Electron excitation of Be-like Fe XXIII for the n = 2,3,4 configurations |

M.C. Chidichimo, G. Del Zanna, H.E. Mason, N.R. Badnell, J.A. Tully and K.A. Berrington |

Astronomy & Astrophysics, 2005, Vol.430, p 331 |

Collision strengths for electron induced transitions in the beryllium-like ion Fe are calculated using the intermediate coupling frame transformation (ICFT) version of the R-matrix programs. Our target has 98 fine structure states 1s nl n'l' SLJ corresponding to n = 2 and n' = 2, 3, 4 . The present calculation is for electron impact energies in the range 3.15 to 380 Ry. When T exceeds about ten million degrees one needs to take account of contributions to the thermally averaged collision strength Upsilon coming from electrons with energies in excess of 380 Ry. We discuss a way of allowing for these contributions. Values of Upsilon for all the transitions between the ground state and the excited states 1s 2l n l n'l' S'L'J', with n'=2,3,4 are tabulated as a function of log T. The temperature range 6.3 <= log T <= 8.1 is centred on log T = 7.1 which is approximately where Fe has maximum abundance in ionization equilibrium. To the best of our knowledge these are the first R-matrix calculations for Fe for excitations to the n = 3,4 levels. Good agreement with previous distored-wave calculations is found. However, the resonance contributions have an important effect on the effective collision strengths and in turn on the level populations.

Full Tables 2, 4 and 6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/331. The full datasets of wavelengths and gf values (Table 4) and of effective collision strengths (Table 7) are only available at the same address. The same data are also available at the TIPbase (http://vizier.u-strasbg.fr/tipbase/home.html) database and as an `adf04´ file at the Oak Ridge National Laboratory's database via http://www-cfadc.phy.ornl.gov/