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1981
Amaro, P., J. P. Marques, P. Indelicato, T. K. Mukherjee, J. K. Saha, L. C. Tribedi, and J. P. Santos. "Double KK excited states in highly charged sulphur ." Journal of Physics: Conference Series 635 (1981): 022071. Abstract
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1997
Moser, I., F. Mota-Furtado, P. F. O'Mahony, and J. P. Santos. "Rydberg wave packets in parallel electric and magnetic fields." Physical Review A 55 (1997): 3724-3729. Abstract

The magnitude of the time autocorrelation function M between states excited by two Gaussian laser pulses is calculated for both hydrogen and rubidium atoms inparallel electric and magnetic fields. M is determined by a full quantum-mechanical calculation but the peaks are identified with the periods of the shortest periodicorbits of the corresponding classical system. Qualitative agreement is obtained with experimental results, however, discrepancies are found in the relative heights ofthe peaks.

1998
Santos, J. P., F. Parente, and P. Indelicato. "Application of B-splines finite basis sets to relativistic two-photon decay rates of 2s level in hydrogenic ions." The European Physical Journal D 3 (1998): 43-52. AbstractWebsite

A theoretical study of the one- and two-photon spontaneous emission rates from the 2 s1/2 state of one-electron ions is presented. High-precision values of the relativistic emission rates for ions with nuclear charge Z up to 100 are obtained through the use of finite basis sets for the Dirac equation constructed from B-splines. Furthermore, we analyze the influence of the inclusion of quantum electrodynamics corrections in the initial and final state energies.

Santos, J. P., J. P. Marques, F. Parente, E. Lindroth, S. Boucard, and P. Indelicato. "Multiconfiguration Dirac-Fock calculation of 2s1/2-2p3/2 transition energies in highly ionized bismuth, thorium, and uranium." The European Physical Journal D 1 (1998): 149-163. Abstract

Structure and QED effects for 2s1/2 and 2p3/2 levels are calculated for lithiumlike U89+ trough neonlike U82+, lithiumlike Th87+ trough neonlike Th80+ and lithiumlike Bi80+ trough neonlike Bi73+. The results of the first two sets are compared with recent measurements of the 2s1/2-2p3/2 transition energy in 3 to 10-electron ions. Good agreement with experiment is found for most of the observed lines. Forty-one possible transitions are calculated for each ion in the eight ionization states, in the experimental energy range. Twenty-eight of these transitions have not been observed, nor calculated previously. We also calculate transition rates, branching ratios, excitation and ionization cross sections and confirm that the thirteen experimental observed transitions correspond to the ones with highest relative intensities. However, we find nineteen more transitions that could be measured in a more sensitive experiment.X

1999
Santos, J. P., J. P. Marques, F. Parente, E. Lindroth, P. Indelicato, and J. P. Desclaux. "Relativistic 2s1/2 (L1) atomic subshell decay rates and fluorescence yields for Yb and Hg." Journal of Physics B: Atomic and Molecular Physics 32 (1999): 2089. AbstractWebsite
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Santos, J. P., F. Mota-Furtado, M. F. Laranjeira, and F. Parente. "Rydberg states of atoms in parallel electric and magnetic fields." Physical Review A 59 (1999): 1703-1706. AbstractWebsite

We present theoretical results for the photoabsorption spectrum of an atom in parallel electric and magnetic fields, using the R-matrix method combined with quantum-defect theory. We introduce a radial basis set which is complete and orthonormal over a semi-infinite interval [r0,(infinity)), to allow calculations to be performed for high Rydberg states in nonhydrogenic atoms without encountering problems due to linear dependence of the basis set. The nonhydrogenic character of the spectra is analyzed for Li and Rb, and a comparison is made with previous high-precision experiments which shows that the theoretical results agree very well with experiment.

