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Theoretical aspects of mineral flotation in particular the adsorption of flotation reagents at the mineral-water interface, were reviewed in 1959 for the last time. Several papers have been published since on this topic. The aim of this chapter is to survey recent publications that have contributed to the development of the flotation theory. [ABSTRACT FROM AUTHOR]

Studies on the solvent extraction of actinide ions by different combinations of extractants have been reviewed. Various equilibria involved in the extraction processes and the formation of the extractable complexes have been considered along with their equilibrium constant data. Various methods which are useful in establishing the composition and the nature of the extractable complexes are presented. The data on isolation and structural studies of some complexes, involved in synergic extraction, are also included. A brief description of the different areas in which synergic extraction is finding application is also given. Many combinations of extractants, where the studies conducted are very few but, which are likely to yield enhanced extractions are indicated. Areas of research, both from the academic and applied points of view, which require attention are suggested. [ABSTRACT FROM AUTHOR]

In a homogeneous chemical reaction maintained far from equilibrium where the reaction mechanism contains coupled feedback steps, oscillations in the concentrations of certain intermediates are possible. Until recently, the few known chemical oscillators were discovered accidentally, were variants of these reactions, or were extracted from biological systems. To provide new chemical oscillators for theoretical and experimental study, a program has been developed to design homogeneous oscillators based on reactions of inorganic compounds and ions. Mechanistic detail is presented for the chlorite-iodide-arsenite oscillator, and other newly designed oscillators are discussed more briefly. A classification scheme for grouping these and related oscillators is presented. [ABSTRACT FROM AUTHOR]

This article gives a review of complexes in which a dioxygen ligand is bonded to a transition metal. Three aspects of these complexes are discussed in detail: the structure, the electronic structure, and the reactivity. The structural section summarises the recent X-ray crystal structure determinations, and the structural data obtained by other methods. The electronic structure is first considered in qualitative terms which allow the rationalisation of the different structures observed, and this qualitative model is compared with the results of calculations and with spectroscopic data. The reactivity of the complexes is discussed separately for each structural class in terms of the electronic structure. An attempt is made to compare the results obtained in historically different areas of research. Our objective is to give a clear summary of current knowledge of these compounds for workers interested in their application to catalysis and in their rôle in biochemical systems. [ABSTRACT FROM AUTHOR]

The aim of the present article is to review several biomolecules, the spectroscopic and structural properties of which have been so far interpreted in the light of the Jahn-Teller effect. Indeed the importance of the vibronic coupling in the interpretation of physical properties of molecules and crystals is widely recognized now, but only a desultory attention has been paid to the role played by such a coupling in biological systems. After a brief outline of the Jahn-Teller effect, the whole problem is critically re-examined separating the systems for which the experimental evidence of the Jahn-Teller effect is clear, from those where its effectiveness is still debated. Furthermore some suggestions are given for a proper inclusion of the vibronic coupling in future analysis on biomolecules. [ABSTRACT FROM AUTHOR]

This review shows that the growing interest aroused by phospholes in coordination chemistry can be attributed to three main reasons: 1. The influence of the partial delocalization of the phosphorus lone pair upon the complexing ability of phospholes. 2. The discovery of phosphametallocenes. 3. The tremendous variety of complexing modes found for the phosphole nucleus. For a given phosphole, no less than ten different types of complexes can be obtained. [ABSTRACT FROM AUTHOR]

