摘要:

AbstractThe rate constant of fluorescence quenching by molecular oxygenk qSwas measured for a series of singlet oxygen (1O2)‐sensitizers in toluene and adopts values between 3.5·1010and 0.4·1010M−1s−1. log(k qS) shows a correlation with the free energy of electron transfer ΔGelas calculated according to Rehm and Weller.k qSdecreases with increasing ΔGelin the endergonic region. The efficiency ϕ ΔSfor1O2‐formation accompanying the S1‐state quenching by energy transfer of the S1‐state of the sensitizer is substantially>0 only in the cases, where the S1‐T1‐energy gap exceeds the excitation energy of1O2(1Δg), 94 kJ/mol, where electron transfer is energetically unfavourable and the T2‐state of the sensitizer is lying above the S1‐state. Furthermore the temperature dependence ofk qSwas measured in toluene for two sensitizers. The quenching process for dicyanoanthracene (DCA) is activationless in the high temperature region which could be explained either by activationless energ

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980802

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe laser photochemistry of 1,2‐naphthoquinone‐diazide‐(2)‐5‐sulfonic acid phenylester in cyclohexane has been investigated. The photolysis experiments have been done using a KrF laser pulse (generation pulse) and a nitrogen laser pulse (transformation pulse) with various time delay from 40 ns up to 1 s. At a time delay between the two laser pulses in the μs‐region, the formation of indene and cyclohexyl‐indene derivatives has been observed, additional to the corresponding indenecarboxylic acid. The laserspecific formation of these compounds is the result of the electronic excitation of the intermediately formed ketene and its reaction by decarbonylation. The time delay for getting a high yield of the indene and the cyclohexyl‐indene derivatives correlates closely with the rise time and the life ti

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980803

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe photodissociation dynamics of NCN3has been investigated by observation of the CN(X2Σ) product molecule. The CN fragment is formed in vibrational states ν = 0,1,2 with a population ratio ofP(ν = 0):P(ν = 1):P(ν = 2) = 0.42:0.33:0.25. The rotational state distribution is broad, a Boltzmann plot shows a nonlinear behavior. The rotational excitation carries 9% of the available energy. The CN recoil velocity distribution is also broad and indicates a significant internal excitation of the N3product molecule. The spin is distributed statistically. The fragmentation does not proceed in the Franck‐Condon limit but strong forces act on the upper potential energy s

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980804

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe electronic absorption spectra of some arylidene‐, arylethylidene‐ and heterocyclicmethylenemalononitriles have been investigated qualitatively and quantitatively. MNDO‐CI calculations were performed to predict the suitable conformer for the studied compounds. The conformer adopted by arylethylidene derivatives is found to be the non‐planar one, while the other two groups of compounds had the planar conformer. The observed transitions are assigned as charge transfer (CT), localized and delocalized according to the contribution of the various configurations in the CI‐states. The correspondence between the calculated and experimental transition energies was sat

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980805

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe decay of the integral band‐to‐band photoluminescence (PL) at (100) orientated n‐doped GaAs (Te;n0= 5×1017… 1×1018cm3) in contact with aqueous 1 M HCl was investigated with the time‐correlated single photon counting technique. The PL‐decay was measured at various externally applied potentials, at constant and low density of injected carriers (pi≪n0), and at an excitation wavelength of λexc= 647.1 nm. The studies included electrodes modified by dipping in a solution of 5×10−3M RuCl3in 1 M HCl for 20 minutes. It was observed that the PL‐decay measured at low injection level shows a reproducible and characteristic dependence on the externally applied potential. Within the accuracy of our time‐correlated single photon counting equipment, the PL‐decay time remains nearly constant and short in the range of potentialU= (−0.3 … −0.9) V(Ag/AgCl). For the nonmodified electrodes the PL‐decay time increases with increasing cathodic polarization in the range of potentialU= (‐0.9 … −1.1) V(Ag/AgCl) up to a maximum atU≈ −1.1 V(Ag/AgCl), which corresponds to the (Mott‐Schottky) flatband potential in the dark. At further cathodic polarization the cathodic current (due to the evolution of hydrogen) during the measurements becomes significant and it was observed that the PL‐decay time decreases. After a treatment with Ru3+, the behaviour in the range of potential on the cathodic side ofU= −0.9 V(Ag/AgCl) is different. The experimental observations could be confirmed qualitatively by results of computer simulations based on theTwo‐dimensionalSemi‐ConductorAnalysis Package (TOSCA). At potentials on the anodic side of the flatband potential (depletion range) the decay times are short as well as independent of the degree of the band bending, of the surface recombination velocity, and of the photocurrent, respectively. This observation will be interpreted qualitatively by including the diffusion of the minority carriers toward the (dark) depletion layer as a competitive process for the radiative recombination in the bulk. Near the flatband potential the decay time of PL increases within a potential range of ΔU≈ 200 mV depending on the density of injected carriers as well as on the rates of the surface recombination and of the minority carrier transfer (photocurrent). Based on a qualitative explanation for this characteristic dependence of the PL‐decay time on the potential, the values of the surface recombination velocity and of the exchange photocurrent density are estimated to beS0<106cm/s andjph,0<10−8A/cm2, respectively, for nonmodified electrodes andS0≥106cm/s and/orjph,0

