Showing papers in "Zeitschrift für Physikalische Chemie in 2003"
TL;DR: In this article, the application of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel in order to reach submicrometer precision and high processing speed.
Abstract: Application of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail
132 citations
TL;DR: The significance of nano-size effects for ion transport in solids is highlighted both experimentally - by presenting various results of recent investigations - and theoretically - by considering expected size effects using a top-down approach.
Abstract: The significance of nano-size effects for ion transport in solids is highlighted both experimentally - by presenting various results of recent investigations - and theoretically - by considering expected size effects using a top-down approach. It is helpful to distinguish between trivial size effects (effects that equally occur at single interfaces but are augmented by the high interfacial density) and true size effects (involving local modifications due to the finite boundary conditions). The latter ones essentially include space charge overlap and structural interference leading to two characteristic sizes with respect to defect chemistry. The contribution also briefly touches upon effects of dimensionality and shape as well as of discreteness of carrier distribution.
78 citations
TL;DR: Neugebauer et al. as mentioned in this paper demonstrated how Raman intensities for selected vibrational normal modes can be calculated by extension of asemi-numerical, very flexible approach to the calculation of vibrational spectra.
Abstract: Since Raman spectra of isolated large molecules are hardly accessible by present day quantum chemical methods, we demonstrate how Raman intensities for selected vibrational normal modes can be calculated by extension of asemi-numerical, very flexible approach to the calculation of vibrational spectra [see J. Neugebauer et al., J. Comp. Chem. 23 (2002) 895-910]. The methodology is applied to a C i -symmetric dinuclear diazene iron-sulfur complex with relevance to the biological nitrogen fixation problem. The accuracy of the vibrational spectra allows us to use the spectra for structure determination and assignment of bands to isomeric structures, which were conjectured to be generated by a photoisomerization process. We can in turn support the photoisomerization hypothesis.
60 citations
TL;DR: In this article, a kinetic model of the processes during hydrogen evolution at a single Pd nanoparticle supported on an Au substrate is studied, which builds the theoretical framework for results of currently performed STM measurements on this system.
Abstract: A kinetic model of the processes during hydrogen evolution at a single Pd nanoparticle supported on an Au substrate is studied. It builds the theoretical framework for results of currently performed STM measurements on this system. The objective of the theory is to establish relations between measured transients and underlying processes. It, thereby, helps to implement the routines for the determination of kinetic parameters from transient currents and supplements the characterization of the Pd/Au system. The balance of hydrogen involves interfacial processes on the Pd/Au substrate surface, hydrogen diffusion in the bulk electrolyte and hydrogen oxidation at the tip. The key parameter of the model is the rate of hydrogen desorption from the Pd surface. If this rate is small hydrogen will spillover from the Pd particle and diffuse on the Au surface from where it will be subsequently released. Thereby, large amounts of hydrogen can be stored on the surface. It is demonstrated, that this mechanism complies with the high turnover rates at the smallest catalyst particles and characteristic time scales observed in experiment.
49 citations
TL;DR: In this paper, the contributions of different vibrationalisotope effects to H/D NMR isotope shifts referred in the literature are estimated using 1 H, 1 9 F magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry.
Abstract: Using ah initio calculations of 1 H, 1 9 F magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry, an attempt is made to estimate the contributions of different vibrationalisotope effects to H/D NMR isotope shifts referred in the literature. It is shown that the contributions of the amplitudes of proton stretching and bending vibrations dominate whereas the contribution of the totally symmetric vibration can be neglected. Different signs of the H/D isotope effects on hydron and fluorine chemical shifts are caused by very strong angle dependence of the fluorine magnetic shielding. The agreement of the calculated and measured values is nearly quantitative. An unusually strong paramagnetic deshielding of hydrogen for the equilibrium geometry of the [FHF] - ion is noted.
39 citations
TL;DR: In this paper, cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance to reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface.
Abstract: The cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2M H 2 S0 4 + 0.3 M CuS0 4 ) is markedly affected by the presence of small concentrations of halide ions. Chloride ions acceleratethe reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuC1 and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3M CuS0 4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.
