Single-photon single ionization of W+ ions: experiment and theory

Experimental and theoretical results are reported for photoionization of Ta-like (W+) tungsten ions. Absolute cross sections were measured in the energy range 16–245 eV employing the photon–ion merged-beam setup at the advanced light source in Berkeley. Detailed photon-energy scans at 100 meV bandwidth were performed in the 16–108 eV range. In addition, the cross section was scanned at 50 meV resolution in regions where fine resonance structures could be observed. Theoretical results were obtained from a Dirac–Coulomb R-matrix approach. Photoionization cross section calculations were performed for singly ionized atomic tungsten ions in their 5s²5p⁶5d⁴(⁵D)6s ⁶Dj.  J = 1/2, ground level and the associated excited metastable levels with J = 3/2, 5/2, 7/2 and 9/2. Since the ion beams used in the experiments must be expected to contain long-lived excited states also from excited configurations, additional cross-section calculations were performed for the second-lowest term, 5d⁵⁶Sj, J = 5/2, and for the 4F term, 5d³6s^{2 4}Fj, with J = 3/2, 5/2, 7/2 and 9/2. Given the complexity of the electronic structure of W+ the calculations reproduce the main features of the experimental cross section quite well.

The validity of classical trajectory and perturbative quantal methods for electron-impact ionization from excited states in H-like ions

To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li 2+ and B 4+ using the R -matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with n and grows substantially worse with Z , while the DW method improves with Z and grows worse with n .

Valence-shell photoionization of chlorinelike Ar+ ions

Absolute cross-section measurements for valence-shell photoionization of Ar + ions are reported for photon energies ranging from 27.4 eV to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the 2P o3/2 ground state and the 2P o1/2 metastable state of Ar +. Photoionization of this Cell-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance lineshapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semi-relativistic Breit-Pauli approximation.

High-resolution photoionization of Xe + ions: Experiment and theory

High-resolution photoionization measurements of Xe + ions have been performed at the Advanced Light Source in Berkeley, California, USA. The experimental cross sections are compared with results from Dirac-Coulomb R-matrix calculations.

Electron-impact excitation of open d-shell ions

Astrophysics is driven by observations, and in the present era there are a wealth of state-of-the-art ground-based and satellite facilities. The astrophysical spectra emerging from these are of exceptional quality and quantity and cover a broad wavelength range. To meaningfully interpret these spectra, astronomers employ highly complex modelling codes to simulate the astrophysical observations. Important input to these codes include atomic data such as excitation rates, photoionization cross sections, oscillator strengths, transition probabilities and energy levels/line wavelengths. Due to the relatively low temperatures associated with many astrophysical plasmas, the accurate determination of electron-impact excitation rates in the low energy region is essential in generating a reliable spectral synthesis. Hence it is these atomic data, and the main computational methods used to evaluate them, which we focus on in this publication. We consider in particular the complicated open d- shell structures of the Fe-peak ions in low ionization stages. While some of these data can be obtained experimentally, they are usually of insufficient accuracy or limited to a small number of transitions.

Electron impact excitation of the Fe-peak ions Ni III and Ni IV

Accurate determination of electron excitation rates for the Fe-peak elements is complicated by the presence of an open 3d-shell in the description of the target ion, which can lead to hundreds of target state energy levels. Furthermore, the low energy scattering region is dominated by series of Rydberg resonances, which require a very fine energy mesh for their delineation. These problems have prompted the development of a suite of parallel R-matrix codes. In this work we report recent applications of these codes to the study of electron impact excitation of Ni III and Ni IV.

Capture and loss of electron by MeV ions penetrating through liquid spray:Formation of negative ion and neutral atom beams

Charge changing processes of MeV ions penetrating through liquid spray is confirmed to be abundant source of various energetic negative ion and neutral atom beams its generic nature is demonstrated.

