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2005
Dyke, J. M., G. Levita, A. Morris, J. S. Ogden, A. A. Dias, M. Algarra, J. P. Santos, M. L. Costa, P. Rodrigues, M. M. Andrade, and M. T. Barros. "Contrasting Behavior in Azide Pyrolyses: An Investigation of the Thermal Decompositions of Methyl Azidoformate, Ethyl Azidoformate and 2-Azido-N, N-dimethylacetamide by Ultraviolet Photoelectron Spectroscopy and Matrix Isolation Infrared Spectroscopy." Chemistry - A European Journal 11 (2005): 1665-1676. Abstract

The thermal decompositions of methyl azidoformate (N3COOMe), ethyl azidoformate (N3COOEt) and 2-azido-N,N-dimethylacetamide (N3CH2CONMe2) have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N2 appears as an initial pyrolysis product in all systems, and the principal interest lies in the fate of the accompanying organic fragment. For methyl azidoformate, four accompanying products were observed: HNCO, H2CO, CH2NH and CO2, and these are believed to arise as a result of two competing decomposition routes of a four-membered cyclic intermediate. Ethyl azidoformate pyrolysis yields four corresponding products: HNCO, MeCHO, MeCHNH and CO2, together with the five-membered-ring compound 2-oxazolidone. In contrast, the initial pyrolysis of 2-azido-N,N-dimethyl acetamide, yields the novel imine intermediate Me2NCOCHNH, which subsequently decomposes into dimethyl formamide (HCONMe2), CO, Me2NH and HCN. This intermediate was detected by matrix isolation IR spectroscopy, and its identity confirmed both by a molecular orbital calculation of its IR spectrum, and by the temperature dependence and distribution of products in the PES and IR studies. Mechanisms are proposed for the formation and decomposition of all the products observed in these three systems, based on the experimental evidence and the results of supporting molecular orbital calculations.

"Relativistic transition probabilities for F-like ions with 10." Nuclear Instruments and Methods in Physics Research Section B 235 (2005): 171. AbstractWebsite
In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.
Santos, J. P., C. Madruga, F. Parente, and P. Indelicato. "Relativistic transition probabilities for F-like ions with 10⩽Z⩽49." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 235 (2005): 171-173. AbstractWebsite

In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.

Santos, J. P., F. Parente, S. Boucard, and J. P. Desclaux. "X-ray energies of circular transitions and electron screening in kaonic atoms." Physical Review A 71 (2005): 032501 EP -. AbstractWebsite

The QED contribution to the energies of the circular (n, = n–1), 2n13, transitions have been calculated for several kaonic atoms throughout the periodic table, using the current world-average kaon mass. Calculations were done in the framework of the Klein-Gordon equation, with finite nuclear size, finite particle size, and all-order Uelhing vacuum polarization corrections, as well as Källén and Sabry and Wichmann and Kroll corrections. These energy level values are compared with other computed values. The circular transition energies are compared with available measured and theoretical transition energies. Electron screening is evaluated using a Dirac-Fock model for the electronic part of the wave function. The effect of electronic wave-function correlation is evaluated.Exo

Santos, J. P., F. Parente, S. Boucard, P. Indelicato, and J. P. Desclaux. "X-ray energies of circular transitions and electrons screening in kaonic atoms." Physical Review A 71 (2005): 032501. AbstractWebsite
The QED contribution to the energies of the circular (n, = n–1), 2n13, transitions have been calculated for several kaonic atoms throughout the periodic table, using the current world-average kaon mass. Calculations were done in the framework of the Klein-Gordon equation, with finite nuclear size, finite particle size, and all-order Uelhing vacuum polarization corrections, as well as Källén and Sabry and Wichmann and Kroll corrections. These energy level values are compared with other computed values. The circular transition energies are compared with available measured and theoretical transition energies. Electron screening is evaluated using a Dirac-Fock model for the electronic part of the wave function. The effect of electronic wave-function correlation is evaluated.
Santos, J. P., F. Parente, S. Boucard, and P. Indelicato. "X-ray energies of circular transitions in sigmonic atoms." Nuclear Instruments and Methods in Physics Research Section B 235 (2005): 206. AbstractWebsite
Energies of the circular (n, ℓ = n − 1) 1 less-than-or-equals, slant n less-than-or-equals, slant 20 levels have been calculated for hydrogenlike sigmonic atoms with 1 less-than-or-equals, slant Z less-than-or-equals, slant 92, using the current world average sigma mass, as well as the electronic shift in Σ− + Ne e− + nucleus systems, where Ne stands for the number of electrons. The electronic influence on sigmonic orbitals has also been investigated through the computation of the hyperfine structure and the anomalous Σ− magnetic moment effects in sigmonic Be 2p states.
Santos, J. P., F. Parente, S. Boucard, and P. Indelicato. "X-ray energies of circular transitions in sigmonic atoms." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 235 (2005): 206-209. AbstractWebsite