2000
Kim, Y. K., J. P. Santos, and F. Parente. "Extension of the binary-encounter-dipole model to relativistic incident electrons." Physical Review A 62 (2000): 052710. AbstractWebsite

Formulas for the total ionization cross section by electron impact based on the binary-encounter-dipole (BED) model and its simpler version, the binary-encounter-Bethe (BEB) model are extended to relativistic incident electron energies. Total ionization cross sections for the hydrogen and helium atoms from the new relativistic formulas are compared to experimental data. Relativistic effects double the total ionization cross section of H and He at incident electron energy 300 keV and dominate the cross section thereafter. A simple modification of the original BED-BEB formulas is proposed for applications to ion targets and inner-shell electrons of neutral atoms and molecules. The relativistic and nonrelativistic BEB cross sections are compared to the K-shell ionization cross sections by electron impact for the carbon, argon, nickel, niobium, and silver atoms. For carbon and argon, the relativistic effects are small, and both forms of the BEB cross sections agree well with available experimental data. For the nickel and heavier atoms, the relativistic increase of cross sections becomes noticeable from about 100 keV and higher in the incident electron energy. The empirical formula by Casnati et al. [J. Phys. B 15, 155 (1982)] after correcting for relativistic effects as shown by Quarles [Phys. Rev. A 13, 1278 (1976)] agrees well with the BEB cross sections for light atoms. However, the peak values of the Casnati cross sections become higher than the relativistic BEB peak cross sections as the atomic number increases. The BEB model is also applied to the total ionization cross section of the xenon atom, and the theory agrees well with experiments at low incident electron energies, but disagrees with experiment at relativistic incident energies.

Santos, J. P., J. P. Marques, F. Parente, P. Indelicato, and J. P. Desclaux. "Relativistic 2s1/2 (L1) atomic subshell radiationless transition probabilities for Yb and Hg." Atomic Data and Nuclear Data Tables 76 (2000): 49-69. Abstract

Radiationless transition rates to L1 vacancy states have been calculated ab initio in the Dirac-Fock approximation. The calculations include quantum-electrodynamic corrections. Results in the jj coupling scheme for all possible L1 transitions are tabulated for elements Yb and Hg.

2001
Santos, J. P., M. F. Laranjeira, and F. Parente. "Calculation of the triple to double ionization cross-section ratio of Li in the suddem approximation." Europhysics Letters 55 (2001): 479. Abstract

The triple-to-double ionization cross-section ratio of Li in the high-energy limit was computed in the sudden approximation with relativistic wave functions. Together with the calculated value of Dalgarno and Sadeghpour (Phys. Rev. A, 46 (1992) R3591), for the Li double-to-single ionization cross-section ratio, the value of 6.263x10-5 was obtained for the triple-to-single ionization cross-section ratio. This value is in full agreement with Wehlitz et al. experimental value of (6.38+-2.40)x10-5 obtained recently with synchrotron radiation (Phys. Rev. Lett., 81 (1998) 1813).

Costa, A. M., M. C. Martins, J. P. Santos, P. Indelicato, and F. Parente. "Dirac-Fock Transition Energies and Radiative and Radiationless Transition Probabilities for Ar8+ to Ar16+ Ion Levels with K-Shell Hole." Atomic Data and Nuclear Data Tables 79 (2001): 223-239. Abstract
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Martins, M. C., A. M. Costa, J. P. Santos, P. Indelicato, and F. Parente. "Interpretation of X-ray spectra emitted by Ar ions in an ECR ion source." Journal of Physics B: Atomic and Molecular Physics 34 (2001): 533-543. AbstractWebsite

We examine the most important processes leading to the creation of excited states from the ground configurations of Ar8+ to Ar16+ ions in an electron-cyclotron resonance ion source, which lead to the emission of K x-ray lines. Theoretical values for inner-shell excitation and ionization cross sections, including double KL ionization, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multi-configuration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical K x-ray spectrum is obtained, which reproduces very closely a recent experimental result.

