Density structures of different carbon ions and their energy levels as returned by Cloudy for the hot Jupiter planet around a G2 star. The blue, pink, green and yellow colors correspond to atomic, single, double and triple ionized carbon, respectively. For each of these, the density structures of the four lowest energy levels are shown in different line styles. We postprocess such density structures with the coefficients from the NIST database to produce synthetic transmission spectra. For example, the C I λ 1657 multiplet is a blend of lines originating from the ³P₀,³P₁ and ³P₂ levels, while the C III λ 977 line originates solely from the ground-state (i.e., ¹S₀).