Energies of the circular (n, ℓ = n − 1) 1 less-than-or-equals, slant n less-than-or-equals, slant 20 levels have been calculated for hydrogenlike sigmonic atoms with 1 less-than-or-equals, slant Z less-than-or-equals, slant 92, using the current world average sigma mass, as well as the electronic shift in Σ− + Ne e− + nucleus systems, where Ne stands for the number of electrons. The electronic influence on sigmonic orbitals has also been investigated through the computation of the hyperfine structure and the anomalous Σ− magnetic moment effects in sigmonic Be 2p states.Exo

2006
Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Relativistic calculation of Kβ hypersatellite energies and transition probabilities for selected atoms with 13 ≤ Z ≤ 80." Journal of Physics B: Atomic and Molecular Physics 39 (2006): 2355-2366. AbstractWebsite

Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.Al_Sc_Mg_Ti

Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Relativistic calculation of Kβ hypersatellite energies and transition probabilities for selected atoms with 13<=Z<=80." Journal of Physics B: Atomic and Molecular Physics 39 (2006): 2355-2366. AbstractWebsite
Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.
Santos, J. P., G. C. Rodrigues, J. P. Marques, F. Parente, J. P. Desclaux, and P. Indelicato. "Relativistic correlation correction to the binding energies of the ground configuration of beryllium-like, neon-like, magnesium-like and argon-like ions." The European Physical Journal D 37 (2006): 201-207. AbstractWebsite
Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.
Santos, J. P., G. C. Rodrigues, J. P. Marques, F. Parente, J. P. Desclaux, and P. Indelicato. "Relativistic correlation correction to the binding energies of the ground configuration of beryllium-like, neon-like, magnesium-like and argon-like ions." The European Physical Journal D 37 (2006): 201-207. AbstractWebsite

Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.

Santos, J. P., M. L. Costa, R. I. Olariu, and F. Parente. "Theoretical study of the molecular properties of benzyl azide, 2-, 3- and 4-methyl benzyl azide." The European Physical Journal D - Atomic, Molecular and Optical Physics 39 (2006): 379-384. AbstractWebsite
Ab initio and density functional calculations have been performed to study the benzyl azide, 2-, 3- and 4-methyl benzyl azides. Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionisation energies were also computed.
Santos, J. P., M. L. Costa, R. I. Olariu, and F. Parente. "Theoretical study of the molecular properties of benzyl azide, 2-, 3- and 4-methyl benzyl azide." The European Physical Journal D - Atomic, Molecular and Optical Physics 39 (2006): 379-384. AbstractWebsite

Ab initio and density functional calculations have been performed to study the benzyl azide, 2-, 3- and 4-methyl benzyl azides. Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionisation energies were also computed.

Martins, M. C., J. P. Santos, A. M. Costa, and F. Parente. "Transition wavelengths and probabilities for spectral lines of Zr III." The European Physical Journal D 39 (2006): 167-172. AbstractWebsite
Wavelengths and oscillator strengths for all dipole-allowed fine-structure transitions in Zr III have been calculated within the Multi-Configuration Dirac-Fock method with QED corrections. These transitions are included in the spectrum of some chemically peculiar stars, like the B-type star Lupi observed by the Hubble space telescope. The results are compared to existing experimental and semi-empirical data.
Martins, M. C., J. P. Santos, A. M. Costa, and F. Parente. "Transition wavelengths and probabilities for spectral lines of Zr III." The European Physical Journal D 39 (2006): 167-172. AbstractWebsite

Wavelengths and oscillator strengths for all dipole-allowed fine-structure transitions in Zr III have been calculated within the Multi-Configuration Dirac-Fock method with QED corrections. These transitions are included in the spectrum of some chemically peculiar stars, like the B-type star Lupi observed by the Hubble space telescope. The results are compared to existing experimental and semi-empirical data. Corr

2007
Mayo, R., M. Ortiz, F. Parente, and J. P. Santos. "Experimental and theoretical transition probabilities for lines arising from the 6p configurations of Au II." Journal of Physics B: Atomic, Molecular and Optical Physics 40 (2007): 4651. AbstractWebsite
Experimental relative transition probabilities for the 16 more pro-eminent lines arising from the 6p configurations of Au II were determined from the emission-line intensities in a laser-produced plasma. The experiment was carried out using a Cu-Au alloy with 10% Au content in order to obtain an optically thin plasma. Transition probabilities were placed on an absolute scale by using theoretical lifetimes calculated in this work, line-strength sum rules and Boltzmann plot. A comparison has been conducted between present experimental results, the theoretical data available and new calculations with the multi-configuration Dirac-Fock method reported in this work, as well as a study of the plasma conditions.
Mayo, R., M. Ortiz, F. Parente, and J. P. Santos. "Experimental and theoretical transition probabilities for lines arising from the 6p configurations of Au II." Journal of Physics B: Atomic, Molecular and Optical Physics 40 (2007): 4651. AbstractWebsite

