摘要:

AbstractThe understanding of photoisomerisation reactions involving large amplitude motion is discussed with special emphasis on the merits of systematic studies over wide ranges of physical conditions. It appears that the friction β in such cases is proportional to macroscopic solvent viscosity η, and the original Kramers theory is sufficient to describe the effect of friction in the range from intermediate to strong damping, i.e. from low viscosity fluid to compressed high viscosity liquid solution. This one‐dimensional model may be connected to multidimensional unimolecular rate theory to obtain a representation of the density dependence of the rate coefficient down to the thermal collisionless regime. The apparent failure of this approach in the case oftrans‐stilbene can be traced to modifications of the excited state PES by the solvent. This interpretation is consistent over the entire range of physical conditions studied, starting at the jet‐cooled isolated molecule and solvent cluster and ending in compressed liquid solution at very high viscosities. It is shown that detailed information about the PES is urgently needed to provide safer ground for a profound understanding of the photoisomerisation d

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010402

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe new technique of free‐jet condensation/scavenging with dimethyl‐disulfide has been applied for the quantitative analysis of hydrocarbon radicals and carbenes in flat premixed hydrocarbon/oxygen flames burning with fuel‐rich mixtures at 27 mbar. The results are reported as profiles of mole fractions of the radicals. The limit of detectability was about 1·10−7mole fraction. Qualitatively the radicals are very similar with the four fuels, but there are large differences in their quantities. While in the methane flame only C1and C2radicals were present in detectable concentration, higher radicals up to naphthyl could be detected with the unsaturated fuels. Although methyl could not be determined quantitatively, it was found to be the major hydrocarbon radical in all flames. Methoxy radical was only found in the methane flame. Whereas, for example, C2, C3H2and C3H are typical high‐temperature species, C2H is surprisingly formed at the beginning of the oxidation zone at relatively low temperature. Vinyl and the vinyl‐type radicals C2nH3(n= 1 to 4) are in equilibrium with acetylene and the polyynes (C2nH2) at maximum flame temperature and in the burned gas. Since phenyl peaks always after benzene, it is concluded that it is mainly a degradation product from benzene and other lower aromatics. The mechanism of formation of C2H and C2, the equilibria of the C2nH3and the relation between aliphatic and aromatic radicals a

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010403

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe solvatochromic shift of the most intensive band of fluorenone radical anion (FN*‐) in the visible region has been examined in 10 polar formally aprotic media. It has been found that this shift depends on the solvent acceptor number (AN) and static dielectric constant (D) according to planar regression:\documentclass{article}\pagestyle{empty}\begin{document}$$ \bar v_{\max } /{{\rm cm}}^{ - 1} = 98.83\;AN - 44890[D - 1)/(2D + 1)] + 38543 $$\end{document}It is suggested that the ground state of FN*‐ is relatively stabilized in a solvent with a high acceptor number and the dipole moment of the solute increases during an excitat

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010404

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractAn ultrathin poly(methyl methacrylate) film, as prepared by a casting‐on‐water method, emitted optical second harmonic (SH) light in association with asymmetric alignment of an amphiphilic dye. Coherent interference due to SH waves from a pair of films in parallel afforded a periodic pattern with the film, and the pattern was 180° phase‐shifted on flipping either one of the films. These observations were ascribed to asymmetric orientation of the dye in the film and negligibly small thickness of the film in comparison with the coherence length. Overall orientation of dyes in the film could be estimated from the exper

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010405

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractThe solvation behavior of various silver(I) salts, viz. silver (I) iodate, bromate and sulfate in iso‐dielectric solvent mixtures of methanol and N‐methyl‐2‐pyrrolidinone (NMP) has been investigated using Gibbs transfer energies and solvent transport number measurements. The Gibbs transfer energies of the salts were split into their individual ionic contributions using both negligible liquid junction potential method (nLJP) and the reference electrolyte method using tetraphenylarsonium tetraphenylborate (TATB). The results show a significant hetero‐selective solvation of all salts beyondXNMP= 0.5 with silver ion being selectively solvated by NMP and the anions by

