bluuebunny/crossref_metadata_2025_split huggingface dataset:
Classical and Quantum Mechanical Features in the Photodissociation of Small Polyatomic Molecules
Authors: Schinke R. , Engel V. , Hennig S. , Weide K. , Untch A. 
Published: March 2014

AbstractWe review some recent progress in theoretical studies of photodissociation of polyatomic molecules. The first part features the inelastic reflection principle which is a straight forward extension of the well known one‐dimensional (elastic) reflection principle. It allows to interprete final rotational‐vibrational state distributions of the fragments in terms of the wavefunction of the parent molecule and the intermolecular interaction in the exit channel (final state interaction). It is discussed for two model systems and the photodissociation of H2O2. In the second part of the article we discuss diffuse structures in the total absorption spectra of H2O (first and second band) and CH3ONO. We present exact quantum mechanical calcualtions using ab initio potential energy surfaces. In each case we compare directly with available experimental data.
Acetylene: Isomerization and Dissociation
Authors: Chen Yongqin , Jonas David M. , Hamilton Charles E. , Green Peter G. , Kinsey J. L. , Field R. W. 
Published: March 2014

AbstractThe Stimulated Emission Pumping (SEP) spectrum at 15600 cm−1 above the HCCH X1σ+g zero point level contains features diagnostic of isomerization to vinylidene. It also illustrates a powerful new way, spectral cross‐correlation, for extracting dynamical information from high resolution spectra. SEP spectra of the same X̃‐state energy region, from two different intermediate levels (33 vs. 2142), are cross‐correlated. The correlation index is expected and found to be insignificant, except for isolated energy regions where a vinylidene basis state promotes acetylene mode mixing. The energy width of the correlated region is a direct measure of the distribution of vinylidene character into predominantly acetylene eigenstates. SEP spectra of HCCD provide additional information about the acetylene‐vinylidene isomerization process. The HCC‐H dissociation energy is poorly known but crucial to kinetic models for hydrocarbon combustion. The presence of a low lying excited state in HCC and HCC+ complicates the interpretation of dissociation and ionization threshold experiments. Zeeman Anticrossing Spectroscopy provides an opportunity to detect the onset of predissociation in a single rovibronic level of the HCCH Ã state by inducing anticrossings with levels of the T1 and T2 surfaces (all three isomers of each, cis‐HCCH, trans‐HCCH, and vinylidene) and, indirectly, with high vibrational levels of the X̃ state. We have detected one predissociative anticrossing in HCCH Ã υ3 = 4, J = Ka = 1.
Infrared Laser Induced Fluorescence Studies of State Mixing in Ground Electronic State Molecules
Authors: Minton T. K. , McDonald J. D. 
Published: March 2014

AbstractDuring the past several years, infrared laser induced fluorescence experiments in our laboratory have been used to probe the nature of state mixing in the C—H stretch fundamental frequency region of various organic molecules. Both total and dispersed IR fluorescence have been collected from molecules, cooled and isolated in a molecular beam, after excitation with an infrared optical parametric oscillator. Measurements of the dilution factor, which is inversely related to the number of coupled states, as a function of molecule, vibrational band, and average J value excited have yielded the result that the extent of state mixing is J dependent and scales linearly with J. The extensive body of data on the dilution factors has also provided an empirical correlation between the dilution factors and the density of rovibrational states. This relationship shows that about 70 rovibrational states/cm−1 of proper J and symmetry are necessary to ensure substantial state mixing, regardless of molecular structure. The relative energy contents of various vibrational modes after laser excitation can also be determined. A statistical mixing model has been refined to the point of being able to predict dilution factors and their J dependence as well as the relative energy contents of the modes which are involved in the makeup of the mixed excited states. This model assumes equal coupling between all the zeroth order rovibrational states that have the correct energy, symmetry, and J to couple to a given optically active state. The only adjustable parameter in this model is the average energy width over which the character of the zeroth order optically active excited state is spread, which is determined to be ˜0.05 cm−1.
Is there a Signature of the Chaoticity of the Asssociated Classical System in the Spectrum of a Quantum System?
Authors: Lombardi M. , Labastie P. , Bordas M. C. , Broyer M. 
Published: March 2014

