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Description
New atomic calculations for Fe X are presented. They focus on the need to model the soft X-ray spectrum and in particular the line at 94.0{AA} which is the dominant contribution to the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94{AA} band in quiet Sun conditions. This line, and others in the band, are due to strong decays from n=4 levels. We present new large-scale R-matrix (up to n=4) and distorted-wave (DW, up to n=6) scattering calculations for electron collisional excitation and compare them to earlier work. We find significant discrepancies with previous calculations. We show that resonances significantly increase the cross-sections for excitations from the ground state to some n=4 levels, in particular to those in the 3s^2^ 3p^4^ 4s configuration. Cascading from higher levels is also important. We suggest a new identification for the 3s 3p^6^ ^2^S_1/2_ - 3s 3p^5^ 4s ^2^P_3/2_ transition, that has a predicted intensity larger than the decays from the 3s^2^ 3p^4^ 4s levels which were identified by Edlen in 1936. The results presented here are relevant to our understanding of transitions from n=4 levels in a wide range of other ions.
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