2019MNRAS.485.2252W

Fe II emission lines are observed from nearly all classes of astronomical objects over a wide spectral range from the infrared to the ultraviolet. To meaningfully interpret these lines, reliable atomic data are necessary. In the work presented here we focused on low-lying fine-structure transitions, within the ground term, due to electron impact. We provide effective collision strengths together with estimated uncertainties as functions of temperature of astrophysical importance (10-100 000 K). Due to the importance of fine-structure transitions within the ground term, the focus of this work is on obtaining accurate rate coefficients at the lower end of this temperature range, for applications in low-temperature environments such as the interstellar medium. We performed three different flavours of scattering calculations: (i) an intermediate coupling frame transformation (ICFT) R-matrix method, (ii) a Breit-Pauli R-matrix (BPRM) method, and (iii) a Dirac Atomic R-matrix Code (DARC). The ICFT and BPRM calculations involved three different AUTOSTRUCTURE target models each. The DARC calculation was based on a reliable 20 configuration, 6069 level atomic structure model. Good agreement was found with our BPRM and DARC collision results compared to previous R-matrix calculations. We present a set of recommended effective collision strengths for the low-lying forbidden transitions together with associated uncertainty estimates.