bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dipole Moments and the Direction of the Transition Dipole Moment of Some Intramolecular Exciplexes
Authors: Baumann Wolfram , Frühling J.‐C. , Brittinger C. , Okada T. , Mataga N. 
Published: March 2014

AbstractThe dipole moments of some intramolecular exciplex systems have been determined from the effect of an electric field on their fluorescence and are compared to those estimated from solvent shift measurements. The charge transfer between the donor and acceptor subunits is between 0.6 and 0.9 of a full charge transfer. The face‐to‐face type exciplexes show considerable deviations from the general behaviour what might be due to some admixture of locally excited configurations to the exciplex wave function, in this way reducing the dipole moment values and changing the direction of the transition dipole moment.
XP‐Spectra, Sputterexperiments and UV‐VIS‐Reflection Spectra of Polyaniline
Authors: Kessel R. , Hansen G. , Schultze J. W. 
Published: March 2014

AbstractElectrochemically formed polyaniline (PANI) films were studied both in situ and ex situ using XPS and UV/VIS spectroscopy. The samples studied ex situ were removed at given potentials and rinsed with water, with no changes in the oxidation state or concentration of counter ions. PANI‐RED (0.0 V (SHE)) contained no anions and the XP‐spectra showed an emeraldine‐like structure and 0.27 protonated nitrogen atoms/monomer. PANI‐OX (1.0 V (SHE)) contained 0.2 — 0.3 counter ions/monomer throughout the film. UV/VIS spectroscopy shows a two step redox mechanism involving radical cations. The extended conjugation of PANI‐OX was followed by both reflection spectroscopy and XP‐shake‐up peaks accompanying the photoionisation process. At potentials above 1.0 V (SHE) overoxidation occurs with the removal of anions from the bulk fil
Enthalpies of Mixing in the Ternary System Aluminium Chloride — Potassium Chloride — Aluminium Chloride Monoamine
Authors: Hatem G. , Gaune‐Escard M. , Bros J. P. , Østvold T. 
Published: March 2014

AbstractQuasi binary enthalpy of mixing experiments have been performed in the ternary liquid system AlCl3 —AlCl3NH3 —KCl by mixing AlCl3 + KCl with AlCl3NH3 keeping the ratio XA1Cl3XKCI = 1.125, 1.5 and 2.0, respectively. At XA1Cl3XNH3 = 0.5 and T = 270°C the enthalpies of mixing were ≃ —430 J mol−1 for all the quasi‐binaries studied. The new enthalpy data are not fully consistent with published vapour pressure data and thermodynamic model calculation
Phase Diagrams with Closed Loop Smectic — Nematic Phase Boundaries
Authors: Illian G. , Kneppe H. , Schneider F. 
Published: March 2014

AbstractA T, x diagram with a closed loop smectic‐nematic phase boundary is observed in mixtures of 4‐n‐heptyloxy‐4′‐cyanobiphenyl and a mixture of 4‐cyanobenzylidene‐4′‐n‐octyloxyaniline and 4‐n‐pentylphenyl 4‐n‐octyloxybenzoate. Application of pressure reduces the smectic phase area and, at a critical pressure of 145 bar, the area is reduced to a point (double critical point) in the T, x diagram. Thermodynamics leads to an appropriate description of the phase boundary.
Far Infrared Absorption and Rotational Motion of CHClF2 to High Pressures and Temperatures
Authors: Bohn M. A. , Franck E. U. 
Published: March 2014

