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R
Szabo, Csilla I., Pedro Amaro, Mauro Guerra, Sophie Schlesser, Alexander Gumberidze, Jose Paulo Santos, and Paul Indelicato. "Reference free, high-precision measurements of transition energies in few electron argon ions." AIP APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY: Twenty-Second International Conference 1525 (2013): 68-72. AbstractWebsite

The use of a vacuum double crystal spectrometer, coupled to an electron-cyclotron resonance ion source (ECRIS), allows to measure low-energy x-ray transitions energies in highly-charged ions with accuracies of the order of a few parts per million. We have used this installation to measure the 1s2p 1 P1 - 1s2 1 S0 diagram line and the 1s2s 3 S1 - 1s2 1 S0 forbidden M1 transition energies in helium-like argon, the 1s2s2p 2 P j 1s2 2s 2 S1/2 transitions in lithium-like argon and the 1s2s2 2p 1 P1 - 1s2 2s2 1 S0 transition in beryllium-like argon. These transition measurements have accuracies between 2 and 4 ppm depending on the line intensity. Thanks to the excellent agreement between the simulations and the measurements, we were also able to measure the transition width of all the allowed transitions. The results are compared to recent QED and relativistic many-body calculations.

Szabo, Csilla I., Pedro Amaro, Mauro Guerra, Sophie Schlesser, Alexander Gumberidze, Jose Paulo Santos, and Paul Indelicato. "Reference free, high-precision measurements of transition energies in few electron argon ions." AIP Conf. Proc. 1525 (2013): 68-72. AbstractWebsite

The use of a vacuum double crystal spectrometer, coupled to an electron-cyclotron resonance ion source (ECRIS), allows to measure low-energy x-ray transitions energies in highly-charged ions with accuracies of the order of a few parts per million. We have used this installation to measure the 1s2p 1 P1 - 1s2 1 S0 diagram line and the 1s2s 3 S1 - 1s2 1 S0 forbidden M1 transition energies in helium-like argon, the 1s2s2p 2 P j 1s2 2s 2 S1/2 transitions in lithium-like argon and the 1s2s2 2p 1 P1 - 1s2 2s2 1 S0 transition in beryllium-like argon. These transition measurements have accuracies between 2 and 4 ppm depending on the line intensity. Thanks to the excellent agreement between the simulations and the measurements, we were also able to measure the transition width of all the allowed transitions. The results are compared to recent QED and relativistic many-body calculations.

Santos, J. P., F. Parente, M. C. Martins, P. Indelicato, E. P. Benis, T. J. M. Zouros, and J. P. Marques. "Radiative transition rates of 1s2s(3S)3p levels for Li-like ions with 5 <= Z <= 10." Nuclear Inst. and Methods in Physics Research, B 408 (2017): 100-102. AbstractWebsite

Nuclear Inst. and Methods in Physics Research, B, 408 (2017) 100-102. doi:10.1016/j.nimb.2017.04.015

Q
Amaro, Pedro, Filippo Fratini, Laleh Safari, Aldo Antognini, Paul Indelicato, Randolf Pohl, and Jose Paulo Santos. "Quantum interference shifts in laser spectroscopy with elliptical polarization." Physical Review A 92 (2015): 062506-5. AbstractWebsite
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Amaro, Pedro, Beatrice Franke, Julian J. Krauth, Marc Diepold, Filippo Fratini, Laleh Safari, Jorge Machado, Aldo Antognini, Franz Kottmann, Paul Indelicato, Randolf Pohl, and Jose Paulo Santos. "Quantum interference effects in laser spectroscopy of muonic hydrogen, deuterium, and helium-3." Physical Review A 92 (2015): 022514-7. AbstractWebsite
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Fratini, F., L. Safari, A. G. Hayrapetyan, K. Jankala, P. Amaro, and J. P. Santos. "Quantized form factor shift in the presence of free electron laser radiation." EPL (Europhysics Letters) 107 (2014): 13002. AbstractWebsite

In electron scattering, the target form factors contribute significantly to the diffraction pattern and carry information on the target electromagnetic charge distribution. Here we show that the presence of electromagnetic radiation, as intense as currently available in free electron lasers, shifts the dependence of the target form factors by a quantity that depends on the number of photons absorbed or emitted by the electron as well as on the parameters of the electromagnetic radiation. As example, we show the impact of intense ultraviolet and soft X-ray radiation on elastic electron scattering by the Ne-like argon ion and by the xenon atom. We find that the shift brought by the radiation to the form factor is of the order of some percent. Our results may open up a new avenue to explore matter with the assistance of laser.

