Comparison of Ni I (left) and Fe I (right) line intensities of our fluorescence model to the observed intensities of comet C/1965 S1 (Ikeya-Seki) as reported in Slaughter (1969) (top) and Preston (1967) (bottom). The model spectra are scaled via a linear fit of all present lines. Doppler line profiles were assumed for equilibrium temperatures derived from the heliocentric distances: 1067 (Slaughter 1969) and 818 K (Preston 1967).