The interstellar C3 chain molecule in different interstellar environments

We present an analysis of spectra of six stars taken with high resolution (R = 220 000). The stars are reddened by molecular clouds that differ by the relative strength of the 5797 and 5780 diffuse interstellar bands (DIBs). The high signal-to-noise ratio of the spectra (S/N approximate to 700-1000) shows that the abundance of the linear molecule C 3 with respect to EB-V varies considerably from one star to an other. There is no correlation with EB-V. The strong variations in the abundance of C-3 must therefore be caused by another circumstance. We point out that this may be the case: from an analysis of the interstellar potassium lines in the same spectra we conclude large differences in the state of ionization produced by interstellar photons with energies below the ionization potential of hydrogen. The ratio of the abundances of C-3 and C-2 varies considerably in different directions, even when the ratio between the strengths of various DIBs remains approximately constant.