Computation of overlapping OH and H₂O lines with FLITS and PRODIMO around 25 μm. The central feature shows two about equally strong water lines: o-H₂O (blue) 9_7,2 → 8_6,3 at 25.0641 μm and p-H₂O (cyan) 9_7,3 → 8_6,2 at 25.0663 μm. Althoughthese two lines overlap spectroscopically, they do not overlap physically, and superposition (grey) still works fine in comparison to the full FLITS model (black). On the right side, there are 3 individual OH lines (hyper-fine splitting) that physically overlap, X_3∕2, v = 0, J = 12 → X_3∕2, v = 0, J = 11 at 25.089950 μm (red, strong), X_3∕2, v = 0, J = 11 → X_3∕2, v = 0, J = 10 at 25.089946 μm (red, strong), and X_3∕2, v = 0, J = 11 → X_3∕2, v = 0, J = 11 at 25.089835 μm (red, very weak). The superposition gives slightly too strong results. On the left side, another case is shown with 1 p-H₂ O line and 3 OH lines.