Time-dependent R-matrix theory applied to two-photon double ionization of He

We introduce a time-dependent R-matrix theory generalized to describe double-ionization processes. The method is used to investigate two-photon double ionization of He by intense XUV laser radiation. We combine a detailed B-spline-based wave-function description in an extended inner region with a single-electron outer region containing channels representing both single ionization and double ionization. A comparison of wave-function densities for different box sizes demonstrates that the flow between the two regions is described with excellent accuracy. The obtained two-photon double-ionization cross sections are in excellent agreement with other cross sections available. Compared to calculations fully contained within a finite inner region, the present calculations can be propagated over the time it takes the slowest electron to reach the boundary.

Competition between memory-keeping and memory-erasing decoherence channels

We study the competing effects of simultaneous Markovian and non-Markovian decoherence mechanisms acting on a single spin. We show the existence of a threshold in the relative strength of such mechanisms above which the spin dynamics becomes fully Markovian, as revealed by the use of several non-Markovianity measures. We identify a measure-dependent nested structure of such thresholds, hinting at a causality relationship among the various non-Markovianity witnesses used in our analysis. Our considerations are then used to argue the unavoidably non-Markovian evolution of a single-electron quantum dot exposed to both intrinsic and Markovian technical noise, the latter of arbitrary strength. 

New source of MeV negative ion and neutral atom beams

The scenario of "electron-capture and -loss" was recently proposed for the formation of negative ion and neutral atom beams with MeV kinetic energies. However, it does not explain why the formation of negative ions in a liquid spray is much more efficient than with an isolated atom. The role of atomic excited states in the charge-exchange processes is considered, and it is shown that it cannot account for the observed phenomena. The processes are more complex than the single electron-capture and -loss approach. It is suggested that the shell effects in the electronic structure of the projectile ion and/or target atoms may influence the capture/loss probabilities.

Rydberg structure associated with core-excited autoionizing states of the LiH radical

We have investigated inner-shell excitation of the LiH + molecular ion by electron impact within several different collision models to delineate Rydberg autoionizing resonance structure associated with the LiH + (1σ2σ 2 2 Σ + ) core-excited threshold. The minimal representation requires only the retention of the 1σ and 2σ molecular orbitals, in which the core-excited state involves the promotion of a single electron into the 2σ orbital. This model is extended to include two further representations, in which both the 3σ and 4σ orbitals obtained from a self-consistent field calculation improve target representation, correlation and support additional autoionization channels. This affects the autoionization widths and to a lesser degree the positions of the LiH (1σ2σ 2 n s, n p 1,3 Σ + ) resonance series. Comparing our work with calculations on the counterpart atomic Be system assists in the assignment of the core-excited molecular resonance states. The results from our investigation provide helpful insights into the study of inner-shell transitions produced by electron or photon impact in more complex diatomic molecules.

Dielectronic recombination of W20 + (4d104f8): Addressing the half-open f shell

A recent measurement of the dielectronic recombination (DR) of W20+ [Schippers et al., Phys.Rev.A 83, 012711 (2011)] found an exceptionally large contribution from near-threshold resonances (1 eV). This still affected the Maxwellian rate coefficient at much higher temperatures. The experimental result was found to be higher by a factor of 4 or more than that currently in use in the 100- to 300-eV range, which is of relevance for modeling magnetic fusion plasmas. We have carried out DR calculations with AUTOSTRUCTURE which include all significant single-electron promotions. Our intermediate-coupling (IC) results are more than a factor of 4 larger than our LS-coupling ones at 1 eV but still lie a factor of 3 below experiment here. If we assume complete (chaotic)mixing of near-threshold autoionizing states, then our results come into agreement (to within 20%)with experiment below 2 eV. Our total IC Maxwellian rate coefficients are 50%–30% smaller than those based on experiment over 100–300 eV.

Cobalt complexes with pyrazole ligands as catalyst precursors for the peroxidative oxidation of cyclohexane: Z-ray absorption spectroscopy studies and biological applications

[CoCl(-Cl)(Hpz(Ph))(3)](2) (1) and [CoCl2(Hpz(Ph))(4)] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))(3) and Hpz(Ph), respectively (Hpz(Ph)=3-phenylpyrazole). The compounds were isolated as air-stable solids and fully characterized by IR and far-IR spectroscopy, MS(ESI+/-), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single-crystal X-ray diffraction. Electrochemical studies showed that 1 and 2 undergo single-electron irreversible (CoCoIII)-Co-II oxidations and (CoCoI)-Co-II reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). Insitu X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co-III site. Complex 2 showed low invitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.

