Table of contents

The reduced density operator of a particle coupled to a fermionic environment (metal electrons) is written in terms of a Feynman-Vernon influence functional. Two different approaches are used in order to achieve this goal. Firstly, the environmental interacting electron gas is treated in RPA and the coupling is correctly accounted for up to second order in perturbation theory. Then the local and tight-binding models are studied. For the latter a second approach for obtaining the influence functional is used in the narrow-band limit. It is found that the popular representation of the environment in terms of a single set of harmonic oscillators is not feasible unless the particle is confined to move in a local region of radial extension r ≃ k_F^-1.

The use of the synchrotron radiation (SR) in the vacuum ultraviolet (VUV) spectroscopy and radiometry opens new doors for a researcher. In this connection a consideration of SR characteristics of small size specialized SR sources, which can be available even in single laboratories, is given below. "TROLL" is an electron synchrotron with a cyclotron preacceleration. It has been developed as a specialized SR source for the calibration of VUV sources as secondary standards in the spectral range of 40-250 nm in the units of spectral radiance. In conclusion there is summary of advantages of small size accelerators.

Some principal problems of theoretical studies of the structure and spectra of complex many-electron atoms and ions, having as a rule several open electronic shells, are surveyed. The usage of various approaches is discussed while calculating energy spectra of the systems mentioned, including the relativistic version of least squares fitting method. It is shown that for many cases the spectra cannot be classified with the help of LS coupling scheme. The method of optimization of coupling scheme is described. The role of group-theoretical methods, namely, the groups of quasispin and isospin as well as the direct usage of corresponding Clebsch-Gordan coefficients, in theoretical atomic spectroscopy is emphasized.

We report the first adiabatic ionization energy (I₁) of benzene, and the ortho, meta and para isomers of fluoro-, chloro- and bromobenzonitrile, extracted from gas-phase photoionization spectra measured up to the LiF cut-off. In every case, I₁ for the disubstituted benzene species is blue-shifted from I₁ in benzene. Moreover, I₁ decreases along the series F, Cl, Br. We explain these trends qualitatively by invoking destabilization/stabilization of the topmost filled π MO of benzene by donor/acceptor substituents.

The subvalence p-shell absorption spectrum of potassium I has been reinvestigated under high resolution using the featureless continuum of synchrotron radiation as the background source. In the wavelength range investigated (400-600 Å), we have found ca. 400 spectral lines of which about half have not been observed in previous experiments [1]. The p-shell spectrum of K I is dominated by strong configuration interaction in the final state, complicating the detailed analysis. Furthermore, the quantum defects modulus 1 of ns- and nd-series are approximately equal, so that lines overlap [2]. At short wavelength (around 424 Å) we have found a Rydberg series with markedly varying autoionizing profiles. We attribute this phenomenon to an interaction with a broad underlying state and continua. The analysis is performed using a formalism due to Lane [3].

A comparison is made between radiative line strengths, or more precisely the square of matrix elements of the electron position vector, calculated fully relativistically and with two quasirelativistic approaches. The calculations are made for all transitions nlj-n'l'j' with n and n' ⩽ 3 and for several transitions with n and/or n' = 4 in hydrogenic ions with nuclear charge number Z = 30, 50, 70 and 90, as well as the nonrelativistic limit. The purpose of the work is to find the optimum quasirelativistic approach to use for rapid calculation of line strengths and collision strengths for highly charged ions and to obtain some indication of the accuracy of the approach.

The use of charge-exchange spectroscopy as a diagnostic tool in fusion plasmas is steadily growing. This technique exploits spectral lines produced by charge transfer from hydrogen atoms into highly excited states of impurity ions. The concentrations and transport properties of the dominant, fully ionized low-Z impurities can, therefore, be measured. In addition, it is possible to observe transitions having wavelengths long enough for obtaining accurate Doppler shifts and widths, even in plasmas with temperatures of several keV, and ion temperatures and plasma rotation are increasingly being determined from such spectral lines. In this paper, the atomic physics considerations, including the influence of the plasma environment, are reviewed, and several recent examples of applications to plasma problems are summarized.

