443 research outputs found
Isotope shift on the chlorine electron affinity revisited by an MCHF/CI approach
Today, the electron affinity is experimentally well known for most of the
elements and is a useful guideline for developing ab initio computational
methods. However, the measurements of isotope shifts on the electron affinity
are limited by both resolution and sensitivity. In this context, theory
eventually contributes to the knowledge and understanding of atomic structures,
even though correlation plays a dominant role in negative ions properties and,
particularly, in the calculation of the specific mass shift contribution. The
present study solves the longstanding discrepancy between calculated and
measured specific mass shifts on the electron affinity of chlorine (Phys. Rev.
A 51 (1995) 231)Comment: 18 pages, 2 figures, 7 table
Accurate solution of the Dirac equation on Lagrange meshes
The Lagrange-mesh method is an approximate variational method taking the form
of equations on a grid because of the use of a Gauss quadrature approximation.
With a basis of Lagrange functions involving associated Laguerre polynomials
related to the Gauss quadrature, the method is applied to the Dirac equation.
The potential may possess a singularity. For hydrogenic atoms,
numerically exact energies and wave functions are obtained with small numbers
of mesh points, where is the principal quantum number. Numerically
exact mean values of powers to 3 of the radial coordinate can also be
obtained with mesh points. For the Yukawa potential, a 15-digit agreement
with benchmark energies of the literature is obtained with 50 mesh points or
less
Atomic Parameters for the Transition of Ne I relevant in nuclear physics
We calculated the magnetic dipole hyperfine interaction constants and the
electric field gradients of and levels
of Ne I by using the multiconfiguration Dirac-Hartree-Fock method. The
electronic factors contributing to the isotope shifts were also estimated for
the nm transition connecting these two states. Electron
correlation and relativistic effects including the Breit interaction were
investigated in details. Combining with recent measurements, we extracted the
nuclear quadrupole moment values for Ne and Ne with a smaller
uncertainty than the current available data. Isotope shifts in the
transition based on the present
calculated field- and mass-shift parameters are in good agreement with the
experimental values. However, the field shifts in this transition are two or
three orders of magnitude smaller than the mass shifts, making rather difficult
to deduce changes in nuclear charge mean square radii. According to our
theoretical predictions, we suggest to use instead transitions connecting
levels arising from the configuration to the ground state, for which
the normal mass shift and specific mass shift contributions counteract each
other, producing relatively small mass shifts that are only one order of
magnitude larger than relatively large field shifts, especially for the
transition
Theoretical isotope shifts in neutral barium
The present work deals with a set of problems in isotope shifts of neutral
barium spectral lines. Some well known transitions
( and ) are first
investigated. Values of the changes in the nuclear mean-square charge radius
are deduced from the available experimental isotope shifts using our ab initio
electronic factors. The three sets
obtained from these lines are consistent with each other. The combination of
the available nuclear mean-square radii with our electronic factors for the
transitions produces isotope shift values in
conflict with the laser spectroscopy measurements of Dammalapati et al. (Eur.
Phys. J. D 53, 1 (2009))
Core correlation effects in multiconfiguration calculations of isotope shifts in Mg I
The present work reports results from systematic multiconfiguration
Dirac-Hartree-Fock calculations of isotope shifts for several well-known
transitions in neutral magnesium. Relativistic normal and specific mass shift
factors as well as the electronic probability density at the origin are
calculated. Combining these electronic quantities with available nuclear data,
energy and transition level shifts are determined for the MgMg
pair of isotopes. Different models for electron correlation are adopted. It is
shown that although valence and core-valence models provide accurate values for
the isotope shifts, the inclusion of core-core excitations in the computational
strategy significantly improves the accuracy of the transition energies and
normal mass shift factors.Comment: 2 figures, submitted to Physical Review
Electronic isotope shift factors for the Ir $5d^{7}6s^{2} \ ^{4}\!F_{9/2} \to (\mbox{odd},J= 9/2)$ line at 247.587 nm
We present the theoretical calculations of the electronic isotope shift
factors of the 5d^{7}6s^{2} \ ^{4}\!F_{9/2} \to (\mbox{odd},J= 9/2) line at
247.587 nm, that were recently used to extract nuclear mean square radii and
nuclear deformations of iridium isotopes [Mukai (2020)]. The
fully relativistic multiconfiguration Dirac-Hartree-Fock method and the
relativistic configuration interaction method were used to perform the atomic
structure calculations. Additional properties such as the , Land\'e factors or were employed to
ensure an adequate description of the targeted odd level.Comment: 33 page
Effects of the electron correlation and Breit and hyperfine interactions on the lifetime of the 2p3s states in neutral neon
In the framework of the multiconfiguration Dirac-Hartree-Fock method, we
investigate the transition properties of four excited states in the
configuration of neutral neon. The electron correlation effects are taken into
account systematically by using the active space approach. The effect of
higher-order correlation on fine structures is shown. We also study the
influence of the Breit interaction and find that it reduces the oscillator
strength of the transition by 17%. It turns out that the
inclusion of the Breit interaction is essential even for such a light atomic
system. Our ab initio calculated line strengths, oscillator strengths and
transition rates are compared with other theoretical values and experimental
measurements. Good agreement is found except for the M2
transition for which discrepancies of around 15% between theories and
experiments remain. In addition, the impact of hyperfine interactions on the
lifetimes of the and metastable states is investigated for
the Ne isotope (I=3/2). We find that hyperfine interactions reduce the
lifetimes drastically. For the state the lifetime is decreased by a
factor of 630.Comment: Accepted by Phys. Rev.
Relativistic semiempirical-core-potential calculations in Ca, Sr, and Ba ions on Lagrange meshes
Relativistic atomic structure calculations are carried out in
alkaline-earth-metal ions using a semiempirical-core-potential approach. The
systems are partitioned into frozen-core electrons and an active valence
electron. The core orbitals are defined by a Dirac-Hartree-Fock calculation
using the grasp2k package. The valence electron is described by a Dirac-like
Hamiltonian involving a core-polarization potential to simulate the
core-valence electron correlation. The associated equation is solved with the
Lagrange-mesh method, which is an approximate variational approach having the
form of a mesh calculation because of the use of a Gauss quadrature to
calculate matrix elements. Properties involving the low-lying metastable
states of Ca, Sr, and Ba are studied, such as
polarizabilities, one- and two-photon decay rates, and lifetimes. Good
agreement is found with other theory and observation, which is promising for
further applications in alkali-like systems.Comment: 15 pages, accepted for publication in Phys. Rev.
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