AbstractThe cause of the appearance of chaos in classical dynamics is the disappearance of first integrals of the movement which restrict the motion of the configuration point in phase space. This enables the system to wander in increasing parts of the phase space. The direct consequence in quantum mechanics is the disappearance of quantum numbers and of the corresponding selection rules. We will discuss two consequences of this disappearance of selection rules.(1) Level repulsion enabled by breakdown of selection rules. While most papers deal with nearest neighbour spacing distribution, we will show that the most relevant consequence on the dynamical behavior is intermediate and long range correlations between level positions. We will display the correspondence between dynamical evolution in classical, semiclassical limit, and full quantum mechanical versions of a given system.(2) Periodic simplification of spectra due to periodic reestablishment of approximate quantum numbers and associated selection rules, and its counterpart in chaotic or regular parts of classical phase space, in the case of molecular Rydberg states.
Dynamics of Molecular Photoionization Studied by Zero Kinetics Energy Photoelectron Spectroscopy
Authors: Habenicht W. , Baumann R. , Müller‐Dethlefs K. , Schlag E. W. 
Published: March 2014

AbstractWe use high‐resolution two‐colour zero kinetic energy photoelectron spectroscopy (ZEKE‐PES) with full ionic rotational state selection to study photoionization processes of NO from selected rovibronic levels of the A2Σ+ (v = 0, NA) state. The angular momentum transfer molecule → ion seems to depend on the transition chosen for the selection of the intermediate rotational level in the NO A state.
Tyrosine Fluorescence Energy Transfer as a Probe for Interactions of Proteins with DNA
Authors: Schwarzwald Ralf , Greulich Karl Otto 
Published: March 2014

AbstractThe fluorescence decay of the aromatic amino acid tyrosine, as well as of symmetric tripeptides is monoexponential, the fluorescence lifetimes can be understood on the basis of a simple empirical equation for first order rate constants of energy transfer from tyrosine to neighboring amino acids. Fluorescence energy transfer from tyrosine to DNA in protein‐DNA complexes can be used to elucidate the role of Tyr‐DNA interaction in the formation of inverted DNA, a postulated new type of DNA structure and gives information on differences of the role of the positively charged amino acids lysine and arginine in electrostatic protein‐DNA interaction.
Dynamic NMR Study of the Interference between Cyclic Proton Exchange, Selfassociation and Hindered Rotation of Diphenylformamidine in Tetrahydrofuran
Authors: Meschede Ludger , Gerritzen Detlef , Limbach Hans‐Heinrich 
Published: March 2014

AbstractThe 90 MHz1H NMR spectra of15N,15N′‐dipentadeuterophenylformamidine (DPFA), a nitrogen analogue of formic acid, dissolved in tetrahydrofuran‐d8(THF) have been measured as a function of concentration, deuterium fraction in the1H‐15N sites, and of temperature. The spectra show characteristic changes, from which thermodynamic and kinetic information on hindered rotation, hydrogen bond association and proton exchange of DPFA in THF are obtained by NMR lineshape analysis. DPFA forms two conformers A and B in THF, to which s‐trans and s‐cis structures have been assigned. At low concentrations both DPFA conformers are located in a hydrogen bond to the solvent molecules. However, as a result of the different structure, only A is able to selfassociate to any observable extent. This effect leads to concentration dependent A/B populations. Higher selfassociates or mixed AB associates are not observed. Whereas B is not able to exchange protons, A is subject to a very fast proton transfer. By measuring proton lifetimes as a function of concentration and of the deuterium fraction in the labile proton sites, it was established that two protons are transferred in every exchange process. Thermodynamic data of the association process obtained by the analysis of the chemical shifts, of the A/B populations and the proton lifetimes as a function of concentration agreed very well. These results are evidence that A forms only selfassociated hydrogen bonded dimers with a cyclic structure in which the double proton transfer takes place. The observation of a kinetic HH/HD isotope effect of 20 at 178 K establishes this transfer as the rate limiting step of the overall proton exchange. Rate constants of the double proton transfer in the cyclic dimer were obtained as a function of temperature from which an activation energy of about 19 kJ mol−1was obtained. In addition, the rates of interconversion between the two conformers were determined as a function of temperature. Details of the reaction mechanism and differences to the related carboxylic acids are discussed. Thus, it is shown that dynamic NMR spectroscopy can be a useful tool for elucidating elementary steps of complex reaction networks.
Quenching of CHF [Ã1 A″ (0,0 ≦ υ′2 ≦ 5,0)] after Single Vibronic Level Excitation by the Diatomic Molecules H2, O2 and CO
Authors: Dornhöfer G. , Hack W. 
Published: March 2014