Lines of the 3d⁹ 4s-3d⁹ 4p transitions in nickel-like Zr XIII, Nb XIV and Mo XV have been identified in the 340-500 Å region in spectra emitted from laserproduced plasmas. All levels of the 3d⁹ 4s and 3d⁹ 4p configurations have been established from the observations. Comparisons with predictions of Wyart and Ryabtsev show a good agreement. The structure has been studied by means of MCDF calculations along the isoelectronic sequence up to Xe XXVII. Tentative identifications are given for the strongest lines of the 3d⁹ 4p-3d⁹ 4d transition in Zr XIII and Nb XIV.

Experimental measurements of the microwave ionization of highly excited hydrogen atoms with principal quantum numbers ranging from n = 32 to 90 are well described by a classical treatment of the nonlinear electron dynamics. In particular, the measurements of the threshold field for the onset of significant ionization exhibits a curious dependence on the microwave frequency with distinct peaks at rational values of the scaled frequency, n³Ω = 1, 2/3, 1/2, 2/5, 1/3, 1/4, 1/5, which is in excellent agreement with the predictions for the onset of classical chaos in a one-dimensional model of the experiment. In the classical theory this frequency dependence of the threshold fields is due to the stabilizing effect of nonlinear resonances ("islands") in the classical phase space which is greatly enhanced when the microwave perturbation is turned on slowly (adiabatically) as in the experiments. Quantum calculations for this one-dimensional model also exhibits this stabilizing effect due to the preferential excitation of localized quasi-energy states.

A generalization of Freidberg's perpendicular MHD model is used to investigate the effect of pressure anisotropy on the small wavelength internal kink (m = 1) mode instability in a Z-Pinch. A normal mode analysis of perturbed motion of an incompressible, collisionless and cylindrical plasma is performed. The stability criterion is (rΣB²)' ⩽ 0, where Σ = 1 - (P_|| - P_⊥)/B². It cannot be fulfilled without violation of the fire hose stability condition Σ ⩾ 0.

Dynamics of drift waves in collision magnetoactive plasma is being studied. The time evolution of integral characteristics of drift vortices was investigated. It was shown that the large-scale vortices are relaxing due to dissipation slower than small-scale ones.

It has been possible to determine analytically the dispersion relation and eigenfunctions for the tearing mode in an incompressible plasma in the presence of an anomalous electron viscosity. Overstability is explicitly taken into account. The anomalism yields an enhanced growth rate.

The inclusion of non-central internal particle-particle forces sustaining magnetized plasma charge neutrality in classical electrodynamics is presented. The model is used to explain the experimentally observed magnetic confinement such as plasma edge and boundary modes. The revised theory allows a reexamination of the concepts of magnetic line reconnection and flux merging. The application to both cosmic and laboratory plasmas are given.

A molecular weight dependence in the hypersonic properties of low molecular weight poly(propylene glycol) (PPG) (400-4000) has been measured. Results for PPG 2000 are emphasized. Sound velocity increases with decreasing molecular weight and the maximum of the hypersonic loss peak shifts to higher temperatures. We ascribe this effect to a decrease in the flexibility of the polymer chain backbone as the molecular weight decreases. Hydrogen bonding involving the "OH" terminating groups causes an increase in the gauche/trans ratio and stiffens the chain.

A positive ion (ionized adsorbate) on atop position surrounded by a cluster of neutral adsorbates is placed on the (100) surface of a simple cubic crystal. An attractive Coulomb interaction between the ion and the metal atom directly below is explicitly included to prevent the ion from being quickly neutralized by electron transfer from the metal. No lateral interactions are placed at the outset, so that only indirect interactions through the metal (Rudeman-Kittel-type) enter.

The degree of coverage (θ) is simulated by considering different clusters of neutral adsorbates and the ion line width, which controls the stimulated desorption ion yield, is calculated by a tight-binding Green function approach. It is found that the neutralization rate reaches a minimum (maximum ion yield) somewhere between θ = 1/4 and θ = 1/2 in agreement with experiment.

The XYV and XVV Auger transitions in Ag_c-Pd_1-c random alloys have been investigated within the framework of the KKR-CPA method, by taking into account the Coulomb matrix elements between initial and final states.

The results of the computations indicate that the usual constant matrix elements approximation lead to an overestimation of the low energy part of the spectra.