36 citations
TL;DR: In this paper, it was shown that a slight reversible-adiabatic alignment of the clusters dipole moment in the electric field increases the average beam deflection and the derived polarizability values.
Abstract: Deflections of semiconductor cluster beams in an inhomogeneous electric field deliver enhanced polarizabilities for cold isolated Ga N As M clusters with odd number of atoms n = N + M up to n = 17. One speculated that the high polarizabilities result from their electronic open shell structure. This was qualitatively confirmed by optical absorption cross section measurements, but the enhancement of polarizability is too large to be explained through a Kramers-Kronig-relation as purely electronic effect. Moreover, quantum chemical calculations gave permanent dipole moments of some tenths of a Debye for certain compositions. The clusters are too heavy to identify these dipole moments by beam broadening effects, but we will show in the present analytic investigation within classical top theory, that a slight reversible-adiabatic alignment of the clusters dipole moment in the electric field increases the average beam deflection and the derived polarizability values. This effect was up to now not taken into account and it offers a consistent explanation of the Ga N As M polarizabilities by small permanent dipole moments of some tenths of a Debye and a reasonable rotational temperature between 2 and 12 K.
35 citations
TL;DR: In this paper, the potential modulation or the subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) experiments have been performed, in order to distinguish between the bulk properties of the Nafion® membrane and the properties of membrane at the interace with the Pt electrode.
Abstract: Infrared Reflection Absorption Spectroscopy (IRRAS) has been applied to study the nature of the co-ordination of Nafion® to a Pt electrode surface. The experiments have been carried out using a Pt electrode coated with athin film of Nation® assembled into a thin layer spectroelectrochemical cell. The potential modulation or the subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) experiments have been performed, in order to distinguish between the bulk properties of the Nafion® membrane and the properties of the membrane at the interace with the Pt electrode. The results showed that the interaction between the membrane and a Pt electrode resembles the interaction between a Pt electrode and a sulfuric acid solution.
34 citations
TL;DR: Pt was deposited onto a Ru(0001) electrode from a PtCl 6 2 -containing HClO 4 solution either electrochemically or spontaneously (i.e. without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy, high energy electron diffraction (RHEED), and scanning electron microscopy (SEM) as discussed by the authors.
Abstract: Pt was deposited onto a Ru(0001) electrode from a PtCl 6 2 - -containing HClO 4 solution either electrochemically or spontaneously (i.e. without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy (AES), high energy electron diffraction (RHEED), and scanning electron microscopy (SEM). At first pseudomorphic growth of a 2D-Pt adlayer takes place, while with higher coverages 3D-clusters develop for which the most densely packed [011]-rows of the Pt(111) planes are parallel with the most densely packed [1120] -rows of the Ru(0001) substrate. These Pt-clusters exhibit typical diameters between 2 and 10 nm, while their average mutual separation varies with the total amount of deposit. If compared with the bare Ru(0001 ) surface, the samples with Pt deposits exhibit considerably enhanced activity with respect to electrooxidation of formic acid or methanol.
33 citations
TL;DR: In this article, the apparent specific volume of dipalmitoylphosphatidylcholine (DPPC)-cholesterol mixtures in excess water as a function of pressure up to 70MPa (700 bar) at 20, 38 and 50°C.
Abstract: We conducted detailed measurements of the apparent specific volume of dipalmitoylphosphatidylcholine (DPPC)-cholesterol mixtures in excess water as a function of pressure up to 70MPa (700 bar) at 20, 38 and 50°C. The volumetric properties and the isothermal compressibility κ T of the lipid vesicles were determined at cholesterol concentrations, Χ c h o l , ranging up to 50 mol%. The thermodynamic data are compared with other physicochemical properties of phospholipid-cholesterol mixtures. Furthermore, the thermodynamic properties of the system are discussed in the light of the various T, Χ c h o l -phase diagrams and computer simulation studies published in the literature.
