Ionization rate for H₂ ζ^(H₂) (defined in Sect. 2.3) and its different contributions, as a function of location in the disk, for the fiducial model described in Sect. 5. For each color, the following nonthermal ionization source dominates ζ^(H₂): decay from short- and long-lived radionuclides (black), galactic cosmic rays (purple), or stellar X-rays (orange and yellow for the scattered and direct contribution, respectively). The solid colored contour lines correspond to the surfaces of constant total ionization rate, ζ^(H₂), ranging from7.6 × 10⁻¹⁹ s⁻¹ to 1.8 × 10⁻¹⁰ s⁻¹. The dashed white lines correspond to the surfaces z = 1 H_gas, z = 2 H_gas, z = 3 H_gas, and z = 4 H_gas, from bottom to top, respectively.