Dynamic polarizability of many-electron systems within a time-dependent density-functional theory

Using the time-dependent extension, proposed by us recently, of the Hohenberg—Kohn—Sham density-functional theory, in the presence of an oscillating electric field, we suggest a Karplus—Kolker-type variation—perturbation method for the calculation of dynamic 2^L-pole polarizability of many-electron systems. As an illustration of the present density-functional formalism, the frequency-dependent dipole polarizability of He atom has been calculated in the frequency range 0 ? ω ? 0.65 au, using local density forms of the exchange and correlation potentials. For ω = 0, the results are numerically better than recent density-functional calculations of the static dipole polarizability of He. The corresponding hydrodynamical formulation, which employs the single-particle density as a basic variable, is also presented.     

Effect of mechanical pretreatment on thermal decomposition of silver oxalate under nonisothermal conditions

The effect of mechanical pretreatment on the thermal decomposition of silver oxalate was investigated using mass-spectrometric thermoanalysis. Starting at different levels of predecomposition, kinetic data were obtained by analysis of the kinetics at the initial rise of decomposition. The observed mechanically induced increase in reactivity of the silver oxalate used is due to three effects: (i) A thermally more stable “phase” at the surface of the grains is rendered ineffective by the creation of new surfaces. (ii) Disintegration processes increase the specific surface by several orders of magnitude. (iii) The number of potential nuclei in the surface is considerably increased by the generation of lattice defects.     

Photogalvanic cells: Part VIII. The theory of the transparent rotating disc electrode

The theory of the transparent rotating disc electrode is first extended to cover the case where two photogenerated species react with second-order kinetics and where one of the species is electroactive and the other is not. Secondly the theory is developed to describe the case where the solution is bleached close to the electrode. Thirdly theory is presented for experiments where the light source is modulated and the phase shift and amplitude of the resulting modulated photocurrent are measured.     

On the theory of polarographic maxima

The theory of polarographic maxima is presented taking into account the interaction of momentum transport, the electrostatic potential field, the adsorption—desorption and the faradaic processes. Several earlier results are generalised. The systems approach employed here is also extended to quasi-linear situations.     

Tunnel electrode: Part II. Electron-transfer theory at an n-type semiconductor tunnel electrode

The formula for the cathodic tunnel current at an n-type semiconductor tunnel electrode was derived from the double adiabatic perturbation theory considering the vibration in the first coordination sphere. In the low-temperature limiting case, the apparent difference between the normal and the abnormal regions was observed in both the transfer coefficient α and the activation energy E* as a function of potential. It was concluded that the semiconductor tunnel electrode has advantageous characteristics for investigation of the electron-transfer mechanism at high overvoltage.     

Polarography with controlled current density — Chronopotentiometry at a dropping ellectrode: Part III. Experimental verfication of the theory

A large number of experiments have been communicated with regard to the operation of a polarograph which shows essentially a galvanostatic character instead of the usual potentiostatic one. A reasonable good agreement could be established between practice and theory. Finally some introductary experiments have been reported concerning phenomena connected with the absence of surfactants in the solution, and other ones observed in the presence of catalysts which promote the evolution of hydrogen.     

Optical autoionization resonance theory as an approach to electron transfer via adsorbed atoms at metal—solution interfaces

Electron transfer between an ion in solution and an impurity atom adsorbed at a metal electrode is sometimes faster than direct electron transfer between an ion and a metal. This process displays close analogies to Fano autoionization resonances in atoms excited to formally bound states broadened by coupling to continuum states. On the basis of this analogy we have derived current—voltage relationships for electron transfer via adsorbed impurity atoms. The most striking effect is that the current passes through a maximum at overvoltages approximately coinciding with the nuclear reorganization enery, then drops, and rises again at still higher voltages. This pattern is quite different from that of direct electron transfer and is caused by the “interference” of metal and impurity wave functions in certain energy ranges. The effect is generally expected only for activationless process, i.e. for large overvoltages, where the current variation directly reflects the behaviour of the pre-exponential factor in the current expressions.The impurity level also modifies the Gibbs energy of nuclear activation due to the solvent configuration dependence of the electron density at the adatoms. This effect is commonly small and in contrast to the electronic structural effects, leads to smooth current-voltage relations.     

Developments in the theory of cationic polymerization-VII [1a,b]: Theoretical attempts at improving initiators for cationic polymerization of alkenes

The initiation of the cationic polymerisation of alkenes is examined in detail by means of simple thermodynamic concepts. From a consideration of the kinetic requirements it is shown that the ideal initiator will yield a stable, singly charged anion and a cation with a high reactivity towards the monomer by simple, well defined reactions. It must also be adequately soluble in the solvent of choice and for the experimental method to be used. The calculations are applied to carbocation salts as initiators and a method of predicting their relative solubilities is described. From established and predicted data for a variety of carbocation salts the position of their ion:molecule equilibria and their reactivity towards alkenes are examined by means of Born-Haber cycles. This treatment established the relative stabilities of a number of anions and the reason for dityl, but not trityl salts initiating the polymerisation of isobutene.The outcome of our treatment is a general method for selecting theoretically promising new initiators.     

Hyperspherical coordinates in quantum mechanical collinear reactive scattering

A new hyperspherical coordinate method for performing atom—diatom quantum mechanical collinear reactive scattering calculations is described. The method is applicable at energies for which breakup channels are open. Comparison with previous results and new results at high energies for H H₂ are given. The usefulness of this approach is discussed.     

