Using the temperature and ionization calculated in our previous paper , we model the spectral evolution of SN 1987A .
We find that the temperature evolution is directly reflected in the time evolution of the lines .
In particular , the IR-catastrophe is seen in the metal lines as a transition from thermal to non-thermal excitation , most clearly in the [ O I ] ~ { } \lambda~ { } \lambda~ { } 6300 , 6364 lines .
The good agreement with observations clearly confirms the predicted optical to IR-transition .
Because the line emissivity is independent of temperature in the non-thermal phase , this phase has a strong potential for estimating the total mass of the most abundant elements .
The hydrogen lines arise as a result of recombinations following ionizations in the Balmer continuum during the first \sim 500 days , and as a result of non-thermal ionizations later .

The distribution of the different zones , and therefore the gamma-ray deposition , is determined from the line profiles of the most important lines , where possible .
We find that hydrogen extends into the core to \lesssim 700 ~ { } km~ { } s ^ { -1 } .
The hydrogen envelope has a density profile close to \rho \propto V ^ { -2 } from 2000 - 5000 ~ { } ~ { } km~ { } s ^ { -1 } .
The total mass of hydrogen-rich gas is \sim 7.7 { ~ { } M } _ { \odot } , of which \sim 2.2 { ~ { } M } _ { \odot } is mixed within 2000 ~ { } km~ { } s ^ { -1 } .
The helium mass derived from the line fluxes is sensitive to assumptions about the degree of redistribution in the line .
The mass of the helium dominated zone is consistent with \sim 1.9 { ~ { } M } _ { \odot } , with a further \sim 3.9 { ~ { } M } _ { \odot } of helium residing in the hydrogen component .
Most of the oxygen-rich gas is confined to 400 – 2000 ~ { } km~ { } s ^ { -1 } , with a total mass of \sim 1.9 { ~ { } M } _ { \odot } .
Because of uncertainties in the modeling of the non-thermal excitation of the [ O I ] lines , the uncertainty in the oxygen mass is considerable .
In addition , masses of nitrogen , neon , magnesium , iron and nickel are estimated .

The dominant contribution to the line luminosity often originates in a different zone from where most of the newly synthesized material resides .
This applies to e.g .
carbon , calcium and iron .
The [ C I ] lines , mainly arising in the helium zone , indicate a substantially lower abundance of carbon mixed with helium than stellar evolution models give , and a more extended zone with CNO processed gas is indicated .
The [ Fe II ] lines have in most phases a strong contribution from primordial iron , and at t \gtrsim 600 - 800 days this component dominates the [ Fe II ] lines .
The wings of the [ Fe II ] lines may therefore come from primordial iron , rather than synthesized iron mixed to high velocity .
Lines from ions with low ionization potential indicate that the UV field below at least 1600 Å is severely quenched by dust absorption and resonance scattering .