AbstractThe elementary deactivation processes of CHF (Ã, υ′2) by H2(X1Σ+g), O2(X3Σ−g), and CO(X1Σ+) were studied in a quasistatic photolysis chamber. Determination of time and spectrally resolved laser‐induced fluorescence of CHF (Ã1 A″, υ′2) in single vibronic excited levels (SVL) (0 ≦ υ′2 ≦ 5) was carried out in the gas phase at room temperature. CHF [X̃1 A′ (0,0,0)] was generated in the fluorescence cell by multiphoton dissociation (MPD) of CH2F2.The overall CHF (Ã, υ′2)‐depletion rate constants:magnified imageA significant increase of the rate constants for higher vibronic states was observed. The contribution of vibration deactivation to the overall depletion of the initially excited state was found to be small (≦ 10%), with approximately the same importance of collision‐induced vibrational quantum change of Δυ′2 = 1 and Δυ′2 = 2 respectively. The reaction mechanisms are discussed.
A Chemical Approach to the Prediction of Thermophysical Properties of Associating Compounds
Authors: Ksiązczak Andrzej , Anderko Andrzej 
Published: March 2014

AbstractA method is presented for predicting gas‐ and liquid‐phase association constants from vapor pressure data using the homomorph concept. The gas‐phase dimerization parameters for alcohols, phenols, amines and carboxylic acids are compared with those obtained from p‐V‐T, thermal conductivity, heat capacity and spectroscopic data. The predicted association enthalpies are in agreement with the results of dilute solution calorimetric measurements. A generalization of the method in terms of topological parameters characterizing molecular structure is proposed. The correlations of association constants with topological parameters allow to reproduce second virial coefficients or vapor pressures on the basis of the structural formula of an associating compound.
Steady Flow Viscosity and Rigidity of Colloidal Spheres in Deionized Suspensions
Authors: Okubo T. 
Published: March 2014

AbstractSteady‐flow viscosities of colloidal spheres, i.e., colloidal silica (8–45 nm in diameter) and monodisperse polystyrene latices (diam. 85 to 780 nm), are measured in deionized suspensions and in the presence of a small amount of NaCl. The plots of shear stress (S) of the crystal‐like structure of the colloids against shear rate (q) show the following features: (1) at very small values of q (smaller than 0.1 s−1), S increases very sharply with increasing q. The S – q curve is S‐shaped, and the rigidity (G) of the colloidal crystal is evaluated from the plots of S against qt/2 (shear strain), where t is time. The G‐values are between 20 and 3000 Pa, which are consistent with those reported hitherto, and increase as the sphere's concentration increases. (2) The sharp increase in S ceases above the critical q value, from which the yield stress of the crystal‐like structure is evaluated to be between 0.1 to 2 Pa. (3) The log (viscosity, η) vs. log q plots shows non‐Newtonian flows: η increases as q decreases and then η reachs a constant value. Furthermore, log η begins to increase linearly as log q decreases with a slope of −1, which supports the crystal‐like nature of the suspensions.
Coherence in Disordered Condensed Matter. II: Size of Coherent Structures in Condensed Systems owing to Luminescent Transitions, and Detection of D‐Fluctuations
Authors: Chatzidimitriou‐Dreismann C. A. , Brändas E. J. 
Published: March 2014

AbstractA connection between complex scaling method (CSM), the Prigogine theory of star‐unitary transformations and the luminescence spectroscopic experiment is presented. CSM predicts the existence of coherent (or: dissipative) structures appearing spontaneously in amorphous matter like liquids, due to the thermal motion. A typical spatial size of these coherent structures is estimated. The connection with measurements of D‐fluctuations is shortly discussed.
Factors Determining the Rate of Dissolution of Metal Oxides in Acidic Aqueous Solutions
Authors: Valverde Nilo 
Published: March 2014

AbstractEmpirical rules governing the dissolution rates of oxides of the transition metals in acidic solutions containing redox systems are exemplified by the dissolution of CoO. Deviations from these rules shown during the dissolution of NiO (and partly of CuO) are discussed. The presence of organic complexing agents in the solution enhances in general the rate of dissolution of metal oxides. In the case of the iron oxides, induction periods of slow dissolution have been observed. An interpretation of these induction periods is based on a particular formation mechanism of metal chelates. The combined action of redox potential and complexing agent in the solution leads to a decrease of the dissolution rates, due possibly to a blocking of crystal surface sites by constituents of the redox couple and the complexing agent.
Cylindrical Poisson‐Boltzmann Equation for Polyelectrolyte Systems and Counterion Condensation Theory
Authors: Cametti C. , Di Biasio A. 
Published: March 2014

