. 
Published: July 2012

AbstractThe complex permittivity of the following neat liquids has been measured in the frequency range from 20 MHz to 36 GHz at 20°C: (1) 2‐pyrrolidinone, (2) N‐methyl‐, (3) N‐vinyl‐, (4) N‐ethyl‐, (5) N‐cyclohexyl‐, (6) N‐benzyl‐2‐pyrrolidinone, (7) N‐methyl‐2‐piperidone and (8) N‐methyl‐caprolactam. The results can be described by one or two superimposed Debye‐type components. One component is due to rotational tumbling of single molecules. The additional component is ascribed to associates, possibly dimers, in the case of (1), but in the other cases, as far as occuring to a significant extent, that is with (4) to (8), to intramolecular motions.
Additivity Rule of the Partial Molal Volume. 3. Anomaly of Cycloalkane Molecules and Volume Change for the Ring Formation Reaction
Authors: Yoshimura Y. , Nakahara M. 
Published: July 2012

AbstractThe semimicroscopic theory of the partial molal volume which takes account of the local molecular packing efficiency through the surface energy has been applied to the cycloalkane by using a simple molecular model to evaluate the core dimensions. The anomalous deviation of the partial molal volume of the cycloalkane from the additivity rule is successfully interpreted; the anomaly arises simply from the geometrical factor that the core dimensions of the cycloalkane are larger than those of the corresponding linear alkane. The semimicroscopic approach provides a new framework for the interpretation of the volume change accompanying the chemical reaction in solution; this is demonstrated in the case of the cycloaddition reaction. The present approach justifies the separation of the overall reaction volume into the components in the additive manner.
Experimental and Theoretical Investigation of the Azide Anion (N−3) in the Gas Phase
Authors: Illenberger Eugen , Comita Paul B. , Brauman John I. , Fenzlaff Heinz‐Peter , Heni Martin , Heinrich Nikolaus , Koch Wolfram , Frenking Gernot 
Published: July 2012

AbstractWe report the formation of the azide anion (N−3) in the gas phase by dissociative electron attachment to benzyl azide in a beam experiment. The electron photodetachment cross section of N−3, generated analogously in an ion cyclotron resonance (ICR) spectrometer has been measured. A threshold of 2.76 ± 0.04 eV was obtained corresponding to the vertical detachment energy in N−3. Ab initio calculations on N−3 and N3 predict similar geometries for both compounds, indicating that the photodetachment threshold can be equated with the electron affinity of the azide radical.
Laser Photolysis and Pulse Radiolysis Investigations on the Triplet Energy Transfer in Aromatic Donor‐Acceptor Systems
Authors: Brede O. , Mehnert R. , Naumann W. , Teply J. 
Published: July 2012

AbstractTo study the relation between the rate and the free energy difference of the TT transfer from some aromatic donors (D) to various preferably aromatic acceptors (A) in benzene solution we combined laser photolysis and pulse radiolysis experiments. Transfer rate constants k1, were determined for DA pairs with differences of the (S0T1) energies ΔE = E(S0T1)D)A between −0.2 and 1.4 eV. A k1 versus ΔE plot shows reaction‐controlled values for ΔE ≤ 0.2 eV. At higher ΔE the diffusion‐controlled limit is reached. By analogy with electron and singlet energy transfer the k1 vs. ΔE relationship was interpreted as arising from the Franck‐Condon effect in the excess energy acceptance by the intramolecular modes.
Another Intermediate in the Photochemistry and Radiation Chemistry of Alkaline Aqueous Solutions
Authors: Telser Th. , Schindewolf U. 
Published: July 2012

AbstractBy UV flash photolytic and pulse radiolytic experiments of aqueous alkaline solutions we confirm older experiments of Walker et al. and Hart et al., showing that the decay of hydrated electrons gives rise to another intermediate X which by light absorption revives hydrated electrons again. X is formed by a reaction of 1. order with respect to hydrated electrons, the rate of its formation increases with pH, and it decays by a second order process with a rate constant not exceeding 5 · 109 M−1 sec−1, probably leading to hydrogen (e− → X; 2X → H2). X has maximum light absorption around 270nm with an extinction coefficient of about 5000 M−1 cm−1. — We will not speculate about the nature of X.
Deuteron NMR Study of Molecular Mobility in a Polymer Model Membrane
Authors: Ebelhäuser R. , Spiess H. W. 
Published: July 2012

