A MODEL FOR GROWTH OF HYDROGENATED CARBON CLUSTERS UNDER INTERSTELLARCONDITIONS

The physico-chemical origin of the hydrogenated carbon clusters (cumul enes, PAHs, graphite or amorphous carbon) in space is still an open qu estion. We have worked out a numerical simulation code in order to bui ld up planar (graphite-like) carbon clusters. We assume that hydrogen atoms can fix on the carbon skeleton following a random process allowi ng for H-2 formation. The structures we have found are very complex. I n a given cluster, several molecular entities can simultaneously be pr esent: (sp(2)) carbon chains, rings or compact formations (aromatic st ructures or small PAHs). We argue that these very contorted hydrogenat ed structures could be ubiquitous in the interstellar medium, in carbo n-rich circumstellar regions and PNe.