bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and 27Al MAS NMR lineshape analysis
Authors: Jäger C. , Hartmann P. , Kunath‐Fandrei G. , Hirsch O. , Rehak P. , Vogel J. , Feike M. , Spiess H. W. , Herzog K. , Thomas B.
Published: July 2012

The recent progress in NMR of glasses is demonstrated using both traditional and improved two‐dimensional (2D) NMR techniques. A novel approach for measuring connectivities Qn units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27Al NMR investigations in mullites and Na2O‐SiO2‐Al2O3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na2O‐Al2O3‐SiO2 glasses we could prove the presence of two AlO4 sites with Al being surrounded by four Q3 units or possibly one terminal oxygen instead of a Q3 unit (60 ppm) and by four Q4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23Na MQ NMR in a glass 22.7 Na2O 0.7 B2O 69.8 SiO2.
Order in li‐silicate glasses by diffraction methods
Authors: Uhlig H. , Lamparter P. , Steeb S.
Published: July 2012

A silicate glass containing 20 mole % Li2O was investigated by X‐ray diffraction as well as neutron diffraction. In the latter case isotopic substitution was done by replacing Li of natural isotopic abundance by 6Li, 7Li, and 0Li, respectively. 0Li is a mixture of Li‐isotopes with resulting scattering length zero. Using the reverse Monte Carlo method, a cluster containing 3000 atoms is constructed which is in accordance with the experimentally obtained total structure factors. This cluster yields the partial pair correlation functions and various angle correlation functions. Further hints on the three‐dimensional arrangement of the bonds are obtained using the method of Steinhardt et al. All data obtained are compatible with a proposed model for the atomic arrangement in lithium‐silicate glasses. This model is characterized by a distinct increased order compared to the structure of the pure silicate. The order is determined by sixfold rings and an oxygen‐sublattice.
X‐ray spectroscopy of ion‐exchanged glasses
Authors: Dubiel M. , Brunsch S.
Published: July 2012

X‐ray absorption Spectroscopy makes it possible to identify the local atomic structure around cations in ion‐exchanged glasses. EXAFS experiments demonstrate that the substitution of sodium by silver leads to local rearrangements below TG whereas the incorporation of Rb or Cs does not generate a cation specific environment. Fe K‐edge XANES spectra confirm that the oxidation of Fe2+ is accompanied by the reduction of silver ions. A structural interpretation of the modified mixed mobile effect as a result of an ion exchange has been developed.
Probe ions for local structure investigations of glasses
Authors: Seeber Wolfgang , Ehrt Doris
Published: July 2012

The successful design of materials for optic and laser technology needs tools of investigation. Besides physical, chemical and optical properties especially the spectroscopic behavior of these materials is important. Knowledge about the local structure of doped active ions may provide the basis for tailoring of spectroscopic properties. Special ions, e.g. Nd3+, Gd3+ or Pb2+ as so‐called probe ions have been incorporated into optical glasses to probe relevant sites of the amorphous network. The Nd3+: 4I9/2→2P1/2 absorption transition has been used to sense the strength of the crystal field in the vicinity of the laser ion and to derive information about emission properties of embedded laser ions. The Gd3+: 6P7/2→8S7/2 emission transition at 315 nm is useful for determination of electron‐phonon interactions. The Pb2+ ion (1S0→3P0 absorption transition) has been applied as probe ion for alkaline earth ion sites. The optical basicity of fluoride phosphate glasses with different phosphate content has been estimated. The application of probe ions for local structure investigations can give assistance in the complex process of material design. However, these methods should not be overestimated because of the huge numbers of parameters affecting the performance of a laser material and complementary investigation methods must be used.
Glasses of sugars and sugar substitutes
Authors: Cammenga H. K. , Zielasko B.
Published: July 2012

Many sugars occur in several crystalline and in an amorphous form. The glass transition temperatures of isomalt and its components and the enthalpies of fusion are reported. Amorphous sugars are extremely hygroscopic and sorb large amounts of water. This gives rise to supersaturated sugar solution, from which the sugar recrystallizes in its stable polymorph while the sample loses water, but if the sugar is able to form a hydrate, most of the water is incorporated as water of crystallization and only the non‐bound water is released.
Wide angle X‐ray studies on molten oxide glasses
Authors: Herms G. , Gerike W. , Sakowski J.
Published: July 2012

High‐temperature diffraction studies on molten oxide glasses show that it is necessary to differentiate in describing the structure of melts. There are glasses in which the short range order (SRO) changes markedly in the temperature range above Tg.
DTA study of rare earth doped ZBYA‐type fluoride glasses
Authors: Rasztovits Z. E. , Szabó I. , Frischat G. H.
Published: July 2012

In the present study the effect of the rare earth elements Ho and Eu on the crystallization behavior of ZBYA‐type fluoride glasses was investigated by means of DTA. Stability criteria like thermal stability range, weighted thermal stability range, crystallization range and Saad and Poulain's criterion were calculated. Furthermore a kinetic analysis was carried out in terms of the Kissinger method and the apparent activation energy of crystallization was evaluated to characterize the crystallization trends as a function of type and concentration of dopants.
Experimental determination of the interface tension of liquid silver halide in a sodium borosilicate melt
Authors: Lembke U. , Blau W.
Published: July 2012

