ISSN:0005-9021    

DOI:10.1002/bbpc.19710750702

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

年代:1971

数据来源: WILEY

摘要:

AbstractThe effects of changes of temperature and pressure and of illumination on the shape and position of the absorption spectrum and ESR saturation curve of electrons trapped in rigid or viscous liquid matrices are described. Data are presented to show that the Arrhenius equation does not adequately describe the influence of temperature on the rates of diffusion‐controlled reactions of the solvated electrons in glassforming liquids, and that pulse‐radiolysis studies of these systems allow a rigorous test of theories of these reactions and in particular demonstrate the reality of the predicted phenomenon of time dependant rate constants.The conclusions drawn from this information are: 1) the wide structureless optical spectrum of es−and et−is partly due to a distribution of electrons in holes of different configurations; 2) that the trapping of electrons is facilitated by the pre‐existence in the medium of “voids” but that reorganisation of some cavities occurs after electron capture; 3) an increase of temperature by increasing the possibility of rotational motion of molecules in the walls of the cavity facilitates both the relaxation of traps and the release of electrons from them and also increases the probability of retrapping a mobile electron; 4) over a large temperature range logk=A‐B/(T‐T0) whereT0is the temperature below which rotation sufficient to permit translation of molecules is impossible and B is inversely proportional to the thermal expansion coefficient of the liquid; 5) that quantum mechanical tunnelling of solvated electrons occurs and is the major factor influencing the rate of reaction of er−at temperatures in the vicinity ofT0and 6) that absorption of light causes mobilisation of et−and hence photo conductivity and use of light of different wavelengths enables perturbation of

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750703

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

年代:1971

数据来源: WILEY

摘要:

AbstractThe F center, an electron trapped at an anion vacancy, is known in a large variety of ionic crystals. F centers in alkali halides of the NaCl‐type have been most extensively investigated, and shall be the main object of this exposition. F centers can be produced by heating the crystals in the alkali metal vapour (“additive coloration”), by high temperature electrolysis, as radiation damage from X‐rays or bombarding particles, and by a number of photochemical reactions involving impurities. The most conspicuous property of the F center is its optical absorption, a band of Gaussian shape and roughly 2000 cm−1width in the visible region (F = Farbe, color). The band maxima for different crystals with lattice constants a are well described by the relationvmax·a2= const. This absorption is interpreted as the transition from an s‐type ground state to a bound p‐type excited state. A number of theoretical approaches on this basis gave good agreement with the observations. Shape and width of the band and their temperature dependence result from coupling to vibrational modes of the lattice. Weaker transitions to higher excited states are also known.Upon excitation in the F band or higher absorptions, F centers luminesce, at low temperatures and low concentrations with quantum efficiency near one. Emission bands lie in the near infrared, with Stoks shifts of typically 10.000 cm−1. The lifetimes of the excited state are ≈︁ 10−6sec, which would be relatively long for an allowed p‐s‐transition. At higher temperatures the luminescence is quenched and photoconductivity appears, showing that the relaxed excited state is close to the conduction band. This implies that the electron is rather delocalized in the relaxed excited state. The low transition moment to the more localized ground state may be understandable in this way. Certain features of the unrelaxed excited state, i.e. before the lattice adjusts to the new electronic state within ≈︁ 10−12sec, can be studied by magnetooptical experiments. For this purpose a modified alkali atom model with inverted spin‐orbit‐splitting between the2P1/2and2P3/2states has turned out appropriate.The unpaired spin of the F electron makes it accessible to spin resonance investigations. ESR spectra show only in a few cases well resolved hyperfine structure, confirming beyond any doubt the atomistic model of the center, and giving precise values of the electron density at the nearest neighbour nuclei. By electron‐nuclear double resonance (ENDOR) hyperfine interactions in many higher “shells” of surrounding ions have been resolved. Thus the ground state wavefunction of the F electron can be analysed in very detail out to several lattice constants from the center. Current theories show good agreement with the experimental data in the region close to the center (nearest and next‐nearest neighbours), but the far out tail of the wavefunction is not yet well understood. In connection with optical pumping and magnetooptic effects, ESR of the relaxed excited state has recently also been observed. So far this has not settled the question if it is a p‐state with static or dynamic Jahn‐Teller effect or an s‐state.A large number of modified F centers have been produced, and their investigation contributed to a refined understanding of this basic defect structure. In alkali halide crystals doped with foreign alkali ions, e.g. KCl: Li, “FAcenters” with one foreign alkali ion as nearest neighbour can be synthesized photochemically and oriented by bleaching with polarized light, showing then anisotropic absorption bands. In crystals with divalent cation impurities a number of different “Z centers” are formed, whose structure is not yet completely known. Dimers and trimers of nearest‐neighbour F centers, known as M centers and R centers, have also been widely investigat