AbstractFIR‐absorption spectra of monochloro‐difluoro‐methane (CHClF2) has been measured between 10 and 260 cm−1 at temperatures between 25 and 175°C. High pressure PVT‐data permit the discussion of the spectra as functions of density. The density has been varied between 0.1 and 1.4 g cm−3 by pressures up to 722 bar. The critical data of CHClF2 are 96.15°C, 49.9 bar and 0.513 cm−3. The dipole moment is 1.43 D. Measurements were made with a modified Fourier‐transform IR‐spectrometer. An optical absorption cell for use to 1000 bar and 200°C is described. It has quartz or silicon windows and the optical path length can be varied at operating conditions between 100 μm and 5 mm. The molar absorptivity band at 125°C and low density (0.1 g cm−3) has a pronounced maximum near 30 cm−1, indicating hindered rotation. With increasing density this band decreases and a growing absorption around 60 cm−1 develops, which is ascribed to intermolecular libration. Analogous behaviour is observed at other temperatures. A model based on a generalized Langevin‐equation and the Mori‐memory formalism serves to describe the spectra. The mean squared intermolecular torque and time correlation functions have been calculated. Orientation correlation time at 125°C and 1 g cm−3 is τOR1 = 5 · 10−13 s. The spectral fourth moment of the power spectrum shows the frequency ranges of rotation and libration very clearly.
High Frequency Ultrasonic Absorption Spectroscopy on Aqueous Solutions of Zwitterionic and Nonionic Micelles
Authors: Kaatze U. , Berger W. , Lautscham K. 
Published: March 2014

AbstractThe ultrasonic absorption coefficient has been measured as a function of frequency between 10 MHz and 3 GHz for micellar aqueous solutions of zwitterionic and nonionic surfactants. All solutions show Debye‐type relaxation behaviour with a time constant between 130 and 290 ps (25°C, 40°C). Comparison with corresponding dielectric spectra and with acoustic spectra of pure n‐alkanes and of solutions of ionic micelles suggests this relaxation process to be due to rotational isomerization mechanisms in the hydrocarbon chains An additional relaxation process with a time constant of 1.4 ns (25°C) has been found with a 0.1 molar solution of lysolecithin. This process is discussed in terms of orientational head group motions and, alternatively, of limited radial diffusive motions of the molecules in micelles. It is not clear why this latter relaxation does not occur in solutions of the other surfactants.
1H NMR and 35Cl NQR Studies on the Motion of Pyridinium Ions in Crystalline Pyridinium Tetrachloro‐ and Tetrabromoaurate(III): (pyH)AuX4 (X = Cl, Br)
Authors: Ito Yukari , Asaji Tetsuo , Ikeda Ryuichi , Nakamura Daiyu 
Published: March 2014

AbstractThe temperature dependences of 1H spin‐lattice relaxation times T1, at the Larmor frequencies of 10.5, 16.0, 20.0, and 45.5 MHz, and of 1H NMR second moments M2 were determined for (pyH)AuCl4 and (pyH)AuBr4, where pyH+ indicates a pyridinium ion. The small M2 data less than 1 G2 obtained above ca. 380 K indicated that the cations perform reorientational motion rapidly enough about its pseudohexad C′6 axis existing at the center of the cation and perpendicular to its plane. Below 140 K, both complexes yielded rigid lattice M2 values of the cation. It is interesting features for these complexes that motional narrowing for the NMR line occurs over an extremely wide range of temperature, the log T1, vs. T−1 plots are asymmetric about the 1H T1 minimum with a gentler gradient on the low temperature side, and the minima are extraordinarily long. These unusual results were interpreted by assuming the C′6 reorientation of the cations having electric dipoles among nonequivalent in‐plane orientations. Three potential barriers to the C′6 reorientation were determined as 21.8, 17.2, and 13.5 kJ mol−1 for (pyH)AuCl4, and 22.2,17.4, and 13.7 kJ mol−1 for (pyH)AuBr4. The fade‐out phenomenon of 3SCl NQR signals observed for (pyH)AuCl4 at ca. 230 K when the sample temperature was lowered is also discussed, by referring to the motion of the pyridinium cations.
Steady State Photocapacitance Study of Semiconductor/Electrolyte Junctions II. Surface State Distribution and Charge Transfer Mechanisms
Authors: Allongue P. 
Published: March 2014