A method for the direct measurement of the interface tension of precipitating silver halide in a photochromic glass melt is presented. The technique is based on the determination of the mean radii of curvature of a glass droplet swimming in the silver halide melt at temperatures above the glass transition temperature. The calculation of the interface tension is performed by means of the Laplace equation taking into account the gravitational force and the force of buoyancy. The results obtained for 610°C and 850°C are used to estimate the nucleation rates for the formation of silver halide phases in photochromic glasses.
Asymmetric properties of ultrathin poly(vinylchloride) films as generated by molecular association of ionic porphyrins at the polymer‐water interface
Authors: Yamada Sunao , Iida Hiroshi , Matsuo Taku
Published: July 2012

An amphiphilic porphyrin derivative, 4,4′,4″,4‴‐(21 H,23 H‐porphine‐5,10,15,20‐tetrayl)tetrakis[1‐hexadecyl‐pyridinium] cation or its zinc complex (abbreviated as MC16TPyP), was preferentially impregnated on a single surface of an ultrathin poly(vinylchloride) film prepared by casting the polymer solution on water. Enrichment of the cationic porphyrin moiety to the polymer‐water interface during the film preparation was strongly indicated by contact‐angle measurement of water‐droplets on the dry surface. A subsequent treatment of the film with an aqueous solution, which contained an anionic porphyrin (4,4′,4″,4‴‐(21 H, 23 H‐porphine‐5,10,15,20‐tetrayl)tetrakis[p‐benzenesulfonate] anion or its copper or zinc complex: MTPPS), led to molecular association of the two‐types of porphyrins (MC16TPyP‐M'TPPS) on the film surface. Spectroscopic evidences for the formation of molecular association on the thin film were obtained by measuring electronic absorption, fluorescence, and optical second‐harmonic generation.
69Ga NMR and 115In NMR in AB2X4 crystals
Authors: Breuer A. , Siebert D.
Published: July 2012

For several Ga defect chalcopyrites and one In spinel we determined nuclear quadrupole coupling constants and electric field gradients (EFG) from NMR measurements of the second order shift of the 69Ga and 115In resonances. A model is proposed for the lattice contribution and the orbital contribution of the EFG.
Molar excess enthalpies of n‐monohaloalkanes + n‐monohaloalkanes mixtures. Estimation of DISQUAC interchange energy parameters
Authors: Artal Manuela , Embid José Muñoz , Otín Santos , Velasco Inmaculada
Published: July 2012

Molar excess enthalpies, H, at 298.15 K and atmospheric pressure were determined for six binary liquid mixtures [x{iodethane or 1‐iodobutane or bromoethane or 1‐bromobutane or 1‐chloropropane or 1‐chloropentane} + (1 ‐ x) 1‐fluoropentane]. These experimental results along with the data available in the literature on molar excess Gibbs energies, G, activity coefficients at infinite dilution, In γ, and molar excess enthalpies, H, for n‐monohaloalkane + n‐monohaloalkane mixtures, are examined on the basis of the DISQUAC group‐contribution model. The interchange energies of the contacts between two different halogen atoms are entirely dispersive and were determined in this work. The model reproduces reasonably well most of the experimental data. For a given n‐monohaloalkane, mixed with the other n‐monohaloalkanes, it can be seen that the values of the dispersive interchange energies coefficients of the Gibbs energy, C, and enthalpy, C, the contact between the two different halogen atoms, X and Y, and the experimental equimolar values of the excess thermodynamic properties G(x1 = 0.5), and H(x1 = 0.5), have the same trend as the gas‐phase electric dipole moment, p, of the molecule X‐Y. The same trend is also observed for the difference in the electric polarizability, Δα, between the halogen atoms X and Y.
An electrochemical study of some spirobenzopyran derivatives in dimethylformamide
Authors: Zhi Jin Fang , Baba Ryo , Fujishima Akira
Published: July 2012

The electrochemical behavior of spirobenzopyran derivatives with substituted groups of OCH3, Br and NO2 in the benzopyran ring and the indoline ring has been studied by cyclic voltammetry and spectro‐electrochemistry in a dimethylformamide (DMF) solvent at a platinum electrode. The six spirobenzopyran derivatives studied can be divided into two groups according to the presence or the absence of a nitro group substituted in the benzopyran ring. In the potential range of −1.8 V ∼ +1.0 V (vs. Ag QRE), neither redox reactivity nor reversible color changes were observed for those derivatives without a substituted nitro group, while the nitro‐substituted spirobenzopyrans exhibited appreciable redox behavior and the electrochromism corresponding to the redox reaction of the nitro group.

In addition, an irreversible oxidation wave observed at about + 1.3 V (vs. Ag QRE) for all the derivatives studied (except SP‐18) was assigned to the oxidation of the nitrogen atom in indoline moiety. These oxidation wave potentials of the nitrogen atom are linear with the Hammett values Σσ* of the substituted group, and thus suggest that a significant electron‐induced interaction existed between the benzopyran and the indoline ring in the spirobenzopyran molecule.
Determination of interdiffusion coefficients in nematic liquid crystals by an optical method
Authors: Heuer H. W. , Kneppe H. , Schneider F.
Published: July 2012

An optical method for the determination of interdiffusion coefficients in mixtures of nematic liquid crystals is described. In this method a liquid crystal mixture with a concentration gradient is placed between the plates of a Fabry‐Perot etalon. Illumination with parallel monochromatic light gives an interference pattern from which the index of refraction and the concentration can be determined as a function of the position. This method of measurement does not require the addition of dyes, chiral substances or radioactive substances.