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750704

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

年代:1971

数据来源: WILEY

摘要:

AbstractA brief review of existing data on the specific conductivity and optical absorption of mercury and cesium at supercritical temperatures as a function of density is given. Since the paper contains a discussion of the metal‐nonmetal transition, its emphasis is on the intermediate range of conductivity between the metallic and nonmetallic state. The results are interpreted in terms of Mott's theory of metal‐nonmetal transition and of the concept of localization of electrons in noncrystalline materi

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750705

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

年代:1971

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750706

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

年代:1971

数据来源: WILEY

摘要:

AbstractEs wurden pulsradiolytische und γ‐strahlenchemische Versuche zur Reduktion von halogenierten organischen Verbindungen durch hydratisierte Elektronen durchgeführt. Dissoziativer Elektroneneinfang setzt aus verschieden chlorierten Methanen, äthylenen sowie fluorierten Benzolen Halogenionen frei. Diese wurden mit Hilfe von Leitfähigkeitsmessungen bei der Pulsradiolyse und mit Ionen‐sensitiven Elektroden bei den γ‐Versuchen quantitativ nachgewiesen. Die Geschwindigkeitskonstanten der Reaktion des eaq−mit den mehrfach halogenierten Verbindungen sind praktisch ausschließlich durch die Diffusion der Reaktionspartner zueinander bestimmt. Bei den wenig halogenierten Substanzen verläuft die Reaktion langsamer, was mit der größeren Stabilität der Halogen‐Kohlenstoffbindung in Einklang steht. Die primären Reaktionsprodukte sind Halogenionen und neutrale, kurzlebige Radikale, die keinerlei optische Absorption im Wellenlängenbereich von 250–800 nm aufweisen.Alkohol‐ und Ätherradikale übertragen ein Elektron auf CCl4. Dies stimmt mit der Tatsache überein, daß die Halbstufenpotentiale für die Oxidation dieser Radikale negativer sind als dasjenige für die Reduktion des CCl4. Die theoretisch ebenfalls mögliche Elektronenübertragung vom CO2−‐Radikalion auf Tetrachlorkohlenstoff findet nicht statt, da offensichtlich eine zu hohe Aktivierun

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750707

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

年代:1971

数据来源: WILEY

摘要:

AbstractThe radiolysis of some tris‐oxalatocomplexes of transition metals has been studied in neutral aqueous solutions. As radiation sources have been used α‐Po210, β‐Sr90, and γ‐Co60.In order to establish the reaction mechanism the influence of the following factors has been investigated: radiation dose, does rate. L.E.T., solute concentration, the presence of some scavangers for reducing and oxidizing species and the presence of oxygen.The predominant process in the radiolysis of these compounds is the reduction of the complex ions by the hydrated electrons and hydrogen atoms:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {e_{aq}^ - + [{\rm Me}^{{\rm III}} ({\rm C}_{\rm 2} {\rm O}_{\rm 4} )_3 ]^{3 - } \to [{\rm Me}^{{\rm II}} ({\rm C}_{\rm 2} {\rm O}_{\rm 4} )_2 ]^{2 - } + {\rm C}_{\rm 2} {\rm O}_{\rm 4}^{{\rm 2 - }} ;} & {{\rm (1)}} \\ {{\rm H} + [{\rm Me}^{{\rm III}} ({\rm C}_{\rm 2} {\rm O}_{\rm 4} )_3 ]^{3 - } \to [{\rm Me}^{{\rm II}} ({\rm C}_{\rm 2} {\rm O}_{\rm 4} )_2 ]^{2 - } + {\rm C}_{\rm 2} {\rm O}_{\rm 4}^{{\rm 2 - }} + {\rm H}^{\rm + } .} & {(2)} \\ \end{array} $$\end{document}The nature of the final radiolysis products as well as the kinetics of their formation during irradiation is different for each c