Fratini, F., L. Safari, A. G. Hayrapetyan, K. Jankala, P. Amaro, and J. P. Santos. "Quantized form factor shift in the presence of free electron laser radiation." EPL (Europhysics Letters) 107 (2014): 13002. AbstractWebsite

In electron scattering, the target form factors contribute significantly to the diffraction pattern and carry information on the target electromagnetic charge distribution. Here we show that the presence of electromagnetic radiation, as intense as currently available in free electron lasers, shifts the dependence of the target form factors by a quantity that depends on the number of photons absorbed or emitted by the electron as well as on the parameters of the electromagnetic radiation. As example, we show the impact of intense ultraviolet and soft X-ray radiation on elastic electron scattering by the Ne-like argon ion and by the xenon atom. We find that the shift brought by the radiation to the form factor is of the order of some percent. Our results may open up a new avenue to explore matter with the assistance of laser.

Guimarães, D., A. A. Dias, M. Carvalho, M. L. Carvalho, J. P. Santos, F. R. Henriques, F. Curate, and S. Pessanha. "Quantitative determinations and imaging in different structures of buried human bones from the XVIII-XIXth centuries by energy dispersive X-ray fluorescence – Postmortem evaluation." Talanta 155 (2016): 107-115. AbstractWebsite

Talanta, 155 + (2016) 107-115. doi:10.1016/j.talanta.2016.04.028

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

P
Martins, M. C., J. P. Marques, A. M. Costa, J. P. Santos, F. Parente, S. Schlesser, Le E. - O. Bigot, and P. Indelicato. "Production and decay of sulfur excited species in an electron-cyclotron-resonance ion-source plasma." Physical Review A (Atomic, Molecular, and Optical Physics) 80 (2009): 032501. AbstractWebsite
The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.
Martins, M. C., J. P. Marques, A. M. Costa, J. P. Santos, F. Parente, S. Schlesser, E. O. Le Bigot, and P. Indelicato. "Production and decay of sulfur excited species in an electron-cyclotron-resonance ion-source plasma." Physical Review A 80 (2009): 032501. AbstractWebsite

The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.

Santos, J. P., M. C. Martins, A. M. Costa, J. P. Marques, P. Indelicato, and F. Parente. "Production and decay of chlorine ion excited species in an electron cyclotron resonance ion source plasma." Physica Scripta T144 (2011): 014005. AbstractWebsite

The most important processes for the creation of chlorine ion excited states from the ground configurations of Cl 10+ to Cl 15+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, were studied. Theoretical values for inner-shell excitation and ionization cross-sections, including double KL and triple KLL ionization, transition probabilities and energies for the de-excitation processes, were calculated in the framework of the multi-configuration Dirac–Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kα x-ray spectrum was obtained, which was then compared with recent experimental data.

Santos, J. P., M. C. Martins, A. M. Costa, J. P. Marques, P. Indelicato, and F. Parente. "Production and decay of chlorine ion excited species in an electron cyclotron resonance ion source plasma." Physica Scripta T144 (2011): 014005. AbstractWebsite

The most important processes for the creation of chlorine ion excited states from the ground configurations of Cl 10+ to Cl 15+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, were studied. Theoretical values for inner-shell excitation and ionization cross-sections, including double KL and triple KLL ionization, transition probabilities and energies for the de-excitation processes, were calculated in the framework of the multi-configuration Dirac–Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kα x-ray spectrum was obtained, which was then compared with recent experimental data.

Ménesguen, Y., {M. C. } Lépy, Y. Ito, M. Yamashita, S. Fukushima, M. Polasik, K. Słabkowska, Syrocki, E. Wȩder, P. Indelicato, {J. P. } Marques, {J. M. } Sampaio, M. Guerra, F. Parente, and {J. P. } Santos. "Precise x-ray energies of gadolinium determined by a combined experimental and theoretical approach." Journal Of Quantitative Spectroscopy & Radiative Transfer 236 (2019). Abstract

We combined different experimental techniques with a theoretical approach to determine a consistent set of diagram lines energies and binding energies. We propose an original approach consisting in determining the mass attenuation coefficients in an energy range covering the L-, M- and N- absorption edges, including a detailed evaluation of the associated uncertainties, to derive precisely the binding energies. We investigated the Lα, Lβ and M spectra of Gd with an independantly calibrated high-resolution anti-parallel double-crystal x-ray spectrometer. All the lines were identified and found in excellent agreement with the binding energies previously derived. Morever, we identified for the first time M5−O2, M4−O2,3 and M4−N2,3 diagram lines.