The set‐up was tested with the isotropic system n‐hexane/n‐dodecane for which the diffusion coefficients are known. The diffusion coefficients in the system 4‐n‐butylbenzoic acid‐4'‐n‐hexylphenyl ester/4,4'‐di‐n‐hexylazoxybenzene were determined as a function of temperature. The system 4'‐n‐butyloxybenzylidene‐4‐n‐butylaniline/ethylhydroquinone‐di‐4‐n‐hexylbenzoate was studied at a temperature for which the first component is in the nematic phase slightly above an SA phase.
The internal conversion rate of the primary donor in reaction centers of Rhodobacter sphaeroides
Authors: Müller Peter , Bieser Gero , Hartwich Gerhard , Langenbacher Thomas , Lossau Harald , Ogrodnik Alexander , Michel‐Beyerle Maria‐Elisabeth
Published: July 2012

The most prominent cornerstone of reaction center function is the high quantum yield of transmembrane charge separation approaching unity in the systems studied so far. This feature necessarily implies that the deactivation rate of the excited primary donor 1P* not involving electron transfer is not accessible in native systems. Therefore, reaction centers of Rhodobacter sphaeroides have been modified via thermal exchange of the relevant primary electron acceptor BA. Substitution of BA with 3‐vinyl‐132‐OH‐bacteriochlorophyll increases the lifetime of 1P* from about 2 to 240 ps at 90 K. Transient absorption studies reveal that this increase is due to a decrease of the rate of charge separation. At 90 K this decrease causes a concomitant drop in the quantum yield of charge separation Y to 78% leading to a fast ground state P recovery of 22%. This directly translates into an internal conversion rate from 1P* to the ground state of kIC = (1.1 ns)−1 at 90 K. The corresponding data at 270 K (τF(1P*) = 66 ps; Y = 91%) result in kIC = (750 ps)−1 suggesting a weak thermal activation as usually observed for internal conversion processes. These internal conversion data constitute an important parameter for theoretical modelling of the primary charge separation along both, the active and inactive pigment branches.
Electrochemical and mass spectrometric investigations on the light‐induced oxygen and hydrogen gas exchange in cyanobacteria
Authors: Bader Klaus P.
Published: July 2012

The filamentous cyanobacterium Oscillatoria chalybea evolves molecular hydrogen upon illumination with one or more short (5 μs) saturating light flashes. This hydrogen evolution appears not to be linked to the nitrogen fixation capacity of this organism as the amplitudes are identical with nitrate‐grown and nitrogen free‐grown cultures. The hydrogen evolution amplitudes remain virtually constant over the whole series of flashes, i.e. no oscillatory pattern is observed. The dependence of the oxygen evolution signal under the third flash of a sequence on the light intensity shows significant differences, if the relative intensities of the first, second or third flash are modulated. In view of current discussions this might be interpreted in terms of a charge transfer between reaction centers and thus of a limited independence of the centers—as it has been suggested for e.g. Synechococcus. Addition of quaternary ammonium salts like alkylbenzyldimethyl ammoniumchloride (ABDAC; zephirol) strongly increases the oscillation of the oxygen evolution patterns but does not induce a (period‐2) oscillation in the case of hydrogen evolution. Our results suggest that also in the case of cyanobacteria (Oscillatoria chalybea) the reaction centers act independently so that the strong damping of the oscillation of the oxygen evolving amplitudes must be explained in terms of the ‘missed’ transitions between the sequential oxidation steps.
Nucleotide binding to chloroplast F1‐ATPase (CF1) cannot be explained by a two‐site model
Authors: Gunther Stephan , Urbanke Claus , Kindler Björn , Huchzermeyer Bernhard
Published: July 2012

The kinetics of nucleotide binding to the chloroplast coupling factor, CF1, have been analysed by stopped‐flow measurements using the fluorescent trinitrophenyl analog TNP‐ADP. Experimental determined time courses were compared with several different theoretical time courses. The following observations were obtained: (a) in stopped‐flow experiments the half time of the reaction was at highest with a ligand‐to‐enzyme ratio of 2:1. The half time of the binding reaction decreased, if the ratio was lower than 2:1. (b) This characteristic cannot be explained by a bimolecular reaction mechanism of several independent (classes of) binding sites, (c) Theoretical time courses according to a “two‐site” model with the inclusion of a conformational change of each site after binding of ligand showed the observed characteristic (see (a)), (d) However, this “two‐site” model including a conformational change of each site after binding of ligand failed to simulate the measured time courses of nucleotide binding.
ATP synthase: Driven and activated by protonmotive force
Authors: Häsle Katrin M. , Fritsch Olaf , Groth Georg , Junge Wolfgang
Published: July 2012

ATP synthase (F‐ATPase) of chloroplasts, CF0CF1, is both activated and driven by transmembtane protonmotive force. We dichotomized between activating and driving proton transfer by specific inhibitors, tentoxin and venturicidin. Thylakoid membranes were submitted to voltage steps (by flashing light) that were superimposed to a steady pH‐difference. Transient proton uptake, transfer and release by CF0CF1 were studied by spectroscopic probes. Both, activation and catalysis required all three partial reactions of the proton. A fast electrogenic reaction preceded the catalytic turnover of CF0CF1. This activating electrogenic event in response to the rapid onset of the electric potential is an integral portion of the reaction sequence producing ATP.
Transient magnetic resonance. Transient spin states in the primary processes of photosynthesis
Authors: Stehli D. , van der Est A. , Kamlowski A.
Published: July 2012

