Secondary ions produced by a primary electron of energy E₀. The solid curves represent different fractional ionisations. We note that these yields refer to energy bins of finite size rather than to the specific energies quoted there. This distinction causes some difference at higher energies because the energy bins are larger for them. We have nevertheless confirmed that this has no significant impact on the overall gas properties and mass-loss rates by running a few tests with a refined spectral grid of 40 bins. Based on calculations from García Muñoz (2023).