Distribution of hydrogen species against radial distance predicted by model#l. Top panel: numerical densities of neutral atomic hydrogen (blue solid line) and its ions (blue dashed), and H⁻ (blue dash-dotted), molecular hydrogen (green solid) and its ions (green dashed), and (violet dashed). Bottom panel: distribution of neutral atomic hydrogen in terms of excitation levels, i.e. numerical densities of hydrogen in 1S (light green solid line), 2S (dark green solid), 2P (dark yellow solid), 3S (black solid), 3P (orange solid), and 3D (violet solid) states. The dotted magenta line gives the summed numerical densities of hydrogen atoms in the energy levels 4S and higher. In both panels, the grey solid line gives the total density of all hydrogen species for reference.