The role of the first stabilized charge separated state, P+•Q−•, generated in the course of the primary processes in photosynthesis is discussed. In particular, the adaptation of the properties of Q−• to the functional requirements in different types of photosynthetic reaction centers is considered. Time resolved EPR is shown to be very well‐suited for the characterization of P+•Q−• and that important structural and functional properties of the radical pair can be obtained from such data. The most recent spectroscopic information is presented and evaluated with the aim of correlating differences in the observed characteristics of the quinone acceptor with differences in the various types of photosynthetic reaction centers. It is suggested that the nature of the acceptors following the primary quinone (either an exchangeable quinone or a series of iron‐sulfur centers) has a marked influence on the nature of the quinone binding.
Photoinduced electron transfer in cyclophane‐bridged porphyrin‐quinone molecules. A subpicosecond transient absorption study
Authors: Pöllinger F. , Musewald C. , Heitele H. , Michel‐Beyerie M. E. , Anders C. , Futscher M. , Voit G. , Staab H. A.
Published: July 2012

Photoinduced charge separation and recombination in a series of cyclophane‐bridged porphyrin‐quinone systems (PQ) in toluene solution have been investigated by means of sub‐ps time‐resolved absorption spectroscopy. Temporal profiles and transient spectra of the porphyrin cation (P+) show the photoinduced formation and decay of the charge‐separated state P+Q−. The rate of charge recombination in these systems (P+Q−→PQ) is investigated as a function of the reaction free energy ΔG in the range (‐ ΔG) = 1.54–1.98 eV, which is in the so‐called inverted region of electron transfer. Combining values for charge separation and recombination the dependence of the electron transfer rate on ΔG fully covers the normal and inverted regions ((‐ ΔG) = (‐)0.02‐1.9 8 eV) with the rate varying over more than three orders of magnitude (≈︁2·109‐5·1012s−1).
Kinetics and molecular modelling of ligand binding to ribulose 1, 5‐bisphosphate carboxylase/oxygenase (RUBISCO)
Authors: Frank J. , Holzwarth J. F. , Koch P. , Vater J.
Published: July 2012

The dye 2‐toluidinonaphthalino‐6‐sulphonate TNS is sensitive to ligand binding events at the active site of RUBISCO purified from spinach or Rhodospirillum rubrum. Equilibrium binding curves of the substrate D‐ribulose 1, 5‐bisphosphate RUBP and the inhibitor 6‐D‐phosphogluconate 6‐PG to RUBISCO from spinach were apparently biphasic. Iodine laser temperature jump (ILTJ) experiments showed a fast and a slow bimolecular binding reaction of both ligands corresponding to a strong and a weak equilibrium binding process. In Stopped Flow (SF) experiments different reaction mechanisms were observed for the binding of the transition state analogue 2‐carboxy‐D‐arabinitol 1, 5‐bisphosphate CABP to RUBISCO in the presence and absence of magnesium ions. In the absence of magnesium ions CABP binds in a reversible bimolecular binding reaction to RUBISCO. In the presence of magnesium ions an irreversible two step reaction mechanism for the CABP binding was detected. Molecular dynamic (MD) simulations of ligand binding to RUBISCO were used for modelling of the strong influence of magnesium ions on the kinetics of ligand binding to RUBISCO.
Adsorption of Rigid‐Rod Trimers from Liquid Mixture with Monomers on Heterogeneous Surfaces
Authors: Borówko M. , Rżysko W.
Published: July 2012

The results of Monte Carlo simulation for adsorption of linear trimers from their mixtures with monomers on homogeneous and heterogeneous surfaces are analysed. The lattice model of the liquid mixture is used. The different surface topographies (strip‐like and chess‐board) are considered. An influence of surface topography, size of homogeneous patches and molecular interactions on adsorption and orientational ordering in the mixed fluid near the boundary plane is discussed.
Shear Viscosity of Hexane+Tetradecafluorohexane near the Upper Critical Endpoint
Authors: Mclure Ian A. , Clements Patricia J.
Published: July 2012

The shear viscosity of hexane+tetradecafluorohexane has been determined from five Kelvins below the upper critical solution temperature Tc – in the region of limited miscibility – to 19 Kelvins above Tc – in the region of total miscibility. The results show a critical anomaly described by a critical expression η = A exp (B/T)ϵ−y with a multiplicative amplitude or background term η0 = A exp (B/T) and a weakly anomalous term ϵ−y, where ϵ is the reduced temperature response function |T − T|/Tc calculated with Tc = 22.385°C, and the critical exponent y takes the universal value 0.040 predicted by the mode‐mode and renormalisation group theories. The measured viscosities show a definite but small dependence on shear gradient. The shear gradient dependence is entirely described by the Oxtoby treatment which yields an estimate of the critical amplitude of the correlation length ξ0 = (5.5 ± 1.5) Å in fair agreement with the light‐scattering value of Skripov et al. of (3 ± 1) Å. The ratio of the limiting amplitudes along the isochoric path and the coexistence path is 0.946 ±0.005, close to that predicted by Calmettes, 0.950.
An FTIR Study of the Products of the Reaction between CH2\documentclass{article}\pagestyle{empty}\begin{document}$$ ({{\rm \bar X}}^3 {{\rm B}}_1) $$\end{document} and NO
Authors: Grußdorf J. , Temps F. , Gg. Wagner H.
Published: July 2012

