Resistivities (ambipolar: black, Ohmic: red, Hall: green and blue) computed with the chemical network introduced by Zhao et al. (2016) in dependence of the number density of molecular hydrogen H₂. Solid lines represent the fiducial case of a cosmic-ray ionization rate of ζ = 10⁻¹⁷ s⁻¹, dashed lines represent the case of an ionization rate of ζ = 10⁻¹⁸ s⁻¹, and dash-dotted lines correspond to ζ = 10⁻¹⁶ s⁻¹.