Several conclusions arise from this work. First, it has been shown that the reliability of A-values for the forbidden transitions within the ground configuration of the carbon and oxygen isoelectronic sequences depends strongly on the inclusion of a complete set of experimental level separations in the computations. Fortunately, in the present case, these are available from the excellent work of Edlén (1983, 1985). Therefore, the FS1 and FS2 datasets, which were calculated with theoretical level energy differences, must be corrected accordingly before they are used in astrophysical applications. For the oxygen sequence the independent BZ, FS2c and present datasets are of comparable accuracy. Most transition probabilities agree to within 10% except some small E2 A-values which are very sensitive to the numerical approximation even for large Z. In our opinion, it would be very difficult to improve their accuracy rating to better than the present 50%.
The standing discrepancies between FS1c and the present results for the carbon sequence are more difficult to explain. They are not reduced if the FS1 configuration expansion is reproduced or the TEC procedure is excluded in SUPERSTRUCTURE runs. The quality of the present radial wavefunctions for C-like ions appears to be established by the excellent agreement of the calculated excitation energies with experiment. Therefore, we are fairly confident about the reliability of the present computation for the carbon sequence. A 10% accuracy rating seems to be justified in this case, excluding of course the weak E2 transitions for .
Table 6: Experimental and calculated excitation energies in cm
from the P ground state
for the oxygen sequence. Expt: experiment. Pres: present results.
BZ: Baluja & Zeippen (1988)). FS2: Froese Fischer &
Saha (1983)
Table 7: Transition probabilities in s within the ground state
configuration of the oxygen sequence. Pres: present results.
BZ: Baluja & Zeippen (1988). FS2: Froese Fischer &
Saha (1983). FS2c: FS2 corrected with the experimental
wavelengths. denotes
Table 7: continued
Acknowledgements
Part of the present work was carried out during visits by MEG and CM to the Observatoire de Paris, Meudon, France. The hospitality received is gratefully acknowledged. The visits were funded by IVIC, CONICIT, Fundación Polar, the Observatoire de Paris and the Ministère des Affaires Etrangères. This research has been supported by CONICIT under contract No. S1-95000521.