AbstractThe numerical solution of the full non‐linear Poisson‐Boltzmann equation for cylindrical polyelectrolyte systems in presence of simple added salts is employed to illustrate the counterion condensation effect occurring at high values of the charge density parameter. The computational results indicate that the main features of counterion condensation remain approximately unchanged upon the adding of simple electrolytes. These results stress the relevance of the Manning condensation theory in the understanding colligative and transport properties of highly charged polyelectrolytes solutions.
Vapour Pressures and Ionic Activity Coefficients in the System KNO3 + H2O from Dilute Solutions to Fused Salts at 425 K, 452 K, and 492 K
Authors: Barry J. C. , Richter J. , Stich E. 
Published: March 2014

AbstractVapour pressure measurements at elevated temperatures in the system KNO3 + H2O over the entire solubility range are reported. The mean ionic salt activities in the pure fused salt standard state and the excess functions of the molar free enthalpy of mixing were computed. Here the activity model of van Laar and one suggested by Pitzer were adopted for analytical treatment of data. Our results match satisfactorily with data from other sources in the lower temperature region. The tendency in this system towards a weakly positive deviation from ideal mixing behaviour is confirmed in the explored temperature range. – Pitzer's formalism is well‐suited for a concentration independent representation of water activity coefficients in this system if the ion size parameter ϱ is allowed to assume larger values than recommended by Pitzer. A rise of ϱ with the temperature seems necessary in view of an optimal representation of the activity data.
Electrochemical Engineering in Disperse Multiphase Systems
Authors: Kreysa G. 
Published: March 2014

AbstractElectrochemical multiphase systems of industrial importance may be divided into dispersed three‐dimensional electrodes, gas evolving electrodes, conversion of gaseous reactants and electrochemical extraction systems. The engineering fundamentals of all these types developed by several groups during the recent years will be summarized. Additionally new electrochemical techniques for studying non‐electrochemical unit operations like absorption and extraction will be introduced.
Reductive Cleavage of the Co,C‐Bond of [(Methoxycarbonyl)methyl]cobalamin
Authors: Tinembart Olivier , Walder Lorenz , Scheffold Rolf 
Published: March 2014

AbstractThe synthesis and characterization of [(methoxycarbonyl)methyl]‐cobalamin 1d is reported. Cyclic voltammetry of 1d in DMSO at a Hg‐electrode shows two irreversible cathodic waves corresponding to the reduction of the base‐off and base‐on forms of 1d. At sweep rates lower than 0.5 V/s, only reduction of the base‐off form is observed (Ep (off) = −0.954 V vs SCE at 0.1 V/s). At sweep rates faster than 10 V/s, reduction of the base‐on form prevails (Ep (on) = −1.422 V vs SCE at 10 V/s). The thermodynamic and kinetic parameters of the base‐off/base‐on equilibrium of 1d in DMSO are estimated. Two electrons are involved in the reduction of 1d in 0.1 M CH3COOH/DMF. In the absence of a proton source, one‐electron reduction predominates. B12s is a sufficiently strong reducing agent to induce reductive decomposition of 1d.
Elektrochemische Grenzstromsensoren für Partialdruckmessungen
Authors: Jahnke H. , Moro B. , Dietz H. , Beyer B. 
Published: March 2014

AbstractPotentiometrie sensors as the λ‐sensor deliver a sufficiently high signal only in a narrow region near the point of equivalence. The reason is the logarithmic dependence of the voltage on the partial pressure of the gas to be measured. For measurements outside of this range limiting current sensors are suitable, their current signal being proportional to the gas concentration. The limiting current can be regulated either by a solid membrane or by gas diffusion, for example in narrow pores. – Depending upon the gas to be converted, the limiting current sensors can be operated cathodically or anodically. All electrochemically convertible gases can be measured in principle. By selection of proper electrode materials and potentials it is possible within limits to gain selective signals. – Sensors with solid as well with liquid electrolytes are dealt with.
Stability of Photoelectrodes Controlled by Electronic Factors: Layered Chalcogenides of Group IV b
Authors: Jaegermann W. , Pettenkofer C. 
Published: March 2014