AbstractThe molecular mobility of a polymer model membrane is studied by 2H NMR. The lipid analogue consists of a quaternary ammonium ion, to which a methacryloylic moiety is attached via a spacer to the hydrophilic head group. A methylene group of the spacer, the methyl‐head group and methylene groups in the 1‐, 2‐, and 7‐position of the lipid chains are selectively deuterated. Temperature dependent 2H NMR spectra are reported for both, the monomer and the polymer membrane below and above the main phase transition. The data are quantitatively analyzed in terms of a simple motional model, in which the complex molecular dynamics is approximated by a six‐site jump model describing rotations about the long axis of the molecule and conformational changes. The increasing mobility with increasing temperature is only in part due to an increase of the jump rate between different sites. It also reflects the increase in the number of conformations accessible. As a quantitative measure of the mobility at a given site, a mean jump frequency is extracted from the data. For the monomer Ω˜ and its temperature dependence in the liquid crystalline phase is almost independent of the site being studied. In the polymer, however, major differences are observed, Ω˜ for the head group and the 7‐position of the lipid chain differing by two orders of magnitude. The mobility of the spacer is even lower. This 2H NMR study thus shows that although the polymerization largely hinders the head group mobility, the chain flexibility most important for membrane applications is retained.
Ethylbenzene Pyrolysis: Benzyl CC or CH Bond Homolysis
Authors: Robaugh David A. , Tsang Wing , Fahr Askar , Stein Stephen E. 
Published: July 2012

AbstractThe thermal unimolecular decomposition of ethylbenzene has been studied by both the very‐low‐pressure pyrolysis and heated single‐pulse shock tube methods in an attempt to resolve a recent controversy as to whether the initial dissociation channel is benzyl C ‐ C,

or benzyl C‐H homolysis,

Observed decomposition products and mass balance studies lead to the conclusion that up tc 1288K the predominant decomposition channel is benzyl C‐C homolysis. Additional support of this conclusion is provided by a study of isopropylbenzene decomposition by these same methods. Arguments are given which strongly suggest that benzyl C‐H homolysis cannot be the major reaction channel even at temperatures as high as 1600K.
The Synchronous 1,4‐Addition of SiH2(1A1) to s‐cis‐buta‐1,3‐diene. A CI and CASSCF Study
Authors: Maier Elisabeth , Olbrich Gottfried 
Published: July 2012

AbstractA minimum energy path for the synchronous 1,4‐addition reaction of SiH2(1A1) with s‐cis‐buta‐l,3‐diene to 1‐silacyclopent‐3‐ene was determined by ab initio SCF and CI calculations. To analyse the changes of electronic structure along the reaction path CASSCF calculations and a population analysis were performed. From these and the geometrical variations it is concluded that the reaction is initiated by an electrophilic step involving the HOMO of butadiene and the empty p orbital of SiH2. Closed shell repulsions play a decisive role for the orientation of the SiH2 relative to the butadiene molecule. An activation energy of 17 kJ/mol is estimated and the exothermicity for the formation of the silacyclopentene is evaluated to be 283.82 kJ/mol. It follows from the CASSCF calculations that the activation barrier of the reaction is due to an avoided crossing between the ground and first excited singlet state of the composite system.
Critical Fluctuations on Solid Surfaces
Authors: Willis Roy F. 
Published: July 2012

AbstractPhase transitions and phase diagrams of two‐dimensional systems are quite distinct from three‐dimensional behaviour. Topological defects such as steps, domains and domain‐wall dislocations play a key role. This paper discusses the nature and scale of the atomic fluctuations at phase boundaries for order‐to‐disorder structural phase transformations on solid surfaces. The question of the rich variety of configurational patterns of “precursor” short‐range order is discussed with reference to reconstructed surfaces of Au(l10)(2 x 1) and W(100)( √2x √2)R45° systems. These systems belong to different two‐dimensional universality classes on account of their different symmetries and serve to illustrate critical precursor fluctuation phenomena of current interest.
2d Krypton, a Model System for a Commensurate‐Incommensurate Transition
Authors: Marx R. , Hoja R. 
Published: July 2012

AbstractWe studied the commensurate‐incommensurate phase transition of krypton physisorbed on graphite foam by adsorption volumetry. The transition can be described by a power law with exponent β of the misfit m versus the difference of the chemical potentials μ—μc of the incommensurate and the commensurate phase, respectively. In the investigated temperature range β is equal to 1/3 and within an uncertainty of ± Δβ = 0.014 independent of temperature.
Photoemission from Ordered Physisorbed Molecular Phases N2/Graphite, N2 and CO/Ag(111)
Authors: Schmeißer D. , Lyo I. W. , Greuter F. , Plummer E. W. , Freund H.‐J. , Seel M. 
Published: July 2012