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750709

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

年代:1971

数据来源: WILEY

摘要:

AbstractAn attempt was made to simulate metal‐organic reactions of the triethylaluminium‐naphthalene‐diethylether‐system by pulse radiolysis. Using 1 μs‐pulses a partial absorption spectrum of esol−in ether in the range from 800 to 1200 nm was obtained at room temperature. The radicals and radical‐ions, produced by the pulse radiolysis of argon saturated ether, possess a total absorption spectrum in the range from 210 to 350 nm. The transient absorption decays with mixed order.The intermediates, obtained in argon‐saturated ether solutions of triethylaluminium (10−3– 10−2M) have a total absorption spectrum between 220 and 340 nm which changes considerably 50 μs after pulse end. Here too, mixed kinetics are occuring (at 250 nm.k1∼ 6 · 104s−1andk2/ε ≈︁ 107cm · s−1). By saturating pure ether with HCl gas the solvated electrons are scavenged. Similar results as in the presence of argon were obtained, showing that the reactivity of H‐atoms is rather high too.A total absorption spectrum of C10H8−and C10H9species was measured by irradiating naphthalene (10−3– 10−2M, argon saturated) in ether. Using again HCl gas as a scavenger for esol−the spectrum of C10H9radicals was obtained with maxima at 300, 307 and 320 nm. It changes strongly 50 and 100 μs after the pulse, indicating that these species are very reactive, probably with HCl. They disappear in a second order reaction (at 330 nmk2/ε = 2.8 · 106cm ≈︁ s−1). Subtracting the spectrum of C10H9from the total one, the absorption spectrum of C10H8−with maxima at 330 and 370 nm was obtained. Its shape does not change very much with time, suggesting that the second order disappearance of the radical‐anions (at 370 nmk2/ε = 5 · 107cm · s−1) is mainly due to a dimerisation process.Investigating the total absorption spectrum of the complete triethylaluminium‐naphthalene‐diethylether‐system (saturated with argon) at different times after the pulse, the appearance of a new maximum at 312 nm was observed. It was attributed to the intermediate, formed by the reaction of Al(C2H5)2+and C10H8−and/or C10H9species. This assumption was supported by analysing the final radiolytic products of the system.A full report of the absorpt

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750710

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

年代:1971

数据来源: WILEY

摘要:

AbstractEnergy surfaces are constructed for the ammoniated and hydrated electron within the cavity model, to illustrate the range of validity of the model as it is currently deployed. From the observed excitation energies the cavity in water is guaged to have a radius of 1.22 Å as compared with 2.12 Å in ammonia.Molecular orbital studies upon some dimer models are discussed. It is seen that though the electron may be localised in a cavity in the ground state the charge may be dispersed by excitatio

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750712

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

年代:1971

数据来源: WILEY

摘要:

AbstractIn charge transfer reactions the influence of the solvent can not be described by the dielectric constant only as the transition state theory does, but the polarisation fluctuations of the solvent have to be taken into account. The theory is given for the reactivity of solvated electrons on the basis of quantenmechanics.

ISSN:0005-9021    

DOI:10.1002/bbpc.19710750713

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

年代:1971

数据来源: WILEY