Etudes ab initio des effets de la température sur le spectre optique des semi-conducteurs

Thèse réalisée en cotutelle avec l'Université Catholique de Louvain (Belgique)

Surface acidity and catalytic activity of mixed Fe-Al and Cr-Al pillared montmorillonites

The incorporation of transition metal oxide pillars such as those of iron and chromium along with Al2O3, pillars within the interlayers of a montmorillonite clay is investigated. The surface acidity of these catalysts has been evaluated for the first time employing the equilibrium adsorption of an electron donor, perylene, and the results are compared with those obtained by temperature programmed desorption of ammonia. The principle is based on the ability of a catalyst surface site to accept a single electron from an electron donor like perylene to form charge transfer complexes and the amount of adsorbed species is measured quantitatively by UV-vis spectroscopy. Fina1ly, an attempt has been made to correlate the acidity determined by the two independcnt methods and the catalytic activity of present systems in the benzoylation of toluene with benzoyl chloride. Incorporation of Fe and Cr has changed the properties of AI pitlared montmorillonite. Fe pillared systems have been found to be vcry good catalysts for benzoylation reaction

Parity violation in Aharonov-Bohm systems: The spontaneous Hall effect

We show how macroscopic manifestations of P (and T) symmetry breaking can arise in a simple system subject to Aharonov-Bohm interactions. Specifically, we study the conductivity of a gas of charged particles moving through a dilute array of flux tubes. The interaction of the electrons with the flux tubes is taken to be of a purely Aharonov-Bohm type. We find that the system exhibits a nonzero transverse conductivity, i.e., a spontaneous Hall effect. This is in contrast to the fact that the cross sections for both scattering and bremsstrahlung (soft-photon emission) of a single electron from a flux tube are invariant under reflections. We argue that the asymmetry in the conductivity coefficients arises from many-body effects. On the other hand, the transverse conductivity has the same dependence on universal constants that appears in the quantum Hall effect, a result that we relate to the validity of the mean-field approximation.

Thermal dependence of the zero-bias conductance through a nanostructure

We show that the conductance of a quantum wire side-coupled to a quantum dot, with a gate potential favoring the formation of a dot magnetic moment, is a universal function of the temperature. Universality prevails even if the currents through the dot and the wire interfere. We apply this result to the experimental data of Sato et al. (Phys. Rev. Lett., 95 (2005) 066801). Copyright (C) EPLA, 2009

Sensor for cysteine based on oxovanadium(IV) complex of Salen modified carbon paste electrode

The electrochemical behavior of a carbon paste electrode modified (CPEM) with N,N′-ethylenebis(salicylideneiminato)oxovanadium(IV) complex ([(VO)-O-IV(Salen)]) was investigated as a new sensor for cysteine. Cyclic voltammetry at the modified electrode in 0.1 mol L-1 KCl Solution (pH 5.0) showed a single-electron reduction/oxidation of the Couple VO3+/VO2+. The CPEM with [VO(Salen)] presented good electrochemical stability in a wide pH range (4.0-10.0) and an ability to electrooxidate cysteine at 0.65 V versus SCE. These results demonstrate the viability of the use of this modified electrode as an amperometric sensor for cysteine determination. © 2004 Elsevier B.V. All rights reserved.

Electrochemical sensor for sulfite determination based on a nanostructured copper-salen film modified electrode

The electrochemical preparation described herein involved the electrocatalytic oxidation of sulfite on a platinum electrode modified with nanostructured copper salen (salen=N,N'-ethylenebis(salicylideneiminato)) polymer films. The complex was prepared and electropolymerized at a platinum electrode in a 0.1 mol L-1 solution of tetrabutylammonium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.4V vs. SCE. After cycling the modified electrode in a 0.50 mol L-1 KCI solution, the estimated surface concentration was found to be equal to 2.2 x 10(-9) Mol cm(-2). This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the copper(II)/copper(III) couple. The potential peaks of the modified electrode in the electrolyte solution (aqueous) containing the different anions increase with the decrease of the ionic radius, demonstrating that the counter-ions influence the voltammetric behavior of the sensor. The potential peak was found to be linearly dependent upon the ratio [ionic charge]/[ionic radius]. The oxidation of the sulfite anion was performed at the platinum electrode at +0.9V vs. SCE. However, a significant decrease in the overpotential (+0.45V) was obtained while using the sensor, which minimized the effect of oxidizable interferences. A plot of the anodic current vs. the sulfite concentration for chronoamperometry (potential fixed = +0.45V) at the sensor was linear in the 4.0 x 10(-6) to 6.9 x 10(-5) mol L-1 concentration range and the concentration limit was 1.2 x 10(-6) mol L-1. The reaction order with respect to sulfite was determined by the slope of the logarithm of the current vs. the logarithm of the sulfite concentration. (C) 2009 Elsevier Ltd. All rights reserved.

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

An electrochemical sensor for dipyrone determination based on nickel-salen film modified electrode

An amperometric dipyrone sensor based on a polymeric nickel-salen (salen = N,N'-ethylenebis(salicydeneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel-salen complex at a platinum electrode in acetonitrile/tetrabuthylamonium perchlorate by cyclic voltammetry. After cycling the modified electrode in a 0.50 mol L-1 KCl solution, the estimated surface concentration was found to be equal to 1.29 x 10(-9) mol cm(-2). This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the nickel(II)/nickel(III) couple. A plot of the anodic current versus the dipyrone concentration for chronoamperometry (potential fixed = +0.50 V) at the sensor was linear in the 4.7 x 10(-6) to 1.1 x 10(-4) mol L-1 concentration range and the concentration limit was 1.2 x 10(-6) mol L-1. The proposed electrode is useful for the quality control and routine analysis of dipyrone in pharmaceutical formulations.

Search for leptonic decays of W ' bosons in pp collisions at root s=7TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)