Are Neutral‐Neutral Reactions Effective for the Carbon‐Chain Growth of Cyanopolyynes and Polyacetylenes in Interstellar Space?

Abstract

Ab initio mol. quantum-mech. methods were applied to explore the possibility of neutral-neutral reactions giving cyanopolyynes and polyacetylenes in interstellar cloud. Potential energy surfaces for the reactions between the CN radical and polyacetylenes indicate that all reactions, C2nH2 + CN (n = 1-4), which form HC2n+1N mols., are exothermic and have no energy barriers. The authors have also examd. the possibility of the various product channels from the reactions C2nH2 + CN based on the thermochem. relations. The theor. results show that none of the product channels is exothermic except the case which produces HC2n+1N, with the C chain being longer than the reactant polyacetylene. Similar results are obtained for the regioselectivity of the reactions, C2nH2 + C2H (n = 1-4), to produce hydrocarbons. The only possible products from the latter reactions are HC2n+2H + H under the conditions of interstellar space. These results clearly demonstrate the importance of the neutral-neutral reactions on the C-chain growth of cyano-polyynes and polyacetylenes. [on SciFinder(R)]