Dissociation of ammonia on clean and oxygen covered Pd surfaces has been studied with a hydrogen sensitive Pd-MOS structure and masspectrometry, at pressures between 10^-10 and 10^-8 Torr and temperatures between 323 and 523 K. The results are compared with the behaviour of hydrogen on the same type of surfaces. It is shown that oxygen is needed for the ammonia dissociation and that water is formed in a Langmuir-Hinshelwood reaction. The possibility to use the Pd-MOS device to determine when the surface is oxygen free is also pointed out.

In this article several ground state properties of diamond and Si are calculated and compared with the existing experimental values. All these properties are derived from the total crystal energy or from the one-particle electron energy. Both quantities are evaluated in the local density approximation using a norm-conserving non-local ionic pseudopotential. The calculated values for the lattice constant, bulk modulus and its pressure derivative, first and second pressure derivatives of the indirect band gap and X-ray structure factors are in good agreement with experiment. Several quantities which have not been measured as yet are predicted.

The magnetic susceptibility of several Fe_xNi_80-xB₁₈Si₂ alloys (3 ⩽ x ⩽ 15) has been studied around and above the Curie temperature. The magnetic inhomogeneity of these alloys sharply increases on approaching the percolation threshold (x_c ≃ 2.5), as evidenced by the enhanced non-monotonic variation of the effective critical exponent, γ*(T), and by the increasing assymetry of the Arrott-Belov-Kouvel plots. The tendency towards homogeneous magnetism for x ⩾ 20 is deduced. The results are compared with those for other glassy Fe-Ni alloys and the origin of the magnetic inhomogeneity discussed.

Cu-Zn (21%) alloy films were deposited onto glass substrates from two separate boats containing Cu and Zn respectively. The substrates were kept at different temperatures from 298 K to 545 K by a heater. Films of 1.4 μm thickness were studied by X-ray diffraction profile analysis and electrical resistivity measurement. After data processing the dislocation density and distribution, the probabilities of stacking faults and twin faults as well as the resistivity have been obtained. The results show that these parameters do not change monotonically with the substrate temperatures, but take minimum values between 410 K and 450 K. The behaviour can be understood by the film growth kinetics.

This work is devoted to show that in the case of small concentration of deep traps in relation with that of the shallow levels, the non-exponentiality of the capture transient, obtained from the capacitance measurements, could be justified, in some cases, by assuming the existence of a hopping process between the deep trap and another shallower level.

The dependence of critical magnetic field for the onset of irreversible magnetic processes has been studied on as cast and annealed Metglas 2705MN samples as a function of the waiting time after demagnetization. The kinetics of the processes has been analyzed through measurements of complex permeability and the results have been correlated to the time behavior of the initial permeability. The atomic structure instabilities characteristic of non-magnetostrictive amorphous alloys account for the obtained results.

The relation between the discrete Surface Green's Function Matching approach of Garcia-Moliner and Velasco (Physica Scripta34, 257 (1986)) and atom-removal or ideal construction approaches is clarified. Both approaches are shown to give identical results for an "ideal" surface in the tight-binding approximation. Here "ideal" is defined by the condition that the Hamiltonian matrix elements in the crystal fragment keep their bulk values.

Angle resolved inverse photoemission from Ag(111) and Pd(111) surfaces has been recorded in the isochromat mode at 9.8 and 10.8 eV photon energies. Unusually large spectral peaks are found in the energy range 10-20 eV above E_F. It is shown that a good qualitative description of the results is provided by a simple model based on k-conserving transitions between free-electron like states. In particular we find no structures due to elastic diffuse scattering.

In our recent paper we found that long lived component of lifetime spectrum τ₂, which is connected with pick-off ortho-positronium annihilation and its intensity do not change monotonically with the concentration of organic components in water. The results obtained confirm the thesis of quasi-crystalline, clathrate-like structure of water-tetrahydrofuran and water-cyclohexylamine systems. The attempt of the present work was to study the structure of water-ethanol, water-n-propanol and water-isopropanol mixtures, their clathrate-likeness and stoichiometry, if any. The results of our measurements of positronium lifetime, in particular the component τ₂ and the intensity I₂ as well as the sound velocity data allow us to suppose that in the systems the liquid clathrate-like hydrates are formed. The stoichiometry of these structures was deduced. The results, although obtained using strongly different experimental methods, i.e., positron annihilation and acoustic measurements, are in very good agreement with the clathrate-like concept of the structure of water-organic mixtures.

