摘要:

AbstractRecently measured broadband ultrasonic spectra of binary mixtures of water with various monohydric alcohols are discussed with respect to precritical behaviour of the liquids. It is shown that the frequency‐dependent excess absorption can indeed be empirically represented by a very few parameters if a special relaxation function is used. Moreover, the coupling of the acoustic field to the heterogeneous structure can be alternatively considered. The interest is particularly focussed on visco‐inertial and thermal conductivity effects which have so far been taken into account in acoustically more heterogeneous systems like emulsions, suspensions, and biological tissues only. Though the shape of the spectra of the alcohol/water mixtures excellently agrees with that predicted by the theories of frequency‐dependent visco‐inertial and thermal conductivity losses some discrepancies in the parameter values result if these theoretical models are fitted to the measured data. It is, however, suggested that such effects, in addition to the previously considered fluctuations in concentration, contribute to the precritical ultrasonic spectra. This view involves not only fluctuations of mass but also special modes of impuls and energy transport to be important at internal interfaces of the micro‐heterogeneou

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980102

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

年代:1994

数据来源: WILEY

摘要:

AbstractAt 25°C the complex dielectric permittivity of mixtures of water with low‐weight poly (ethylene glycol) monoalkyl ethers (CiEj) has been measured as a function of frequency v (1 MHz ≤ v ≤ 55 GHz) and mole fractionx(0 ≤x≤ 1). Various relaxation spectral functions are fitted to the measured spectra. It is found that the dielectric relaxation of all liquids (i, j = 2,2; 4,2; 6,2; 4,3; 4,1) can be consistently described by a sum of a Debye term with discrete relaxation time and a Davidson‐Cole term with an underlying unsymmetrical relaxation time distribution. With the exception of the C4E3/H2O mixtures the Debye term vanishes at high content of CiEjmolecules (x>0.25). It is assumed that this term represents a water‐rich subphase while the Davidson‐Cole term reflects a microphase of low water content. With the C4H3/H2O system crankshaft‐like motions of the C4E3molecule obviously also contribute to the Debye term which exists also in the spectrum of the pure organic liquid. The parameters of all spectra are discussed with respect to the composition of the microphase of low water content, to effects of dipole orientation correlation, and to the mechanism of dielectric relaxation in

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980103

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

年代:1994

数据来源: WILEY

摘要:

Abstract7,14‐Dithioketo‐5,7,12,14‐tetrahydroquinolino‐[2,3‐b]‐acridine (DTQ) is a thionated derivative of quinacridone (QA) that is known as a red pigment. Thionation of QA brings about an intense near‐IR absorption in the solid state which is of practical importance for GaAsAl‐laser printers and optical information storage systems. The electronic properties of DTQ have been investigated in solution and in the solid state in order to characterize the near‐IR absorption from the standpoint of intermolecular hydrogen bonding. The electronic state of the DTQ‐chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group of the chromophore. In solution, the hydrogen bonds between the NH group and the O atom of a solvent cause a bathochromic shift by 5 – 15 nm relative to the absorption spectrum in dioxane. This is interpreted as being due to electron transfer from the proton to the nitrogen atom, thereby increasing the electron density in the chromophore. A similar increase in electron density is also operative in the solid state through the intermolecular hydrogen bonds between the NH group of one DTQ and the S atom of the neighboring molecule. This is mainly responsible for the bathochromic displacement of DTQ in going from solution to the solid state. The near‐IR absorption is, however, not explicable in terms of the hydrogen bonding interaction alone. Another intermolecular interaction, such as π‐π interactions along the stacking axis, appears to be operative that might l

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980104

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

年代:1994

数据来源: WILEY

摘要:

Abstract1,4‐Dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole (DTPP) is known as the material suitable for laser printers and optical information storage systems using GaAsAl‐diode lasers. Hydrogen‐bonded complexes of DTPP with N‐methyl‐2‐pyrrolidone (NMP) and Dimethylsulfoxide (DMSO) have been grown from solution as single crystals: DTPP/(NMP)2and DTPP/(DMSO)2. In both complexes, one DTPP molecule is bonded to two solvent molecules through the hydrogen bonds between the NH group of DTPP and the O atom of the solvent. The hydrogen bonding effect on the electronic spectra has been investigated in these complexes on the basis of the PPP, CNDO/S and INDO/S calculations. The hydrogen bonding in solution and in complexes displaces the longest‐wavelength π ‐ π*visible absorption band towards longer wavelengths. This is interpreted as being due to CT type interaction of hydrogen bonding which involves a partial electron transfer from the oxygen atom to the NH bond. The longest‐wavelength absorption bands in both complexes are polarized along the hydrogen bonding axis, and this agrees with the direction of the transition moment predicted from the calculations. On the other hand, a prominent reflection band appears in DTPP/(DMSO)2for the polarization perpendicular to the hydrogen bonding axis. This is assigned to an intermolecular CT transition along the stacking columns composed of alte

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980105

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

年代:1994

数据来源: WILEY

摘要:

