The formation of carbon chain molecules in IRC + 10216

This paper considers the formation of carbon-chain molecules, including C2nH, CnS, HC2n+1N (n = 1-3) and SiCn (n = 1-4), in the outflowing envelope of the late-type carbon star IRC + 10216. The results suggest that the organo-sulphur species C2S and C3S can be formed in ion-molecule reactions involving acetylene ions and parent CS and SiS molecules. In addition to ion-molecule processes, neutral-neutral reactions can play a significant role in the formation of hydrocarbons and cyanopolyynes with up to six heavy atoms and in the formation of SiC4, and suggest that SiC3 might be observable. However, the short time-scales available in the outflow are such that the observed abundances of the cyanopolyynes larger than HC5N cannot be reproduced using the parent molecules and abundances adopted here. (author)