  We analyze mutual relations between interstellar extinction E(B-V) and column
densities of diatomic molecules such as CN, CH and CH cation observed along
translucent sightlines. Observational material acquired using five echelle
spectrographs, situated in both northern and southern hemispheres, was used in
this study. While column densities of CH, CH+ correlate reasonably tightly with
E(B-V) the similar relation built for CN shows a large scatter. This result
suggests that CH and CH+ molecules are quite well spatially correlated to
interstellar dust while CN requires another conditions to be formed. The CH
molecule is closely related to H_2 as it was demonstrated already; the fact is
interesting since H_2 is believed to be formed on grain surfaces rather than in
the gas phase.
