On the relation between diffuse bands and column densities of H₂, CH and CO molecules

Mutual relations between column densities of H2, CH and CO molecules as well as between the latter and strengths of the major 5780 and 5797 diffuse bands are presented and discussed. The CH radical seems to be a good H2 tracer, possibly better than CO. It is also demonstrated that the molecular fraction of the H2 molecule is correlated with an intensity ratio of 5797 and 5780 DIBs, suggesting the possible formation of narrow DIB carriers in denser clouds, dominated by molecular hydrogen and reasonably shielded from ionizing UV radiation by small dust grains.