32 citations
TL;DR: In this article, the infrared spectrum of the O-H-O fragment of malonaldehyde was studied using a four-dimensional model and the full anharmonic potential energy and dipole moment surfaces were calculated using density functional theory.
Abstract: The infrared spectrum of the O-H-O fragment of malonaldehyde is studied using a four-dimensional model. This comprises the OH stretching and the two OH bending vibrations as well an O-O ring deformation mode under the assumption of overall C, symmetry. The full anharmonic potential energy and dipole moment surfaces are calculated using density functional theory and the respective vibrational eigenvalue problem is solved by an iterative Lanczos method. Fundamental and combination transitions are discussed for the normal species and the symmetrically deuterated isotopomer. Special emphasis is paid to the OH/OD stretching region which reveals the signatures of strong mode mixing what renders a simple assignment in terms of fundamental transitions difficult. In addition results for hot transitions are presented which show a rather different OH/OD band due to the topology of the potential energy surface. The influence of H atom tunneling on the spectrum is briefly addressed employing an alternative three-dimensional model which takes into account the in-plane H atom motion as well as the O-O distance.
TL;DR: In this article, a large number of copper(I) and cobalt(III) complexes, behaving as strong 1:1 electrolytes, have been measured in acetonitrile and n-butyronitrile (n-BTN) at 298.15K.
Abstract: Molar conductances of a large number of copper(I) and cobalt(III) complexes, behaving as strong 1:1 electrolytes, have been measured in acetonitrile (AN) and n-butyronitrile (n-BTN) at 298.15K. The conductance data have been analyzed by the Shedlovsky method to evaluate Λ 0 and K A values of these electrolytes. Limiting ion conductances (λ 0 i ) for various ions in AN have been calculated by using transference number data. In n-BTN, where no transference number data is available, such values have been calculated by an indirect method using Bu 4 NBPh 4 as a reference electrolyte. The actual ionic radii (r i ) for various ions in solution have been calculated using a modified form of Stokes' law. The ionic radii (r,) for various complex ions have been compared with the ionic radii of two reference ions, Bu 4 N + and Ph 4 B - , which are not solvated in dipolar aprotic solvents, to throw light on the solvation behaviour of these complex ions.
TL;DR: In this article, the authors report the various structural phases and their potential dependence of electrochemically deposited sulfide layers on Cu(100) and a full description of their concentration dependence is given in a forthcoming paper.
Abstract: In-situ EC-STM has been used to examine distinct phases of electrochemically deposited sulfide layers on Cu(100). The observed structures can be clearly assigned to specific ranges of the electrode potential and the sulfide concentration in solution. The scope of the present contribution is to report the various structural phases and their potential dependence. A full description of their concentration dependence will be given in a forthcoming paper. All incipient adsorption processes have been performed exclusively at negative electrode potentials close to the on-set of the hydrogen evolution reaction in order to avoid heavy surface reactions of the copper substrate with sulfide as seen at positive electrode potentials. In a very early stage of the sulfidation first a metastable, transient p(2 x 2)-S layer with a nominal coverage of Θ = 0.25 ML is formed which gets irreversibly replaced by an energetically more stable c(6 x 2)-S phase with Θ = 0.33 ML. This process at constant potential is kinetically hindered and depends on the sulfide supply from the electrolyte of given concentration. All further phase transitions induced by a positive going potential sweep are influenced by the sulfide supply from the electrolyte phase as well. A low sulfide supply from a low concentration electrolyte during a positive going potential sweep provokes a uniaxial compression of the preexisting c(6 x 2)-S phase ending up with a striped c(4 x 2)-S phase. Conversely a high sulfide supply from a high concentration solution during a positive going potential sweep causes a massive reorganization of both the atomic structure and the surface morphology on a mesoscopic scale. This latter process involves a massive transport of copper material out of the topmost copper layer and is, hence, identified as an adsorbate induced reconstruction of the copper substrate. The symmetry of the resultant sulfide structure on-top of the reconstructed copper substrate is similar to a square c(2 x 2) arrangement but on a copper surface whose lattice constants are expanded by 9% with respect to the copper bulk structure. Hence, the atomic surface structure is denoted as a pseudo-c(2 x 2)-S reconstruction.
