Comparison between the CR ionisation rate evaluated with the code described in the paper, solid contours, and with Eq. (23), dashed contours for the case C in Table 1. The grey shaded area shows the region where the difference among contours is larger than a factor of 3 and the black solid contour refers to the region where | B| = 1 G. Green, orange, blue, cyan, and red contours are related to log ₁₀(ζ^H₂/s^-1) = −17, −17.5, −18, −19, and −20, respectively.