The product channels were investigated of the reaction between CH2

and NO in the gas phase at room temperature and near ambient pressure. Mixtures of CH2CO/NO/Ar were photolyzed at λ = 312 nm in a static reactor. The reaction products were analyzed by Fourier transform infrared (FTIR) spectroscopy. The main product (≈︁ 84%) was found to be fulminic acid, HCNO. A second channel (≈︁ 15%) was found to lead to HCN. Other products which were detected include CO, N2O, H2O, HONO, H2CO, and CO2. These are formed (except for the CO from the CH2CO photodissociation) in consecutive reactions of the accompanying H atoms and OH radicals from the HCNO and HCN reaction channels.
Multidimensional solid state NMR: A unique tool for the characterisation of complex materials
Authors: Spiess Hans Wolfgang
Published: July 2012

A survey is given on new developments in multidimensional solid state NMR which evolves as an indispensable tool of materials characterisation. After a short introduction NMR is compared with other techniques, in particular X‐ray and neutron scattering. The unique information available by solid state NMR is demonstrated by specific examples of structural studies of chain conformation, advanced aspects of chain dynamics, phase separation and interfacial effects as well as non‐linear plastic deformation in polymers. Emphasis is placed on the new development of high resolution multiple quantum NMR spectroscopy of abundant nuclei in solids with first experimental examples on the location of hydrogen positions in organic solids, structure of inorganic glasses and chain order in polymer melts and elastomers.
The electrical conductivity of CoO: Experimental results and a new conductivity model
Authors: Lange F. , Martin M.
Published: July 2012

The electrical conductivity of the transition metal oxide Co1‐σO has been measured as a function of the oxygen activity and the temperature in the whole stability field of CoO using a very pure single crystal. The results are modelled in terms of a new conductivity model in which free electron holes as well as electron holes which are trapped by cation vacancies contribute to the conductivity. At low oxygen activities also electrons are considered. Within this model the following parameters are obtained: the two mass action constants,K1andK11, for the incorporation of oxygen and the formation of singly ionized vacancies, the mobilities of free and trapped electron holes,b0andb1, and the product of the electron mobility and the electronic mass action constant,Kebe. A microscopic interpretation of the model is made possible by translating the so‐called five‐frequency model for impurity diffusion to the conductivity problem. Then it is also possible to estimate the lifetime of the associate consisting of a doubly ionized vacancy and an electron hole, which is about twenty times larger than the residence time of an electron hole on a cation site.
Mechanism and rate constants for the reactions of Cl atoms with HOCl, CH3OCl and tert‐C4H9OCl
Authors: Kukui A. , Roggenbuck J. , Schindler R. N.
Published: July 2012

Reactions of Cl atoms with HOCl (1), CH3OCl (2) and C4H9OCl (3) have been investigated at 300 K using discharge flow LIF/MS technique. The mechanism and reaction rate constants were determined by monitoring absolute rates of hypochlorite and CI atom consumption together with the build‐up of reaction products. Based on the yields of CI2 and OH in (1a), Cl2 and CH3O in (2a) and Cl2 in (3a), as measured by MS/LIF, the reactions of Cl atom with the hypochlorites investigated in this work were found to proceed predominantly via the Cl atom abstraction channel with k1a/k1 = (0.96±0.05), k2a/k2 = (0.85 ± 0.06), k3a/k3 = (1.01 ±0.05).

The reaction rate constants were determined to be k1 = (2.28±0.09)·10−12, k2 = (6.0±0.2)·10−11, and k3 = (4.26±0.2)·10−11, all in units cm3·molecule−1·s−1. A reevaluation of the heat of formation of HOCl yielded ΔH0f (298 K) = −75.1 kJ·mol−1.
State‐resolved intramolecular dynamics in highly excited HOCl
Authors: Abel B. , Charvàt A. , Deppe S. F. , Hamann H. H.
Published: July 2012

The features and mechanisms of intramolecular energy redistribution (IVR) and state mixing of HOCl at chemically significant energies have been investigated using intra‐cavity laser absorption spectroscopy (ICLAS). These studies revealed that for the observed vibrational states up to about 75% of the dissociation energy E0 both strong and weak interactions (Fermi‐type, Coriolis) exist but producing only localized perturbations in the spectra. The 5v1 band, however, at about 85% of the dissociation threshold E0 (O‐Cl bond) has been found to be globally and strongly mixed with the 4v1 + 2v2 + v3 zero‐order vibrational state, and both states appeared in turn coupled to other background states by additional (weaker) interactions. The transfer from frequency to time domain led to the conclusion that this spectral signature is characteristic for efficient but nevertheless restricted intramolecular vibrational energy redistribution in the overtone spectrum of HOCl. The intramolecular dynamics of HOCl is compared to the dynamics of HCN and discussed in terms of low‐order interactions between zero‐order states (ZOS) grouped in different tiers.
Intramolecular dynamics and density of states for HN
Authors: Schmatz Stefan , Mladenović Mirjana
Published: July 2012