TL;DR: In this paper, the rates of adsorption of seven aromatic heterocyclic compounds at an high-area carbon-cloth material have been investigated in relation to waste-water purification.
Abstract: Adsorption behaviours of some structurally related aromatic heterocyclic compounds at an high-area carbon-cloth material have been investigated in relation to waste-water purification. Adsorption processes were followed by monitoring the concentration of adsorbates in a specially designed cell using an in situ UV spectrophotometric method. The rates of adsorption were compared by treating the data according to first-order kinetics. Among the seven heterocyclic compounds studied, thiophene was found to exhibit the highest adsorption rate. This was attributed to the presence of the electron-donative S heteroatom in the structure of this compound. The influences of the dipole moment, the orientation at the C-cloth surface and the size of the heterocyclic adsorbate compound, as well as the type of heteroatom in the ring and the adsorbates' hydration parameters, on the extent of adsorption of these compounds at the C-cloth were investigated.
TL;DR: In this article, strong collision falloff curves for barrierless recombination reactions at low temperatures are calculated taking into account transitional modes only, and broadening factors of the falloff curve are found to depend only weakly on the temperature.
Abstract: Strong collision falloff curves for barrierless recombination reactions at low temperatures are calculated taking into account transitional modes only. Specific rate constants k(E, J) from statistical adiabatic channel/classical trajectory (SACM/CT) calculations are used. Broadening factors of the falloff curves are found to depend only weakly on the temperature. A systematic analysis of the influence of the centrifugal barriers E 0 (J), which are governed by the potential energy surface of the bond energies E 0 , and of the number of transitional modes is made. Guidelines for estimating center broadening factors and shape functions for the broadening factors are given.
TL;DR: In this article, pressure perturbation calorimetry (PPC) was used to study the solvation and volumetric properties of the enzyme ribonuclease A (RNase A) in its native and unfoldedstate.
Abstract: In this study, pressure perturbation calorimetry (PPC), a relatively new and efficient technique, was used to study the solvation and volumetric properties of the enzyme ribonuclease A (RNase A) in its native and unfoldedstate. In PPC, the coefficient of thermal expansion of the partial volume of the protein is deduced from the heat consumed or produced after small isothermal pressure jumps (′5 bar), which strongly depends on the interaction of the protein with the solvent or co-solvent at the protein-solvent interface. The effects of various chaotropic and kosmotropic co-solvents (glycerol, sorbitol, urea, guanidinium hydrochloride, K 2 SO 4 ) on the solvation and unfolding behaviour of RNase A was investigated as well, and the observed volume and expansivity changes are correlated with further thermodynamic properties obtained from differential scanning calorimetry (DSC). Depending on the type of co-solvent and its concentration, specific differences are found for the solvation properties of the protein, and the volume change upon unfolding may even change sign. Taken together, the data obtained lead to a deeper understanding of the solvation process of proteins in different co-solvents in their native and unfolded states.
TL;DR: Ausgehend von Beobachtungen durch Döbereiner und zahlreiche andere führte Berzelius 1835 den Begriff Katalyse ein, deren Wirkung häufig mit dem Stein der Weisen verglichen wird as discussed by the authors.
Abstract: Ausgehend von Beobachtungen durch Döbereiner und zahlreiche andere führte Berzelius 1835 den Begriff Katalyse ein, deren Wirkung häufig mit dem ,Stein der Weisen‘ der mittelalterlichen Alchemie verglichen wird. Erst gegen Ende des 19. Jahrhunderts erfolgte durch Ostwald eine klare Definition auf der Grundlage der Reaktionskinetik. Schließlich wird der heutige Stand der Erkenntnis kurz an einem Beispiel erläutert.
TL;DR: In this article, the decomposition of Ru(cod)(cot) under an H 2 atmosphere (3 bars) in pure heptanol produces crystalline monodisperse nanoparticles of 3nm mean size characterized by TEM and WAXS techniques.