Proton and carbon-13 chemical shifts: Comparison between theory and experiment

A series of ab initio ¹H and ¹³C NMR chemical shifts are presented for all molecules for which gas-phase experimental measurements exist. Quantitative agreement with this large set of data is achieved by the use of gauge-invariant atomic orbitals in an SCF perturbation theory approach. The effect of basis set completeness on these ¹H and ¹³C chemical shifts is also examined. The 4-31G basis set is found to provide internally consistent results and give satisfactory agreement with gas-phase experimental data. Errors within 6% for ¹H shifts and 3% for ¹³C shifts result. Increasing the basis set to the 6-31G^* level does not significantly improve the agreement. For ¹H shifts only, the 3-21G basis set is adequate. The validity of the particular computational approach employed here is further substantiated by comparison to another ab initio magnetic shielding method.     

A kinematic approach to ionic transport in aqueous electrolyte solutions and structural theory of hydration of alkali metal ions

While considering the self-diffusion processes in aqueous electrolyte solutions, transport of ions, not only by jumps of single ions, but also by jumps of their solvation shells, are to be taken into account. Samoilov estimated the relative number of the two kinds of ionic jumps from experimental data on diffusion assuming an approximately uniform value for the α factor. In the present paper entirely different theory of the α factor based on the structural hydration model of one of the authors (S.V.T.) for alkali metal ions is given and its ion-wise values are calculated at different temperatures. The theory not only dispenses with the approximate fixation of α but also throws light on the structure of water, formation of clusters and their population variation with temperature.     

He-HF vibrational inelasticity at low and intermediate energies from quantum collision theory

The rotational-sudden approximation (IOSA) has been applied to He-HF scattering at intermediate energies by using an ab initio computed potential-energy surface which explicitly included the dependence on the internal molecular coordinate. The vibrational degree of freedom has therefore been treated exactly by solving the coupled radial equations that were obtained after expanding the target vibrations over a large number of HO wavefunctions. The radial behaviour of the computed coupling matrix elements between lower-lying target states is analyzed at various relative orientations of the atom-to-target vector with respect to the molecular bond. The present results clearly show that the coupling strength and range can be directly related to the specific anisotropic behaviour of the potential surface and to the varying efficiency of (V, T) coupling as the He atom probes different molecular regions. The computed relaxation times are compared with experiments at various temperatures and with previous calculations performed via different surfaces and dynamical models and show satisfactory agreement with observations, thus markedly improving the quality of earlier computed cross sections.     

Binuclear metal carbonyl dab complexes : VII. A 13C NMR investigation of MM′(CO)6(DAB) complexes (M = M ′ = Fe,Ru; M = Mn,Re and M′ = Co; DAB = 1,4-diazabutadiene). Dynamic behaviour of σ2-N, σ2-N′, η2-C=N coordinated dab in MnCo(CO)6(DAB) and local scrambling of the carbonyl groups

The ¹³C NMR spectra of MM′(CO)₆(DAB) complexes (M = M′ = Fe, Ru; M = Mn, Re and M′ = Co; DAB = 1,4-diazabutadiene) show very characteristic features which are directly related with the bonding mode of the DAB ligand to the binuclear metal carbonyl fragment. In these complexes the DAB ligand is σ²-N, μ²-N′, η²-C=N or σ²-N, σ²-N′, η²-C=N coordinated. Chemical shifts of about 175 ppm are observed for the σ-coordinated imine fragments and about 60 or 80 ppm for the η²-C=N coordinated imine fragments.In MnCo(CO)₆[diacetylbis(cyclopropylimine)] the DAB ligand is fluxional, and the changes in the spectra when recorded at various temperatures can be interpreted in terms of an exchange between the σ- and π-coordinated part of the DAB ligand.The homodinuclear M₂(CO)₆(DAB) complexes (M = Fe or Ru) contain M(CO)₃ fragments on which the carbonyl groups are involved in a local scrambling process with very different activation parameters (T_c = ?50°C and +85°C).MCo(CO)₆(DAB) complexes (M = Mn, Re), which contain a semi-bridging carbonyl group according to the crystal structure, show rapid interchange of this carbonyl group with the terminal carbonyl groups on cobalt. The electronic balance is kept in equilibrium by an internal compensation within the DAB ligand.     

Analytical applications of liquid-liquid phase equilibria: analysis of binary mixtures of chemically similar components

A new, simple and rapid method based on the principle of liquid-liquid phase equilibria has been developed for the analysis of binary mixtures of chemically similar organic compounds. The method does not require elaborate instrumentation and can be used to analyse mixtures of members of homologous series. The application of the method has been illustrated by analysing binary mixtures of n-hexane and n-octane; the maximum uncertainty in this analysis is ~2%.     

A molecular-orbital theoretical classification of reactions of singlet ground-state molecules

The reaction mechanisms of molecular systems in the ground singlet state are discriminated with the triplet stability—instability criterion of the restricted Hartree—Fock (RHF) solution for the entire system and with the phase continuity criterion of the highest occupied orbital involved. The criteria used are discussed in relation to the outcomes from the configuration-interaction approach.     

Synthesis of cytosinine,the nucleoside component of antibiotic blasticidin S

The first total synthesis of cytosinine (2) is described.     

Spectrophotometric determination of microamounts of gold(III) with propericiazine

Propericiazine is proposed as a new reagent for the spectrophotometric determination of gold(III). The reagent forms an orange-red-colored species with gold(III) instantaneously in 4–8 M phosphoric acid. The orange-red species exhibits maximum absorbance at 511 nm. Beer's law is valid over the concentration range 0.1–7.0 μg/ml. The molar absorptivity is found to be 3.85 × 10⁴ liter mol⁻¹ cm⁻¹. The effects of acidity, time, order of addition of reagents, temperature, reagent concentration, and diverse ions are investigated.