AbstractUsing angle resolved ultraviolet photoelectron spectroscopy (ARUPS) the two dimensional energy dispersions of ordered physisorbed monolayers of N2 and CO/Ag(111) has been measured. For N2/graphite the ordered herringbone structure can be identified by correlating the ARUPS data to recent LEED studies. For all systems investigated we observe a k dependent splitting of the 5 σ (3 σg) level which is a consequence of the intermolecular interaction of two molecules in the unit cell. The splitting is largest in the center of the Brillouin zone of the overlayer and disappears towards its zone boundary. The observed dispersion can be understood by a simple tightbinding calculation and is in good agreement with an ab initio bandstructure calculation.
Ordering Kinetics for O on W(110)
Authors: Tringides M. , Wu P. K. , Moritz W. , Lagally M. G. 
Published: July 2012

AbstractAn analysis of peak‐intensity‐vs‐time data for LEED from W(110)p(2 × 1)‐O at saturation coverage is made to emphasize early times. From this analysis an exponent x ∼ 0.33 for the growth of the average size of ordered domains is extracted. Experimental evidence for a ground‐state degeneracy p = 8 in this system is presented, supporting the existence of slow domain growth that is suggested by the growth exponent. The relationship to recent theoretical results is discussed.
Reactive Transformation of Surface Structure
Authors: Ertl G. 
Published: July 2012

AbstractKinetic and energetic aspects of adsorbate‐induced first‐order phase transitions of the structure of single crystal surfaces are illustrated by the examples H/Ni(110) and CO/Pt(100). During the catalytic oxidation of CO on Pt(100) even periodic changes and spatial pattern formation of the surface structure may occur which effects are coupled to temporal oscillations of the reaction rate.
Statistical Model for the Hydrogen‐Induced Reconstruction of the Ni(110) Surface
Authors: Rys Franz S. , Müser Horst E. 
Published: July 2012

AbstractA recently proposed statistical model for the two‐dimensional reconstruction transition of H/Ni(110) is investigated using a suitable fast Monte Carlo formalism. The phase diagram is presented for some range of the parameter values. Various low temperature (LT) non‐reconstructed, and homogeneous and pairing‐row reconstructed phases are found. Near the phase boundaries the approach to equilibrium is strongly slowed down due to topological constraints. Similar features are reported from experimental studies on the clean Pd(110) surface.
Reversible and Irreversible Phase Transitions in the Surface Segregation of Sn, Sb, and Al on Iron Single Crystals
Authors: Rüsenberg M. , Viefhaus H. 
Published: July 2012

AbstractLow index ((100), (110), (111)) single crystal surfaces of binary alloys Fe‐X (X = Sn, Sb, Al) with different bulk concentrations were studied by AES, LEED, and XPS. The surface segregation of the alloying elements was investigated in the temperature range 400…700°C.—Irreversible order‐order or order‐disorder transitions in dependence on the surface coverage during the segregation process were detected. Reversible order‐disorder transitions in dependence on bulk concentration and temperature were observed for (110) oriented surfaces.
Phase Transitions in Chemisorbed Hydrogen Layers
Authors: Christmann K. 
Published: July 2012

AbstractA brief survey is given about hydrogen‐transition metal systems which exhibit adsorbed hydrogen phases with long‐range order that can undergo order‐order and order‐disorder transitions depending upon the surface coverage θHand the temperature, respectively. A distinction has to be made between genuine lattice gas phases in which the H atoms simply occupy lattice sites with identical local symmetry without affecting the positions of the underlying metal atoms and those chemisorbed H phases which involve a distortion of the surface geometry of the substrate leading to the well‐known surface reconstruction. The systems H/Ni(111), H/Pd(111), H/Pd(100) and H/Fe(110) belong to the first category whereas H/Ni(110) and H/Pd(110) represent examples of the latter category, i.e., that involves surface reconstructed phases. As far as they have been determined the phase diagrams of the ordered H phases will be described and interpreted in terms of the mutual H‐H interactions.
Die zweiten Virialkoeffizienten von Helium‐Gasmischungen im Bereich unterhalb Zimmertemperatur
Authors: Elias E. , Hoang N. , Sommer J. , Schramm B. 
Published: July 2012