Amaro, P., F. Fratini, S. Fritzsche, P. Indelicato, J. P. Santos, and A. Surzhykov. "Parametrization of the angular correlation and degree of linear polarization in two-photon decays of hydrogenlike ions." Phys. Rev. A 86 (2012): 042509. AbstractWebsite

The spontaneous two-photon emission in hydrogenlike ions is investigated within the framework of second- order perturbation theory and Dirac’s equation. Special attention is paid to the angular correlation of the emitted photons as well as to the degree of linear polarization of one of the two photons, if the second is just observed under arbitrary angles. Expressions for the angular correlation and the degree of linear polarization are expanded in powers of cosine functions of the two-photon opening angle, whose coefficients depend on the atomic number and the energy sharing of the emitted photons. The effects of including higher (electric and magnetic) multipoles upon the emitted photon pairs beyond the electric-dipole approximation are also discussed. Calculations of the coefficients are performed for the transitions 2s1/2 → 1s1/2, 3d3/2 → 1s1/2, and 3d5/2 → 1s1/2, along the entire hydrogen isoelectronic sequence (1

Amaro, P., F. Fratini, S. Fritzsche, P. Indelicato, J. P. Santos, and A. Surzhykov. "Parametrization of the angular correlation and degree of linear polarization in two-photon decays of hydrogenlike ions." Physical Review A 86 (2012): 042509. AbstractWebsite

The spontaneous two-photon emission in hydrogenlike ions is investigated within the framework of second- order perturbation theory and Dirac’s equation. Special attention is paid to the angular correlation of the emitted photons as well as to the degree of linear polarization of one of the two photons, if the second is just observed under arbitrary angles. Expressions for the angular correlation and the degree of linear polarization are expanded in powers of cosine functions of the two-photon opening angle, whose coefficients depend on the atomic number and the energy sharing of the emitted photons. The effects of including higher (electric and magnetic) multipoles upon the emitted photon pairs beyond the electric-dipole approximation are also discussed. Calculations of the coefficients are performed for the transitions 2s1/2 → 1s1/2, 3d3/2 → 1s1/2, and 3d5/2 → 1s1/2, along the entire hydrogen isoelectronic sequence (1 Z 100).

O
Togawa, M., S. Kühn, C. Shah, P. Amaro, R. Steinbrügge, J. Stierhof, N. Hell, M. Rosner, K. Fujii, M. Bissinger, R. Ballhausen, M. Hoesch, J. Seltmann, S. Park, F. Grilo, F. S. Porter, J. P. Santos, M. Chung, T. Stöhlker, J. Wilms, T. Pfeifer, G. V. Brown, M. A. Leutenegger, S. Bernitt, and Crespo J. R. López-Urrutia. "Observation of strong two-electron–one-photon transitions in few-electron ions." Physical Review A 102 (2020). AbstractWebsite
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Kasthurirangan, S., J. K. Saha, A. N. Agnihotri, S. Bhattacharyya, D. Misra, A. Kumar, P. K. Mukherjee, J. P. Santos, A. M. Costa, P. Indelicato, T. K. Mukherjee, and L. C. Tribedi. "Observation of 2p3 d (1Po)→ 1s3d (1De) Radiative Transition in He-like Si, S, and Cl Ions." Physical Review Letters 111 (2013): 243201. AbstractWebsite
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Kasthurirangan, S., J. K. Saha, A. N. Agnihotri, S. Bhattacharyya, D. Misra, A. Kumar, P. K. Mukherjee, J. P. Santos, A. M. Costa, P. Indelicato, T. K. Mukherjee, and L. C. Tribedi. "Observation of 2p3 d (1Po)→ 1s3d (1De) Radiative Transition in He-like Si, S, and Cl Ions." Physical Review Letters 111 (2013): 243201. AbstractWebsite
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N
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. "Nuclear spin–spin constants, rotational g factor and susceptibility of sulphur hexafluoride." Mol. Phys. 110 (2012): 2163. AbstractWebsite

Following our previous study on spin–rotation and shielding constants of the SF6 molecule, the rotational g factor and the magnetic susceptibility are calculated here, using ab initio methods to evaluate the electronic contribution to the nuclear hyperfine constants, and compared with experimental results. It is shown, for the first time, that the electronic component of the rotational g factor is proportional to a constant, which is given by a sum over electronic states. We also evaluate for the SF6 molecule the indirect, or electron-coupled spin–spin interaction, theoretically described by Ramsey, and show that it gives non-negligible corrections to direct coupling constants d1 and d2. The contributions of the terms included in this interaction (DSO, PSO, SD and FC) are also analysed.

Palma, M. L., and J. P. Santos. "Nuclear spin–spin constants, rotational g factor and susceptibility of sulphur hexafluoride." Molecular Physics 110 (2012): 2163. AbstractWebsite

Following our previous study on spin–rotation and shielding constants of the SF6 molecule, the rotational g factor and the magnetic susceptibility are calculated here, using ab initio methods to evaluate the electronic contribution to the nuclear hyperfine constants, and compared with experimental results. It is shown, for the first time, that the electronic component of the rotational g factor is proportional to a constant, which is given by a sum over electronic states. We also evaluate for the SF6 molecule the indirect, or electron-coupled spin–spin interaction, theoretically described by Ramsey, and show that it gives non-negligible corrections to direct coupling constants d1 and d2. The contributions of the terms included in this interaction (DSO, PSO, SD and FC) are also analysed.