Illustration of the ejecta and radiation properties versus velocity in the SN IIn model at 300 d after explosion and used for comparison to SN 1998S at 375 d in Section 5. The main feature of this model is the presence of a massive dense shell at 5000 km s⁻¹ and powered by interaction (the interaction power absorbed is 2×10⁴¹ erg s⁻¹ in this model). From top to bottom, we show the mass fractions and ionization state of H, He, O, and Fe (a value of zero corresponds to a neutral state, of one to once ionized etc), the free-electron density, the electron temperature, the absorbed powers from radioactive decay and ejecta/CSM interaction, some line emission measure denoted $\overline{\zeta }$ (ζ is defined such that ${\int }_a^b\zeta \mathit{dr}$ gives the fractional line flux originating between radii a and b, and for better visibility we show its scaled value $\overline{\zeta }$; for details see Hillier 1987), and the outward integral of the flux in the ultraviolet, optical, and infrared.