Same as Figure 7, but now with contours of ﹩N({\mathrm{OH}}^{+})/N({\rm{H}})﹩ and ﹩N({\mathrm{OH}}^{+})/N({{\rm{H}}}_{2}{{\rm{O}}}^{+})﹩ in the plane of the model parameters ﹩{A}_{{\rm{V}}}(\mathrm{tot})﹩ and ﹩{\zeta }_{p}({\rm{H}})/{n}_{50}﹩. Blue contours are labeled with ﹩{\mathrm{log}}_{10}[N({\mathrm{OH}}^{+})/N({{\rm{H}}}_{2}{{\rm{O}}}^{+})]﹩, and red contours are labeled with ﹩{\mathrm{log}}_{10}[N({\mathrm{OH}}^{+})/N({\rm{H}})]﹩.