AbstractGaAs/electrolyte junctions are characterized by steady state photocapacitance measurements without (single beam experiment) or with added interband illumination (dual beam experiment). This original approach allows to give unambiguously the surface state distribution and to follow its evolution during electrochemical processes: results show the presence of two corrosion related states at EC −0.98 eV and EC −1.14 eV which behave differently under corrosion or photocorrosion conditions. It is shown that surfaces modified by electro‐deposition of discontinuous metal films exhibit metal‐induced surface states responsible for charge transfers.
The Electrical State of an Ion‐Exchange Membrane Surface after Emersion from Liquid Electrolytes
Authors: Cappadonia Marcella , Doblhofer Karl , Jauch Matthias 
Published: March 2014

AbstractElectrodes are coated with membrane‐type polymer films containing fixed pyridinium groups. The coated electrodes are withdrawn from various electrolytes (“emersion” under potentiostatic control). In the emersed state the work function of the solvated polymer is determined with Kelvin's method of the vibrating capacitor plate. The determined values are compared with the work function of the electrolyte at the same electrode potential. It is concluded that a surface potential χMex ≈ −0.3 V exists at the emersed polymer surface. Its exact value depends on the type of counter ions. Secondly, it is shown that the concentration dependence of the work function is directly related to the equilibrium potential drop across the intact membrane/solution interface which prevailed before emersion (the “Donnan”‐potential). This suggests that such work‐function measurements yield quantitative information on the electrical work term in the description of the ion‐exchange equilibria.
Reactions of Ethynyl Radicals with Alkynes in the System Sodium Vapour/Ethynylbromide/Alkyne
Authors: Brachhold H. , Alkemade U. , Homann K. H. 
Published: March 2014

AbstractThe radicals were generated from the respective halide RX by the reaction Na + RX → R + NaX in a low‐pressure flow reactor fed by a multi‐slit diffusion burner. Test results are reported for the system Na/CH3I givingk(Na + CH3I) = 6.0 · 10−3andk(CH3+ CH3) = 2.8·1013cm3mol−1s−1. The main part deals with the production of C2H in the system Na/C2HBr and its consecutive reactions with C2HBr and added C2H2and C4H2. The rate constantk(Na + C2HBr) was found to be 2.9 · 1013cm3mol−1s−1. The bimolecular rate constants of C2H with the compounds above have been determined to 1.0·1014, 2.3 · 1013and 4.0·1013cm3mol−1s−1, respectively, at a temperature of 603 K. – The main products in this reaction system are polyynes with a minor formation of ethyne and very little hydrogenated polyynes. The formation of an aromatic compound (ethynylbenzene) is negligibly small, a fact which is discussed in its relation to aromates in hydrocarbon flames. The primary reaction Na + C2HBr and its products are discussed as well as the unimolecular decomposition and stabilization of energized adducts formed by C2H.
Structure and Dynamics of Lipid Model Membranes: FT‐IR‐ and 2H‐NMR‐Spectroscopic Studies
Authors: Blume A. , Hübner W. , Müller M. , Bäuerle H. D. 
Published: March 2014

AbstractFT‐IR and 2H‐NMR‐spectroscopy has been used to study structure and dynamics of specifically labeled phospholipids in model membranes. Three examples for the application of these two spectroscopic techniques are given. 1. 2H‐NMR‐spectroscopy can be used to study the behavior of pure specifically deuterated model compounds of phospholipids with different head groups like phosphatidylcholines (PC**)) and phosphatidylethanolamines (PE). Line shape simulations of powder spectra and of spectra of oriented samples provide information on the mechanism and correlation times of the molecular reorientations. In mixtures of phospholipids with different head groups 2H‐NMR‐spectroscopy can be used to study the mixing behavior of lipids. Evidence for lipid clustering in the liquid‐crystalline phase comes from different splittings observed for the two components. 2. FT‐IR‐spectroscopy of 13C = O labeled phospholipids gives information on the hydration behavior of the glycerol back bone. Because of the vibrational isotope effect both carbonyl bands of the ester groups of the lipid can be observed separately when one of the C = O groups is labeled with 13C. FT‐IR spectra indicate that both ester carbonyl groups of lipids in hydrated membranes are in contact with water. The amount of hydration depends on the phase state and the nature of the lipid head groups. 3. A combination of 2H‐NMR and FT‐IR‐spectroscopy was used to determine structure and dynamics of phospholipids with ω‐cyclohexyl fatty acids. Drastic differences in conformational and dynamical behavior between odd‐ and even‐numbered members of this lipid class could be detected.
Cation Selectivity of Membrane Proteins
Authors: Mezele Martin , Lewitzki Erwin , Ruf Horst , Grell Ernst 
Published: March 2014

