Interstellar extinction and abundances of simple diatomic molecules
  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. 
T. Weselak, J. Kre{\l}owski
astro-ph.GA