Atomic data from the IRON Project. XXI. Electron excitation of fine-structure transitions involving the 3d^64s^2 ^5D ground state and the 3d^74s 5F metastable state of Fe i
Low energy electron excitation collision strengths for fine-structure transitions involving the 3d^64s^2 ^5D_J ground term and the 3d^74s ^5F_J first excited term of neutral Fe are calculated. The model target atom includes the lowest three terms (5D, 5F and 3F) together with four pseudo-states (5Po, 5Do, 5Fo, 5Go) chosen to represent the dipole polarizability of the ground term and first excited term of Fe. The Breit-Pauli R-matrix method is used to calculate the fine-structure collision strength, which is averaged over a Maxwellian velocity distribution to obtain effective collision strengths as a function of electron temperature in the range 100-4000 K. The low-temperature form of the collision strength is established for the first time for Fe i.