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980806

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe electrochemical reduction of isatoic anhydride and its derivatives was studied by simultaneous electrochemical and ESR‐measurements. For the first time 9 new radicals were characterized by its formal redox potentials, hyperfine coupling constants,g‐factors and lifetimes. The advantage of measuring the kinetic data in stagnant and renewed electrolyte combined with accumulation of the ESR‐spectra is demonstrated in the case of shortlived radicals. It is shown that the electrochemical reduction of isatoic structures follows a self protonation mech

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980807

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

年代:1994

数据来源: WILEY

摘要:

AbstractElectrolytic conductivity of mixed electrolyte solutions has been studied theoretically and experimentally on the basis of recent phenomenological theories of conductivity. For 1:1 electrolytes a generalised mixture rule is deduced, applicable to mixtures of any number of ionic species. For mixtures of dissimilar electrolytes the simple mixture rule does not apply. However, for mixtures of 1:1 electrolytes with electrolytes of other charge type (2:2, 2:1 electrolytes), when the 1:1 electrolyte is present in marginal quantities, a modified additivity rule is established. In this case the 1:1 electrolyte can be used to probe the properties of the dominant electrolyte in the solution.

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980808

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe surface properties of two commercially available polysiloxanes, AK 1000 and AV 1000, have been examined at the air/water (A/W) interface in terms of the surface quasi‐elastic light scattering technique (SLS) in conjunction with surface pressure‐area (II–A) isotherm studies. Both are found to form stable, insoluble and promptly equilibrating monolayers at A/W. Being a mixture of linear poly(dimethylsiloxanes) (PDMS), AK 1000 is shown to follow the well established surface properties of PDMS. On the other hand, AV 1000, a mixture of linear and phenylsiloxane‐branched PDMS, referred to as PPMS, shows a different isotherm. The profiles of the surface dynamic viscoelastic parameters deduced from SLS, i.e., the surface dilational elasticity, ϵd, and the corresponding viscosity,K, relative to the surface mass density, γ, are rather different. The magnitudes of ϵdandKfor both monolayers are comparable, while small but distinct differences are observed. In particular, in the high surface mass density region, the dynamic surface viscosity of PPMS films is about twice that of PDMS, but all values are still in the regime of very small viscosities (K<5×10−8kg/s). These findings are discussed in the context of the differences found in thermocapillary experiments between the

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980809

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe rate of water transport across porous membranes with a hydrophobic matrix (porosity ϵ ≈ 0.5; characteristic length of voids ξ ≈ 150 nm; thickness δ ≈ 30 μm) caused by a temperature difference between the bulk phases is studied. The voids of the membrane are filled with water vapour. The effective temperature difference (T′–T″) across the membrane is smaller than the temperature difference (T′–T″) between the bulk phases (“temperature polarization”) caused by heat conduction and by heat flow associated with the water transport. An experimental method is described and tested to determine the temperature polarization coefficient τ ( = (T′–T″)/(T′–T″) for a given experimental situation. The phenomenological transport coefficient of the membrane for water vapour has to be known from independent experiments. This method is a simple alternative to the method developed by Schofield et al. (J. Membrane Sci.33, 299 (1987)). The dominating factor determining the temperature polarization coefficient is the value of the thickness of the two boundary layer of heat conduc

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980810

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

年代:1994

数据来源: WILEY

摘要:

AbstractAdsorption of calcium and europium from 0.001‐1 M solutions of different 1:1 electrolytes on silica and alumina was studied as a function of pH, surface charge density σ0, ionic strength and temperature. Adsorption of multivalent cations on a negatively charged surface is competitive with respect to monovalent cations, i.e., the increase of the ionic strength leads to a decrease of multivalent ions adsorption. In contrast, adsorption of multivalent cations on a positively charged surface is insensitive to the concentration of monovalent cations or even increases with the ionic streng

ISSN:0005-9021    

DOI:10.1002/bbpc.19940980811

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

年代:1994

数据来源: WILEY