The ability of coordination polyhedra of different central atoms in the solid state to undergo distortions has often been discussed. These distortions are also correlated with the nature of the central atom. This paper deals with the conception of crystal structure non-rigidity for central atoms of some selected complexes by the using of statistical distributions of interatomic distances central atom-nearest ligand atom (M-L; M=Mn(II), Fe(II), Fe(III), Co(II), Co(III), Ni(II), Cu(II) and Zn(II)). Based on the vector equilibrium principle the dispersion of these empirical distributions has been introduced as a measure of non-rigidity of central atoms, decreasing in the order: Cu(II) > Fe(II)HS > Mn(II)HS > Ni(II)LS > Zn(II) > Fe(III)HS ≈ Co(II)HS > Ni(II)HS > Co(III)LS, where LS and HS denote low-spin and high-spin states, respectively. Starting from the distribution of M-L distances for certain types of central and ligand atoms, the contribution of atoms of the inner coordination sphere to the vector equilibrium of crystal structures is discussed. The structures of complexes with all M-L bond lengths of at least one symmetrically independent central atom in the interval of maximum frequency exhibit in the appropriate set the most stable inner coordination sphere. These compounds are classified both with respect to the geometry of their inner coordination sphere fulfilling the above condition and to their crystal structure aspect. The square-planar geometry is found to be the most stable for Cu(II) and Ni(II)LS complexes, tetragonal-pyramidal for Zn(II) complexes, while for Fe(II)HS, Mn(II)HS, Fe(III)HS, Co(II)HS, Ni(II)HS and Co(III)LS complexes it is the regular octahedral geometry. Except for one Mn(II)HS complex, in the discussed structures chromophores with the most stable geometry of the coordination polyhedron form part of the final relatively isolated structural unit (island) with expressively chemical bonds between atoms. These facts are illustrated by the stabilization effected by the crystal field and by the properties of the ligands. [ABSTRACT FROM AUTHOR]

Mixed valence has been considered with reference to three model systems: Fe3O4 (magnetite) is a representative of the ferrospinels and the iron oxides with spinel-related structures, Fe1−δO (wüstite) illustrates a system with random defects and clustering, CaFeO3 (a perovskite) illustrates the consequences of strong Fe4+-O-Fe4+ interactions. The influence of counter cations is particularly marked in systems like the spinels Fe2SnO4 and Fe2MoO4; more subtle effects are illustrated by a comparison of CaFeO3 with SrFeO3. The time τh for an electron transfer between cations of different valence has been considered relative to two times: the period ωR−1⋍10−12s of an optical-mode lattice vibration that traps a mobile electron and the time τn for a Mössbauer nuclear excited state to decay to its ground state. The full range of electron-transfer times τh<10−12s to τh>10−8s has been found for both Fe-Fe interactions across shared site edges or faces and Fe-O-Fe interactions across shared site corners. Perturbations of the periodic potential of an iron array by lattice defects or substitutional ions is shown to increase τh. Moreover, electron-lattice interactions were found to induce cooperative Jahn-Teller distortions in some compounds and charge-density waves (CDW) in others. In the mixed-valent compound Fe3O4, electrostatic interactions between mobile ions combine with electron-lattice interactions to produce, with increasing temperature, transitions from ionic ordering (or a static CDW) in the temperature interval 120

Sulphur containing amino acid residues are found among the structural and functional constituents of many proteins. The ease of oxidising sulphur in these biologically important polymers is well known. At present, there is no simple and fast technique available to monitor the respective oxidation states using chemical reactions. X-ray photoelectron spectroscopy has proven to be both convenient and efficient to follow these electron transport reactions. In the present survey a choice of some sulphur and selenium bearing proteins and metalloproteins will be examined upon excessive irradiation, treatment with hydrogen peroxide and cleavage of metal sulphur bonding. It will also be shown that the use of this technique in general will allow a quick decision on the rate of deterioration of a protein. The limitations of this spectrochemical approach will be debated. [ABSTRACT FROM AUTHOR]

The alternative approach to structures is an inversion of the traditional one: we concentrate on a packed array of cations, into the interstices of which the anions are inserted, rather than putting cations into a packed anion array. Even in conventional terms the logic of the new approach can be justified, since many structures have their own antitypes (and even more show a partial structure/antistructure relation). In this way we find that, in oxides for example, many cation arrangements are identical to the arrangements of the atoms in known (or plausible) alloy structures. (In some cases the cations and atoms are identical in the two cases.) This is particularly helpful in those oxide examples where it has not previously been possible to describe the structure in any simple terms, often because the anion array is not regular in any simple way, for instance in many metal sulphates. But it is also revealing in some cases that are describable in conventional terms, e.g. the humites. A long (but still incomplete) list of examples is given in Table 3. Sufficient specific cases are described and discussed in detail in the text in order to expose the principles and some of the advantages of this unfamiliar approach. One of these advantages is that, in favourable cases, it leads at once to complete quantitative descriptions of the structures (i.e. until cell dimensions and anion position parameters), e.g. for spinel, garnet, bixbyite etc. Another is that it throws a new light on possible martensitic mechanisms for phase transformations (e.g. β- → γ-Ca2SiO4, low- → high-temperature K2SO4), and on the possibility of anomalous substitution (e.g. of CO32− for PO43− in apatite). It also reveals an explanation for those phase transitions, due to high pressure, that are not attended by an increase in primary coordination number, e.g. olivine → spinel, zircon → scheelite. [ABSTRACT FROM AUTHOR]