AbstractResults of a systematic study of clusters KnClnand LinFnup ton= 32 are reported within self‐consistent‐field (SCF), second‐order Møller‐Plesset perturbation theory (MP2), and the single‐ and double‐excitation coupled cluster method with a perturbational estimate of triple excitations CCSD(T). Stationary geometries are characterized as local minima by SCF force field calculations up to K9Cl9and Li8F8, respectively.The clusters KnClnshow great similarities with previously studied NanCln. The energetically most stable isomers of even the smaller potassium chloride clusters show a clear preference for geometries which are fragments of the solid state lattice. This effect is enhanced by electron correlation.Lithium fluoride clusters, LinFn, show a different behaviour: hexagonal structures (stacked six‐rings) are prefered to lattice fragments (cubic) on the SCF level at least up to Li18F18. This preference is only slightly reduced by electron correlation.The present results for KnClnand LinFnallow for an estimate of lattice energies by extrapolationn→ ∞, which is in good agreement with, experiment. The structure constants found for K32Cl32approach that of the solid. This is different for Li32F32: clusters of LiF show a slower convergence towards bulk properties on incre

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980106

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

年代:1994

数据来源: WILEY

摘要:

AbstractA Monte Carlo algorithm tailored to fast equilibration of binary mixtures is applied to Lennard‐Jones fluids and solids. In order to study phase transitions as functions of interaction parameters as well as of the temperature, a measure of the mixing is defined which is based on the normalized differences of radial distribution functions. At all temperatures sharp transitions are observed when the ratio of the interaction strengths of like and unlike particles reaches a threshold valu

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980107

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe Generalized van der Waals model has been examined and discussed using high‐pressure experimental data previously reported for tetramethylsilane over a wide range of temperature. The study has been focused on the temperature dependence of the two following characteristic quantities: the effective volume of the hard convex body ν*, which represents the molecules of the fluid, and the attractive van der Waals parameter (a/ν*). It has been confirmed that the nearly universal relation found between the medium densities correction to the compressibility factor (in the formulation of Móritz and Kohler) and the limiting value of the attractive parameter at high densities (a0/ν*) holds for tetramethylsilane. In addition, it has been studied the general form of the low density correction, which can be directly related to third virial coeffi

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980108

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe formation of an iron(III) complex with a new multidentate ligand, Nα‐pyridoxyl‐L‐tryptophan(1, H2pltp), has been investigated thermodynamically and kinetically in an aqueous 0.10 mol dm−3sodium perchlorate solution at 25°C. A 1:2(metal : ligand) complex of 1 forms with much higher stability constant (logβ12/mol−2dm6= 38.29±0.28) than the related complex, bis(pyridoxylidene‐L‐tryptophan)iron(III), having the azomethine group (logβ12/mol−2dm6= 18.38±0.10 [3]). This effect was explained by the contribution of amino nitrogen of higher basicity to the thermodynamic stability. The complex formation reaction proceeds through two parallel pathways of Fe3++H3pltp+and FeOH2++H4pltp2+and also another pathway of FeOH2++H3pltp+with slower coordination of the first ligand to iron(III). The mechanistic rate‐determining step for the formation of the complex was the coordination of the phenolato oxygen to a central metal atom, followed by the rapid donations of the amino nitrogen and c

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980109

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe coordination reaction characteristics and mechanisms of the title new ligands (1(H2plpa), 2(H2plal), and 3(H3plas) stated in the order) to iron(III) have been investigated in an aqueous 0.10mol dm−3sodium perchlorate solution at 25°C by means of electronic absorption spectral and stopped‐flow spectrophotometric methods. They equally form the corresponding bis(ligand)iron(III) complexes with slower coordination of the first one through the same two parallel pathways of Fe3++H3+L+ (or 0)and FeOH2++H4L2+(or +)and also another pathway of FeOH2++H3L+(or0)(L is fully deprotonated species of 1, 2, and 3); the mechanistic rate‐determining step is the coordination of phenolato oxygen of the first ligand. The thermodynamic stability constant (logβ12/mol−2dm6. 0.10mol dm−3(NaClO4), 25°C) of iron(III)‐3 complex (48.33±0.21) is very large in comparison with the constants of the iron(III) complexes of 1(39.06 ±0.26) and 2(39.81 ± 0.20). A possibility is concluded for the formation of more stable iron(III) complexes without changing the complex formation reaction mechanism by designing the ligand structure of the amino acid moiety of pyridoxal‐L‐amino acid derivat

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980110

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

年代:1994

数据来源: WILEY

摘要:

AbstractKinetics of product accumulation during the oxidative decarboxylation of cyclohexane monocarboxylic acid has been followed by GCMS, inhibitor and chemiluminescence methods. Results indicate that in the degenerate branching chain process selective (peroxy) radicals abstract predominantly tertiary hydrogen atoms from the substrate while non‐selective (e.g. hydroxyl, alkoxy) radicals attack also secondary hydrogen atoms. The rate constant of the chain propagation was found to bekp= 7.5×106exp(‐57.6kJmol−1/RT) 1mol−1s−1. Furthermore it has been established, that the oxidative decarboxylation proceeds via two parallel pathways: one resulting in cyclohexanone, while the other avoiding the formation of

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980111

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

年代:1994

数据来源: WILEY