Depth of a gap for three different molecules/transitions over velocity and weighted by the ALMA noise level σ. The disk has an outer radius of 144 AU and the disk mass amounts to 2.67 × 10^-3 M_⊙ and the disk heated by the Herbig Ae star. For this disk model, all considered transitions are optically thick at the line center and the detection of the gap is only feasible with ¹²C¹⁸O due to its low abundance. Nevertheless, at the line wings other molecules transitions allow for gap detection too, and in this particular case the gap depth has a maximum value when using the CS (7−3) transition.