Excess absorption predicted for a GJ 436 b-like exoplanet under a range of XUV fluxes. On its current orbit, GJ 436 b receives a XUV flux of about 278 erg cm⁻²s⁻¹ (Table B.1). Simulations based on the various rate coefficients for reaction R₂. For small XUV fluxes, the EA varies by up to a factor of 2 depending on the rate coefficient for reaction R₂ that is adopted. For strong XUV fluxes, the choice of reaction rate coefficient is, in relative terms, weaker. This figure complements the EA quoted in Table 1 for HAT-P-11 b, GJ 3470 b, and GJ 436 b.