Thiram in the environment: effect of humic substances and Cu(II) ions

Em Portugal, o tirame é um dos fungicidas mais utilizados, cujas vendas aumentaram significativamente nos últimos anos, sendo também um dos fungicidas mais utilizados em todo o mundo. No entanto, em comparação com outros pesticidas, existe falta de informação na literatura sobre o seu comportamento em sistemas ambientais, nomeadamente, no que diz respeito à sua degradação no solo ou em águas e produtos a que dá origem. Neste contexto, o objetivo deste trabalho foi estudar a influência das substâncias húmicas e iões cobre no comportamento e destino do tirame no meio ambiente. Foram realizados vários estudos para analisar o comportamento do tirame em solos com diferentes conteúdos de matéria orgânica e de iões cobre, e em águas naturais, estudando como as substâncias húmicas, os iões cobre e a luz solar podem afetar a sua degradação. Os estudos de adsorção-desadsorção do tirame nos solos revelaram que a matéria orgânica do solo e o conteúdo de cobre afetavam os processos de adsorção-desadsorção do tirame, influenciando a sua lixiviação e persistência no solo. De facto, verificou-se que o teor de cobre do solo tinha um efeito bastante marcante no processo de adsorçãodesadsorção do tirame. Verificou-se a ocorrência de reações entre o tirame e os iões cobre, cuja extensão durante os estudos de adsorção pode ser fortemente dependente do teor de cobre do solo e da concentração inicial de tirame em solução. Assim, a escolha do tempo de equilíbrio em estudos de adsorção e a determinação das isotérmicas de adsorção ao solo torna-se uma tarefa difícil. Além disso, os complexos formados com o cobre existente no solo são persistentes, não sendo facilmente lixiviados para as águas subterrâneas. Conclui-se que os iões cobre(II) podem contribuir para a imobilização do tirame no solo e o aumento da persistência dos seus resíduos ligados ao cobre. A partir de estudos de recuperação do tirame em águas naturais verificou-se a ocorrência de uma rápida degradação do tirame, devido provavelmente aos iões metálicos, nomeadamente, iões cobre. Verificou-se que dependendo da razão tirame:Cu podiam ocorrer dois processos: (i) complexação entre o tirame e o cobre, quando não há excesso de iões cobre, sendo o complexo formado mais persistente que o tirame; (ii) ou, quando há um grande excesso de iões cobre, a degradação do tirame e a estabilização dos produtos de degradação por complexação, podendo formar-se complexos que permanecem sem alteração em solução durante pelo menos dois meses. No geral, foi possível, pela primeira vez, identificar alguns dos complexos de cobre formados ao longo do tempo. Por fim, estudou-se a cinética de fotodegradação do tirame em solução aquosa sob a ação da luz solar e identificaram-se, pela primeira vez, três fotoprodutos. Verificou-se um aumento da velocidade de fotodegradação do tirame na presença de substâncias húmicas. Assim, podemos concluir que a matéria orgânica, os iões cobre(II) e a luz solar têm um efeito importante no comportamento do tirame no meio ambiente. Contudo, os iões cobre têm um efeito mais marcante na degradação e persistência dos produtos que são formados.

Unusual framework stabilization of Cu(II) and Cu(I) ions in a novel copper-substituted aluminophosphate with AEN topology prepared by one pot synthesis

A novel copper-substituted aluminophosphate (CuIST-2) has been synthesized using methylamine as a templating agent. X-Ray diffraction studies provide evidence for an AEN topology similar to the parent Cu-free IST-2.

Metal ions and protein folding: conformational and functional interplay

Dissertation presented to obtain a PhD degree in Biochemistry at Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa

Metal ions modulate the folding and stability of the tumor suppressor protein S100A2

Febs Journal (2009)276:1776-1786

(Un)suitability of the use of pH buffers in biological, biochemical and environmental studies and their interaction with metal ions – a review

The use of buffers to maintain the pH within a desired range is a very common practice in chemical, biochemical and biological studies. Among them, zwitterionic N-substituted aminosulfonic acids, usually known as Good’s buffers, although widely used, can complex metals and interact with biological systems. The present work reviews, discusses and updates the metal complexation characteristics of thirty one commercially available buffers. In addition, their impact on biological systems is also presented. The influences of these buffers on the results obtained in biological, biochemical and environmental studies, with special focus on their interaction with metal ions, are highlighted and critically reviewed. Using chemical speciation simulations, based on the current knowledge of the metal–buffer stability constants, a proposal of the most adequate buffer to employ for a given metal ion is presented.