AbstractIn order to investigate the high‐affinity K+ binding to proteins, alkali ion binding studies were performed on a fluorescent derivative of membrane‐bound Na,K‐ATPase in buffered aqueous solution at 37°C employing a specially designed automatic spectrofluorometric titration system. The comparison of the obtained apparent stability constants, which reached values for K+ even over 104 M−1 with those of a simpler cyclic peptide, acting as a suitable model compound, provides suggestions concerning the molecular nature of the binding sites involved.
Specific Activation of CH‐ and CC‐Bonds by Bare Transition‐Metal Ions
Authors: Eller Karsten , Karraß Sigurd , Schwarz Helmut 
Published: March 2014

AbstractChemists are continuously facing questions and problems as follows: Is it possible to direct the course of a reaction according to one's intentions? Is the activation of specific bonds that are either remote or adjacent to a functional group feasible? What factors dictate the different behaviour of transition‐metal ions in their reactions with organic substrates? Answers to these and other questions are provided by studying the gas‐phase chemistry of “naked” first‐row transition‐metal ions with aliphatic nitriles and some other simple organic substrates. By systematically modifying both the organic molecules and the metal ions, a quite detailed insight is achieved into the mechanisms that are operative, and knowledge is accumulated which permits to specify the conditions that are to be met in order to bring about specific processes. “Remote functionalization”, the generation of ion/dipole intermediates, and the formation of multi‐ligated metal‐ion alkene complexes turn out to be the most important mechanisms in the reactions of aliphatic nitriles with transition‐metal ions in the gas phase. In addition, results will be presented which point to degenerate isomerizations involving metallacycles as intermediates. We will also demonstrate that direct CC bond activation prior to CH bond activation can be achieved, a process for which no analogue exists in solution chemistry. The studies have been performed by using tandem mass spectrometry techniques in a sector‐field mass spectrometer as well as ion/molecule reactions in a Fourier transform ion cyclotron resonance (FTICR) instrument.
Preparation of Single Rotation Vibration States of CH3O (X̃2E) Above the H – CH2O Dissociation Threshold by Stimulated Emission Pumping
Authors: Geers A. , Kappert J. , Temps F. , Wiebrecht J. W. 
Published: March 2014

AbstractBy the technique of Stimulated Emission Pumping (SEP), single high‐lying rotation vibration states of CH3O (X̃2E) with defined total energy Err and total angular momentum J were probed in the regime 3000 cm−1 ≤ Err ≤ 9300 cm−1, up to well above the H – CH2O asymptotic dissociation limit (≈ 6800 cm−1). Observed low resolution SEP spectra exhibit distinctive vibrational band structure. Spectra recorded at high resolution reflect intramolecular dynamical processes occuring on different time scales. The detailed spectroscopic characterization of the level structure of highly excited CH3O provides the basis for critical tests of models for unimolecular reactions.
Quantum Phenomena and Solvent Effects on Addition of Hydrogen Isotopes to Benzene and to Dimethylbutadiene
Authors: Roduner E. , Louwrier P. W. F. , Brinkman G. A. , Garner D. M. , Reid I. D. , Arseneau D. J. , Senba M. , Fleming D. G. 
Published: March 2014

