for the values for all other species. As in @Hobbs19, I use in this paper the equation for the molecular diffusion coefficients for the $i$th species, $D_i$, derived by [@ChapmanCowling70], given by $$D_i = \frac{3}{8 N \left[ 0.5 ( d_i + \bar{d} ) \right]^2} \left[ \frac{k_\mathrm{B} T \left( m_i + \bar{m} \right) }{ 2 \pi m_i \bar{m} } \right]^{\frac{1}{2}}$$ where $N$ is the total number density of the gas, $d_i$ is the particle diameter of the $i$th species, $\bar{d}$ is the average particle diameter of the entire gas, $k_\mathrm{B}$ is the Boltzmann constant, $T$ is the gas temperature, $m_i$ is the molecular mass of the $i$th species, and $\bar{m}$ is the average molecular mass of the entire gas. For both $\bar{d}$ and $\bar{m}$, the number density weighted averages are used. The motivation for using this approach for diffusion coefficients is that in the atmospheres considered in this paper, molecular diffusion is especially important in a small region immediately above where H$_2$O is photodissociated and the gas composition changes rapidly from H$_2$O to H and O. In this region, which typically extends a few hundred km in altitude, the composition of the background gas changes from being dominated by water molecules 