Observed molecular line ratios compared with C-type (red dashed lines) and J-type (blue lines) model predictions from Flower & Pineau des Forêts (2015). The circles, diamonds, triangles, and squares correspond to pre-shock densities of 10³ cm^-3, 10⁴ cm^-3, 10⁵ cm^-3, and 10⁶ cm^-3, respectively, with shock velocities (V_shock) from 10 km s^-1 to 40 km s^-1 (C-type) or from 10 km s^-1 to 30 km s^-1 (J-type). Filled symbols indicate the position of the lowest velocity (V_shock=10 km s^-1). Black filled circles represent detections and arrows are upper limits. Solid error bars are the intrinsic errors of the line fluxes and dotted error bars are obtained by adding a 30% error due to the PACS flux calibration.