Heating efficiency η_hν with (solid curve) and η_pe without (dashed curve) the photoelectron impact processes (5) in the H₂ →H transition region in the upper atmosphere of HD 209458b. For comparison the heating efficiency presented in Fig. 4 in the study by Yelle (2004) is shown as the dotted-dashed line. The dotted line represents the heating efficiency η_pe reduced by a factor 0.63 in accordance with the approach applied by Yelle (2004).