ISSN:0005-9021    

DOI:10.1002/bbpc.19890931002

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

年代:1989

数据来源: WILEY

摘要:

AbstractFluorescence excitation and line narrowing spectra of oxazine dyes adsorbed on porous silica gels show maintenance of vibrational structure and small shifts in electronic absorption when compared to the spectra of the same molecules embedded in an ethanol glass. Persistent spectral holes burnt into the longwavelength tail of the S0—S1absorption of the adsorbed species are broader than in bulk. This phenomenon is thought to be caused by low frequency adsorbate motions of the adsorbed molecule

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931003

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

年代:1989

数据来源: WILEY

摘要:

AbstractInitiated by the recent observation of liquid‐liquid phase separation in aqueous solutions of tetra‐n‐butylammonium thiocyanate, a treatment of the thermodynamic properties of aqueous electrolyte solutions in relation to liquid‐liquid phase equilibria is given. For analyzing the thermodynamic data, the ion interaction approach of Pitzer is used in which the osmotic coefficient is described by a long‐range term for Coulombic interaction plus a virial coefficient series to account for short‐range specific interactions. It is shown that the ion‐interaction approach is flexible enough to incorporate liquid‐liquid phase equilibria in a natural and simple way. For 1:1 electrolytes liquid‐liquid coexistence curves are predicted if the second virial coefficients entering into Pitzer's theory are large and negative and the third (or higher) virial coefficients are positive. Experimental data show that largely negative second virial coefficients are generally present if large cations are combined with large anions, so that coexistence curves are predicted for aqueous solutions of tetraalkylammonium salts with large anions. Many of these salts are practically insoluble at room temperature, but at higher temperatures, where crystallization does not interfere, these predictions are experimentally confirmed for tetrabutylammonium iodide, tetrapropylammonium perchlorate and tetrapropylammonium picrate. For 2:2 electrolytes phase separation can result from the behaviour of the long‐range contribution to the osmotic coefficient alone, even if the virial coefficients are positive. Thermodynamic data for aqueous MgSO4solutions at elevated temperatures indicate a coexistence curve with a lower consolute point at about 239°C, submerged by the crystallization curve. The same approach predicts a coexistence curve for aqueous UO2SO4solutions, in qualitative agreement with the observation of a lower critical point at 286°C. In earlier interpretations this coexistence curve has been attributed to the peculiar properties of the uranyl ion, but it would appear that to a first approximation the miscibility gap in aqueous UO2SO4at elevated temperatures represents a general property of 2:2 electrolytes, which for UO2SO4becomes visible due to the high so

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931004

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe mechanism of the high electric conductivity of molten alkali chlorides is analysed in the light of the Complex Scaling Method (CSM) and its extension to quantum statistics of condensed phases. It is argued that the considered conductivities are due to quantum delocalization of the ions in the melt. Within the CSM‐treatment, a novel relation concerning the considered molar conductivities is derived. Its connection with experimental results on LiCl, NaCl, KCl and RbCl in the temperature rangeT= 800°C‐900°C reveals that the charge fluctuations in all these melts exhibit the same relaxation time. CsCl shows deviations from the above relation. A possible connection of this finding with the crystalline structures of the corresponding compounds is suggested. The “practical” importance of the relation derived is

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931005

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe equilibrium vapour of the systems Cr ‐ Ge, Cr ‐ Sn, and Cr ‐ Pb was investigated by using Knudsen effusion mass spectrometry in the temperature ranges of 1609 ‐ 1808 K, 1409 ‐ 1641 K, and 1526 ‐ 1745 K, respectively. The gaseous heteronuclear diatomic species CrM (M = Ge, Sn, Pb) were observed in each case in addition to the species Cr, Cr2, Gen, (n= 1 – 9), Sn, (i= 1–5), and Pb, (j= 1 – 4). CrGe2was the only heteronuclear species detected as being larger than the dimer. The appearance potentials of the ions CrGe+and CrSn+were determined by ionization efficiency measurements as 6.71 ± 0.02 and 6.31 ± 0.02 V, respectively. The enthalpy changes of the following dissociation and pressure‐independent isomolecular exchange reactions were evaluated according to the second‐ and third‐law methods:The enthalpy of dissociation of the dimer M2obtained in this work agrees excellently with the values from the literature thereby demonstrating the accuracy of the measurements. The following enthalpies of dissociation and bond energies result for the diatomic heteronuclear species and for CrGe2in kJ mol−1:The dif

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931006

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe phase diagram of the Cs/CsBr system has been determined by differential thermal analysis. The results show complete miscibility of Cs and CsBr in the liquid phase and no indication of any noteworthy solubility of cesium in crystalline CsBr. The shape of the liquidus line indicates a clear demixing tendency in the liquid phase as is expected in analogy to the other alkali metal/alkali halide systems.

