Column densities of CH⁺, CO, OH, and H₂O calculated across shocks propagating at 5 (left panels), 10 (middle panels), and 20 (right panels) km s⁻¹ in media of density n_H = 10² (empty orange squares), 10³ (empty green circles), 10⁴ (filled green squares), and 10⁵ (filled blue circles) cm⁻³, as function of the impinging radiation field G₀, and for a buffer visual extinction . All other parameters are set to their standard values (see Table 1).