(a) Values of ζ₂ inferred from HINSA abundances. The solid, dashed, and dash-dotted black curves denote the theoretical CR attenuation models ℒ, ℋ, and 𝒰 from Padovani et al. (2024). (b) Time dependence of atomic fraction at n_H = 10^3.0, 10^3.5, 10^4.0, and 10^4.5 cm⁻³ with the assumption of ζ₂ = 2 × 10⁻¹⁷ (solid) and 2 × 10⁻¹⁶ s⁻¹ (dashed), colored with orange, yellow, green, and purple. The oblique black and red lines represent two cutoffs at which solutions are close to chemical equilibrium under ζ₂ = 2 × 10⁻¹⁷ and 2 × 10⁻¹⁶ s⁻¹.