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931007

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

年代:1989

数据来源: WILEY

摘要:

AbstractPrecipitation of lead ions by hydrogen sulfide in the presence of poly(vinyl alcohol) in aqueous or methanolic solution yields Q‐PbS particles (quantized particles) which have a structured absorption spectrum. The particles have a rod‐like or spherical shape (size quantization mainly in two or three dimensions, respectively). PbS with a structured absorption can also be made in acetonitrile using poly(ethylene oxide) as stabilizer. PbS stabilized by sodium polyphosphate has a structureless absorption spectrum. — Depending on the method of preparation and surface modification after preparation PbS samples fluorescing in the red or/and infrared are obtained. Methyl viologen generally quenches but can in certain cases promote the fluorescence when it is present in low concentration. Oxygen quenches when the colloid is stabilized by polyphosphate. — The rate of the photoanodic dissolution in the presence of air is increased by methyl viologen. Half reduced methyl viologen does not transfer an electron to Q‐PbS but can do so in the case of larger particles. — Illumination under argon leads to increased Ostwald ripening of the particles. However, when sulfite is present in the deaerated solution, photoanodic dissolution takes place. — Attack by hydroxyl radicals generated radiolytically leads to Pb2++ SO2−4. The fluorescence of a Q‐PbS particle is efficiently decreased after the attack by a single OH radical (i.e. after injection of one positive hole). — Single electron transfer from 1‐hydroxy methyl ethyl radicals, (CH3)2COH, to Q‐PbS also leads to a decrease in fluorescence. These effects are attributed to interactions of the charge carriers deposited by the radicals on the colloidal particles with the exitonic state produced by light absorption. — Accumulated electron transfer to PbS‐particles from organic radicals yields lead metal and organic sulfur compounds. In the beginning of this process, the fluorescence strongly increases (10% quantum yield) which is explained by destructi

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931008

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

年代:1989

数据来源: WILEY

摘要:

AbstractPartition of MgCl2, CaCl2, BaCl2, CuCl2, ZnCl2and water between the aqueous phase and n‐octanol at 298.15 K was considered. Extraction of the chlorides is represented by the formation of partially dissociated complexes in the organic phase. The equilibrium constant for the formation of MgCl2(H2O)6(ROH)6is 1.0·10−5mol−1kg; 6.3·10−7mol−1kg for CaCl2(H2O)5(ROH)5; 3.1·10−5mol−1kg for CuCl2(H2O)4(ROH)2and 4.1 · 10−3mol−1kg for ZnCl2(H2O)3(ROH)3. No detectable quantities for BaCl2are extracted by n‐octanol. Activities of n‐octanol in the organic phase were evaluated by numerical integration of the Gibbs‐Duhem equa

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931009

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe quenching of the luminescence anodic of the flat band potentialUFBis discussed in terms of the “dead layer” model. Properties of the bulk of the semiconductor can be deduced in this model. NearUFB, the potential dependence can only be explained, if the diffusion of minority carriers and surface recombination is properly taken into account. The relation between photoluminescence and photocurrent is discussed in the framework of this model. As examples, photoluminescence (PL) intensity and photocurrents at n‐GaP, n‐GaAs, n‐CdSe and n‐TiO2semiconductor electrodes in dependence of the bias were measured in aqueous electrolytes. Absorption coefficients and the rate of surface recombination

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931010

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe additional impedance observed at n‐GaAs and N‐GaP electrodes under conditions of hole injection or illumination was measured as a function of the frequency, the generation rate of holes and the electrode potential. The additional capacitance in the potential region where the minority carriers (holes) recombine with electrons is analysed on the basis of two models, one accounting for recombination at the surface, the other dealing with recombination in the depletion layer. It could be concluded that in n‐GaAs electrodes surface recombination prevails, while in n‐GaP electrodes recombination in the depletion layer must also be taken into account. These results are compared with those obtained from independent measurement tec

ISSN:0005-9021    

DOI:10.1002/bbpc.19890931011

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

年代:1989

数据来源: WILEY