A numerical method for solving the time-dependent Schrödinger equation for a one-electron atomic system in an intense, short-pulsed laser field is presented. An effective potential formalism is proposed and tested for representing the excitation of the valence electrons in rare gases. Results for ion production yields, photoelectron distributions and harmonic conversion are presented and compared to recent experimental results. [ABSTRACT FROM AUTHOR]

Using Rydberg atoms and microwave fields it has been possible to observe virtually all one electron strong field phenomena. The attraction of these experiments is that they can be more controlled than most laser experiments, with the result that more quantitative information can be extracted. The insights gained from these experiments can be profitably transferred to optical experiments. To demonstrate the latter point we demonstrate that apparently non-resonant microwave ionization, in fact, occurs by resonant transitions through intermediate states. These experiments demonstrated clearly the power of Floquet analysis of such processes, and the ideas were subsequently applied to the analogous problem of laser multiphoton ionization. [ABSTRACT FROM AUTHOR]

One-electron atoms subjected to a time-dependent external field provide physically realistic examples of scattering systems with chaotic classical dynamics. Recent work on atoms subjected to a sinusoidal external field or to a periodic sequence of instantaneous kicks is reviewed with the aim of exposing similarities and differences to frequently studied abstract model systems. Particular attention is paid to the fractal structure of the set of trapped unstable trajectories and to the long time behavior of survival probabilities which determine the ionization rates of the atoms. Corresponding results for unperturbed two-electron atoms are discussed. [ABSTRACT FROM AUTHOR]

To afford a basis for constructing Thomas-Fermi-like approximations to the electronic structure of atoms in intense applied fields, the canonical density matrix (or equivalently the Feynman propagator) for free electrons is first set up. This is done for both intense magnetic and intense electric fields: in each case, exact results are available for arbitrary static field strengths. Physical properties of atoms and ions in intense magnetic fields are hence obtained in the statistical limit of Thomas-Fermi theory. This discussion is then supplemented by the ‘hyperstrong' limit, considered especially by Lieb and co-workers. Chemistry in intense magnetic fields is thereby compared and contrasted with terrestrial chemistry. Some emphasis is then placed on a model of confined atoms in intense electric fields: the statistical Thomas-Fermi approximation again being the central tool employed. [ABSTRACT FROM AUTHOR]

In the presence of a homogeneous magnetic field the center of mass and internal motion of a neutral or charged two-body system cannot be separated. We review the effects and phenomena which occur due to the inherent two-body character of these systems. The most prominent effects that occur for neutral species are the chaotic classical diffusion of the center of mass, the intermittent near-threshold behavior and the appearance of weakly bound states with an extraordinarily large electric dipole moment in crossed electric and magnetic fields. For ionic two-body systems the regions of strong mixing of the center of mass and internal motion are identified and investigated. As major effects we observe the classical self-stabilization as well as selfionization processes of the ion. [ABSTRACT FROM AUTHOR]

When molecules are subjected to intense laser fields, they undergo multielectron dissociative ionization (MEDI), a process that is, as yet, little understood. This chapter gives a brief overview of some of the experimental techniques used to study the process. At present there are two models that attempt to explain the facts, inertial confinement (with rapid ionization at a critical inter-ion separation) and laser-induced stabilisation. In order to ascertain which, if either, of these models is correct, more definitive experiments are required, involving interferometric control of laser parameters, good laser characterisation, and a more careful analysis of the dissociation dynamics. [ABSTRACT FROM AUTHOR]