The rovibrational (J = 0–4) level structure of protonated nitrogen (HN+2) is investigated in detail for the CCSD(T) potential energy surface of Schmatz and Botschwina. The discrete variable representation (DVR) for the angular coordinate in conjunction with a distributed Gaussian basis set (DGB) for the radial degrees of freedom was used to perform the nuclear dynamics calculations. Both low lying and highly excited states are examined. The total number of bound states with J = 0 up to the first dissociation threshold at 44409 cm−1 is determined to be about 5000. We propose an empirical model for the level structure of HN+2 which incorporates Roe's suggestion for stretch‐bend coupling. The empirical numbers and densities of states agree well with the corresponding numerically exact quantum mechanical values for the given surface.
Stationary points of the potential surface for the reaction F− + CH3Cl → FCH3 + Cl−: Results of large‐scale coupled cluster calculations
Authors: Botschwina P. , Horn M. , Seeger S. , Oswald R.
Published: July 2012

Stationary points of the potential surface for the SN2 reaction F− + CH3Cl → FCH3 + Cl− have been investigated by large‐scale CCSD(T) calculations. The ion‐dipole complexes in the reactant and product channels have well depths of 15.8 and 9.6 kcal mol−1, respectively, and are separated by a small barrier of 3.3 ± 0.3 kcal mol−1. The molar reaction enthalpy at 298 K is obtained to be −31.5 kcal mol−1.
K‐Conservation in the dissociation of singlet ketene
Authors: Mellinger Axel , Hall Melonie A. , Wade Elisabeth A. , Moore C. Bradley
Published: July 2012

The effect of K‐conservation on the photodissociation of ketene has been investigated. Rate constants and photo‐fragment excitation (PHOFEX) spectra have been calculated using phase space theory (PST) in a helicity basis. While the effect of K‐conservation on rate constants is relatively subtle, PHOFEX spectra with state‐selected reactant molecules appear to provide a feasible way to experimentally resolve the question of K‐conservation.
Ultrafast photochemical pericyclic reactions and isomerizations of small polyenes
Authors: Fuß Werner , Hering Peter , Kompa Karl L. , Lochbrunner Stefan , Schikarski Thomas , Schmid Wolfram E. , Trushin Sergei A.
Published: July 2012

Potential energy surfaces for pericyclic reactions can easily be predicted by means of correlation diagrams. Whereas the initially excited state (called 1 B in this paper) may vary from molecule to molecule, its population is collected by a lower, dark state (2A) of always the same nature, which corresponds to a two‐electron excitation. From there, the system leaves to the ground states of educt and product(s) via a conical intersection (CI). Using transient absorption and transient ionization spectroscopy, we measured the lifetimes t1B and t2A of these states after initiating electrocyclic ring opening of 1,3‐cyclohexadiene and some of its derivatives (α‐terpinene, α‐phellandrene and 7‐dehydrocholesterol). t2A can be considered the reaction time constant. Whereas t2A = 5.2 ps for dehydrocholesterol. it is 80–100 fs for the other three molecules. We suggest that the former system needs some time to find the exit (the CI) from the 2A surface, whereas in the latter cases the CI is located right in the line of the steepest descent. We apply the same scheme to, and compile the time constants for, some other fast processes: the [1.3] sigmatropic reactions of norbornene and norbornadiene (t2A = 220 and 210 fs) and the fast internal conversions of cycloheptatriene (80 fs) and several UV stabilizers. The latter two processes are suggested to take the same pathway as the pericyclic hydrogen shifts in these molecules. We also point out the similarity of the pericyclic potential surfaces to those of cis‐trans isomerizations and give evidence that cis‐stilbene (t2A < 300 fs), too, is accelerated directly in the direction of the CI. For cis‐trans isomerization of longer polyenes there are however several 2A minima and conical intersections. We also give examples where additional branchings and competing reactions play a role.
A state‐to‐state statistical‐dynamical theory for large molecule collisional energy transfer
Authors: Barker John R.
Published: July 2012

A statistical‐dynamical theory of large molecule energy transfer based on state‐to‐state transition probabilities is derived and a demonstration calculation is presented for cyclopropane deactivation by helium. For demonstration purposes, the SSH(T) theory is used for calculating state‐to‐state transition probabilities, and thus the present calculations are expected to provide only general trends. Various tests for convergence of the calculations are described. The calculations are shown to be practical even for energies where the vibrational state densities exceed 1010 states cm−1. The results predict that energy transfer propensities persist even at very high vibrational energies. The predicted collision step size distributions resemble the exponential model, but with strong fluctuations about the mean. The predicted average energy transferred in deactivation collisions (<ΔE>down) depends on vibrational energy, due to the changing fraction of inelastic collisions; the shape of the distribution function remains nearly unchanged. In future calculations, the SSH(T) theory will be replaced by other theories in order to obtain more accurate predictions.
Collisional deactivation of vibrationally highly excited azulene in supercritical xenon/ethane mixtures
Authors: Schwarzer D. , Troe J. , Votsmeier M. , Zerezke M.
Published: July 2012

The collisional deactivation of vibrationally highly excited azulene was studied in equimolar supercritical mixtures of xenon and ethane at 385 K from gas to liquid phase densities. Azulene with an energy of 18000 cm−1 was generated by laser excitation into the St‐ and subsequent internal conversion to the S*σground state. The loss of vibrational energy was monitored by transient absorption at the red edge of the S3←S0 absorption band at 290 nm. Transient signals were converted into energy‐time profiles using hot band absorption coefficients from shock wave experiments for calibration and accounting for solvent shifts of the spectra. Under all conditions, the decays were monoexponential. At densities below 10−3mol/cm3, the observed collisional deactivation rate constants kc of the mixture were equal to the sum of the individual contributions of ethane and xenon collisions as expected from simple gas kinetics. At mixture densities above 2×10−3 mol/cm3, kc is smaller than the deactivation rate constant found in neat ethane at half the density. This behavior can be rationalized by a model employing an effective collision frequency which is related to the finite lifetime of collision complexes; the required parameters follow from experiments in neat xenon and ethane.
Equilibrium glass transition in a polymer‐solvent system
Authors: Frank W. , Schwarz J.
Published: July 2012

