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Paper XXI

Electron excitation of fine-structure transitions involving the $3d^{6}4s^2$ $^{5}D$ ground state and the $3d^74s$ $^{5}F$ metastable state of Fe I
J. Pelan and K.A. Berrington
Astronomy & Astrophysics Supplement Series, 1997, Vol.122, No.1, pp.177-180

Low energy electron excitation collision strengths for fine-structure transitions involving the $3d^{6}4s^2$ $^{5}D_J$ ground term and the $3d^74s$ $^{5}F_J$ first excited term of neutral Fe are calculated. The model target atom includes the lowest three terms ($^{5}D$, $^{5}F$ and $^{3}F$) together with four pseudostates ( $\overline{^{5}P^{\rm o}}$, $\overline{^{5}D^{\rm o}}$, $\overline{^{5}F^{\rm o}}$, $\overline{^{5}G^{\rm o}}$) 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 100-4000K. The low-temperature form of the collision strength is established for the first time for Fe I.