COMBINED CROSSED MOLECULAR-BEAMS AND AB-INITIO INVESTIGATION OF THE FORMATION OF CARBON-BEARING MOLECULES IN THE INTERSTELLAR-MEDIUM VIA NEUTRAL-NEUTRAL REACTIONS

The crossed molecular beams reaction of atomic carbon C(P-3(j)) with h ydrogen sulfide, H2S, aliene, H2CCCH2, the vinyl radical, C2H3, and de utero-acetylene, C,HD, have been studied at different collision energi es up to 42.2 kJ mol(-1) and combined with high level ab initio calcul ations. All reactions are barrier-less and are dominated by a carbon-h ydrogen exchange to form thioformyl (HCS), butatrienyl (HCCCCH2, C3H2 isomer(s), and deuteriated tricarbon hydride(s). This carbon-hydrogen replacement channel represents a one-step alternative reaction pathway to competing ion-molecule reactions to form complex, carbon-bearing m olecules in the interstellar medium as well as in the outflow of carbo n stars.