Abundance profiles modelled with FastChem for a selection of neutral atoms (solid lines) and ions (dashed lines), as well as molecules, H⁻ and electrons. The model assumes an isothermal structure at 4000 K and solar metallicity. Over most of the modelled pressure region, molecules tend to be dissociated and metals tend to be singly ionized. The decrease of ion abundances towards higher altitudes (pressures below ~ 10⁻¹² bars) indicates the emergence of doubly ionized species at low pressures. The effects of photo-ionization are not included, as these are predicted to be small in the denser parts of the atmosphere (Kitzmann et al. 2018).