Ga. Galazutdinov et al., ON THE RELATION BETWEEN THE CARRIERS OF DIFFUSE INTERSTELLAR BANDS AND SIMPLE MOLECULAR-SPECIES, Monthly Notices of the Royal Astronomical Society, 292(2), 1997, pp. 414-418
The interstellar clouds composed mostly of neutral hydrogen (H I cloud
s) show evident differences in the pattern of interstellar absorptions
: in the shapes of the extinction curves, the strengths of the diffuse
interstellar bands and the intensities of the features originating in
simple molecular species. It is well known that the ratio of the two
prominent diffuse bands (5780 and 5797 Angstrom) varies strongly from
cloud to cloud; our data suggest that this phenomenon is related to th
e intensities of the absorption features of interstellar molecules suc
h as CH+ or CH. However, the intensity ratio of the diffuse bands can
change gradually, suggesting a 'smooth' variation of the carrier abund
ances, while the strength ratios of molecular features and the colour
excesses change rather stepwise when the diffuse band ratio reaches a
certain value.