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010406

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractFrom 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 reinterpre

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010407

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractAqueous two‐phase systems are effective extraction systems for separating peptides and enzymes from aqueous phases. Such extraction processes are based on the finding that peptides and enzymes show different preferences for the coexisting phases. Methods to calculate and predict the liquid‐liquid phase equilibrium in those systems can only be developed when an extensive experimentally determined data base is available. The present contribution contributes to that goal by presenting experimental data for the partitioning of small amounts (micrograms solute per kilogram of solution) of low molecular‐weight combination peptides of glycine, 1‐glutamic acid, 1‐phenylalanine, and 1‐lysine in aqueous two‐phase systems of di‐potassium hydrogen phosphate and poly(ethylene glycol) of molecular mass of about 6000 and 35000 at about 293 K. A group‐contribution model for the excess Gibbs energy is used to predict liquid‐liquid phase equilibrium. A preliminary set of binary interaction parameters was taken from the literature. These model parameters were determined using experimental results for the partitioning of single amino acids and some of their peptides in the same aqueous two‐phase system. No experimental results for the partitioning of combination peptides had been used for parameter estimation, i.e. those peptides were products of condensation reactions of molecules of a single amino acid. Therefore, partition coefficients calculated for combination peptides are predictions. For some peptides predicted and measured partition coefficients agree within experimental uncertainty. In a few cases predicted partition coefficients deviate from experimental results by a factor of about two. However, the model always correctly predicts which phase (polymer‐rich or salt‐rich) is

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010408

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractAn optical high‐pressure cell has been developed for spectroscopic investigations of rapid high‐pressure reactions. It can be coupled with commercial Raman spectrometer. The measuring cell is suitable for use at pressures of up to 2000 bar and temperatures of up to 200°. The advantages of in situ Raman spectroscopy are demonstrated in the course of an investigation of the decomposition of tertiary butyl peroxypivalate in solution. This organic peroxide is a standard initiator for the radical high‐pressure polymerisation of olefins for which it is used at pressures of 1300 to 3000 bar and temperatures of 160 to 190°. The rate of decomposition was measured within a wide pressure and temperature range. From the results the half‐life, the frequency factor, the energy of activation and the activation volume of the peroxide decomposition reaction were determined. The data thus obtained were compared with data in the literature which had been obtained by othe

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010409

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractResults of measurements of the stress‐optical coefficient and the Young elasticity modulus of ‐SO3−and ‐CH2‐SO3−polyelectrolyte gels are reported. Upon stretching the gels become birefringent. The birefringence is assumed to be caused by a partial orientation of optical anisotropic structures formed by highly cross‐linked regions which are embedded in nonbirefringent regions with a lower concentration of cross links. These results give support to a proposed structural model of the gels which takes into account small‐angle and ultrasmall‐angle X‐ray scattering data as well as information about the transport properties of the gels i

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010410

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY

摘要:

AbstractHigh‐pressure thermal conductivities of H2O+LiCl and H2O + LiBr have been measured with a parallel‐plate apparatus. Data cover the pressure range from 0.1 to 100 MPa at temperatures from 293 to 473 K. The concentrations studied were 0.025, 0.05, 0.10. 0.15, 0.20, and 0.25 mass fraction of salts. The estimated accuracy of the method is about ± 1.6%. The pressure, temperature, and concentration dependence of the thermal conductivity has been studied. Measurements were made on six isobars, namely: 0.1, 20, 40, 60, 80, 100 MPa. The thermal conductivity shows a linear dependence on pressure and concentration at all isotherms. Along each isobar a given concentration shows the thermal‐conductivity maximum at temperatures about 413 K. The measured values of thermal conductivity are compared with the results of other investi

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010411

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1997

数据来源: WILEY