Representative spectra of comet P/Halley are shown in Figs. 4 (click here)a-f. These spectra were created by averaging spectra from selected coma areas in order to enlarge their signal-to-noise ratio. The slit positions of the selected spectra are marked in Figs. 4 (click here)g-l by filled circles. The averaged spectra were normalized to the band intensity of their CN (0-1) emission (see scaling factors on the intensity axis of Figs. 4 (click here)a-f).
The averaged tail spectrum in Fig. 4 (click here)d reveals the dominant
plasma tail emissions at a mean projected distance from the nucleus of about
. The (4-0),
(3-0), and (2-0), double bands of the 
Comet Tail System and
the (0-1) and (1-2) bands of the 
Fox Duffendack Barker
System were identified. Additionally, there is a large number of emissions
heavily blended or too weak to be measured. The peak around 3575 Å is a
blend of emissions from CN, , , 
, and
. The latter emission should be the dominating contribution in the
present case (see Wyckoff & Theobald 1989; Arpigny
et al. 1986b). The (0-0) band of the First Negative
System at 3914 Å is the strongest emission in this system (Lutz
et al. 1993). But in the present spectra it is fairly weak and
contaminated by other emissions (see Wyckoff & Theobald 1989).
The peak at 4235 Å represents the 
(0-0) AX band which is
the strongest emission in the observed spectral range (Lutz
et al. 1993), but rather weak in most spectra. The emission around
4130 Å could not be identified with certainty (see Jockers et al.
1987). Interestingly, the ion emissions, especially the
(2-0) band, are not only limited to the plasma tail but are also visible
in the head spectrum (Fig. 4 (click here)b) and even in the spectrum of
the sunward coma (Fig. 4 (click here)a). This suggests the presence of a
large halo around the comet (see also Jockers et al.
1987; Jockers & Bonev 1997).
In contrast to the tail spectrum, the head spectrum at 
is dominated by neutral gas emissions. Most prominent is the
Violet System of CN with its (0-0) and (0-1) bands which are visible in
all spectra. The rich 
emission around 4050 Å has eight
certainly identifiable peaks which are partly blended with weaker emissions
of , , , and (see Wyckoff &
Theobald 1989). In our spectra, there is some evidence for
also contributing to the emissions at wavelengths shorter than CN (0-0)
(see Gausset et al. 1965; Valk et al. 1989).
Finally, the CH radical is represented by its (0-0) AX band. The
band of the 
Swan band system around 4360 Å is
much weaker than the other bands of that system which were analysed with
regard to spatial distribution by several other authors (see e.g.
Kidger et al. 1987; Combi & Fink 1993).