Accurate wavelengths for Xray spectroscopy
and the NIST
Hydrogen and HydrogenLike ion databases
S. A. Kotochigova^{1;2},
K. P. Kirby^{3}, N. S. Brickhouse^{4}
^{1}National Institute
of Standards and Technology, 100 Bureau Drive, stop 8423, Gaithersburg,
Maryland 20899 USA
^{2}Department of Physics,
Temple University, Philadelphia, PA 19122 USA
^{3}Institute for Theoretical
Atomic and Molecular Physics, HarvardSmithsonian Center for
Astrophysics, 60 Garden St., Cambridge, MA 02138 USA
^{4}HarvardSmithsonian
Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 USA
We describe our ab initio relativistic approach that
is developed to provide accurate wavelengths for Xray spectroscopy.
This approach is based on computational techniques that are well
suited to treat relativistic and correlation effects in highly
charged ions. We use the largescale configurationinteraction
(CI) DiracFock method to solve the DiracCoulombBreit equation
and calculate energies, transition frequencies and probabilities,
using nonorthogonal bases. To generate CI basis sets we solve
DiracFock equations for occupied orbitals and the DiracFockSturm
equations for virtual or nonoccupied orbitals numerically. Since
the DiracFockSturm operator has a complete and discrete set
of eigenfunctions, the basis set includes the continuous part
of the spectrum.
The performance of our computational technique is tested by
comparing our calculations of the p  s and p  d transitions
in Fe XVIII and Fe XIX to known experimental results. An estimate
of the Lamb shift for these transitions shows that it may start
to play a role at this level of 103Å accuracy and
therefore it has to be included for more precise calculations.
Finally, I will present my work on NIST databases. In particular,
I will show two interactive databases designed to calculate total
energies and transition frequencies of hydrogen and deuterium
as well as hydrogenlike ions. The values are highly accurate
and based on current knowledge of the relevant theory, which
includes relativistic, quantum electrodynamic, recoil, and nuclear
size effects. The hydrogenlike ion database is possibly of interest
for Xray spectroscopy, whereas the hydrogen and deuterium data
base lays the theoretical groundwork for precise determination
of ground and excited energies.
