Comparison between the best-fit model (coloured points) from comparisons of a grid of models from the Paris-Durham shock code with observations (black squares) of H₂ (from the Spitzer-IRS telescope) and CO (from the APEX telescope). The target position is the southern knot D shock where the blue lobe of the outflow driven by IRS1 overlaps with that driven by IRS2. We consequently fitted two shock layers in this position: one on the red-shifted, one on the blue-shifted gas component. Upper panel, left: CO integrated intensity diagram for the blue component. Upper panel, right: CO integrated intensity diagram for the red component. Lower panel, left: H₂ excitation diagram, the three empty symbols correspond to fluxes extracted with different methods (see text for details), the filled squares indicates the average values. Lower panel, right: [O i] line flux.