Electron-impact excitation cross sections for Fe I

Extensive calculations are reported for electron collision strengths, rate coefficients, and transitions probabilities for a wide range of transitions in Fe I. The collision strengths were calculated using the B-spline Breit-Pauli R-matrix approach [1]. The MCHF method in connection with adjustable configuration expansions and a semi-empirical fine-tuning procedure was employed to accurately represent the target wavefunctions. The close-coupling expansion contained 221 $LS$ states of Fe I, including all levels of the $3d^6 4s^2$, $3d^7 4s$, $3d^8$, $3d^6 4s4p$, and $3d^7 4p$ configurations. Effective collision strengths were obtained by averaging the electron collision strengths over a Maxwellian distribution of speeds at electron temperatures from $10^2$ to $10^5$ K. The tabulated results for 24,531 transitions between all the above $LS$ terms considerably expand the few existing, sparse datasets for Fe I. They allow a more detailed analysis of the measured spectra from various space observatories and the nonlocal thermodynamic equilibrium modeling of late-type stars [2], for which large amounts of collisional data for the atomic species of interest are required. [1] O.~Zatsarinny, Comp.\ Phys.\ Commun.~{\bf 174} (2006) 273. [2] P.~S.~Barklem, A\&ARv~{\bf 24} (2016) 9.