\[figcollision\] shows the ionization distribution of iron for the collisional ionization case. Figure \[figphoto\] shows a similar calculation for photoionization equilibrium. Both show two hydrogen densities, 1 cm$^{-3}$, where collisional suppression of DR should be negligible, and 10$^{10}$ cm$^{-3}$, where collisional suppression should greatly affect the rates for lower charges and temperatures. The upper panel shows the ionization fractions themselves, for these two densities, while the lower panel shows the ratio of the high to low density abundances.

![\[figcollision\] Upper panel: collisional ionization fractional abundance vs. electron temperature for all ionization stages of Fe. The solid curves correspond to a density of 1 cm$^{-3}$ and the dashed curves correspond to a density of $10^{10}~\rm{cm}^{-3}$. From left to right, the curves range from to . Lower panel: ratio of the calculated fractional abundances for the two densities. ](Fig6.eps){width="\textwidth"}

![\[figphoto\] Upper panel: photoionization fractional abundance vs. the ionization parameter $U$ for all ionization stages of Fe. The solid curves correspond to a density of 1 cm$^{-3}$ and the dashed curves correspond to a density of $10^{10}~\rm{cm}^{-3}$. From left to right, the curves range from to . Lower panel: ratio of the calculated fractional abundances for the two densities. ](Fig7.eps){width="\textwidth"}

Cloudy’s assumptions in 