ISSN:0005-9021    

DOI:10.1002/bbpc.19840880402

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe rate constantsk1, andk2of the self exchange reactions between the half oxidized and the totally oxidized or the reduced forms of some p‐phenylenediamine derivatives are investigated at 293 K by ESR line‐broadening in various aprotic solvents (dielectric constants ϵ between 4.7 and 49). The dimerization constants of the radicals at 183 K and the enthalpies of dimerization are measured, too. The results are discussed in terms of Marcus' theory. Ink1, is found to depend linearly on γ = 1/n2‐ 1/ϵ (n= refractive index), the covered range being 0.27<γ<0.53. The distance parametergis obtained from the slope and compared with values derived from different molecular models. The results are represented satisfactorily by ellipsoidal molecules with half axes obtained from crystallographic data, the distance in the activated complex being approximately the same as in the radical dimers. The inner reorganization energy is calculated by Hückel methods and compared with experimental values obtained from the intercept of the straight line lnk1(γ). The deviations are considerable. The calculated Marcus activation free enthalpies are smaller then the measured ones. — The slow rate constantk2of the second step can be computed, if the Coulomb forces between the radical cation and the dication of the quinone diimine are considered. The inner reorganization energy of the transformation between aromatic and quinoidic structures is negligible. The rate constants of different cross reactions with p‐phenylene diamines are calculated with Marcus' formula which, however, has to be extended by work terms. The symproportionation rate is nearly diffusion controlled. With some other reactions the conformity of measured and calculated rate constan

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880403

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

年代:1984

数据来源: WILEY

摘要:

AbstractUsing ESR‐line broadening the rate constants of electron self exchange between five substituted p‐phenylenediamines, semiquinonediimines, and quinonediimines in six aprotic solvents are measured in the temperature range 230 K

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880404

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe structure of Cu adsorbates, deposited electrochemically up to one monolayer onto Au(111) at underpotentials, has been investigated using LEED and RHEED after transfer of the gold electrode from the electrochemical cell into an UHV chamber. Before electrochemical deposition, the gold surface was thoroughly cleaned in the UHV‐chamber by argon bombardment and subsequent annealing. The Cu adsorbate is then found to yield a (√3 × √3)R30° superstructure at medium coverages, which is in clear contrast to the growth behaviour for Cu evaporated in UHV onto a bare Au(111) surface, where pseudo‐morphic growth is observed from the very

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880405

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

年代:1984

数据来源: WILEY

摘要:

AbstractThin films of anion exchangers were prepared from quaternized polyvinylpyridine on glassy carbon and Pt electrodes. To render the polymer insoluble in aqueous electrolytes it was cross‐linked chemically or by exposing the coated electrodes to synchrotron‐radiation. With these electrodes the redox system [Fe(CN)6]3‐/4‐was investigated with electrochemical methods, including the rotated ring/disk technique. The high equilibrium concentration of [Fe(CN)6]3‐in the polymer matrix leads to extensive cross‐linking and desolvation of the film rendering its permeability low. During cathodic reduction a large fraction of the produced [Fe(CN)6]4‐leaves the polymer phase. Anions from the background electrolyte replace the redox‐system; the film swells. The electrochemical phenomena associated with this reversible film structure change are discussed, in particular, a remarkable electrochemical recti

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880406

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe surface plasmon absorption band of small metal particles or large clusters (diameter ≤ 100 Å) is known to shift and to broaden with decreasing diameter. It is argued and experimentally proven at Ag‐colloids that this size effect depends sensitively on the microscopic surface properties of the clusters, which are influenced by the interaction with the embedding ma

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880407

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

年代:1984

数据来源: WILEY

摘要:

AbstractUsing low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS) and measurements of work function changes (Δø), the coadsorption of water and ions on metal surfaces has been studied in ultrahigh vacuum. As an example of anion specific adsorption, the hydration of bromide on Cu(110) has been characterized with regards to inner layer composition, surface hydration number and the formation of long‐range order. Simulation of non‐specific adsorption of lithium ions has also been attempted. On Ag(110), a drastic reduction of the binding energy of lithium in the presence of water is attributed to this type of surface hydration. Such evidence is not observed on Cu(111), where substantial fragmentation of the water seems to occur. The electrochemical relevance of these results is disc

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880408

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

年代:1984

数据来源: WILEY

摘要:

AbstractWith the addition of Ag‐sol to extremely diluted rhodamine 6G solutions (ca. 10−10M/l) the prevalent fluorescence can be replaced by surface fluorescence and surface enhanced resonance Raman scattering (SERRS) of similar intensity, however only in presence of coadsorbed anions such as chloride. For strong bands the Raman cross sections are as high as 10−19cm2sr−1molecule−1. Referred to the extinction of the sol which is much larger than that of the dye solution, the mean quantum yield for the surface Raman scattering is estimated to 0.0004. In addition, SERRS consisting of a set of fundamental vibrations, overtones and combination modes and a broad continuum shows throughout the spectral range a significant, but identical polarisation (I(sp):I(ss) = 0.55), whereas the solution as well as surface fluorescence is completely de

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880409

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

年代:1984

数据来源: WILEY

摘要:

AbstractExposure of the ZnO(1010) prism face to NO at 90 K leads to two molecularly adsorbed NO species. The weakly bound form desorbs at 110 K and the strongly bound form desorbs at 420 K for low exposure and at 300 to 450 K for high exposures. Adsorption of the strongly bound form is activated and slower than of the weakly bound NO. Simultaneously, NO reacts partly to N2O at 90 K. N2O desorbs at 140 K, oxygen desorption is not observed and it is concluded that the oxygen formed during the NO to N2O conversion diffuses into the substrate. After annealing to 190 K, the weakly bound NO and N2O desorb. After several cycles of reexposing and annealing to 190 K, N2O formation is completely suppressed due to accumulation of either oxygen or the strongly bound form of NO or both. The strongly bound NO increases, the weakly bound NO decreases the electron affinity χ. After saturation with the strongly bound form, the final increase of χ amounts to 1.2 e

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880410

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe have used our very fast “Iodine‐Laser Temperature‐Jump” technique with a time resolution between 10−10and 100s to investigate the intercalation of proflavine into calf thymus DNA. Salt concentrations between 10−2and 1 M and temperatures from 290 to 320 K were used. The DNA concentration ranged from 10−3to 10−5M and was always in large excess of the proflavine concentration to avoid aggregation of the dye in solution as well as on the surface of DNA. Under all experimental conditions only a single relaxation time which varied between 10−4and 10−3s could be detected. This result is in contrast to all temperature jump experiments performed so far using “Joule‐heating” equipments. The reason for this behaviour is that our technique is the only one which avoids the electric field effects inevitably associated with the “Joule

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880411

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

年代:1984

数据来源: WILEY