(a) The C II 2p:²P_3/2–²P_1/2 fine‐structure ground‐state transition at 157.7 μm. (b) The C I 2p²:³P₁–³P₀ transition at 609.1 μm. (c) The C I 2p²:³P₂–³P₁ transition at 370.4 μm. This is residual after subtracting an estimate of the CO 7–6 emission. (d) The ratio of C II to total far‐infrared continuum emission at wavelengths longer than 105 μm (dimensionless scale). (e) The N II 2p²:³P₁–³P₀ fine‐structure ground‐state transition at 205.3 μm. (f) The N II 2p²:³P₂–³P₁ transition at 121.9 μm. (g) The ratio of N II 122 μm to N II 205 μm emission for the central Galactic region (dimensionless scale). Farther from the Galactic center, the ratio is dominated by noise. (h) The N II 205 μm–to–C II 157 μm ratio (dimensionless scale). The dotted and dashed lines are predictions from simple models (see text).