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Subsections
The new R-matrix calculations of
Ramsbottom et al. (1994, 1995)
are adopted in the CHIANTI 2.0 version.
These calculations provide thermally-averaged collision strengths for transitions
between the 9 lowest configurations ([2s 2], [2s2p ], [2p 2],
[2s3s ], [2s3p ], [2s3d ], [2p3s ], [2p3p ] and [2p3d ])
corresponding to 46 fine-structure energy levels.
The experimental energy levels are taken from the NIST database
(Martin et al. 1995).
Radiative transition probabilities
and theoretical energy levels come from the same source as in the CHIANTI v. 1.0 version
(Zhang & Sampson 1992;
Muhlethaler & Nussbaumer 1976),
although the original
Ramsbottom et al. (1994, 1995)
theoretical energies have been used for fitting the
thermally-averaged collision strengths in CHIANTI format.
For some transitions the behaviour of the thermally-averaged collision strengths as a
function of electron temperature is quite complex and the 5-point spline interpolation
is not able to reproduce with the required accuracy their dependence on
.For this reason values of the thermally-averaged collision strengths for temperatures
lower than 104.7 K have been omitted from the database, so that the interpolation
technique could reproduce adequately the behaviour of the curve. The omission of these
points should not have any consequence as they are outside the temperature range in
which Ne VII has significant population.
The use of the R-matrix thermally-averaged collision strengths
instead of the Distorted Wave collision strengths has significant effects in
the lower level populations and theoretical line intensities.
A problem with the original CHIANTI model of Mg IX was that level 26
([3p3d ] [3 F 4]) became incorrectly metastable on account
of the absence
of published allowed transition probabilities to de-populate the level,
although the level would clearly decay via allowed transitions to the
[2s3d ] [3 D 3] and [2p3p ] [3 D 3] levels. To correct this
in v. 1.0 of CHIANTI, the gf values for these transitions were taken
from the CHIANTI O V model
(Hibbert 1980)
and scaled with Mg IX
energies to yield A-values for the transitions.
For a more correct approach, it was decided to use SSTRUCT
(Eissner et al. 1974;
see also Sect. 3 of
Paper I)
to calculate A-values for all transitions between the 46 levels of the
CHIANTI model. This data is now in the CHIANTI 2.0 database. Care was
taken to ensure that the SSTRUCT level ordering matched that in the
CHIANTI database. The SSTRUCT model included the [3s 2],
[3p 2], [3d 2], [3s3p ], [3s3d ] and [3p3d ]
configurations in addition to the 9 configurations of the CHIANTI model already
mentioned for Ne VII.
The S XIII, Ar XV, Ca XVII,
Fe XXIII and Ni XXV atomic models have been extended up to 46
fine-structure energy levels, including the n=3 configurations. These additional
configurations were already part of the 1.0 version of the database for the lighter
ions. Experimental energy levels come from
the NIST database
(Martin et al. 1995)
for all the ions, but have been complemented with
other sources where necessary:
Khardi et al. (1994)
(S XIII, Ar XV),
Martin
et al. (1990)
(S XIII),
Sugar & Corliss (1985)
(Ca XVII) and
Kelly (1987)
(Ca XVII). Theoretical energy levels are taken from
Zhang & Sampson (1992)
and from
Sampson et al. (1984).
Radiative and collisional transition probabilities for transitions from the n=3
levels have been taken from
Sampson
et al. (1984).
The authors provide Coulomb-Born-exchange collision strengths calculated for nine
values of the incident electron energy
in threshold units, in the range
. Also electric dipole radiative transition probabilities
for transitions from the n=3 levels are supplied.
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