Abstract: The decomposition of Ru(cod)(cot) ( 1 ; cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) under an H 2 atmosphere (3 bars) in pure heptanol produces crystalline monodisperse nanoparticles of 3nm mean size characterized by TEM and WAXS techniques. Solution NMR studies demonstrate the presence of surface hydrogens due to the synthesis process and suggest a fast exchange between free and coordinated heptanol molecules.
TL;DR: The use of single-crystal electrodes with atomically well-defined surface structures allows a view of electrochemical interfaces and simple electrochemical reactions at a level of sophistication unheard of at the time of Wilhelm Ostwald.
Abstract: Modern surface-science techniques like scanning tunnelling microscopy and the use of single-crystal electrodes with atomically well-defined surface structures allow a view of electrochemical interfaces and of simple electrochemical reactions at a level of sophistication unheard of at the time of Wilhelm Ostwald.
TL;DR: In this article, the authors measured the 1 2 9 Xe NMR chemical shift in the supercritical state up to a pressure of about 70MPa, i.e., a density of 440 amagat' at 298 K.
Abstract: The measurement of the 1 2 9 Xe Nuclear Magnetic Resonance (NMR) chemical shift as a function of density is reported The apparatus used in this study enabled us to measure the 1 2 9 Xe NMR chemical shift in the supercritical state up to a pressure of about 70MPa, i.e., a density of 440 amagat' at 298 K.
TL;DR: Two-, three-, and four-bond spin-spin coupling constants for a set of small fluoro-substituted organic molecules have been computed using ab initio equation-of-motion coupled cluster singles and doubles (EOM-CCSD) theory as mentioned in this paper.
Abstract: Two-, three-, and four-bond 1 9 F- 1 9 F spin-spin coupling constants ( n J F F ) for a set of small fluoro-substituted organic molecules have been computed using ab initio equation-of-motion coupled cluster singles and doubles (EOM-CCSD) theory. The computed values reproduce the experimental signs and magnitudes of n J F F . The straight line that relates the experimental and computed coupling constants has a slope of approximately 1 and passes through the point (0,0 Hz) within the uncertainties of the fit. Hence, EOM-CCSD values of n J F F should be excellent predictors of experimental values when these are not available. All of the components of n J F F except for the diamagnetic spin-orbit term may be large and must be evaluated if agreement between theory and experiment is to be obtained.
TL;DR: In this article, the reaction between permanganate and nicotinate ion in alkaline medium exhibits 2 : 1 stoichiometry (KMnO 4 : Nicotinate ions).
Abstract: The kinetics of oxidation of nicotinate ion by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and nicotinate ion in alkaline medium exhibits 2 : 1 stoichiometry (KMnO 4 : Nicotinate ion). The reaction shows first order dependence of rate on permanganate concentration and less than unit order dependence each in nicotinate ion and alkali concentrations. Reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of an intermediate complex between oxidant and substrate has been proposed. The rate and the activation parameters for the slow step have been evaluated.
TL;DR: In this article, the SAC-CI general-R method was applied to the outer and inner-valence ionization spectra of N 2 O and HN 3.
Abstract: Fine theoretical spectroscopy for the outer- and inner-valence ionization spectra has been presented by using the SAC-CI (symmetry adapted cluster-configuration interaction) general-R method applied to N 2 O and HN 3 . The SAC-CI general-R method accurately simulated the experimental spectra and the detailed assignments of the satellite peaks were proposed. The continuous peaks I∼V of N 2 O observed by the dipole (e,2e) spectroscopy were finely reproduced. In particular, the low-lying satellites were calculated in good agreement with the experiment; two 2 Π shake-up states at the foot of the C state, 2 Σ and 2 Π states for the peak I. For HN 3 , new interpretation was proposed for the outer-valence region, namely, peaks 3∼5 5 are composed of the mixture of the single-electron main peaks and the two-electron shake-up peaks. Inner-valence ionization spectrum of HN 3 was theoretically predicted for which no experimental spectrum has been reported.
