The H+ Region Contribution to [C II] 158 Micron Emission
  The [C II] 158 micron line is an important emission line diagnostic in Photodissociation Regions (PDRs), but this emission line can also emerge from ionized gas. This work calculates the contribution of [C II] emission from ionized gas over a wide range of parameter space by considering the simplified case of an H+ region and PDR in pressure equilibrium. Additionally, these calculations also predict the strong correlation observed between [N II] 205 micron emission and [C II] discussed by previous authors. Overall, the results of these calculations have wide-ranging applications to the interpretation of [C II] emission in astrophysical environments. 
N. P. Abel