Same as Fig. 10, but for a hydrogen-dominated atmosphere exposed to 3 (upper left panel), 7 (upper right panel), 10 (lower left panel) and 20 (lower right) times the current Earth XUV level. One can see that unlike a nitrogen-dominated atmosphere, hydrogen-dominated atmospheres produce a noticeable Ly-α signature in all cases, however, the deepest in-transit absorption exceeding the observational errors in the blue wing of the line is obtained for the most expanded exospheres at 10 and 20 XUV. Although the red wing of the line also shows some absorption, it does not exceed the observational errors.