Comparison of the CRIRs derived in the present study with previous estimates obtained by IM12 and I15. The labels underneath the plotted points indicate the background source for each CRIR determination and the velocity interval to which the determination applies. Top row: ﹩{\zeta }_{p}({\rm{H}})/{n}_{50}﹩, derived for diffuse atomic gas in which the column densities of OH⁺, ﹩{{\rm{H}}}_{2}{{\rm{O}}}^{+}﹩, ArH⁺, and H have all been measured. Middle row: ﹩{\zeta }_{p}({\rm{H}})/{n}_{50}﹩, derived for diffuse atomic gas in which ArH⁺ observations are not available. Bottom row: CRIRs derived for diffuse molecular gas from observations of ﹩{{\rm{H}}}_{3}^{+}﹩. Bottom left: clouds in which H₂ is measured directly. Bottom right: clouds in which H₂ is only measured indirectly. Blue diamonds: values obtained previously using a simple analytic treatment of the chemistry (IM12 or I15). Red diamonds: values obtained using detailed diffuse cloud models, but without any correction for HI in the small diffuse atomic clouds responsible for the observed ArH⁺ absorption. Magenta diamonds: values obtained using detailed diffuse cloud models with the inclusion of the aforementioned correction.