TL;DR: In this paper, the intermolecular interaction potential is strongly affected by intramolecular hydrogen bonding, which is assumed to be responsible for the deviations in the absorbance of the terminal OH groups.
Abstract: Abstract Solute descriptors characterizing major interactions in solution are accessible based on quantitative structure-property relationships (QSPR). Parameters of such relationships should be additive for functional groups. Because added parameters of monools describing molecular interaction do not meet the experimentally found intermolecular interaction parameters of diols and triols, it is assumed that intramolecular hydrogen bonding is responsible for these deviations. In this paper the intramolecular interactions in several diols are illuminated by IR measurements. Particularly, the influence of intramolecular hydrogen bonding on the absorbances of the OH groups is subject of investigation. Two conclusions can be drawn from the results: The terminal OH groups, which underlie an OH–OH interaction, also change their absorbance intensity in comparison to the free OH band. Secondly, the intermolecular interaction potential is strongly affected by intramolecular hydrogen bonding. The first observation is tentatively quantified as well as the position of the equilibrium between intramolecularly bonded and free diols.
Abstract: In this work the results of numerous experiments on carbon particle formation in combustion and pyrolysis of various carbon bearing molecules behind shock waves in the wide temperature range from 1200K to 3500K are analyzed. It is shown, that the discrepancy in the temperatures of the maximum particle yield could be attributed to the differences in the endothermicy of the pyrolysis of various molecules and the maximum optical density at 633 nm in all mixtures can be related to the same temperture T=1600K. Based on this consideration, several statements were formulated. First -particle growth in all mixtures can be described by the uniform dependence of optical density D (at 633 nm) on time D ∼ aτ 0 . 4 indicating, that particle formation proceeds via homogeneous condensation. The second - decrease of the optical density at 633 nm with the temperature rise is caused not by the decrease of particle yield, but the decrease of their size resulting in the fall of extinction at the given wavelength. Third - the reason of the fall of the final particle size with the temperature rise is the acceleration of the initial cluster formation process and a corresponding increase if the particle number density. And the last statement -- the secondary particle growth, observed at T>2200K is completely determined by the primary clusters (nucleus) formed behind the incident wave and the coagulation of small carbon particles formed behind the reflected shock wave using these clusters.
TL;DR: In this paper, a simple set of rules for the development of the ion dynamics with time has been provided by the MIGRATION concept, the acronym standing for Mismatch Generated Relaxation for the Accommodation and Transport of IONs.
Abstract: Since Ostwald's times, the concepts of ionic motion in condensed matter have been extended to comprise systems with increasingly complex dynamic properties. Today, one of the central problems in the field of SOLID STATE IONICS consists in finding simple, yet relevant rules for the correlated hopping motion of the mobile ions in structurally disordered ionic materials. Rubidium silver iodide, RbAg 4 I 5 , belongs to this class of materials. To analyse the hopping dynamics of the mobile silver ions in the three phases of RbAg 4 I 5 , we have taken conductivity spectra at frequencies up to the far infrared. Also, a simple set of rules for the development of the ion dynamics with time has been provided by the MIGRATION concept, the acronym standing for Mismatch Generated Relaxation for the Accommodation and Transport of IONs. In the phases a and β, an increasing tendency for correlated forward-backward hopping is observed as the temperature is decreased from 298 K to 129K. At the first-order β-γ phase transition at 121.8 K, the number of translationally mobile silver ions is found to be markedly reduced. The conductivity spectra of the different phases of RbAg 4 I 5 are well explained by the MIGRATION concept as long as the angular frequency does not exceed the elementary hopping rate of the mobile silver ions. At higher frequencies, an additional dynamic feature is encountered, which is superimposed onto the MIGRATION-type conductivity. This feature, which shows a nearly constant loss (NCL) behaviour, becomes increasingly pronounced as the temperature is lowered. It is caused by a strictly localised motion of interacting silver ions. In our model treatment for the MIGRATION and NCL parts of the dynamic conductivity, the potentially translational and the strictly localised ionic hopping motion are best described with a single elementary hopping rate. Consequently, this rate marks the beginning of the NCL behaviour on the angular frequency scale. This observation is in agreement with earlier results obtained by Leon et al. on solid lithium-ion conductors.