Experimental relative transition probabilities for the 16 more pro-eminent lines arising from the 6p configurations of Au II were determined from the emission-line intensities in a laser-produced plasma. The experiment was carried out using a Cu-Au alloy with 10% Au content in order to obtain an optically thin plasma. Transition probabilities were placed on an absolute scale by using theoretical lifetimes calculated in this work, line-strength sum rules and Boltzmann plot. A comparison has been conducted between present experimental results, the theoretical data available and new calculations with the multi-configuration Dirac-Fock method reported in this work, as well as a study of the plasma conditions.

Indelicato, P., J. P. Santos, S. Boucard, and J. P. Descalux. "QED and relativistic corrections in superheavy elements." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 45 (2007): 155-170. AbstractWebsite
In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.
Indelicato, P., J. P. Santos, S. Boucard, and J. P. Descalux. "QED and relativistic corrections in superheavy elements." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 45 (2007): 155-170. AbstractWebsite

In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.Topical Issue on the Atomic Properties of the Heaviest Elements

Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Relativistic calculation of Kα hypersatellite line energies and transition probabilities for selected atoms with 12<=Z<=80." Journal of Physics B: Atomic, Molecular and Optical Physics 40 (2007): 57. AbstractWebsite
The transition probabilities of Kα hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac–Fock model for several values of atomic number Z throughout the periodic table. The influence of the Breit interaction on the Kα1h/Kα2h line intensity ratio, Kα1h and Kα2h line energy shifts and Kα1h to Kα2h line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 ⩽Z⩽ 30, calculated within the same approach, are compared with available experimental results.
Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Relativistic calculation of K&alpha; hypersatellite line energies and transition probabilities for selected atoms with 12 ≤ Z ≤ 80." Journal of Physics B: Atomic, Molecular and Optical Physics 40 (2007): 57. AbstractWebsite

The transition probabilities of K&alpha; hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac&ndash;Fock model for several values of atomic number <I>Z</I> throughout the periodic table. The influence of the Breit interaction on the K&alpha;<SUB>1</SUB><SUP>h</SUP>/K&alpha;<SUB>2</SUB><SUP>h</SUP> line intensity ratio, K&alpha;<SUB>1</SUB><SUP>h</SUP> and K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy shifts and K&alpha;<SUB>1</SUB><SUP>h</SUP> to K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 &les;<I>Z</I>&les; 30, calculated within the same approach, are compared with available experimental results.

2008
Santos, J. P., and F. Parente. "Ionisation of phosphorus, arsenic, antimony, and bismuth by electron impact." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 47 (2008): 339-350. AbstractWebsite
Abstract.  Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp4 excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.
Santos, J. P., and F. Parente. "Ionisation of phosphorus, arsenic, antimony, and bismuth by electron impact." The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics 47 (2008): 339-350. AbstractWebsite

Abstract.&nbsp;&nbsp;Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et&nbsp;al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp4 excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et&nbsp;al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.

Morrison, J. C., S. Boyd, L. Marsano, B. Bialecki, T. Ericsson, and J. P. Santos. "Numerical methods for solving the Hartree-Fock equations of diatomic molecules I." Communications in Computational Physics 5 (2008): 959-985. AbstractWebsite
The theory of domain decomposition is described and used to divide the variable domain of a diatomic molecule into separate regions which are solved independently. This approach makes it possible to use fast Krylov methods in the broad interior of the region while using explicit methods such as Gaussian elimination on the boundaries. As is demonstrated by solving a number of model problems, these methods enable one to obtain solutions of the relevant partial differential equations and eigenvalue equations accurate to six significant figures with a small amount of computational time. Since the numerical approach described in this article decomposes the variable space into separate regions where the equations are solved independently, our approach is very well-suited to parallel computing and offers the long term possibility of studying complex molecules by dividing them into smaller fragments that are calculated separately.
Palma, M. L., and J. P. Santos. "Spin-rotation and nuclear shielding constants of sulfur hexafluoride." Molecular Physics 106 (2008): 1241-1247. AbstractWebsite
We present a first theoretical determination of the hyperfine coupling constants of a spherical top molecule using ab initio methods. The scalar and tensorial contributions to the spin-rotation constants and the diamagnetic and paramagnetic contributions to the nuclear shielding constant are calculated for the 32SF6 molecule. The corrections to the spin-rotation constants due to nuclear Thomas precession are evaluated and discussed. Our results are compared with previously reported experimental values.