The exchange and correlation energy of the electron-hole plasma in Ge and Si is calculated in RPA. The structure of the valence band is fully accounted for by use of the q and ω dependent dielectric function which includes both the symmetry of the band at the Γ point and transitions between the light and heavy hole bands. The exchange energy of electrons is corrected by the anisotropy of bands but the correlation energy is treated in the spherical approximation. The results are in close agreement with both experiment and previous theories which included local field corrections but treat the actual band structure with more approximations.

The density functional formalism is used to study the adhesive energies at interfaces of disordered alkali-metal alloys: K-Cs, K-Rb, K-Na. Similarly like for pure metals the range of strong bonding is about 4-5 a.u. The possibility of metal transfers is discussed. The calculated adhesion binding energy curves can be scaled into a universal curve as a function of separation.

The band structures of PuS, PuSe and PuTe were calculated from self-consistent energy band calculations in a number of ways: (1) With 5f electrons treated as localized and Pu divalent. In this case insulators were obtained which would have non-magnetic J = 0 ground states, in agreement with experiment. However the calculated lattice constants were far too large. (2) With 5f electrons treated as localized and Pu trivalent. Metals were obtained, and trivalent Pu systems are normally magnetic. In addition the calculated lattice constants were too large. (3) With 5f-electrons treated as itinerant but with spin-orbit coupling neglected. All three systems were found to be metallic and the Stoner criterion for ferromagnetism was easily satisfied although experimentally no moment has been observed in these systems. The calculated lattice parameters were also too small. (4) With 5f-electrons treated as itinerant and fully relativistically. In this case all three systems were found to be semiconductors with calculated lattice constants in agreement with experiment and band gaps of between 0.2-0.4 eV.

The angular correlation of annihilation photons (ACAP) for multilayer aluminium-aluminium oxide sandwich had been measured. The ACAP observed for the sandwich plane parallel to the annihilation spectrometer axis appeared to be broader than the one observed when the plane was perpendicular to the axis.

Specific heat measurements by Amitin et al. [12], Jayasuriya et al. [5] and resistance measurements by Rao et al. [2] have been analyzed in the temperature region close to T_N (≈ 180 K) and compared to resistance measurements by Humble and Källbäck [14]. All these measurements show a structure that supports the idea of a transition to a first order behaviour.

Thus we have found the existence of an "inner" region, within which data points are described by a non-singular parabolic expression. The limits for this region are |t| = 2 × 10^-3, t being the reduced temperature (T - T_N)/ T_N. In the "inner" region increased scatter in experimental data is observed, which for the resistance measurements takes the form of sudden decreases in resistance for increasing temperature.

From very high precision resistance measurements on nickel we have identified, inside the ordinary critical region, a crossover region and a non-singular "inner" region. The transition region ranges from |t| ≈ 2 × 10^-3 to |t| ≈ 5 × 10^-5, t being the reduced temperature (T - T_c)/T_c.

Within the very narrow "inner" region discontinuous changes in the resistance values are observed. The possibility that these effects are of first order, and can be explained by the results from renormalization group calculations for a compressible cubic Heisenberg model is discussed.

Photoemission core level spectroscopy using synchrotron radiation was employed to study the effect of alkali metals on semiconductor oxidation. In presence of a cesium monolayer on InP(110), we found an exceptionally large increase of the oxidation by 10¹³. On Si(100), a similar effect was observed with cesium and sodium with the oxidation enhanced by 3-5 orders of magnitude. Furthermore, in this latter case, it was possible to remove Cs and Na catalysts by annealing at low temperatures, and to form a SiO₂-Si interface.

The statistical properties of one-dimensional strings of symbols are investigated. For this purpose several measures of complexity are applied to a DNA sequence and various reference strings as Markov chains, chaotic sequences and languages. With respect to Shannon entropies of words the DNA strings is comparable to Markov chains. However, the long-range correlations detected by mutual information remind more to the statistical properties of a computer language. This similarity to languages is confirmed by another powerful statistical approach: the analysis of Hamming distances between words. Moreover, stochastic evolutionary games are discussed which might be related to the complexity of biomolecules. It is argued that an appropriate compromise between sharp selection and variability can result from chaotic dynamics or frustrated rules.