AbstractRate constants have been measured for the reaction of the light hydrogen isotope muonium with benzene and 2,3‐dimethylbutadiene‐1,3 in the gas phase and in several solvents. Comparison with H atom data reveals (1) appreciable kinetic isotope effects, (2) a strong contribution of tunnelling for the activated reaction with benzene, (3) encounter controlled reaction for Mu addition to the diene, (4) a mass dependence of the diffusion constant of hydrogen isotopes in solution, and (5) an enhancement of the rate constant in solution over that in the gas phase by a factor, except for water, of the inverse Ostwald solubility coefficient for hydrogen. The isotope‐dependent reduction of the solvent effect in water is tentatively ascribed to the dynamics of the clathrate‐like structure when the hydrogen atom reacts.
FTMS Studies of Sputtered Metal Cluster Ions (III): The Chemistry of Ni+n, Co+n, V+n, Ag+n, Au+n and Fe+n with C2H4, C6H6 or NH3
Authors: Irion Manfred P. , Schnabel P. , Selinger Adrian 
Published: March 2014

AbstractAs previously described in greater detail, diverse transition metal cluster cations are produced in an external source by sputtering with 20 keV Xenon ions and transferred to the ICR cell of a home‐built Fourier transform mass spectrometer. There, they are thermalized by collisions with Neon atoms and stored for up to tens of seconds. They undergo a variety of reactions in the presence of ethene, benzene or ammonia, displaying different size‐specific effects. Depending upon the metal and the actual cluster size, mere physical adsorption or dehydrogenation is prevailing.
The Photodissociation of Jet‐cooled Methyl Thionitrite in the Visible
Authors: Pfab Josef , Wetzel Donna M. , Young Victor M. 
Published: March 2014

AbstractThe Dynamics of the photodissociation of jet‐cooled CH3SNO from the S1 (n,π*) state in the visible spectral range has been studied for the first time by pulsed laser photolysis and laser‐induced fluorescence probing of the nascent NO fragment. NO is formed vibrationally cold and rotationally hot confirming that the dissociation is a direct process, and that the structure in the S1 (n,π*) ← S0 absorption does not arise from predissociation. Scalar and some vector properties have been measured, and the fine structure selectivities of the NO fragment have been evaluated. NO is aligned strongly (A(2)0 = +0.75) with the E‐vector of the dissociation light and recoils perpendicularly to the transition dipole μ confirming the symmetry of the S1‐state as A″ and the electronic character as (n,π*). The observed dissociation dynamics of CH3SNO are compared with that of CH3ONO and with recent calculations by Schinke et al.
Investigation of Reaction Barriers in Mixed Organic Aggregates by Two‐Color Resonant Two Photon Ionization
Authors: Awdiew J. , Riehn Ch. , Brutschy B. , Baumgärtel H. 
Published: March 2014

AbstractWe used two‐color resonant two‐photon ionization combined with time‐of‐flight mass spectrometry to study nucleophilic ipso‐substitution reactions with halobenzenes radical cations. Molecular clusters serve as microscopic test tubes to tackle the reactivity problem of solvated radical cations. The reaction paths – van der Waals fragmentation and chemical reaction – could be energetically separated. The substitution reactions turned out to be nearly activationless. The particularities of the excitation process are discussed.
Kinetics of the Reactions of CH2(X̃3B1) with HCl and HBr
Authors: Goldbach A. , Temps F. , Wagner H. Gg. 
Published: March 2014

AbstractThe reactions of CH2(X̃3B1) with HCl (1) and HBr (2) have been studied in an isothermal discharge flow system. CH2 radicals were generated via the reactions of O atoms with a large excess of CH2CO. Their concentration‐versus‐time profiles were measured under pseudo first‐order conditions using Laser Magnetic Resonance (LMR) detection. The rate coefficients of reactions (1) and (2) were found to be kexp1 = (1.7 ± 0.3) · 1012 · exp [–(436 ± 45) K/T] cm3/mol · s in the temperature range 296 K ≤ T ≤ 670 K and k2 = (6.9 ± 1.4) · 1012 cm3/mol · s at T = 296 K. CH3 + Cl or Br, respectively, are suggested to account for the main reaction products.
Adduct Formation of OH Radicals with Benzene, Toluene, and Phenol and Consecutive Reactions of the Adducts with NOx and O2
Authors: Knispel Ralf , Koch Rainald , Siese Manfred , Zetzsch Cornelius 
Published: March 2014