Variational Monte Carlo study of core-valence separation schemes for first-row atoms and positive ions /

All-electron partitioning of wave functions into products ^core^vai of core and valence parts in orbital space results in the loss of core-valence antisymmetry, uncorrelation of motion of core and valence electrons, and core-valence overlap. These effects are studied with the variational Monte Carlo method using appropriately designed wave functions for the first-row atoms and positive ions. It is shown that the loss of antisymmetry with respect to interchange of core and valence electrons is a dominant effect which increases rapidly through the row, while the effect of core-valence uncorrelation is generally smaller. Orthogonality of the core and valence parts partially substitutes the exclusion principle and is absolutely necessary for meaningful calculations with partitioned wave functions. Core-valence overlap may lead to nonsensical values of the total energy. It has been found that even relatively crude core-valence partitioned wave functions generally can estimate ionization potentials with better accuracy than that of the traditional, non-partitioned ones, provided that they achieve maximum separation (independence) of core and valence shells accompanied by high internal flexibility of ^core and Wvai- Our best core-valence partitioned wave function of that kind estimates the IP's with an accuracy comparable to the most accurate theoretical determinations in the literature.

Continuous hydride generation in the presence of L- cysteine for the determination of arsenic, bismuth, antimony and tin in steels by inductively coupled plasma atomic emission spectrometry

Arsenic, bismuth, germanium, antimony and tin were simultaneously determined by continuous hydride generation and inductively coupled plasma-atomic emission spectrometry . I Hydrides were introduced into four different types of gas-liquid separators. Two of the gas-liquid separators were available in-house. A third was developed for this project and a fourth was based on a design used by CET AC. The best signal intensity was achieved by the type II frit-based gas-liquid separator, but the modified Cetac design gave promise for the future, due to low relative standard deviation. A method was developed for the determination of arsenic, bismuth, antimony and tin in low-alloy steels. Four standard reference materials from NIST were dissolved in 10 mL aqua regia without heat. Good agreement was obtained between experimental values and certified values for arsenic, bismuth, antimony and tin. The method was developed to provide the analyst with the opportunity to determine the analytes by using simple aqueous standards to prepare calibration lines. Within the limits of the samples analyzed, the method developed is independent of matrix.

Préparation d'échantillons pour l'étude par GISAXS des mécanismes de déformation des matériaux par faisceaux d'ions lourds de haute énergie.

Le mécanisme menant à des déformations structurales suivant le bombardement d'échantillons de a-Si d'un faisceau d'ions lourds et rapides est sujet de controverses. Nous nous sommes penchés sur l'hypothèse de la formation d'une zone liquide causée par la déposition d'énergie des ions incidents dans le contexte de la théorie du pic thermique. Des échantillons de silicium amorphe furent préparés dans le but d'observer les indices d'une transition de phase l-Si/a-Si suivant la déposition locale d'énergie sur le parcours d'un ion lourd énergétique dans le a-Si. Les échantillons furent implantés d'impuretés de Cu ou d'Ag avant d'être exposés à un faisceau d'ions Ag12+ de 70 MeV. L'utilisation de l'analyse GISAXS est projetée afin d'observer une concentration locale d'impuretés suivant leur ségrégation sur la trace de l'ion. Des masques d'implantation nanométriques d'oxide d'aluminium ont été fabriqués afin d'augmenter la sensibilité de l'analyse GISAXS et une méthode d'alignement de ces masques selon la direction du faisceau fut développée. Le bombardement d'échantillons au travers de ces masques a donné lieu à un réseau de sites d'impacts isolés presque équidistants.