Kim, Y. K., and P. M. Stone. "Ionization of boron, aluminum, gallium, and indium by electron impact." Physical Review A 64 (2001): 052707. AbstractWebsite

Measurements of electron impact ionization of neutral Al, Ga, and In show large cross sections compared to other elements in the same rows of the periodic table. Semiempirical and classical calculations of direct ionization cross sections are all substantially smaller. Calculations by McGuire [Phys. Rev. A 26, 125 (1982)] for aluminum that include excitations to autoionizing 3s3p2 doublet levels are 2.5 times higher than experiment at the peak. We report the direct ionization cross sections based on the binary-encounter-Bethe model of Kim and Rudd [Phys. Rev. A 50, 3954 (1994)], which is an ab initio theory. We add the autoionization contribution using scaled plane-wave Born cross sections as recently developed by Kim [Phys. Rev. A 64, 032713 (2001)] for excitations to the first set of autoionizing levels. Dirac-Fock wave functions are used for the atomic structure. Our results are in excellent agreement with experimental values and support substantial contributions from excitation-autoionization to the total ionization cross sections for these elements. We also compare the total ionization cross section of boron to available theories, though no experimental data are available.

Indelicato, P., G. C. Rodrigues, E. Lindroth, M. A. Ourdane, F. Parente, J. P. Santos, P. Patté, and J. Bieron. "Relativistic and many-body effects on total binding energies of Cesium and other highly-charged ion." Physica Scripta T92 (2001): 327. Abstract

The determination of atomic masses from highly ionized atoms using Penning Traps requires precise values for electronic binding energies. In the present work, binding energies of several ions (from several elements) are calculated in the framework of two relativistic many-body methods: Relativistic Many-Body Perturbation Theory (RMBPT) and Multi-Configuration Dirac– Fock (MCDF). The ions studied in this work are: Cl (He and Li-like), Se (F and Ne-like), Cs (He, Be, Ne, Al, Cl, Ar, K, Kr, Xe-like and neutral Cs), Hg, Pb and U (Br and Kr-like). Some of them are presented in this paper. Cesium has been treated in more details, allowing for a systematic comparison between MCDF and RMBPT methods. The Cs ions binding energies allow for the determination of atomic Cs mass, which can be used in a QED-independent fine structure constant determination.

Indelicato, P., E. Lindroth, T. Beier, J. Bieron, A. M. Costa, I. Lindgren, J. P. Marques, A. M. Martenson-Pendrill, M. C. Martins, M. A. Ourdane, F. Parente, P. Patté, G. C. Rodrigues, S. Salomonson, and J. P. Santos. "Relativistic Calculations for Trapped Ions." Hyperfine Interactions 132 (2001): 347-361. AbstractWebsite

We present recent results in the field of total binding energy calculations, Landщ factors, quantum electrodynamics corrections and lifetime that are of interest for ion traps and ion sources. We describe in detail MCDF and RMBPT calculation of ionic binding energies, which are needed for the determination of atomic masses from highly charged ion measurements. We also show new results concerning Landщ factor in 3-electron ions. Finally we describe how relativistic calculations can help understand the physics of heavy ion production ion sources.

Santos, J. P., P. Patté, F. Parente, and P. Indelicato. "Spontaneous relativistic two-photon decay rate mathematical expression in heliumlike systems." The European Physical Journal D 13 (2001): 27-31. AbstractWebsite

We derive a theoretical expression for the two-photon emission rate of two-electron systems, in a form suitable for easy implementation in numerical calculations. Racah algebra techniques were used to extended previous work on two-photon emission in hydrogen-like systems to more complex ones. The obtained expression is, as far as we are aware, the first general expression that gives the spontaneous two-photon decay rates of helium-like systems for any combination of multipoles.

2003
Santos, J. P., F. Parente, and Y. K. Kim. "Cross sections for K-shell ionization of atoms by electron impact." Journal of Physics B: Atomic and Molecular Physics 36 (2003): 4211-4224. AbstractWebsite

The relativistic version of the binary-encounter Bethe (BEB) model is used to calculate cross sections for K-shell ionization of atoms by electron impact. The BEB model requires only two atomic constants, the binding energy and kinetic energy of the K electrons. These constants are listed for carbon to antimony. Comparisons with available experimental data on N, O, Na, Al, Cl, Ca, Cu, Se and Sb show good agreement. The K-shell ionization cross sections for C, Mg, P, S, Cr, As and Cd are tabulated.