AbstractThe formation of the adducts of OH with benzene, toluene and phenol and consecutive reactions of the adducts with NO, NO2 and O2 are investigated in the temperature range from ∼298–374 K employing the flash photolysis/resonance fluorescence technique in Ar at 133 mbar. Biexponential decays of OH can be observed over at least 2 orders of magnitude in the presence of the aromatics, and the three reaction channels: abstraction of H by OH, addition of OH and unimolecular decomposition of the adduct are distinguished in overlapping temperature ranges. Rate constants and preliminary Arrhenius parameters are obtained for these channels for benzene, toluene, and phenol. The reactions of the adducts with NO are very slow and can be neglected (<10−13 cm3 s−1) in all three cases. Values of ∼3·10−11 cm3 s−1 are obtained for the rate constants of the reactions of the adducts with NO2, almost independent of reactant and temperature. Preliminary determinations of the adduct reactivities against O2 ∼ 2 · 10−16 (benzene‐OH) and ∼5 · 10−16 cm3 s−1 (toluene‐OH) near room temperature indicate that this path predominates under tropospheric conditions. The results for O2 are confirmed by direct observations of the adduct benzene‐OH by the cw UV‐laser longpath absorption technique.
A Study of the Reaction between CH3 and NO at High Temperatures
Authors: Hoffmann A. , Wagner H. Gg. , Wolff Th. , Hwang S. M. 
Published: March 2014

AbstractThe reaction between CH3 and NO was investigated behind incident shock waves at temperatures between 1470 K and 2040 K. Using an Ar‐ion‐laser pumped cw ring dye laser hydroxyl radicals were found to be a primary product of this reaction. The rate constant for the OH forming channel can be expressed by

At temperatures around 2000 K the contribution of the “OH channel” to the total rate constant of the reaction CH3 + NO is about 40%.
High Temperature Reactions of Benzyl Radicals
Authors: Braun‐Unkhoff M. , Frank P. , Just Th. 
Published: March 2014

AbstractThe thermal decomposition of benzyl radicals has been investigated behind reflected shock waves by monitoring the formation of hydrogen atoms. The results reported here have been obtained by using a shock tube in conjunction with atomic resonance absorption spectrometry (ARAS). The temperatures ranged between 1450 and 1700 K at total pressures around 2 bar. The test gas mixtures consisted of argon with relative concentrations of a few ppm benzyliodide, C7H7I. From the measurements of the temporal H‐atom concentrations, in connection with thermochemical restraints, it was deduced that the benzyl decay is preceded by isomerization of benzyl. Due to the low initial concentration of the radical precursor, it was possible to evaluate a first order rate coefficient for the initiation reaction:magnified imageThe heat of formation of the benzyl radical is discussed. A value of ΔH0f, 298 = 215.5 kJ mol−1 fits best to the experimental results.
Measurements of the Second Virial Coefficients of Some New Chlorofluorocarbons and of Their Binary Mixtures at Temperatures in the Range from 296 K to 475 K
Authors: Schramm B. , Hauck J. , Kern L. 
Published: March 2014

AbstractWe present measurements of second virial coefficients of the chlorofluorocarbons R12 (CCl2F2), R22 (CHCIF2), R114 (CClF2—CClF2), R134a (CH2F—CF3), R142b (CH3—CClF2), R152a (CH3—CHF2) and of the binary mixtures R12/R22, R22/R114, R22/R142b, R22/R152a, and R134a/R152a in the temperature range from 296 K to 475 K. The data are combined with earlier measurements of the same systems at low temperatures (J. Chem. Thermodyn.23, 281 (1991)) for a critical discussion on the basis of the Stockmayer intermolecular potential model.