4 Discussion and conclusions

New electron collisional data for 3s²3p³ - 3s3p⁴ and 3s²3p³ - 3s²3p²3d electric dipole transitions in FeXII have been presented in this paper and compared with previous available computations.

A comparison with the calculations by F77 and TH88 is possible for the 3s²3p³ - 3s3p⁴ transitions. Despite the use of the same R-matrix approach for the scattering problem in TH88 and in the present work, we get marginally better agreement with the data obtained by F77 in a distorted wave approximation. This is probably due to the inclusion of orbitals of correlation type in the target wavefunctions adopted by TH88. It is pointed out that the most serious discrepancies between the different data sets occur at small collision strength values, where cancellation effects due to the particular choice of target representation are likely to play a bigger role. This shows the importance of using a comprehensive target expansion in the electron scattering computation.

The only set of 3s²3p³ - 3s²3p²3d electric dipole collisional data previously published is that of F77. As stressed in Sect.3 our results benefit from a greatly improved target representation, a more sophisticated scattering technique, proper inclusion of resonance effects and provision of data over a wide range of electron energies and temperatures. A careful comparison between the two data sets has made possible the identification of some problems in the F77 data, such as mislabellings and observed energies misassignments. These are thoroughly discussed in Sect.3.2.

In summary, the data presented in this paper represent a significant improvement over previous computations. These data, together with those reported in BMS, should provide a valuable tool for future astrophysical and plasma diagnostic work involving the FeXII ion.

Acknowledgements

This research was supported by PPARC grants GR/H94979 and GR/K98506 for the IRON Project meetings and CRAY computing time.