Santos, J. P., F. Parente, S. Boucard, and P. Indelicato. "Energy levels of hydrogenlike kaonic atoms." Hyperfine Interactions 146-147 (2003): 325. AbstractWebsite

Energies of the [( n ,l= n -1),1= n =20] and the [( n ,l= n -2),2= n =20] levels have been calculated for several hydrogenlike 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 and all-order vacuum polarization corrections.

Indelicato, P., G. C. Rodrigues, J. P. Santos, P. Patté, J. P. Marques, and F. Parente. "Systematic calculation of Total Atomic Binding Energies." Hyperfine Interactions 146-147 (2003): 115-119. Abstract
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Santos, J. P., M. L. Costa, and F. Parente. "Theoretical study of the molecular properties of methyl azidoformate and ethyl azidoformate." Journal of Molecular Structure: THEOCHEM 639 (2003): 109-115. AbstractWebsite

Ab initio calculations have been performed to study the methyl azidoformate (N3COOCH3) and the ethyl azidoformate (N3COOCH2CH3). Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionization energies based on Koopman's theorem were also computed.

Santos, J. P., M. C. Martins, A. M. Costa, P. Indelicato, and F. Parente. "Two-Electron One-Photon Transtion Relativistic Calculations for Low-Z Elements." Nuclear Instruments and Methods in Physics Research B 205 (2003): 102-105. Abstract

Energies of two-electron one-photon transitions from initial double K-hole states and the transition energies of competing processes, namely K hyper-satellites, were computed for low-Z elements, using the multi-configuration Dirac–Fock method. Transition rates are also evaluated.

2004
Martins, M. C., A. M. Costa, J. P. Santos, F. Parente, and P. Indelicato. "Relativistic calculation of two-electron one-photon and hypersatellite transition energies for 12<=Z<=30 elements." Journal of Physics B: Atomic and Molecular Physics 37 (2004): 3785-3795. AbstractWebsite

Energies of two-electron one-photon transitions from initial double K-hole states were computed using the Dirac–Fock model. The transition energies of competing processes, the Ka hypersatellites, were also computed. The results are compared with experiment and to other theoretical calculations.

Dyke, J. M., G. Levita, A. Morris, J. S. Ogden, A. A. Dias, M. Algarra, J. P. Santos, M. L. Costa, P. Rodrigues, and M. T. Barros. "A Study of the Thermal Decomposition of 2-Azidoacetamide by Ultraviolet Photoelectron Spectroscopy and Matrix-Isolation Infrared Spectroscopy:  Identification of the Imine Intermediate H2NCOCHNH." The Journal of Physical Chemistry A 108 (2004): 5299-5307. AbstractWebsite

The thermal decomposition of 2-azidoacetamide (N3CH2CONH2) has been studied by matrix-isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N2, CH2NH, HNCO, CO, NH3, and HCN are observed as high-temperature decomposition products, while at lower temperatures, the novel imine intermediate H2NCOCHNH is observed in the matrix-isolation IR experiments. The identity of this intermediate is confirmed both by ab initio molecular orbital calculations of its IR spectrum and by the temperature dependence and distribution of products in the photoelectron spectroscopy (PES) and IR studies. Mechanisms are proposed for the formation and decomposition of the intermediate consistent both with the observed results and with estimated activation energies based on pathway calculations.

Rodrigues, G. C., P. Indelicato, J. P. Santos, P. Patté, and F. Parente. "Systematic calculation of total atomic energies of ground state configurations." Atomic Data and Nuclear Data Tables 86 (2004): 117-233. AbstractWebsite

We present a systematic study of atomic binding energies, in the Dirac–Fock approximation, for the Lithium (3 electrons) to the Dubnium (105 electrons) isoelectronic series. In each series we have considered all atomic numbers from the one corresponding to the neutral atom up to Z=118. We have obtained the ground state configurations for several heavy ions with charge larger than one.

Santos, J. P., and M. F. Laranjeira. Métodos Matemáticos para Físicos e Engenheiros., 2004. Abstract
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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.