From the results of long time measurements on the dependence of the mole fraction on temperature and solvent activity in the system atactic polystyrene‐cyclohexane we see evidence for an equilibrium glass transition range, which begins closely below the kinetically caused glass transition at a cooling rate of about 1 K min−1. The thermodynamic background is discussed, starting from the so called Kauzmann paradox and the extension of the Ehrenfest equations on mixed phases with the additional variable mole fraction. The results of Rehage from swelling curves in the glass transition range are reinterpreted.
On the sequence of events in H2S oxidation reactions
Authors: Melsheimer J. , Schlögl R.
Published: July 2012

In‐situ reflectance UV‐VIS spectroscopy and on‐line GC were performed on pressed and powdered wafers made from industrial aluminas in different microreactor cells at 400 K. At a steady state conversion of 60–70% a very strong absorption band formed initially at 290 nm. A broadening of this peak with time on stream was observed during the modified Claus reaction (2H2S + SO2  (3/x)Sx + 2H2O) in these cells.

A conversion of < 10% was measured for the Claus reaction (2H2S + O2  (2/x)Sx + 2H2O) during which the response was similar to that recorded in the reaction given above.

The results of reference spectra obtained on sulfur‐containing compounds showed that an attribution of the observed absorption bands to various sulfur species is possible. A deconvolution of the reflectance data and an analysis of peak areas indicated that the species S2O2−2 and S2O2−2 affect the steady state for the modified Claus reaction and the species S2O2−3 for the Claus reaction. Reaction sequences are suggested for these H2S oxidation reactions.
Comments on time‐resolved charge transfer with hot electrons at the silver/electrolyte interface
Authors: Kulmala S. , Ala‐Kleme T.
Published: July 2012

Additional information is presented to that previously published by Diesing et al. in this journal considering metal/insulator/metal tunnel junctions in contact with aqueous solution. Hot electron injection into aqueous electrolyte solutions from metal/insulator/metal/electrolyte and metal/insulator/electrolyte tunnel junctions is considered and the thermodynamic basis of probable electrochemical generation of hydrated electrons is discussed.
Thermodynamics of the amalgam cell: {MexHg1‐x|MeCl(m)| AgCl| Ag} (with Me = K, Rb) in (methanol+water) solvent mixtures
Authors: Basili Alessandro , Mussini Patrizia R. , Mussini Torquato , Rondinini Sandra , Vertova Alberto
Published: July 2012

The electromotive force E of the amalgam cell {MexHg1‐x|MeCl(m)|AgCl|Ag}, where Me = K or Rb, has been measured at the temperature 298.15 K as a function of the molality m of MeCl in (methanol + water) mixed solvents up to 0.8 mass fraction of methanol, with relative permittivities ϵ>40, and as a function of the mole fraction x of Me in amalgam. The respective standard electromotive forces E0m have been determined, together with the mean molal activity coefficients y ± of the relevant MeCl as a function of its molality. For interpolation purposes the E0m values can be expressed as a function of the methanol mass fraction wM by the following polynomials, valid for 0≤wM≤0.8:

These results for standard e.m.f.s, interpreted in terms of primary medium effects, lead to primary hydration numbers nhydr = 6.6 for KCl, and = 6.7 for RbCl, in good agreement with previous results using different methods.
Matrix‐theoretical calculation of diffusion parameters for composite membranes with periodic structure
Authors: Chen Jenn‐Shing , Shi Way‐Chia
Published: July 2012

Based on the Siegel's theory, the diffusion parameters of steady‐state permeability (P), downstream time Lag (tL), forward and backward mean first passage time \documentclass{article}\pagestyle{empty}\begin{document}$ (\bar t_ + {{\rm and}}\;\bar t_\_ ) $\end{document} for absorptive unidirectional permeation for a membrane with n‐periodic structure have been calculated from the transmission matrix in the Laplace domain with the help of the Caley‐Hamilton theory. The results of calculation give that \documentclass{article}\pagestyle{empty}\begin{document}$ P = P^{(i)} /n,\;t_L = t_L^{(i)} + \frac{1}{6}(n^2 - 1)(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ,\;\bar t_ + = n\bar t_ + ^{(i)} + \frac{{n^2 - n}}{2}(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ),\;\bar t_ - = n\bar t^{(i)} + \frac{{n^2 - n}}{2}(\bar t_ + ^{(i)} + \bar t_ - ^{(i)} ) $\end{document}, where the diffusion parameter with a superscript (i) denotes its corresponding entity for a single unit period. The consistency with the previous results obtained by repeated integration is also discussed.
On the mechanism of the reaction of CF3 radicals with C6F5Cl in the temperature range 318–473 K
Authors: Nieto J. D. , Lane S. I. , Oexler E. V.
Published: July 2012

