Dominant de-excitation process of CH⁺J = 1 as a function of the density n_H, and the equivalent black body temperatures T_vib and T_ele, for T_rot = 2.7 K. In the blue, purple, red, and brown regions, the de-excitation of CH⁺J = 1 is dominated by pure rotational, rovibrational, and rovibronic radiative transitions and by the photodissociation. In the empty space above, the de-excitation occurs through reactive and nonreactive collisions depending on T_K and the chemical composition of the gas (see main text).