Top row: Spectral evolution of models H_R61 (left) and H_R601 (right) in the ultraviolet and optical ranges from 2–4 d until 25 d after explosion. Bottom row: Evolution of the Hα region in velocity space up to 25 d after explosion for model H_R61 (left) and H_R601 (right). The shaded area corresponds to the contribution from Hα. In practice, we compute the formal solution of the radiative transfer equation for each model but without the bound-bound transitions from H i. The shaded area corresponds to the flux offset between that solution and the solution for the model that accounts for all bound-bound transitions.