The gas‐phase reaction of CF3 radicals, generated by photolysis of perfluoroacetic anhydride, with C6F5Cl was studied in the temperature range 318–473 K and total pressures between 23 and 41 Torr. CF3 radicals react with C6F5Cl according to the following mechanism:

magnified image

It was found that the addition reaction becomes reversible above 390 K. The addition rate parameters can be summarized in the following equation:

where θ = 2.303 R T kJ mol−1 and kc is the recombination constant of CF3 radicals. A correlation between log [(kadd/k1/2c) and the ionization potentials for 15 aromatic compounds was found.
Chiotti integration of Gibbs‐Duhem relation and unequivocal determination of limiting partial thermodynamic quantities at infinite dilution of binary solution system
Authors: Cho Seung‐Am , Ochoa José Luis
Published: July 2012

Chiotti has made a breakthrough in the thermodynamic theory of solution after nearly a century of frustration. Activity α,i, activity coefficient γi, Darken function αi = In γi/(l‐xi)2 and other partial thermodynamic quantities \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta \bar Q_i^{{\rm{xs}}} \;{\rm{and}}\;\Delta \bar Q_i $\end{document}, where i = Bi and Sn, of binary liquid Bi‐Sn alloy solution system are critically assessed by means of the authentic Chiotti integration, as all those quantities oscillate along composition which made their procurement through classical routes, Gibbs‐Duhem and Darken integrations, impossible. The unambiguous partial quantities at their infinite dilution are obtained from the genuine Chiotti slopes. Interrelations among partial quantities in terms of composition and temperature are presented in detail. We reveal that the apparent Raoultian and Henrian α, vs. Xi behaviors are false and then demonstrate neither Bi nor Sn complies with the Raoult's law and Henry's law. The molten Bi‐Sn system is the athermal type but the behavior of the solution is rather complex and it is definitely neither subregular nor regular solution. In this context the subregular and various symmetrical solutions are systematically developed in relation to function αi and discussed in great detail. A new method of classification of complex solution systems beyond subregular and regular in terms of the difference quantities \documentclass{article}\pagestyle{empty}\begin{document}$ (\Delta \bar Q_B^{{\rm{xs}}} {\rm{-}}\Delta \bar Q_A^{xs} ) $\end{document} is proposed.
Influence of the crystallization process on the photoelectrochemical behaviour of anodic TiO2 films
Authors: Piazza S. , Calá L. , Sunseri C. , Di Quarto F.
Published: July 2012

On the basis of kinetic and photoelectrochemical studies we show that the formation of amorphous or strongly disordered TiO2 films on electropolished titanium rods can occur upon anodization in 0.5 M H2SO4 solution in a range of thickness which depends on the anodization rate. This finding is confirmed both by the changes in the shape of the photocurrent vs. potential curves with the energy of the incident photons, and by the impedance behaviour of the junction.

Our data indicate that TiO2 films having different degree of disorder are formed depending on the anodization rate and oxide thickness. Crystalline films are formed at very low growth rates since very low thicknesses. Amorphous or strongly disordered films can be grown at high oxidation rates (≥ 100 mV/s) before the onset of a crystallization process. At higher thicknesses a gradual crystallization process takes place, as revealed both by the decrease of the anodizing current during the tensiodynamic growth and by the changes in the shape of the photocurrent vs. potential curves. The onset of the crystallization process of the film occurs at higher thicknesses with increasing the growth rate.
Spectroscopic and chromatographic investigations of sulfur ammonia solutions
Authors: Schindewolf U. , Herrguth J. , Zhou D.
Published: July 2012

Elemental sulfur dissolves in liquid ammonia to form an anionic adduct S5NH−2 (sulfur in zero oxidation state) which by redox reactions leads to the anionic species S3N− and S4N− (positive oxidation state), and S3− as well as its dimer S62‐ (negative oxidation state). By anion exchange chromatography under HPLC conditions the species of a sulfur ammonia solution (SAS) are separated and (using radioactive sulfur) their absolute concentrations and absorption spectra are obtained. With these the absorption spectra of SAS taken in wide concentration and temperature ranges are analysed without separation to get quantitative data of the concentrations of all species and thus of the equilibrium constants, the reaction enthalpies and entropies of the two reactions in which the species are involved. The variations of the spectra due to shifts of the equilibria by changes of the pH of the solutions or by changes of their redox potential are simulated. Finally the time dependence of the spectra during the slow dissolution process of sulfur in ammonia gives information on the solubilization process.
Surface tension of a binary liquid mixture in the vicinity of its critical point
Authors: Mainzer‐Althof T. , Woermann D.
Published: July 2012

Results of measurement of the temperature and composition dependence of the surface tension σα,βγ of 2,6‐dimethylpyridine (abbreviated 2,6‐dp)/water mixtures are reported. The index α refers to the vapor phase and the index βγ to the homogeneous 2,6‐dp/water mixture. The experiments are carried out at constant temperatures T below and at the critical temperature Tc (= 33.87°C) in the entire composition range (0≤x≤ 1; x, mole fraction of 2,6‐dp). For mixtures with compositions in the range −0.04<(x‐xc)<0.10 (xc = 0.640) the experimental σα,βγ (x, Tc) data can be represented by the theoretically established equations σα,βγ = σc + C(xc‐x)μ*/β* for xxc (Nagarajan, Webb, Widom, J. Chem. Phys. 77, 5771 (1982)). The constants C and D have different values of opposite signs. The value of the exponent (μ*/β*) obtained from experimental data with compositions x<xc is consistent with the theoretically predicted value (μ*/β*) = 3.88.