Electron (open circles) and hydrogen (filled circles) collision rates of representative transitions in Fe i (left column) and Fe ii (right column) as a function of the transition energy in the model 5780/4.44/0 at a depth point of log τ₅₀₀₀ = −0.5, where T = 5583 K, n_H = 0.922 × 10¹⁷, and n_e = 0.137 × 10¹⁴ (top row), and in the model 4600/1.60/−2.50 at a depth point of log τ₅₀₀₀ = −0.5, where T = 4174 K, n_H = 0.212 × 10¹⁷, and n_e = 0.286 × 10¹¹ (bottom row). We assumed S_H = 0.1 throughout.