TL;DR: In this paper, the wavepacket dynamics of the diatomic molecule in reduced dimensionality are described in terms of 1 and 2-or 3-dimensional wavepackets, respectively.
Abstract: Quantum dynamical simulations of ultrafast processes of F 2 in an Ar matrix induced by a pump laser pulse show that photoexcitation (i) is followed by (ii) a stretch of the dissociative bond, (iii) collision with, vibrational excitations of, and possible exit through the nearest neighbour atoms of the surrounding cage, and (iv) finally, subsequent rescattering of the dissociated atoms causing vibrations of additional matrix atoms. If the laser pulse ended before the onset of process (iii), the initial steps (i) and (ii) are similar to photodissociations in the gas phase and are, therefore, well described in terms of the wavepacket dynamics of the diatomic molecule in reduced dimensionality. For specific symmetry constraints, the initial processes (i), (ii), and (iii) may be described in terms of just 1- and 2- or 3-dimensional wavepacket dynamics, respectively. At the end of the laser pulse, this low-dimensional wavepacket may serve to prepare the high-dimensional one for the subsequent laser-free dynamics of the total system.
TL;DR: In this paper, the spin polarization of a non-equilibrium system of N coupled nuclei is analyzed and applied to photo-reactions exhibiting chemically induced dynamic nuclear polarization (CIDNP), based on the Fourier analysis of the variation of NMR line intensities as a function of the radio frequency excitation pulse length.
Abstract: A new, convenient method of analyzing the spin polarization of a non-equilibrium system of N coupled nuclei is described and applied to photo-reactions exhibiting chemically induced dynamic nuclear polarization (CIDNP). It is based on the Fourier analysis of the variation of NMR line intensities as a function of the radio frequency excitation pulse length. A relationship between the spectral components at various harmonic order and the alignment in the spin multiplet is established. In application to the Norrish type I photolysis of cyclodecanone we demonstrate that at low magnetic field the rate determining step in the reaction kinetics depends on the mutual orientation of at least four pairs of non-equivalent spins.
TL;DR: In this article, a quantitative model of oscillations observed during hydrogen oxidation on platinum in the presence of electrosorbing metal ions and specifically adsorbing anions is presented and the model predictions are compared with experiments.
Abstract: A quantitative model of oscillations observed during hydrogen oxidation on platinum in the presence of electrosorbing metal ions and specifically adsorbing anions is presented and the model predictions are compared with experiments. Mass and charge balances of all reactants lead in a first step to a seven variable model which is governed by reaction steps that have been widely studied. We demonstrate that attractive interactions between metal and halide ions on the electrode surface, which were recently reported [1], are crucial for the observed dynamics. The model parameters were almost exclusively taken out of the literature. The model is then reduced to its minimal form without losing dynamic features arriving at a four variable system. Experimental time series of three of the four variables of the model and measured bifurcation diagrams are presented. It is shown that the integrated time evolution and the calculated bifurcation diagrams of the model agree almost quantitatively with the experiment.
TL;DR: In this article, the effects of pressure on the inclusion of β- and γ-cyclodextrins (CDs) with 4-substituted phenols were examined.
Abstract: The effects of pressure were examined for the inclusion complexation of β- and γ-cyclodextrins (CDs) with 4-substituted phenols. The reaction volume for the CD inclusion complexation with 4-substituted phenols, which is the change in volume accompanied by CD inclusion, was estimated from the pressure dependence of the inclusion equilibria. The reaction volumes estimated for the phenols/β-CD system were positive values in the range of 2.5 and 14.0cm 3 mol - 1 , while those for the phenols/y-CD system were negative in the range of -11.8 and -0.8 cm 3 mol - 1 . The difference in the reaction volumes for the inclusion complexation of β- and γ-CDs is explained in terms of the difference in the number of water molecules repelled from the CD cavity. Based on the results, the inclusion behavior of CD complexation is discussed.