AbstractMeasurements of second interaction virial coefficients of mixtures He/O2, CO, NO, CH4, CF4, CO2, N2O, SF6, and NH3are presented. Temperatures range from 300 K to temperatures as low as the boiling temperature of the molecular components. New experimental data of second virial coefficients for most of the pure components are presented also and are critically compared with literature data. Recently published anisotropic intermolecular potential energy surfaces and several combining rules were tested with the new data.
Kinetic Isotope Effects for Hydrogen Abstraction from Various Saturated Hydrocarbons by Deuterium Atoms in the Gas Phase
Authors: Fujisaki Noboru , Gäumann Tino , Ruf Amanz 
Published: July 2012

AbstractUsing deuterium atoms produced in the radiolysis of heavy water vapor, the kinetic isotope effects kH/kD were determined by the isotope competitive method for the abstraction reaction D* + RH(R′D)→HD(D2) + R′(R′), where RH is an alkane and R′D is the corresponding perdeuterated alkane. The alkanes RH investigated include isobutane, 2,3,4‐trimethylpentane, neopentane, cyclopentane, cyclohexane, cycloheptane, and n‐heptane. The results were represented in terms of the Arrhenius‐type expression kH/kD = AH/ADexp((ED‐EH) (kJ mol−1)/RT), over the temperature range 363–473 K. The pre‐exponential factor ratios AH/AD vary from 0.36 for neopentane to 0.70 for 2,3,4‐trimethylpentane, the ED—EH values from 6.4 for 2,3,4‐trimethylpentane to 10.4 kJ mol−1 for neopentane. The variation in the ED—EH values was correlated with the bond strength of the C‐H bond being broken. The deuterium and hydrogen atoms, as the attacking species, are found to show essentially the same magnitude of the kinetic isotope effects in the hydrogen abstraction from a given alkane. The theoretical calculations of the isotope effects have been carried out on the basis of transition‐state theory combined with the London‐Eyring‐Polanyi‐Sato potential energy surface. Good agreement was obtained between experiment and theory, when tunnel effects were taken into consideration.
Flow Method Vapour Pressure Determination and Characterization of Tetrakis(Trifluoropentanedionato)‐Thorium(IV) and Tetrakis (Heptafluorodimethyloctanedionato)‐Thorium(IV)
Authors: Gärtner G. , Janiel P. , Rau H. , Hal H. A. M. Van , Nabben H. J. P. 
Published: July 2012

AbstractTetrakis β‐diketonates were synthesized with quadrivalent thorium and 1,1,1‐heptafluoro‐7,7‐dimethyloctane‐4,6‐dione (fod) and with 1,1,1‐trifluoropentane‐2,4‐dione (tfa). They were characterized by elemental analysis. Temperature‐dependent X‐ray diffraction data were recorded. It was found that Th(tfa)4 can be obtained as a hydrate Th(tfa)4 · H2O and also water‐free. Visual determination gives a melting point of 423 K for Th(tfa)4 · H2O and DSC gives a melting point of 407 K for water‐free Th(tfa)4. DSC also showed a phase transition in Th(fod)4 at 366 K, the second phase transition at 424 K being identical with the melting point. Vapour pressures of Th(tfa)4 and of Th(fod)4 were determined by the flow method using nitrogen as a carrier gas. The experimental data have been fitted to an equation of the form

The results are ΔRH298 = 151.2 kJ · mol−1, ΔRS298 = 310.0 J · K−1 · mol−1, ΔRcp = −259.2 J · K−1; · mol −1; for the low temperature α‐modification of Th(fod)4, ΔRH298 = 130.6 kJ · mol−1, ΔRS298 = 253.5 J · K−1 · mol−1 and ΔRcp = −259.2 J · K−1 · mol−1 for the β‐modification at temperatures above 366 K, and ΔRH298 = 154.6 kJ · mol−1, ΔRS298 = 326.1 J · K−1 · mol−1, ΔRcp = −170.8 J · K−1 · mol−1 for water‐free Th(tfa)4.
Photoelectrochemical Etching of n‐MoSe2
Authors: Tenne R. , Wold A. 
Published: July 2012

AbstractThe photoelectrochemical etching of n‐MoSe2 was investigated. The photocurrent of a regenerative photoelectrochemical cell comprising the above material in polyiodide solution is improved quite significantly following that treatment. Best results were obtained when the photoelectrode was photoetched under short circuit conditions and high irradiance. As was previously observed, for other layered compounds, very few etch pits are produced. This is rather surprising in view of the morphology of photoetched CdSe and the like. We discuss this point in detail and give first hints to explain this difference.