Photo-absorption (thick black and thin grey lines) and photo-ionisation (thin black lines) cross sections used in the ionospheric model for the three neutral species considered and their associated ions. Panel a) shows cross sections for H₂; in thick black we show the low-resolution (LR) photo-absorption cross section and in thin grey the high-resolution (HR) version (at 700 K) including structure beyond the ionisation threshold. The thin solid line plots the production of H, the dashed line the production of H⁺+H, and the dashed-dotted line the production of 2H⁺. Panel b) shows the photo-absorption cross section of H as a thick black line, which is indistinguishable from the production of H⁺ through photo-ionisation, which is shown as a thin solid line. Panel c) shows the photo-absorption cross section of He as a thick black line, which is indistinguishable from the production of He⁺, which is shown as a thin solid line, and the production He²⁺ (the dashed line).