AbstractThe reactivity of group IV B semiconducting layered compounds (ZrSe2 and ZrS2) has been investigated with surface science techniques (XPS, UPS, and LEED). The surface has been analyzed after chemical and electrochemical oxidation. Type and concentration of oxidation products have been determined. An increased reactivity compared to group VI B layered chalcogenides is found. The semiconductor/electrolyte interface is simulated by adsorption of halogens onto UHV cleaved (0001) surfaces. A light induced reaction of the interface is observed in contrast to the ideal Schottky type behaviour found for MoSe2 for which surface photovoltages have been obtained. The differences in reactivity are discussed in relation to the different electronic structure of the chalcogenides (valence band edges of metal d‐character for MoSe2 and chalcogenide p‐character for ZrSe2 and ZrS2).
An Electrochemical Study on Titanium‐ and Titanium Oxide Electrodes with Oscillating Quartz Crystals
Authors: Müller A. , Wicker M. , Schumacher R. , Schindler R. N. 
Published: March 2014

AbstractThe electrochemical passivation of titanium was investigated by using oscillating quartz crystals as electrode supports. In addition complex plane impedance diagrams and potentiodynamic data were registrated. The results show, that only a fraction of the anodic charge passed through the cell leads to oxide formation. It could be demonstrated, that surface reactions to form hydroxilated surface sites give rise to significant frequency changes. The shifts were attributed to coupling/decoupling of the hydroxilated surface to/from the electrolyte bulk.
Synthesis of 5,10,15,20‐Tetrakisphenylporphins on a Carbon Support for the Cathodic Reduction of Oxygen in Fuel Cells
Authors: Kirschenmann M. , Wöhrle D. , Vielstich W. 
Published: March 2014

AbstractSeveral substituted Fe‐ and Co‐containing tetraphenylporphins 1 were loaded on carbon either by adsorption from acetone or by in situ synthesis on the carbon support. The porphin/carbon combinations were pyrolyzed at 800°C. The electrocatalytic activities in the reduction of dioxygen were investigated in alkaline (KOH) and acid (H2SO4) solutions using porous Teflon‐bonded carbon electrodes impregnated with the catalysts. At 700 mV high current densities of 75 mA/cm2 in acid solution and up to 90 mA/cm2 in alkaline solution were obtained.
Cyclovoltammetric Characterization of Carbon Black Slurry Electrodes
Authors: Heydecke Gabriele , Beck F. 
Published: March 2014

AbstractSlurry electrodes in 1 M H3PO4, made from carbon blacks with a specific surface ranging from 28 to 1475 m2 g−1, were studied by cyclovoltammetry (5 mV s−1) at potentials between −0.1 V and +2.3 V vs. SHE. A large anodic peak and a small cathodic one is found, with an extreme peak separation (1.5 V) and with a charge ratio of 3:1 to 5:1. Charge transfer at the feeder is hindered by insulating surface layers on the carbon black. Part of the anodic peak is due to the irreversible oxidation of the solid. The initial curves are governed by the large capacity of the system. – This slurry electrode differs widely from that made with metal powders or hard graphite. The particles strongly adhere to the feeder and build up a porous system. The exchange with the dispersed particles is poor. In spite of this, the curves are reproducible, they reflect the specific surface and it is possible to recognize features with respect to the anodic oxidation of carbon black.
Herstellung eines Berberin‐Sensors und seine Eigenschaften
Authors: Aubeck R. , Hampp N. , Bräuchle C. 
Published: March 2014

AbstractThe fabrication and the properties of a berberine‐sensitive electrode are reported. It is based on a highly lipophilic ion pair from berberine and tetraphenylborate (BerbTPB). PVC liquid membranes containing 10% BerbTPB were characterized by use of a newly developed transducer (BIOBRID‐module). The detection limit of the berberine‐sensor is 10−8 mol/l, the linear response range is observed from 10−7 to 10−5 mol/l. Interference of inorganic cations like Na+, K+, Li+, Mg2+ and Ca2+ is negligible (Apotij < 10−4). The logarithmic cross selectivity coefficients for some structural related alkaloids show that BerbTPB is a suitable selective ion pair for the manufacture of a liquid membrane based potentiometric berberine sensor (Coralyne 10−0.6, Papaverine 10−2.1, Atropine 10−4.2).