Dust-induced chemical differentiation in dense regions

Dust grains respond to the physical and chemical conditions of the interste llar region in which they are embedded. The interaction produces an extinct ion curve which depends on the local environment and on the past history of the dust grains. In this work we present a theoretical study of the effect s of radial variations of dust extinction properties on gas-phase chemistry in spherical core-halo clouds. We use observational constraints on the var iation range of the extinction curve, and we analyse if the degree of dust environmental processing could be reflected by chemical signatures in the g as-phase molecular concentrations. The results of this work show that signi ficant variations in the photodestruction rates and in the thermal profile of the cloud might induce chemical patterns otherwise excluded in the stand ard dense-cloud chemistry. Some discrepancies between observations and theo retical provisions are discussed in the light of the present results.