high-energy photoelectrons created by photoionization reactions.

The cooling model includes the emission of radiation to space by H$_2$O, H, and O. For H$_2$O cooling, I use the method by @Hollenbach79 and summarized by @Kasting83 who used this method for calculating cooling from water vapor in planetary atmospheres; this model considers excitation of water molecules by atomic hydrogen and takes into account non-local thermodynamic equilibrium effects. For H cooling, I consider the effects of Ly-$\alpha$ emission to space using the method given by @MurrayClay09 and @Guo19. For O cooling, I consider emission at 63 $\mu$m and 147 $\mu$m using the parameterisations derived by @Bates51 and commonly used for calculating cooling in the upper thermospheres of planets. In future work, I intend to implement in the model a more sophisticated treatment of radiative cooling.

Another change to the model that I make for this study is the way that the molecular diffusion coefficients are calculated. Molecular diffusion coefficients are different for different chemical species and depend on the composition of the background gas. In previous models, I used measured diffusion coefficients for several common species (see Eqn. 25 of @Johnstone18) assuming a background atmosphere composed of N$_2$, and then made reasonable guesses 