1,329 research outputs found
Metastable level properties of the excited configuration
Metastable levels in rhodium-like ions with the ground configuration
and the excited configurations and
are investigated. The {\sl ab initio} calculations of the level
energies, radiative multipole transition probabilities are performed in a
quasirelativistic Hartree-Fock approximation employing an extensive
configuration interaction based on quasirelativistic transformed radial
orbitals. A systematic trends in behavior of calculated radiative lifetimes of
the metastable levels are studied for the ions from to . The
significance of the radiative transitions of higher multipole order ( and
) for the calculated radiative lifetimes is demonstrated and discussed.Comment: Lithuanian Journal of Physics (in press
Methods, algorithms and computer codes for calculation of electron-impact excitation parameters
We describe the computer codes, developed at Vilnius University, for the
calculation of electron-impact excitation cross sections, collision strengths,
and excitation rates in the plane-wave Born approximation. These codes utilize
the multireference atomic wavefunctions which are also adopted to calculate
radiative transition parameters of complex many-electron ions. This leads to
consistent data sets suitable in plasma modelling codes. Two versions of
electron scattering codes are considered in the present work, both of them
employing configuration interaction method for inclusion of correlation effects
and Breit-Pauli approximation to account for relativistic effects. These
versions differ only by one-electron radial orbitals, where the first one
employs the non-relativistic numerical radial orbitals, while another version
uses the quasirelativistic radial orbitals. The accuracy of produced results is
assessed by comparing radiative transition and electron-impact excitation data
for neutral hydrogen, helium and lithium atoms as well as highly-charged
tungsten ions with theoretical and experimental data available from other
sources.Comment: Lithuan. J. Physic
Study of the correlation effects in Yb^+ and implications for parity violation
Calculation of the energies, magnetic dipole hyperfine structure constants,
E1 transition amplitudes between the low-lying states, and nuclear
spin-dependent parity-nonconserving amplitudes for the ^2S_{1/2} -
^2D_{3/2,5/2} transitions in ^{171}Yb^+ ion is performed using two different
approaches. First, we carried out many-body perturbation theory calculation
considering Yb^+ as a monovalent system. Additional all-order calculations are
carried out for selected properties. Second, we carried out configuration
interaction calculation considering Yb as a 15-electron system and compared the
results obtained by two methods. The accuracy of different methods is
evaluated. We find that the monovalent description is inadequate for evaluation
of some atomic properties due to significant mixing of the one-particle and the
hole-two-particle configurations. Performing the calculation by such different
approaches allowed us to establish the importance of various correlation
effects for Yb^+ atomic properties for future improvement of theoretical
precision in this complicated system.Comment: 11 pages;v2: minor changes and one reference adde
Metal-insulator transition and glassy behavior in two-dimensional electron systems
Studies of low-frequency resistance noise demonstrate that glassy freezing
occurs in a two-dimensional electron system in silicon in the vicinity of the
metal-insulator transition (MIT). The width of the metallic glass phase, which
separates the 2D metal and the (glassy) insulator, depends strongly on
disorder, becoming extremely small in high-mobility (low-disorder) samples. The
glass transition is manifested by a sudden and dramatic slowing down of the
electron dynamics, and by a very abrupt change to the sort of statistics
characteristic of complicated multistate systems. In particular, the behavior
of the second spectrum, an important fourth-order noise statistic, indicates
the presence of long-range correlations between fluctuators in the glassy
phase, consistent with the hierarchical picture of glassy dynamics.Comment: Contribution to conference on "Noise as a tool for studying
materials" (SPIE), Santa Fe, New Mexico, June 2003; 15 pages, 12 figs.
(includes some low-quality figs; send e-mail to get high-quality figs.
Energy levels and radiative rates for transitions in Fe V, Co VI and Ni VII
Energy levels, Land\'{e} -factors and radiative lifetimes are reported for
the lowest 182 levels of the 3d, 3d4s and 3d4p configurations of
Fe~V, Co~VI and Ni~VII. Additionally, radiative rates (-values) have been
calculated for the E1, E2 and M1 transitions among these levels. The
calculations have been performed in a quasi-relativistic approach (QR) with a
very large {\em configuration interaction} (CI) wavefunction expansion, which
has been found to be necessary for these ions. Our calculated energies for all
ions are in excellent agreement with the available measurements, for most
levels. Discrepancies among various calculations for the radiative rates of E1
transitions in Fe~V are up to a factor of two for stronger transitions (), and larger (over an order of magnitude) for weaker ones. The reasons for
these discrepancies have been discussed and mainly are due to the differing
amount of CI and methodologies adopted. However, there are no appreciable
discrepancies in similar data for M1 and E2 transitions, or the -factors for
the levels of Fe~V, the only ion for which comparisons are feasible.Comment: This paper of 78 pages including 9 Tables will appear in ADNDT (2016
Transition frequency shifts with fine-structure constant variation for Yb II
In this paper we report calculations of the relativistic corrections to
transition frequencies (q factors) of Yb II for the transitions from the
odd-parity states to the metastable state 4f^{13}6s^2 ^2F_{7/2}^o. These
transitions are of particular interest experimentally since they possess some
of the largest q factors calculated to date and the state can be
prepared with high efficiency. This makes Yb II a very attractive candidate for
the laboratory search for variation of the fine-structure constant alpha.Comment: 5 page
Atomic data for S II - Toward Better Diagnostics of Chemical Evolution in High-redshift Galaxies
Absorption-line spectroscopy is a powerful tool used to estimate element
abundances in the nearby as well as distant universe. The accuracy of the
abundances thus derived is, naturally, limited by the accuracy of the atomic
data assumed for the spectral lines. We have recently started a project to
perform the new extensive atomic data calculations used for optical/UV spectral
lines in the plasma modeling code Cloudy using state-of-the-art quantal
calculations. Here we demonstrate our approach by focussing on S II, an ion
used to estimate metallicities for Milky Way interstellar clouds as well as
distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the
spectra of quasars and gamma-ray bursts (GRBs). We report new extensive
calculations of a large number of energy levels of S II, and the line strengths
of the resulting radiative transitions. Our calculations are based on the
configuration interaction approach within a numerical Hartree-Fock framework,
and utilize both non-ralativistic and quasirelativistic one-electron radial
orbitals. The results of these new atomic calculations are then incorporated
into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative
purposes. The new results imply relatively modest changes (~0.04 dex) to the
metallicities estimated from S II in past studies. These results will be
readily applicable to other studies of S II in the Milky Way and other
galaxies.Comment: Accepted for publication in The Astrophysical Journal; 34 pages, 10
figure
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